Random distribution of mixed species malaria infections in Papua New Guinea

Plasmodium falciparum (Pf), P. vivax (Pv), P. malariae (Pm), and P. ovale ( Po) infections are endemic in coastal areas of Papua New Guinea. Here 2,162 individuals living near Dreikikir, East Sepik Province, have been analyzed for complexity of malaria infection by blood smear and polymerase chain re action (PCR) diagnoses. According to blood smear, the overall prevalence of Plasmodium infection was 0.320. Most individuals (0.283) were infected wit h a single species only. The prevalence of mixed species infections was low (0.037). Further analysis of a 173-sample subset by nested PCR of small su bunit ribosomal DNA resulted in an overall 3.0-fold increase in prevalence of infection, with a 17.5-fold increase in the frequency of mixed species i nfections. Among mixed species infections detected by PCR, the frequency of double species was 0.364, and that of triple species was 0.237. Nine indiv iduals (0.052) were infected with all 4 species. To determine if infection status (uninfected, single, and multiple infections) deviates from an indep endent random distribution (null hypothesis), observed versus expected freq uencies of all combinations of Plasmodium species infections, or assemblage s (Pf-, Pv-, Pm-, Po-, to Pf+, Pv+, Pm+, Po+), were compared using a multip le-kind lottery model. All 4 species were randomly distributed whether diag nosed by blood smear or PCR in the overall population and when divided into age group categories. These findings suggest that mixed species malaria in fections are common, and that Plasmodium species appear to establish infect ion independent of one another.