A high prevalence of asymptomatic malaria in a tribal population of Eastern India
Asymptomatic infection mainly by P. falciparum is an important obstacle to eliminate malaria. Asymptomatic carriers do not seek treatment for their infection, constituting a reservoir and thus pose a real public-health risk. The systematic identification and treatment of asymptomatic infection should reduce the parasite reservoir, if this pool is greatly reduced, it will have an impact on disease transmission.
A tribal population of 1040 individuals in Purulia district, West Bengal were screened by Rapid Diagnostic Kit (dual antigen), microscopy and species specific PCR. All the positive cases were treated by Artemisinin-based Combination Therapy (Artesunate+Sulphadoxine-Pyrimethamine) and followed-up for 42 days. Polymorphisms in candidate genes were screened by DNA sequencing method.
Significant proportion (8.4%) of the study population was infected with P. falciparum without any clinical manifestations. The PCR method was more sensitive than RDK and Microscopy. The efficacy of used ACT was 97%. In pfcrtgene K76T was found in100 % cases. In pfmdr1, mutant N86Y and Y184F were noted in 55.5% and 11% cases respectively. Six different haplotypes were noticed in pfdhfr-pfdhps genes. Most importantly a quintuple mutant A16I51R59N108I164-S436G437E540A581A 613 was found in 10% isolates, which is potentially important for Sulphadoxine-Pyrimethamine resistance.
A significant proportion of study population harbouring P. falciparum, do not seek treatment, thus acting as reservoir of parasite, maintaining the natural cycle. If Malaria Control Programmes really emphasise to eliminate malaria, then this hidden parasite burden should be addressed properly. Similar study in other parts of the country could help to determine the problem magnitude.
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