Infectivity of Anopheles darlingi with symptomatic and asymptomatic Plasmodium vivax infections in the Peruvian Amazon

Asymptomatic carriers of Plasmodium vivax, an infected person who does not show any symptom, have been already described in the Peruvian Amazon malaria transmission setting. Furthermore, most of these infections are submicroscopic and only detected by molecular methods. Because the lack of symptoms and likely untreated, they may act as Plasmodium vivax reservoir and maintain the malaria cycle. The objective of this study was to evaluate the roll of asymptomatic patients in malaria transmission in Anopheles darlingi, the main malaria vector in the Peruvian Amazon. Two subgroups were defined within the asymptomatic patients (blood smear positive and blood smear negative/RT-PCR positive) and experimental infections of An. darlingi were performed by a standard membrane-feeding system, besides symptomatic patients with high parasitemia were used as controls. Three patients out of fifteen asymptomatic with positive blood smear infected An. darlingi ( 20%) with a mean of 1.4 ± 0.163 oocysts by mosquito whereas 17 (77%) of twenty-two symptomatic development oocysts in mosquitoes with a mean of 23.9 ± 8.34. Neither asymptomatic negative blood smear/RT-PCR positive (n=23) infected mosquitoes. Although the asymptomatic group did infect mosquitoes at a very low rate, these subjects supposedly remain with parasitemia longer than the treated symptomatic patients. These results have implications for the malaria control program in Peru, which focuses essentially on the treatment of symptomatic patients. Further follow-up studies of asymptomatic carriers are needed to determine variations of transmission ability.