Plasmodium knowlesi and human malaria parasites in Khan Phu, Vietnam: Gametocyte production in humans and frequent co-infection of mosquitoes.

Four species of malaria parasite, Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae and Plasmodium knowlesi infect humans living in the Khanh Phu commune, Khanh Hoa Province, Vietnam. The latter species also infects wild macaque monkeys in this region. In order to understand the transmission dynamics of the three species, we attempted to detect gametocytes of the three species in the blood of infected individuals, and sporozoites in the salivary glands of mosquitoes from the same region. For the detection of gametocyte-specific mRNA, we targeted region 3 of pfg377, pvs25, pmg and pks25 as indicators of the presence of P. falciparum, P. vivax, P. malariae and P. knowlesi gametocytes, respectively. Gametocyte-specific mRNA was present in 37, 61, 0 and 47% of people infected with P. falciparum (n = 95), P. vivax (n = 69), P. malariae (n = 6) or P. knowlesi (n = 32), respectively. We found that 70% of mosquitoes that had P. knowlesi in their salivary glands also carried human malaria parasites, suggesting that mosquitoes are infected with P. knowlesi from human infections.

A field test of a biochemical key to identify members of the Anopheles gambiae group of species in north-east Tanzania.

The usefulness of a proposed biochemical key to the species of the Anopheles gambiae complex is tested against the standard chromosomal method in N.E. Tanzania. The chromosomal identifications indicate the presence of three sibling species of the complex in this area, partly in coexisting populations. The electromorph frequencies at the diagnostic enzyme loci, octanol-dehydrogenase (Odh) and superoxide dismutase (Sod), show neither significant geographical nor seasonal variation. It is confirmed that A. merus can be distinguished unambiguously on its Sod genotype. A. gambiae s.s. and A. arabiensis can be identified, using the differences in their Odh polymorphism, with an average error of misidentification of 1 in 300. It is concluded that the biochemical key is sufficiently reliable to be a valuable additional taxonomic tool in the study area.