Main Faculty Dr. Shiroma Handunetti serves as our collaborator in Sri Lanka. Dr. Handunnetti has extensive training experiences in the Unites States, France and Sri Lanka, where she currently serves as the Director of the Malaria Research Unit, at the University of Colombo. She has wide experience in the field of malarial epidemology, both at the molecular and immuologic level; and in addition directs major research projects on malarial vaccines in Sri Lanka. Dr. Handunetti's laboratory has expertise in a diverse range of techniques aimed at examining the molecular epidemiology of malaria, malarial immunology, malarial entomology, malarial pathogenesis, antigenic diversity of malaria parasites, and interaction of nutritional status and malaria.

Dr. Preethi Randeniya's research focuses on the immunologic and molecular aspects of malarial epidemiology in Sri Lanka. She has directed a number of projects aimed at uncovering the immunologic determinants of malarial disease outcome and has wide experience with a range of immunological and molecular techniques specific to the malarial system. Mr. Thilan Wickramarachchi is a senior graduate student at the Malaria Research Unit, University of Colombo. Mr. Wickramarachchi is currently finishing up his thesis project, which involves the characterization of host immune response to the vaccine candidate AMA-1.

Dr. Sunil Premawansa has extensive experience in all techniques relevant to the molecular epidemiology of malaria, and has been instrumental in setting up the transfer of technology related to various aspecpt of molecular biology in Sri Lanka. He has directed a number of projects aimed at defining parasite virulence factors, such as var genes, as well as host genetic polymorphisms which affect severity of disease, underlying pathology and outcome of malarial infection.

Dr Renu Wickramasinghe is a malarial epidemiologist focusing on malarial immunity during pregnancy. She has wide experience with both immunologic and molecular techniques relating to malaria and was involved in a joint project with the Wirth lab, where she established transient transfection system for the first time in the Plasmodium system. Dr. Nadira Karunaweera serves as the head of the Parasitology department and her work involves studying cytokine mediated immune response to P.vivax malaria. She also has extensive clinical experience and knowledge of malaria in Sri Lanka and has published widely on anti-parasite immunity against the disease and pathophysiology of malaria.

Research Plan
Genetic diversity of the vaccine candidates, AMA-1 and MSP-1, from clinical isolates of Plasmodium falciparum and Plasmodium vivax in Sri Lanka

The most lethal form of malaria, caused by the parasite Plasmodium falciparum, has an annual case prevalence of 300-500 million in tropical regions around the world. P.vivax, the most widespread of human malarial parasites, accounts for another 70-80 million cases per year.  Although less virulent than P.falciparum, sporadic reports of fatal P.vivax infections together with growing resistance to chloroquine in both, calls for the deployment of effective vaccines.  The assessment of genetic diversity among parasite populations has significant relevance for both the control and epidemiology of malaria. In fact, the recent availability of parasite genome sequence has helped to advance our knowledge of its population structure (1-6), which in turn, has provided useful leads for vaccine and drug target identification, as well as raised interesting questions about its evolutionary past. 

For example, some population genetic studies in P.falciparum propose that the extant population includes multiple ancient lineages (1, 7, 8), whereas others find evidence for its derivation from a small number of haploid progenitors via the selectively driven "sweep" of its genome (2, 4, 5, 9). Additional analyses of diversity among independent isolates, different species of Plasmodium, as well as other coding and non-coding sequence, as proposed in the current study, will help resolve this debate (10). 

In addition these studies reveal uneven distribution of polymorphism across the parasite genome (3, 6), strongly suggesting that certain sequences may be under varying selective constraints due to immune or drug pressure, for example. Indeed, numerous genetic analyses in parasite antigens such as AMA-1 (apical membrane antigen) and MSP-1 (merozoite surface protein) have identified polymorphisms that are likely maintained by diversifying selection due to immunity (11-16). 

We wish to extend a similar analysis to parasite populations in Sri Lanka by examining diversity at the AMA-1 and MSP-1 gene loci in clinical isolates of P.vivax and P. falciparum. The co-existence of both species in the same locality gives us a unique opportunity to compare the evolutionary and selective constraints affecting each.  In addition, the island biogeography of this site may impose unique selective pressures on its parasite population, resulting in a genetic structure that may be distinct from that of other endemic regions.  An extensive analysis of this type has yet to be conducted from field isolates in Sri Lanka, and will prove useful for identifying those regions that are under selection and hence immunologically relevant for vaccine development.  Lastly, we will ascertain the level of DNA polymorphism in 5' and 3' regulatory sequences relative to corresponding coding sequence, in order to determine whether the former are subject to similar selective constraints; these data will independently test the selection sweep hypothesis and should also help identify functionally relevant variation which may be important for gene regulation in the parasite.

References

1.         J. Mu et al., Nature 418, 323 (Jul 18, 2002).

2.         S. K. Volkman et al., Science 293, 482 (Jul 20, 2001).

3.         S. K. Volkman et al., Science 298, 216 (Oct 4, 2002).

4.         S. M. Rich, R. R. Hudson, F. J. Ayala, Proc Natl Acad Sci U S A 94, 13040 (Nov 25, 1997).

5.         A. A. Escalante, A. A. Lal, F. J. Ayala, Genetics 149, 189 (May, 1998).

6.         X. Feng et al., Proc Natl Acad Sci U S A 100, 8502 (Jul 8, 2003).

7.         J. C. Wootton et al., Nature 418, 320 (Jul 18, 2002).

8.         A. L. Hughes, Mol Biol Evol 9, 381 (May, 1992).

9.         D. L. Hartl et al., Trends Parasitol 18, 266 (Jun, 2002).

10.       X. Z. Su, J. Mu, D. A. Joy, Microbes Infect 5, 891 (Aug, 2003).

11.       D. J. Conway et al., Nat Med 6, 689 (Jun, 2000).

12.       S. D. Polley, D. J. Conway, Genetics 158, 1505 (Aug, 2001).

13.       M. Figtree et al., Mol Biochem Parasitol 108, 53 (Apr 30, 2000).

14.       A. A. Escalante et al., Mol Biochem Parasitol 113, 279 (Apr 6, 2001).

15.       A. Cortes et al., Infect Immun 71, 1416 (Mar, 2003).

16.       C. Putaporntip et al., Proc Natl Acad Sci U S A 99, 16348 (Dec 10, 2002).