Longitudinal study of Plasmodium falciparum and Plasmodium vivax in a Karen population in Thailand

Abstract

<p>Abstract</p> <p>Background</p> <p>Clinical case treatment of malaria infections where <it>Plasmodium falciparum </it>and <it>Plasmodium vivax </it>are sympatric has achieved effective reductions in <it>P. falciparum </it>prevalence and incidence rates, but has been less successful for <it>P. vivax</it>. The high transmissibility of <it>P. vivax </it>and its capacity to relapse have been suggested to make it a harder parasite species to control.</p> <p>Methods</p> <p>A clinical malaria case treatment programme was carried out over a decade in a Karen community composed of seven hamlets on the Thai-Myanmar border.</p> <p>Results</p> <p>From 1994 to 2004, prevalence rates of both <it>P. falciparum </it>and <it>P. vivax </it>decreased by 70–90% in six of the seven study hamlets, but were unchanged in one hamlet. Overall, incidence rates decreased by 72% and 76% for <it>P. falciparum </it>and <it>P. vivax </it>respectively over the period 1999–2004. The age-incidence and prevalence curves suggested that <it>P. vivax </it>was more transmissible than <it>P. falciparum </it>despite a greater overall burden of infection with <it>P. falciparum</it>. Male gender was associated with increased risk of clinical presentation with either parasite species. Children (< 15 years old) had an increased risk of presenting with <it>P. vivax </it>but not <it>P. falciparum</it>.</p> <p>Conclusion</p> <p>There was a considerable reduction in incidence rates of both <it>P. vivax </it>and <it>P. falciparum </it>over a decade following implementation of a case treatment programme. The concern that intervention methods would inadvertently favour one species over another, or even lead to an increase in one parasite species, does not appear to be fulfilled in this case.</p