Abstract
Natural antibody (IgG + IgM) responses to putative vaccine candidate, Plasmodium vivax Merozoite Surface Protein-4, in acute vivax malaria patients in endemic and non-endemic areas of Sri Lanka, were assayed by indirect ELISA using PvMSP-4 baculovirus derived recombinant protein. The study populations were from two vivax malaria endemic areas, Anuradhapura and Kataragama and from a non-endemic area, Colombo. PvMSP4 appeared to be immunogenic in all test populations with a prevalence of 80%, 62% and 62% from Colombo, Anuradhapura and Kataragama, respectively. A significantly higher prevalence and antibody magnitude was recorded for non-endemic Colombo, but with no significant differences between individuals previously not exposed to malaria and those with prior exposure. A positive trend in responders from Kataragama was evident between the antibody prevalence and previous exposure. We previously reported the antibody response to PvMSP-1 (p19 and p42) using the same battery of sera, and when comparisons were drawn, more than 80% from each test area responded to at least one of the three antigens tested. Importantly, 7%, 11% and 4% of individuals from Colombo, Anuradhapura, and Kataragama, respectively, preferentially recognized PvMSP-4. Responders to MSP-1p42 and p19 in paired combination showed higher prevalence compared with combinations of MSP-1 with MSP-4. doi: 10.4038/cjsbs.v37i1.499 Cey. J. Sci. (Bio. Sci.) 37 (1): 97-105, 2008
Highlights
The global burden of malaria due to Plasmodium vivax is ~70-80 million cases annually
We report a cross sectional study examining for the first time the naturally acquired antibody responses to P. vivax MSP-4 by ELISA using baculovirus expressed recombinant protein, in test populations living in two malaria endemic regions (Anuradhapura and Kataragama) and a nonendemic region (Colombo) in Sri Lanka
As most malaria infections are symptomatic in patients from Sri Lanka (Mendis et al, 1990, Gunewardena et al, 1994) and malaria episodes are routinely confirmed by microscopy prior to treatment, the self-reported number of past clinical episodes (P. vivax and P. falciparum) was used to classify these patients in to four categories based on number of previous exposure to malaria: i) 0 infections, ii) 1-2 infections, iii) 3-5 infections, iv)>5 infections
Summary
The global burden of malaria due to Plasmodium vivax is ~70-80 million cases annually. Alternative control measures such as impregnated bed nets show some promise, it is agreed that an effective subunit vaccine would be an important advance in combating this disease (Hoffman et al, 1991) Such an effective malaria vaccine containing multiple proteins from all stages of parasite development, including the asexual blood stage, should elicit an immune response that either destroys the parasite or its infected host cell, or inhibit a function that is crucial to its survival (Hoffman et al, 2002). Considerable effort is devoted to identify asexual stage antigens that are exposed proteins of the parasite, as these would induce host protective responses and would be promising targets for vaccines Immune responses to such antigens were shown to interfere with merozoite invasion in vitro and in some cases to offer protection from infection in animal models (Anders et al, 1993)
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