Purpose of Study In Peru, the incidence of malaria has increased dramatically since the early 1990s and Plasmodium vivax remains the predominant species. Although P. vivax does not cause life-threatening disease, it is still a considerable source of morbidity but has been widely understudied. This study was conducted to determine the transmission patterns of P. vivax from naturally infected patients in the Peruvian Amazon to Anopheles darlingi mosquitoes.
Methods The study was conducted over a period of 14 months from May 2004 to June 2005 and included symptomatic patients with P. vivax malaria from Iquitos, Peru. The widely used artificial membrane feeding method was used to infect mosquitoes. Mosquito midguts were dissected after a week and oocysts were counted by microscopic examination.
Summary of Results A total of 102 patients with symptomatic P. vivax infection were enrolled in the study. Approximately 50% (50/102) of the patients were febrile, with a temperature of 37.7°C or more. Pallor was noted in 64.7% (66/102) patients. Gametocytemia ranged from 0-106 with a mean of 20.61. A total of 4,017 mosquitoes successfully fed on the blood using the artificial membrane feeding technique, with 2,631 (65%) surviving until the time of midgut dissection. Approximately 50% (52/102) of the patient specimens infected mosquitoes and 23% (602/2,631) of the mosquitoes had at least one reported oocyst. The mean oocyst load per infected midgut was 21.1 with a range of 0-395.
Conclusions This is the first study of its kind conducted in the Peruvian Amazon. There were 2 important observations: (1) only half of the patients were able to infect mosquitoes and (2) there was substantial variation in the transmission of infection to mosquitoes as measured by oocyst loads and percentage mosquitoes infected. Determining factors that affect transmission (eg, anemia, gametocyte count and maturity, fever, anti-inflammatory medications, antigametocyte antibodies) will help identify alternative interventions that can be used in addition to the current control measures. Patients who are more efficient transmitters can then be targeted first for these interventional methods.