High prevalence and gender bias in distribution of Plasmodium malariae infection in central east-coast India.

Light microscopy, the mainstay of malaria diagnosis in epidemiologic studies, exhibits limited sensitivity for detecting low level infections and often under-estimates the frequency of mixed Plasmodium species infections. To overcome these shortcomings we performed the PCR method for detection and identification of Plasmodium species in blood specimens from 242 individuals collected during the peak season of malaria incidence (July-October). Malaria prevalence was 81.4% and 43.4% by PCR and microscopy respectively. Moreover, while PCR detected Plasmodium malariae DNA in 108 (44.6%), microscopic examination detected only 20 (8.3%) individuals parasitized with this species. Further data analysis revealed an independent random distribution pattern of parasites irrespective of age groups (0-5 yrs, chi-square7df=2.77, P>0.95; 6-15 yrs, chi-square7df=4.82, P>0.50; >15 yrs, chi-square7df=4.4, P>0.70) and sexes (for male chi-square7df=2.48, P>0.95; for female, chi-square7df=1.85, P>0.95). However, although the parasite distribution is random irrespective of sex, females had more P. malariae infections (P=0.004, OR=2.312, 95% CI=1.3-4.1). Our study demonstrates that the parasite distribution in Orissa is random with substantially higher prevalence of P.malariae than previously suspected and this may be seasonal. A study of the bionomics of vector(s) responsible for P. malariae transmission in Orissa is needed to provide information for the control of malaria in the state.