International symposium
on
Challenges in Malaria and Prospects for Research
October 29-31, 2002
Malaria Research Centre (ICMR)
22, Sham Nath Marg, Delhi-110054, India
Programme
Venue: SCOPE Convention Centre, CGO Complex, Lodhi Road,
New Delhi – 110 003
Date: 29 October, 2002
Inaugural Function (1000-1100 hrs)
Chief Guest Professor P.N. Tondon, President, National Brain Research Centre, New Delhi and Meghnad Saha Professor of the National Academy of Sciences, India
Professor R.C. Mahajan, PGIMER, Chandigarh will preside over the function
MRC Foundation day lecture (1130-1230 hrs)
Speaker Professor V.S. Chauhan, Director, ICGEB, New Delhi
Chairperson Dr. S. Pattanayak, New Delhi
Technical Programme (1400-1800 hrs)
Session I: Malaria Disease Burden
Chairperson Dr. P.R. Arbani, WHO-SEARO, New Delhi
Co-Chairperson Dr. Arvind Pandey, IRMS, New Delhi
Rapporteurs Dr. R.C. Dhiman, MRC, Delhi
Coordinator Dr. Neena Valecha, MRC, Delhi
Lead Papers
· Malaria burden in the country- Dr. Jotna Sokhey, National Anti Malaria Programme (NAMP), Delhi
· Climate and malaria– Dr. A.P. Mitra, National Physics Laboratory, New Delhi
Remarks by Chairperson and Co-chairperson
Resource & Research Inputs
Chairperson Professor R.C. Mahajan, PGIMER, Chandigarh
Co-Chairperson Dr. J. Mahanta, Regional Medical Research Centre, Dibrugarh, Assam
Rapporteurs Dr. P.R. Bhattacharya, MRC, Delhi & Dr. B. Shahi, MRC, Shankargarh, U.P.
· Malaria morbidity in tribal population of Orissa - Dr. S.K. Sharma, MRC, Rourkela, Orissa
· Relapses and P.vivax burden – Dr. T. Adak, MRC, Delhi
· EDPT by NGOs in Orissa – Dr. Raja Ratnam Abel, Christian Medical College, Vellore, T.N.
Remarks by Chairperson and Co-Chairperson
Discussion
Date: 30 October, 2002 (0900–1300 hrs)
Session-II: Understanding of Vectors: The targets for effective malaria control
Chairperson Professor K.S. Rai, Jalandhar
Co-Chairperson Dr. A.P. Dash, Life Sciences Institute, Orissa
Rapporteurs Dr. Vas Dev, MRC, Sonapur, Assam & Dr. K. Raghavendra, MRC, Delhi
Coordinator Dr. Neeru Singh, MRC, Jabalpur
Lead Papers
· Interrupting malaria transmission by genetic manipulation of anopheline mosquitoes – Professor Marcelo Jacobs - Lorena, Deptt. of Genetics, Case Western Reserve University, Cleveland, Ohio, USA
· Indian anopheline vector species population structure – Dr. Sarala K. Subbarao, MRC, Delhi
Remarks by Chairperson and Co-Chairperson
Resources & Research Inputs
Chairperson Sh. N.L. Kalra, New Delhi
Co-Chairperson Professor N.J. Shetty, Bangalore University, Bangalore
Rapporteurs Dr. Hema Joshi, MRC, Delhi & Dr. Alex Eapen, MRC, Chennai
· Taxonomic surveys: Anopheline species diversity – Dr. B.N. Nagpal, MRC, Delhi
· GIS for mapping of malaria vectors – Dr. Aruna Srivastava, MRC, Delhi
· Biological and ecological distinctness among sibling species – Dr. Nutan Nanda, MRC, Delhi
· Tools for identification of cryptic anopheline species – Mr. O.P. Singh, MRC, Delhi
Remarks by Chairperson and Co-Chairperson
Discussion
Date: 30 October, 2002 (1400 – 1800 hrs.)
Session-III: Vector Control Options
Chairperson Dr. P.K. Das, Vector Control Research Centre, Pondicherry
Co-Chairperson Dr. S.C. Das, Defence Research Laboratory, Tejpur, Assam
Rapporteurs Dr. Ashwani Kumar, MRC, Goa, Dr. C.P. Batra, MRC, Delhi
Coordinator M.A. Ansari, MRC, Delhi
Lead Papers
· Challenges in vector control in India- NAMP
· Bioenvironmental control of Malaria in India – Dr. V.P. Sharma
Resource and Research Inputs:
Chairperson Dr. P.K. Rajagopalan, Tamil Nadu
Co-Chairperson Dr. S.J. Rehman, NAMP, Delhi
Rapporteurs Dr. M.S. Malhotra, MRC, Delhi & Dr. M.K. Das, MRC, Car Nicobar
· Insecticide resistance and biochemical mechanisms in malaria vectors – Dr. K. Raghavendra, MRC, Delhi
· Larvivorous fish in malaria control in Karnataka – Dr. S.K. Ghosh, MRC, Bangalore, Karnataka
· Biocides in Vector Control – Challenges and Prospects– Dr. P.K. Mittal, MRC, Delhi
· Insecticide treated mosquito nets: efficacy and sustainability – Dr. R.S. Yadav, MRC, Nadiad, Gujarat
· Comprehensive management of disease vectors in Ahmedabad City – Dr. R.M. Bhatt, MRC, Nadiad, Gujarat
Remarks by Chairperson and Co-Chairperson
Discussion
Date: 31 October, 2002 (0900 – 1500 hrs.)
Session IV: Parasite Biology/Vaccines/Drugs
Chairperson Dr. Shiv Lal, National Institute of Communicable Diseases, Delhi
Co-Chairperson Dr. Deepali Mukherjee, Indian Council of Medical Research, New Delhi
Rapporteurs Dr. Arun Sharma, MRC, Delhi & Dr. Usha Devi, MRC, Delhi
Coordinator Dr. T. Adak, MRC, Delhi
Lead Papers
· How specific is the immune response to malaria in endemic adults – Dr. Shobhona Sharma, Mumbai
· Hemebiosynthetic Pathway in the Malarial Parasite Unique Features and Drug Target – Dr. G. Padmanabhan, Indian Institute of Science, Bangalore
Remarks by Chairperson and Co-Chairperson
Resources & Research Inputs
Chairperson Dr. Deepali Mukherjee, Indian Council of Medical Research, New Delhi
Co-Chairperson Professor D.N. Rao, All India Institute of Medical Science, New Delhi
Rapporteurs Dr. S. Biswas, MRC, Delhi, Dr. R.P. Shukla, MRC, Haldwani
· Parasite Bank: A national resource at MRC – Dr. C.R. Pillai, MRC, Delhi
· Glycolipid antigen – A tool for malaria parasite diagnostics – Dr. Arti Roy, MRC, Delhi
· Markers for malaria parasite population structure analysis – Dr. Hema Joshi, MRC, Delhi
· New compound with antimalarial activity – Dr. V.K. Dua, MRC, Hardwar
· Clinical drug trials at MRC – Dr. Neena Valecha, MRC, Delhi
Remarks by Chairperson and Co-Chairperson
Discussion
Foundation Day Lecture
Malaria research: incredible possibilities and ground realities
Professor V.S. Chauhan
Director
International Centre for Genetic Engineering and Biotechnology, New Delhi– 110 067
Malaria has remained a major threat to public health and economic development in the tropical and subtropical regions of the world. With upto 500 million malaria cases and upto 3 million deaths each year, malaria ranks at the top of the killer diseases, particularly for the young children. Efforts to control or eradicate malaria have largely failed and with resistance to well known drugs for the parasite and to insecticides for the vector, the situation has become desperate. Efforts to develop vaccines and new drugs have not yet yielded any major break through. However there is more concerted effort now to combat diseases like malaria both at the individual national as well as international levels. Scientifically, the knowledge of understanding the disease has progressed enormously. There is a large, focussed international effort to develop vaccine and drugs against malaria. More recently, a great leap in this knowledge has been taken with the availability of the three genomes – of the host, of the parasite and the vector. These events have brought out unprecedented possibilities in malaria research leading to its control. Ground realities may however be different and it may has long time before one reaps the fruits of these outstanding attachment.
The research at ICGEB, in the malaria group, is focussed on the same of the above issues. The major focus has been on the development of blood stage vaccine, understanding the mechanism of action of anti malarial and development of technologies that can be used to exploit the vast information that Genome sequences has provided.
Research results in the above areas will be discussed in some details.
Session-I
Malaria Disease Burden
1.1 Burden of Malaria in India
Jotna Sokhey
National Anti Malaria Programme (NAMP) (Directorate General Of Health Services), 22, Sham Nath Marg, Delhi-110054, India
India contributes nearly 70-75% malaria cases in the SEARO Region. Nearly 95% of the population is at risk due to conditions which are conducive for mosquito breeding. Malaria cases are detected by active case detection (ACD) and passive case detection (PCD) mechanisms. Each year 80-90 million fever cases are screened for the presence of malaria parasites, of which 2 to 3 million cases are detected parasite positive. NAMP’s surveillance system is applied uniformly to the entire country, regardless of malaria situation. In many areas of the country disproportionate efforts are made to detect malaria cases. Even with the nation-wide surveillance, estimates of malaria burden remain unclear; the epidemiology of malaria is complex and the disease is unevenly distributed in time and space. It is notable to mention that malaria has been contained to a large extent in 80% of the country’s population. The remaining 20% population lives in highly malarious areas. This comprises of 7% tribal population (70 million) in peninsular India that contributes 30% malaria cases and >50% P. falciparum cases. Likewise 4% population in the 7-north eastern states have high proportion of P. falciparum and the drug resistant malaria. Another 9% population (85 million) contributes 22% malaria cases, 18% P. falciparum cases and 20% deaths due to malaria in the country. There are two prevalent malaria parasite infections viz., P. vivax and P. falciparum. These parasites are in equal proportion in the country. However, parasite formula varies from place to place and seasonally, and profoundly affects the burden of the disease. Disease burden estimates may be more reliable for small homogeneous populations for a specified time period, and such estimates will lead to better targeting of malaria control operations to enhance sustainability of interventions.
1.2 Estimation of burden of disease on account of malaria in India
P. Mahapatra
National Institute of Health Systems, Hyderabad, A.P.
1.3 Clinical manifestations and drug options in P. falciparum infections
B.S. Das (e-mail: bsdas@hotmail.com)
Ispat General Hospital, Rourkela, Orissa, India
Published information from India on clinical manifestation of P. falciparum malaria is sketchy and scanty. Whatever is available from a few centres of the country and information collected through personal interaction with doctors from different states indicate febrile episodes of malaria as well as complicated malaria occur in all age groups. Cerebral malaria and hypoglycemia are seen in almost equal frequency in both children and adults. While children suffer more from severe anemia and multiple convulsions, adults suffer more from jaundice, acute renal failure, acute lung injury and ARDS, and multiple complications. Pregnant women manifest more of severe anemia, hypoglycemia, and pulmonary edema along with other complications. Malaria related deaths are highest in pregnant women followed by adults and lastly children. There has been a significant change in the clinical manifestation of severe malaria in the last one-decade. Incidence of jaundice, acute renal failure and multiple complications have increased and therefore death rate has also gone up.
Majority of the deaths and malarial complications are reported from high endemic areas of the country. An epidemiological study conducted in a hyper-endemic village of Sundergarh District of Orissa State, indicated that while prevalence and incidence are highest in the children between 1-5 years of age, no age is immune to febrile episodes of malaria. Absence of severe complications or death in the village could be an aberration.
Currently available antimalarial drugs should be judiciously used till better antimalarial drugs are available. Strategies of antimalarial treatment need to be clearly defined vis a vis chloroquine resistance. Artemisinin derivatives, particularly arteether are most suited for use in the periphery because of the ease of administration, effectiveness, and absence of major adverse reactions. However, more pharmacokinetic information is needed on optimum dosage schedule, frequency, and duration of their administration, and their safety in children and pregnant women. Known, adverse reactions of intravenous quinine administrations, importance of constant rate infusion, and regular check up of vitals need be periodically reiterated.
1.4 Drug resistance in malaria
WRJ Taylor and P. Olliaro.
Tropical Disease Research (TDR), World Health Organisation, Geneva 27
Drug resistance represents one of the critical challenges for
effective malaria control. The inexpensive and widely used chloroquine and
sulfadoxine/pyrimethamine (SP) are already ineffective in many malaria endemic
countries. Certain areas such as the Thai-Burmese border have multidrug
resistant Plasmodium falciparum malaria. Chloroquine resistant P.
vivax has now been present for some 12 years. Chloroquine resistant P.
malariae was reported this year from Indonesia.
New drugs are few and costly. Simply replacing one drug with another is not sustainable. One approach to treating drug resistant P. falciparum is to use artemisinins with other antimalarial drugs. These drugs improve efficacy and reduce gametocyte carriage, and may retard the development of resistance. This presentation will summarise the epidemiology of drug resistant malaria, its causes, and discuss the results of recent TDR sponsored trials of artesunate in combination with amodiaquine, chloroquine and SP for treating P. falciparum in several African countries.
1.5 Climate and malaria
A.P. Mitra
National Physics Laboratory, New Delhi
1.6 Malaria morbidity in pregnant women in Madhya Pradesh
Neeru Singh1 and A. C. Nagpal2
1Malaria Research Centre, Field Station, Jabalpur, 2Department of Medicine, NSCG Medical College, Jabalpur
Sinton (1935) was the first to describe the vulnerability of pregnant women and their unborn children to malaria in India. These two groups remain at particularly high risk of malaria attributable morbidity till today.
Analysis of three years of data from a malaria clinic operated by the Indian Council of Medical Research (ICMR) in the Government Medical College Hospital in Jabalpur, central India, showed a high malaria prevalence among pregnant women, which was statistically highly significant (P <0.0001) compared with the situation among nonpregnant women. Cerebral malaria was a common complication of severe Plasmodium falciparum infection, with a high mortality during pregnancy, requiring immediate attention. The study also showed that malaria infection was more frequent in primigravidae, falling progressively with increasing parity. Mean parasite densities were significantly higher in pregnant women compared with nonpregnant women for both P. falciparum (P <0.001) and P. vivax (P <0.05) infection. Pregnant women with falciparum or vivax malaria were significantly more anaemic than noninfected pregnant women or infected nonpregnant women.
Recently samples of placental blood were collected from all pregnant women who delivered at the hospital with or without fever history. About 7% placenta were found infected of which 6% P. falciparum and remaining P. vivax. Of these only 3% showed matching peripheral smear positive.
The mean birth weight of the babies was significantly lower in the infected group than in the non-infected group (P <0.0001), the mean birth weight of babies in the falciparum infected group was lower than that in the vivax infected group (P <0.05). We conclude that pregnant women from this geographical area require systematic intervention owing to their high susceptibility to malaria during pregnancy.
1.7 Malaria morbidity in tribal population of Orissa
S.K. Sharma
Malaria Research Centre, Field Station, Sector-5, Rourkela-769002, Orissa, India
In India, about two million cases of malaria are reported annually out of which Orissa state alone contribute 22 % of total malaria cases, 43 % of falciparum cases and 50% of all reported deaths due to malaria although it constitute only 4 % of the total population of India. The high malaria morbidity and mortality are mainly due to high prevalence of falciparum malaria and large pockets of tribals represented by 62 tribal communities that constitute 44 % of the total population of Orissa. Sundargarh district located in the northern part of Orissa is predominantly inhabited by tribals. Therefore, a detailed epidemiological study was undertaken in 13 tribal villages located in two distinct ecotypes of forest & plain area to study malaria morbidity in tribal population. The longitudinal and cross-sectional parasitological surveys were conducted in all the villages. The annual parasite index (API) among the tribal living in forest & plain area was 347.9 and 61.0 respectively. Malaria incidence was more in younger age groups as compared to adults. The malaria prevalence rate in these areas was 16.8 and 2.8 respectively and highest parasite rate was in the 1-5 year age group with gradual decline as the age increases. Highest average attack rate of 1.7 episodes/year was recorded in 1-5 year age group. The maximum number of malaria episodes was 8. The spleen rate was between 50-80 thereby indicating meso-to hyperendemic malaria situation in the area. There are nine ethnic tribal communities in the study area out of which Oram., Munda and Kishan are predominant. The highest malaria prevalence was recorded in Gond tribes (142.8 %) followed by Kishan (75.7 %), Munda (70.0 %) and Oram (63.6 %). The study showed that malaria is one of the major diseases affecting the tribals to the greatest extent and putting a lot of burden on the economic upliftment of these communities.
1.8 Malaria morbidity and mortality in Uganda
Gertrude N. Kiwanuka
Department of Biochemistry, Mbarara University of Science and Technology, Mbarara, Uganda
Malaria is the leading cause of morbidity and mortality in Uganda especially in children under 5 years. Transmission of malaria is perennial though there are seasonal exacerbations. Up to 70% of out-patient cases and over 50% of in-patient admissions in the under fives is caused by malaria. It is responsible for a specific death rate among the age group of 37/1000 live births and 18/1000 live births in high and low malaria endemic areas respectively or a total of 70,000 – 110,000 child health deaths annually. It is also the major killer of refugees and internally displaced people in Uganda. Malaria cases increased from 1,444,352 in 1995 to 2,923,620 in 1999.
There is considerable malaria morbidity due to repeated low level and mostly non-febrile infections with the parasites resulting into chronic anemia in children and pregnant women particularly primigravidae. Severe malarial anemia is responsible for a case fatality rate of 8-25% among pediatric admissions. It is responsible for nearly 60% abortions or miscarriages. High levels of resistance to classical malaria drugs have resulted in increased malaria morbidity.
1.9 Relapses and P. vivax burden
T. Adak (e-mail: adak@vsnl.com)
Malaria Research Centre (ICMR), 22 Sham Nath Marg, Delhi 110054, India
Plasmodium vivax malaria constitutes about 60-65% of all malaria cases in India with pronounced morbidity particularly in the socio-economically weaker communities. The clinico-epidemiological picture of P. vivax is not well understood due to the phenomenon of latency/relapse. Due to the persistence of the hepatic or hypnozoite form of the parasite, relapses occur in P. vivax infections and it is difficult to predict their timing. Blood schizontocidal drugs are not effective against persistent hypnozoite form of the parasite in the liver. Primaquine, an 8-aminoquinoline, is the only available drug active against hypnozoites of relapsing malaria parasites. National Anti Malaria Programme (NAMP) of India recommends 600 mg chloroquine base on day ‘0’ and Primaquine 15 mg/day for 5 days (adult doses) as radical treatment for P. vivax infections, whereas WHO recommends primaquine for 14 days or more along with 1500 mg chloroquine base. Due to logistic and operational reasons and potential side effects of Primaquine, 5-day primaquine treatment is being followed in India at present.
Malaria Research Centre has conducted a number of studies on the epidemiology of P. vivax and to evaluate efficacy of chloroquine plus 5-day Primaquine compared with chloroquine alone in different eco-epidemiological zones of India with predominance of either P. vivax or P. falciparum. Outcome of these studies with reference to relapse rate, incubation interval, seasonal pattern in understanding P. vivax transmission dynamics and efficacy of drugs in deciding drug policy for malaria control in India would be discussed.
1.10 Early diagnosis and presumptive treatment by NGOs in Orissa
Rajaratnam Abel
Christian Medical College, Vellore, T.N.
Over a twelve month period starting in July 2001, RUHSA Department, Christian Medical College, Vellore carried out EDPT of malaria through 20 NGO partners in Orissa. Following a consultation in Bhubaneswar, capacity building of the NGO partners was provided in strategic planning for malaria control as well as on the basic concepts of malaria. Clear cut messages on malaria were developed in English and then translated into Oriya. This was followed by preparing a set of flash cards. Volunteers from different villages covering a total population of over 130,000 people from 16 districts were selected. The NGO staff trained the volunteers who in turn empowered the community. Besides distributing pamphlets on malaria, flash cards were used individually and in groups, school programmes were conducted, street theatre was performed, megaphones were used in public places, padayatras and other campaigns were used to educate the community on all aspects of malaria control.
As Drug Distribution Centres (DDCs) and Fever Treatment Depots (FTDs) were actively promoted with Government support, these became the most popular among the people. Every person who had fever had easy access to a DDC or FTD. Full course of 10 chloroquine tablets were provided either with or without a blood smear being taken.
Baseline KAP and blood smear survey (BSS) in July 2001, BSS in March 2002 and a post evaluation KAP, BSS in July 2002 were carried out. There were significant changes in knowledge averaging about 30% from baseline to an average of about 70% at post evaluation. People could differentiate the malaria parasite from the mosquito as a cause of the diseases. A large proportion could state that 10 tablets of chloroquine was the full course of treatment. The smear positivity rate (SPR) was 17.5% at baseline; it was 61.7% in March 2002 and 22.5% at post evaluation. Qualitative data indicated that deaths due to fever suspected of malaria and referrals due to complicated malaria had decreased. There was considerable shift from seeking magicians for fever treatment to the volunteers for complete treatment with chloroquine. Pf% continued to be high ranging from 62.3% at baseline to 81.0% at post evaluation. If this level of EDPT can bring about such change within one year, a more intensive programme over a three years period could significantly bring down malaria in Orissa.
1.11 Assessment of therapeutic efficacy of chloroquine and sulpha-pyrimethamine in uncomplicated falciparum malaria
S. Biswas
Malaria Research Centre (ICMR), 22 Sham Nath Marg, Delhi, India
A standardized protocol has been developed by WHO to assess the therapeutic efficacy of antimalarial drugs against clinically manifest infection with Plasmodium falciparum in individuals of various age groups. The therapeutic efficacy protocol is based on clinical and parasitological responses of the patients and it has the purpose of determining the practical efficacy of the drug regimen in study areas with the ultimate objective of ascertaining its continued usefulness or the necessity for replacing it in the routine treatment. Present study has been conducted at six sites: Kathiatali and Simanabasti of District Nagaon, Assam; Sonapur and Boko of District Kamrup, Assam; Keonjhar Town and Padampur of District Keonjhar, Orissa. In order to reduce the patient recruitment time, health center close to well-defined community was identified to conduct the activities at peak malaria season by selecting local pockets and organizing mobile clinics. Microscopically confirmed cases of P. falciparum were enrolled according to the criteria given for inclusion and exclusion. Treatment with recommended drug was given under supervision and the test schedule to follow-up the patients at various intervals for 28 days was maintained. The data will be discussed.
Session-II
Understanding of Vectors– The Targets for Effective Malaria Control
2.1 Plasmodium sporozoites modulate insect immune pathways: strategy for survival in the mosquito hemolymph
Mohammad Shahabuddin (e-mail: MSHAHABUDD@niaid.nih.gov)
National Institute of Health, Bethesda, Maryland, USA
Malaria remains the most devastating insect borne diseases of humans because of its persistent transmission by mosquitoes. Incessant transmission of the malaria parasite by mosquitoes suggests that the parasite sporozoite is able to evade the potent insect antimicrobial immune response, which efficiently clears inoculated bacteria and fungi from the hemolymph. Earlier we showed, like in the mosquito, infectious sporozoites can also develop in Drosophila melanogaster (Science, 2000, 288:2376), and Drosophila can serve as a model for malaria transmission biology study. To understand the molecular basis of Plasmodium survival in vector insects we expressed two sporozoite surface proteins in transgenic Drosophila and examined their effects on all known immune related genes. The results showed that Plasmodium sporozoite proteins induce expression of the extracellular serine protease inhibitor, serpin43Ac, which blocks the activation of the Toll ligand, Spatzle. The sporozoite proteins also induce the intracellular mammalian IkB homologue, cactus, which inhibits activation of NFkB homologues Dif and Dorsal, the activators of antimicrobial gene expression. Furthermore, expression of Dif and Dorsal were not induced by the malaria proteins. As a consequence most known antimicrobial peptide genes are not expressed. These results suggest that malaria sporozoites are able to modulate the insect innate immune response leading to survival and transmission to human. A major implication of this work is that it provides a mechanism by which the malarial parasites may evade killing by the mosquito immune system. We will describe use of the information obtained from the transgenic Drosophila and the recently available genomic sequence of Anopheles gambiae for cloning immune related genes of the human malaria vector and study of regulation of Plasmodium survival in naturally infected mosquitoes. These may lead to developing strategies to modify anti-plasmodial immune response in mosquitoes and control of transmission of malaria.
2.2 Interrupting malaria transmission by genetic manipulation of anopheline mosquitoes
Marcelo Jacobs-Lorena (e-mail: mxj3@po.cwru.edu)
Case Western Reserve University, School of Medicine, Department of Genetics, Cleveland, OH 44106.
Malaria is among the deadliest infectious diseases and kills more than one million persons every year. The mosquito is an obligatory vector for malaria transmission. In the mosquito, Plasmodium undergoes a complex series of developmental events that includes transformation into several distinct morphological forms and the crossing of two different epithelia: midgut and salivary gland. Circumstantial evidence suggests that crossing of the epithelia requires specific interactions between Plasmodium and epithelial surface molecules.
By use of a phage display library we have identified a small peptide - SM1 - that binds to the surfaces of the mosquito midgut and salivary glands. Transgenic Anopheles stephensi mosquitoes expressing a SM1 tetramer from a blood-inducible and gut-specific promoter are substantially impaired in their ability to sustain parasite development and transmission. A second effector gene, phospholipase A2, also impairs parasite transmission in transgenic mosquitoes.
These findings have important implications for the development of new strategies for malaria control.
2.3 Insect cell lines as a tool for vector biology research
Dilip N. Deobagkar1,2 (e-mail: dndeo@unipune.ernet.in) and Prafulla K. Chandra1,
1Molecular Biology research lab, Department of Zoology 2Institute of Bioinformatics and Biotechnology, University of Pune, Ganeshkhind Road, Pune-411007, India
Like in the mammalian system, where the cell culture has played a pivotal role in the development of experimental system to explore responses to specific environmental factors, nuances of cell division and finally cell differentiation; the invertebrate cell culture system has also contributed to our understanding of biochemical and molecular events specific to them. However, in case of insects, where the adult differentiation takes place uniquely through imaginal discs, very limited, but useful information has been gathered using cell cultures. The insect cell culture systems, particularly those derived from mosquitoes, have been effectively used to carry out biochemical and molecular analysis of gene expression and environmental response to stress, pesticides etc. Early experiments on heterologous gene transfer and expression in mosquitoes have also been carried out using cells in culture. To a limited extent, insect cell systems have been used for the culture of protozoan and helminth parasites in order to understand host-parasite relationship. Gene expression using homologous and heterologous promoter elements have also been studied in mosquito cells.
In our laboratory, extension and application of results obtained with in vitro cell culture system to mosquitoes have been carried out in two different programs. The first one involves isolation of middle repetitive DNA sequences from Anopheles stephensi cell line and their use for integration of associated foreign DNA in the cellular genome. This was then successfully used to introduce foreign DNA in animal tissues by homologous recombination through such repeat sequences. Thus, these sequences could be potentially used to introduce desired DNA sequences so as to either interrupt specific genes or introduce new genes. Similarly, in the second system, using cultured cells of mosquitoes, it was shown that different stress conditions confer adaptive tolerance onto the cells. The stress condition could be temperature, pesticide, or a metabolite. These observations were again extended to show that Anopheles and Aedes mosquito larvae develop adaptive cross-tolerance through the stress protein (hsp) interactions. The in vitro cultured cell system, thus has high potential to be used for further understanding of various protein-protein interactions and also to analyse predicted protein functions from functional genomics, using genomic data
2.4 Indian anopheline vector species population structure
Sarala K. Subbarao (e-mail: sks2000@vsnl.com)
Malaria Research Centre (ICMR), 22 Sham Nath Marg, Delhi-110054, India
Anopheline fauna in India is rich with 58 morphologically identified species distributed all over the country. Of these 9 species are responsible for transmission of malaria in various capacities, which are An. annularis, An. culicifacies, An. dirus, An. fluviatilis, An. minimus, An. nivipes/philippinensis, An. stephensi, An. sundiacus and An. varuna. The nine vector species with their diverse characterstics in resting, feeding and breeding behaviour have occupied all varieties of ecological niches found in the country and have therefore become responsible for transmitting malaria throughout the country. But a closer look at the vector and malaria in the country shows distinct differences in the prevalence of both with the recognition of morphologically indistinguishable cryptic species within vector species (except in An. stephensi and An. varuna), the variation in malaria prevalence can now be explained. Using cytotaxonomic method, we recognized An. culicifacies having 5 cryptic species, An. fluviatilis 4, An. annularis 2, a single species of An. nivipes – philippinensis complex, and a new cytotype in An. sundaicus that is distinct from 3 species identified in other countries. Isoenzyme method has identified a single cryptic species of An. minimus. An. dirus in India is yet to be examined for identifying the members of the complex. An. stephensi is a single biological species comprising, 3 ecological variants, having distinct distribution.
The success of malaria control programme greatly relies on vector control and so far it has been on insecticies. Unfortunately major vectors have developed resistance to the commonly used insecticides, and responses of members of the species complexes especially those of An. culicifacies, greatly vary to different insecticides. Keeping in view that each species has a distinct pool differs in biological and ecological factors, a macro-stratification of the country for malaria control has been proposed. To develop/plan alternate and selective vector micro-level control strategies, new tools to study cryptic species populations are needed. To overcome the difficulties of identifying members of the complexes by cytotaxonomic methods, simple PCR assays are developed. As DNA markers provide powerful tools for population genetic studies, for An. culicifacies species A we have developed microsatellite markers. The markers developed are highly polymorphic, as high as 22 alleles at a single locus were found. Field populations of species A as well as Species B, have been genotyped using 12 and 9 loci respectively. These markers would also aid in mapping the genes, and for each cryptic species identifying effective breeding unit (deme) and levels of gene flow, which are being planned.
2.5 Taxonomic surveys: anopheles species diversity
B.N. Nagpal, Aruna Srivastava and Rekha Saxena
Malaria Research Centre (ICMR), 22 Sham Nath Marg, Delhi-110054, India
Ross' discovery in 1987 of malaria transmission by Anopheles mosquitoes triggered studies on the distribution of the Anopheles mosquitoes in the country to map out malaria endemicity and vector species. These studies were carried out under the auspicious of Malaria Institute of India. These surveys listed forty species and culminated in the publication of Fauna of British India. DDT spray under NAMP resulted in control of malaria and subsequently there were large scale development activities associated with ecological changes. This necessitated revalidation of Taxonomical surveys to update the knowledge on the distribution of Anopheles mosquitoes in different geo-geographical regions of the country. These surveys under taken by MRC revealed the changes in distribution of anopheles species and also ecological succession of vector and non_vector species. Important findings included i) disappearance of An. sundaicus from coastal Orissa and appearance in Kuch Bhuj area ii) reappearance of An. minimus in Northeastern region and Banbasa, Uttranchal iii) established the vectorial role of An. culicifacies in Orissa iv) confirmation of An. nivipes and An. dirus in north eastern region etc. This information helped in reorganization of existing control strategies and for development of new tools for vector interventions. Since terrain systems are ever changing such studies need to be maintained continually for appraising the changing distribution pattern of Anopheles species
2.6 GIS for mapping of malaria vectors
Aruna Srivastava, B.N. Nagpal and Rekha Saxena
Malaria Research Centre (ICMR), 22 Sham Nath Marg, Delhi-110054, India
In India, malaria is transmitted by six major vectors of malaria namely An. culicifacies, An. stephensi, An. minimus, An. fluviatilis, An. dirus, and An. sundaicus. They differ greatly in their biology, behaviour, breeding and distribution habitats. Looking to the vast areas, the reports on vector distribution are scanty as manual surveys are not only time consuming & labour intensive but many areas are inaccessible. GIS was applied to map distribution of malaria vectors using ecological parameters namely, soil type, altitude, rainfall, temperature and forest. Thematic maps in the scale of 1: 6,000,000, published by National Thematic Mapping Organization (NATMO), Govt. of India, on ecological parameters were digitized. Favourable conditions for different parameters for each species were identified from reported distribution. These conditions were extracted from each thematic map for each species and integrated to predict the distribution of vector species using ESRI Arc View 3.2.
Validation of the results were done by overlaying the maps showing location of reported distribution of the species on GIS predicted distribution and these were found to be in good coherence. For field validation of An. minimus, precision field surveys in nine locations of four states were conducted. Interestingly An. minimus could be found in all GIS predicted locations. In two districts, namely, Banbasa, distt. Nainital, and Dhubri distt., Assam, in the former, the species was reported to have disappeared after 1950s, and in later, it was not reported in earlier surveys. Amazingly, GIS predicted precisely the location in these districts to conduct entomological surveys and the species could be found there.
The technique is good specially to cover vast and inaccessible areas and can be easily duplicated in other parts of the country/ world. The technique can delineate the areas favorable for any species of flora and fauna, and is extremely useful for precision surveys to economize on survey cost and time.
The authors intend to emphasize that this unique technique identifies the favourable location for species prevalence and also identifies the areas which do not carry the breeding potential for the species. This approach can help in stratifying the areas into endemic and non-endemic areas of species for building up cost effective and sustainable control strategy.
2.7 Delineation of breeding habitats and landscape features suitable for Anopheles culicifacies
R.C. Dhiman (e-mail: dhiman1@vsnl.com)
Malaria Research Centre (ICMR), 22 Sham Nath Marg, Delhi-110054, India
Satellite remote sensing has opened new vistas of mapping of mosquitogenic conditions and identification of malaria seasons in different parts of the world. In India studies undertaken in this regard with Landsat or Indian Remote sensing satellite (IRS 1A&B) revealed that remote sensing is useful for macro-stratification of malarious areas and the breeding habitats of anopheline mosquitoes are difficult to map. With the advent of better resolution of satellites with 23.5 metre in 4 bands and 5.8 m in Panchromatic, the feasibility of mapping smaller breeding habitats increased. Therefore a study to apply remote sensing at village level was undertaken in three Primary Health centers (PHC) of Tumkur district, by selecting 10 villages in each category of high, moderate and no(least) malarious PHCs. Ground surveys for geographic reconnaissance of breeding habitats, larval density per dip, man hour density of adult An. culicifacies and other anophelines and ecological changes in landscape features were recorded in low (December/January) and peak transmission seasons of malaria. False colour composite images were developed from IRS 1C/D LISS III and PAN data and classification was done for generating statistics for different land use categories like water bodies, coconut/areca nut plantation, moist land, barren areas, agricultural plantation rocks with and without vegetation etc.
It was found that tanks, ponds, streams are easily detectable by remote sensing while irrigation wells (which were found supporting mainly An. barbirostris) were rarely detectable. Presence of water in water bodies, rocks with vegetation, coconut/arecanut plantation and less barren area were found as the landscape elements critical to malaria endemicity.
It was found that remote sensing could be used for change detection in ecology of an area at village level resulting into reduction/increase in malaria endemicity.
2.8 Biological and ecological distinctness among sibling species
Nutan Nanda
Malaria Research Centre (ICMR), 22, Sham Nath Marg, Delhi-110 054, India
Cytotaxonomic studies of natural populations of malaria vectors carried out at MRC led to the recognition of An. culicifacies, An. fluviatilis and An. annularis as species complexes. Of these the former two are primary vectors of malaria responsible for 80-85% of malaria cases in India. Spot surveys and longitudinal studies carried out in different parts of the country have revealed distinct differences in biological characteristics of the members of these complexes and their role in malaria transmission.
An. culicifacies sibling species (A, B, C, D & E) have specific distribution pattern and vary in their feeding preference, peak biting time and response to insecticides. Incrimination studies have shown species A, C, D and E to be the vectors of vivax and falciparum malaria and species B to be a poor vector, if at all. Laboratory feeding experiments with An. culicifacies sibling species have further confirmed these observations. Likewise, studies on bio-ecology of species S, T and U in An. fluviatilis complex have shown that species T and U prefer to rest in cattlesheds and are primarily zoophagic. These species appear to be playing a very minor role in malaria transmission. In contrast, species S prefers to rest in human dwellings, is highly anthropophagic and a very efficient vector in areas of its distribution.
The discovery of species complexes in malaria vectors and the differences observed in biological characteristics and vectorial potential among sibling species have added a new dimension to vector control strategy. Therefore, mapping the geographic distribution of sibling species and information generated on their biology have been very useful in malariogenic stratification of different geographical areas and in formulating situation specific vector control operations.
2.9 Tools for identification of cryptic anopheline species
O.P. Singh (e-mail: singhop@satyam.net.in), N. Nanda, K. Raghavendra, D. Chandra, G. Goswami, S. Sunil and Sarala K. Subbarao
Malaria Research Centre (ICMR), 22 Sham Nath Marg, Delhi-110054, India
Most of the malaria vectors found in Indian subcontinent are known to be complexes of morphologically indistinguishable cryptic species, some of which have been found to differ significantly in vectorial competence, host preference and susceptibility to insecticides. Identification of cryptic members of the complex is therefore necessary for any vector control programme.
Cytotaxonomical method based on species-specific paracentric inversions present in polytene chromosome or arrangement of metaphase chromosomes is the classical method which has been used for discovering 5 cryptic species in Anopheles culicifacies (responsible for 70% of total malaria cases in India), 3 species in An. fluviatilis and 2 in An. annularis, by Malaria Research Centre.
Due to technical difficulties associated with cytotaxonomy, and the fact that only small proportion of population is suitable for examination by this method, search is on for developing alternative methods, which can be used for all mosquitoes, irrespective of their stage and sex. Attempt to identify cryptic members using allozymes was not very much successful except for the differentiation of species A or D from rest of the members of An. culicifacies complex.
Molecular methods based on the ribosomal (rDNA) and mitochondrial DNA (mtDNA) have been of great interest for the identification of cryptic species. rDNA cistron, one of the multigene families, which is frequently distributed in genome in an array of tandem repeats, is preferred candidate region for PCR based species-diagnostic assays because of useful features of its sequence organization and evolution. Concerted evolution acting on rDNA arrays is believed to maintain sequence homogeneity within species. The mtDNA on the other hand being maternally inherited is of great phylogenic significance. Recently, we have developed a PCR assay based on D3 domain of rDNA, for the differentiation of all the three cryptic members of An. fluviatilis complex. PCR based methods have also been developed for the differentiation of species A/D from species B/C/E of An. culicifacies complex. More recently, a two-step PCR method based on mtDNA has been developed; the species–specificity of this assay is under evaluation.
Session-III
Vector Control Options
3.1 Prospects for comprehensive vector control in South East Asia
Chusak Prasittisuk
World Health Organization, SEARO, Indra Prastha Estate, New Delhi-110002
3.2 Challenges in vector control
National Anti Malaria Programme, 22 Sham Nath Marg, Delhi- 110054
3.3 Bioenvironmental control of Malaria in India
V.P. Sharma
Former Director, Malaria Research Centre (ICMR), Delhi-110054, India
In the mid-eighties malaria incidence in India fluctuated around 2 million parasite positive cases annually. Malaria control was becoming problematical due to the emergence of triple resistance in Anopheles culicifacies, chloroquine resistance in P. falciparum and high cost of insecticides. Epidemics and deaths due to malaria re-appeared. The over all malaria situations were deteriorating rapidly. There were no alternatives but for repeated spraying and use of new, more toxic and still more expensive insecticides. It was obvious that even the introduction of new insecticide strategy was bound to fail eventually. Faced with this formidable challenge, Malaria Research Centre drafted an innovative malaria control strategy by integrating biological and environmental management methods. This strategy was first implemented in a group of villages in Nadiad Taluka, Kheda district, Gujarat. This area had faced a serious malaria epidemic that was building up despite of insecticide spraying. Impact of bioenvironmental interventions produced spectacular results, but required to be tested in other malaria endemic ecotypes of the country. Therefore MRC expanded to new locations and tested the feasibility of malaria control in highly diverse and epidemic prone areas in the country. Results of these interventions were very encouraging in the control of industrial, urban, tribal, and coastal malaria. It was pointed out that the new technology was working in the hands of research scientists and may not work under the primary health care system, which is very important consideration for the NAMP. This exercise was undertaken in collaboration with the Health Department, Karnataka Government. In this region IRS was not acceptable by the villagers due to possible loss of silk culture, although malaria cases were rising each year, and deaths due to malaria were being reported. Implementation of bioenvironmental methods completely interrupted malaria transmission in about 400 villages within 2 years and malaria free status is being maintained in these villages for 8-10 years. In contrast malaria in the villages with DDT spraying has remained high throughout. In villages with synthetic pyrethroid spraying, malaria was initially decimated but returned with vengeance within 2 years of break in spraying. Bioenvironmental methods are indigenous, low cost, appropriate, low cost, environmentally friendly, elicited community participation and sustainable. Maharashtra government applied bioenvironmental methods in 3/4th of the state. The implementation resulted in dramatic improvement in malaria situation and has remained so for >4 years since introduction. The technology has emerged as a viable and cost effective method of malaria control in India. Most of the experience in malaria control has been with An. culicifacies and Anopheles stephensi transmitted malaria. Together these two vectors are responsible for ~ 80% malaria cases in the country. Highlights of last 20-years of the field experience would be presented as an alternative strategy to control malaria in India.
3.4 Insecticide treated nets: impact on vector populations and relevance of initial intensity of transmission and pyrethroid resistance
C.F. Curtis
London School of Hygiene & Tropical Medicine, London WC1E 7HT, U.K.
Insecticide treated bednets locate a deposit of quick-acting insecticide of low human toxicity between a sleeper and host-seeking mosquitoes. Thus a chemical barrier is added to the often incomplete physical barrier provided by the net. Treated nets may be considered as mosquito traps baited by the odour of the sleeper. Several trials, in Tanzania, Assam and elsewhere, have shown that, when a whole community are provided with treated nets, so many mosquitoes of anthropophilic species are killed on them that the density and/or the sporozoite rate of the vector population is reduced. In order to gain this “mass effect”, in addition to the personal protection of the individual net user, and thus to achieve the full potential of the treated net method, high % population coverage is necessary. This indicates that organised free provision of treated nets, comparable to a house spraying programme, is likely to be more cost effective than trying to market nets and insecticide to poor rural people.
In areas with high malaria transmission, where immunity to malaria is important, it has been argued that vector control (without vector eradication) could, in the long run, make the situation worse by preventing normal build up of immunity. However, our data from Tanzania do not support this idea: 3-4 years after provision of nets (which are re-treated annually), young children are still showing clear health benefits and older children are not “paying” for this by showing worse impact of malaria. There is less malaria morbidity in a highland area, where malaria transmission is about 20x less intense than in a nearby lowland area. The % impact on malaria morbidity of introduction of treated nets was remarkably similar in the two areas.
At present only pyrethroids are used for net treatment which suggests that emergence of pyrethroid resistance could have a disastrous effect. However, in West Africa, where there is now a high frequency of the kdr resistance gene in An. gambiae, it is reported that treated nets still have a “mass effect” on vector populations. Nevertheless, research on non-pyrethroid alternative insecticides of low human toxicity is important as a precaution against emergence of stronger forms of resistance.
3.5 Insecticide resistance and biochemical mechanisms in malaria vectors
K. Raghavendra, P.K. Mittal, O.P. Singh and Sarala K. Subbarao
Malaria Research Centre (ICMR), 22 Sham Nath Marg, Delhi-110 054, India
Use of insecticides for vector control has been the main strategy since last five decades of Indian anti-malaria campaign. Sequential introduction of new groups of insecticides to control insecticide-resistant disease vectors has led to multiple resistance in a few species.
Anopheles culicifacies is the major vector of malaria in India and is responsible for the transmission of ~ 60-70% of new cases of malaria in India. Control of malaria in India is actually control of An. culicifacies and each year ~ 70% of the allotted budget for malaria is spent for control of this species. The understanding of the transmission of malaria is further complicated by the existence of species complexes.
An. culicifacies is reported widely resistant to different insecticides used in public health: DDT - 286 districts in 18 states, DDT and HCH- 233 districts in 16 states, DDT, HCH and malathion – 72 districts in 8 states and to DDT, HCH, malathion and deltamethrin in 2 districts in 2 states. It may be mentioned that DDT-resistant An. culicifacies has not shown cross-resistance to synthetic pyrethroids as is the case with a few anophelines. An. stephensi was reported resistant to DDT in 34 districts in 7 states, to DDT and HCH - 27 districts in six states and to DDT, HCH and malathion in 8 districts in 3 states. Other vector species are mostly susceptible to these insecticides used in anti-malaria sprays.
The selection of resistance was mainly due to insecticides used in public health sprays. Studies in the state of Andhra Pradesh have shown development of malathion-resistance in this species owing to the selection by pesticides used in agriculture and in the absence of malathion spray in public health. Recently a focus of malathion-resistant-An. culicifacies was found in district Chhindwara of Madhya Pradesh, selected due to use of pesticides in agriculture and forestry.
DDT metabolism studies have indicated involvement of glutathione-S-transferases (GSTs). Biochemical assays with different malathion resistant An. culicifacies populations have indicated absence of elevated levels of esterases (Est) and insensitive acetylcholinesterase (i AChE) mechanisms indicating the possible involvement of malathion carboxylesterase (MCE). This was confirmed by specific synergistic bioassays. Synergist bioassays on deltamethrin resistant An. culicifacies have indicated involvement of mixed function oxidases.
Studies on monitoring of organophosphate and carbamate resistance in An. culicifacies in different states have indicated this species exhibits narrow spectrum resistance i.e. only to malathion. Thus, other organophosphate and carbamate insecticides can be still be used for vector control though the species has shown resistance to malathion.
3.6 Larvivorous fish in malaria control in Karnataka
S. K. Ghosh, S. N. Tiwari, A. K. Kulshrestha, T. S. Sathyanarayan and T. R. R. Sampath.
Malaria Research Centre, Epidemic Diseases Hospital, Old Madras Road, Bangalore - 560 038
Control of malaria using larvivorous fish was carried out in rural and urban areas of Karnataka from 1993 to 2001. In the rural areas, PHC Kamasamudram (93 villages, population 36,627), district Kolar where sericulture is the main occupation and PHCs Banavara and Kanakatte (160 villages, population 85918), district Hassan were selected to demonstrate the efficacy of larvivorous fishes Guppy (Poecilia reticulata) and Gambusia affinis for malaria control. Geographical Reconnaissance (GR) of larval breeding habitats revealed that wells, irrigation tanks and streams are the major breeding habitats for the main vector species An. culicifacies. In all the areas Guppy was found to be suitable in wells and streams while Gambusia in tanks. Entomological monitoring revealed significant impact on both larval and adult densities of An. culicifacies (P<0.001). Impact on malaria annual parasitic incidence was highly significant. At PHC Kamasamudram API was 41.8 in 1993, 15.0 in 1994, 11.1 in 1995, 12.3 in 1996, 4.0 in 1997, 1.2 in 1998, 0.1 in 1999, 0.05 in 2000 and 0.1 in 2001. At PHCs Banavara and Kanakatte API was 133.8 in 1995, 54.3 in 1996, 3.8 in 1997, 2.1 in 1998,4.8 in 1999,8.0 in 2000 and 14.6 in 2001.
In the urban coastal city of Mangalore malaria was problematic in the mid-nineties due to more construction activity. From meagre 198 cases in 1991 it went upto 9874 in 1996 and subsequently came down to 2874 in 2001. Entomological studies carried out from 1998 to 2002 revealed that Anopheles stephensi is the main vector and found to breed in over head tanks, cemented tanks, wells, fountains, curing tanks/water. Breeding site wise strategic control measures were undertaken and majority of vector breeding was controlled releasing Guppy in wells, fountains and cemented tanks resulting in control of malaria. Presently a separate `Malaria Cell’ has been initiated in the health department of City Corporation. The work is being carried out with the active participation of local health, fisheries, rural development departments and NGOs. This method is sustainable and economical than any other method.
3.7 Biocides in vector control: challenges and prospects
P.K. Mittal
Malaria Research Centre, 22, Sham Nath Marg, Delhi-110054, India
Biocides, based on mosquitocidal toxins of certain strains of Bacillus sphaericus and Bacillus thuringiensis var. israelensis H-14 (Bti) are highly effective against mosquito larvae at very low doses and safe to other non-target organisms. During past two decades various biocide formulations produced in India and abroad have been tested at MRC and some formulations have undergone large scale operational trials.
Biocide formulations of B. sphaericus are useful in the control of Culex and certain Anopheles spp., such as An. stephensi and An. subpictus, but not much effective against An. culicifacies and almost ineffective against Aedes aegypti. Repeated application of B.sphaericus in same habitat, however, results in the development of resistance in larvae of target mosquitoes. In view of its low specificity for An. culicifacies and the potential for resistance in An.stephensi, B.sphaericus has limited prospects for control of malaria vectors. However with some resistance management, B. sphaericus can still be used against Culex mosquitoes. On the other hand Bti formulations, which have broader spectrum of activity including Aedes, Culex, and also against Anopheles spp, have not shown significant development of resistance in mosquitoes but their activity in field, particularly against surface feeding anopheline larvae is affected by various bio-environmental factors, thus requiring weekly application in most habitats. To overcome this problem development of slow release formulations and genetically engineered biocides by transplanting mosquitocidal toxin genes of Bti and B. sphaericus in some other environmentally compatible organisms have been investigated by different scientists.
3.8 Insecticide treated mosquito nets: efficacy and sustainability
Rajpal S. Yadav (e-mail: rajpal_Yadav@yahoo.com)
Malaria Research Centre, Field Station, Nadiad 387001, Gujarat, India
Mosquito nets or curtains have been in use since long for personal protection against blood sucking and nuisance insects. Development of pyrethroid insecticides during the 1980s led to evaluation of pyrethroid treated netting and clothing materials against mosquito vectors. By 1990 small-scale trials in various countries demonstrated the effectiveness of nets treated with pyrethroids in reducing malaria and vector populations. Since 1986 efficacy of insecticide treated mosquito nets (ITNs) have been evaluated in different epidemiological situations in India. Various formulations of pyrethroids used to treat nets included deltamethrin, lambdacyhalothrin, cyfluthrin, permethrin and bifenthrin. In areas under the influence of malaria vectors An. minimus in Assam and An. fluviatilis in Orissa, ITNs remarkably reduced vectorial potential and malaria morbidity. In area with malaria transmitted by An. culicifacies, the efficacy of ITNs varied from a high in the Orissa State to a moderate-to-low in Madhya Pradesh state owing to factors such as vector- and human-behaviour and climatic conditions. A recently concluded study in Gujarat showed high persistence and wash-fastness of insecticidal action of nets treated with deltamethrin-tablet formulation against An. culcifacies and An. stephensi. Though untreated nets protected users over nonusers, insecticidal treatment of nets improved their protective efficacy markedly. ITNs have been shown to provide personal protection, as well as community protection when used by a majority of the people in a locality.
A programme to scale up the use of ITNs under governmental effort is now underway in India. Though some NGO-supported village-scale programmes have shown success in introducing nets under community financing, wider community usage of ITNs would require development and promotion of appropriate mechanisms. These may still be preceded by assessment of operational issues such as knowledge of socio-cultural preferences, extent of community affordability, IEC needs, knowledge of the sale and distribution systems of nets/insecticides in towns/countryside, safe and retail packaging of insecticides, and institutional/technical support needed by communities. India has a well-developed market to produce a variety of netting fabrics and readymade nets. The Bureau of Indian Standards and WHO have decided specifications of nets. From global experiences, doses of hitherto tested pyrethroids appropriate for treatment of nets are now known. An overview of the outcome of efficacy trials in India and issues related to up scaling and sustainability of ITNs will be discussed.
3.9 Comprehensive management of disease vectors in Ahmedabad city
R. S. Yadav1, S. Haq1, R. M. Bhatt1, V. K. Kohli2, S. K. Subbarao3 and V. P. Sharma3
1Malaria Research Centre, Field Station, Nadiad 387001, Gujarat, India; 2Ahmedabad Municipal Corporation, Ahmedabad, India; 3Malaria Research Centre (ICMR), 22 Sham Nath Marg, Delhi, India.
In 1995, the National Anti-Malaria Programme identified Ahmedabad City as one of the high malaria risk cities of India. Malaria is endemic in cities of Gujarat and dengue is now emerging in many urban areas. Though malaria control in Ahmedabad is undertaken as part of the national Urban Malaria Scheme, there was no comprehensive strategy against dengue. Between 1996 and 2001, an operational project on malaria and dengue was undertaken in Ahmedabad City in collaboration with the Ahmedabad Municipal Corporation. It led to development of a comprehensive strategy for management of malaria and dengue mosquito vectors. In two municipal wards (pop. 160,176) routine vector control by chemical larviciding, fogging and general health education was continued under the ongoing Urban Malaria Scheme. In another two municipal wards (pop. 165,584), integrated method of vector control was implemented, which included larval control by use of larvivorous fish, engineering improvements, cooperation of various urban development/services sectors, tyre/scrap removal, source reduction and elimination of intradomestic mosquito breeding, health education and community participation. During the baseline period malaria incidence and vector densities were comparable. During the intervention period beginning July 1999, the integrated strategy reduced malaria incidence and the densities of malaria (Anopheles stephensi) and dengue (Aedes spp.) vectors. The per capita annual operational cost of the integrated strategy was found comparable or even marginally lower than chemical control. Thus, it is possible to manage the vectors of malaria and dengue by adopting a comprehensive strategy which is cost-effective than routine control and has scope to reduce use of insecticides, improve the urban environment, decrease school absenteeism, generate community awareness, and encourage long-term sustainability.
Session-IV
Parasite Biology/Vaccines/Drugs
4.1 Erythrocyte invasion by malaria parasites: opportunities for vaccine development
Chetan Chitnis
International Centre for Genetic Engineering and Biotechnology (ICGEB), New Delhi
Erythrocyte invasion by malaria parasites is mediated by specific molecular interactions. Plasmodium vivax is dependent on interaction with the Duffy antigen and P. falciparum commonly uses sialic acid residues on glycophorin A as receptors for invasion. The P. vivax Duffy binding protein (PvDBP) and P. falciparum sialic acid binding protein (also known as EBA-175) are responsible for binding to these receptors during invasion. The binding domains of PvDBP and EBA-175 lie in conserved cysteine-rich regions that are referred to as P. vivax region II (PvRII) and P. falciparum region F2 (PfF2) respectively. We have developed methods to produce recombinant PvRII and PfF2 in their functional conformations. Recombinant PvRII and PfF2 were expressed in E. coli, purified from inclusion bodies under denaturing conditions, refolded by rapid dilution and purified to homogeneity by ion-exchange and gel filtration chromatography. Refolded PvRII and PfF2 were characterized to confirm that they were pure, homogenous and functional in that they bound erythrocytes with specificity. The immunogenicity of recombinant PvRII formulated in adjuvants such as SBAS2, Montanide ISA720, MF59, QS21 and alum was tested in small animals. Recombinant PvRII is highly immunogenic in mice and elicits high titre binding inhibitory antibodies. Purified rabbit antibodies raised against refolded PfF2 were tested for inhibition of erythrocyte invasion in vitro. Importantly, anti-PfF2 rabbit antibodies block erythrocyte invasion of P. falciparum isolates that use multiple sialic acid-glycophorin A independent invasion pathways. These studies provide support for the inclusion of PvRII and PfF2 in vaccines for P. vivax and P. falciparum malaria.
4.2 Top-down and bottom-up approaches to understand malaria transmission biology- investigations in progress!
Nirbhay Kumar (e-mail: nkumar@jhsph.edu), Mrinal Bhattacharyya, Darin Kongkasuriyachai, Cevahir Coban, Mobolaji Okulate,
Johns Hopkins Malaria Research Institute, Molecular Microbiology and Immunology, Bloomberg School of Public Health, Baltimore, MD 21205, USA.
Sexual differentiation and subsequent development of gametocytes infectious to mosquitoes occupies a central role in the process of malaria transmission biology. Not only is it important for continued survival of the parasite species, sexual development also facilitates genetic recombination (inter-strain and intra-strain) leading to generation of the genetic diversity in the parasite species. The biology of the sexual stages and the molecular mechanisms involved in genet