Asymptomatic Carriers of Plasmodium spp. as Infection Source for Malaria Vector Mosquitoes in the Brazilian Amazon

Abstract

We have described the existence of asymptomatic carriers of Plasmodium vivax and Plasmodium falciparum infections in native Amazon populations. Most of them had low parasitemias, detected only by polymerase chain reaction (PCR). Because they remain symptomless and untreated, we wanted to determine whether they could infect Anopheles darlingi Root, the main Brazilian vector, and act as disease reservoirs. Fifteen adult asymptomatic patients (PCR positive only) were selected, and experimental infections of mosquitoes were performed by direct feeding and by a membrane-feeding system. Seventeen adult symptomatic patients with high parasitemias were used as controls. We found an infection rate in An. darlingi of 1.2% for the asymptomatic carriers and 22% for the symptomatic carriers. Although the asymptomatic group infected mosquitoes at a much lower rate, these patients remain infective longer than treated, symptomatic patients. Also, the prevalence of asymptomatic infections is 4 to 5 times higher than symptomatic infections among natives. These results have implications for the malaria control program in Brazil, which focuses essentially on the treatment of symptomatic patients.

Urban malaria in the Brazilian Western Amazon Region I: high prevalence of asymptomatic carriers in an urban riverside district is associated with a high level of clinical malaria

“…We also demonstrated under laboratory conditions that asymptomatic carriers could infect mosquitoes (Alves et al 2005). In addition, analysis of the genetic make-up of P. falciparum parasites obtained from asymptomatic individuals and clinical P. falciparum malaria cases examined in 2001 and 2002 showed a similar haplotype composition with regard basis of microsatellite markers (Dalla-Martha pers.…”

Urban and suburban malaria in Rondônia (Brazilian Western Amazon) II: perennial transmissions with high anopheline densities are associated with human environmental changes

“…Vila Candelária is a riverside district of the city, less than 2 km far from the city center. In the longitudinal follow up, from 2001 to 2004, it was observed a period of high malaria incidence in the rainy season, peaking in April-May, and a season of lower incidence in the dry season (June to August) characteristic of flooding areas of the rural riverine profile model described for Amazonian localities (Alves et al 2002(Alves et al , 2005. However, other high incidence periods were irregularly observed in the dry season, as described in dry land areas of Rondônia (Camargo et al 1994(Camargo et al , 1996.…”

Malaria Parasites in the Asymptomatic: Looking for the Hay in the Haystack

“…Symptomless infections that persist during the dry season in areas of seasonal transmission have been suggested to seed the malaria outbreaks after annual rains when mosquitoes reappear [3]. Similarly, asymptomatic parasitemia may potentially contribute to persistence of transmission in low-transmission settings [4]. However, the precise contribution of asymptomatic malaria to transmission in areas that have achieved substantial reductions in the malaria burden remains a matter of debate [5], as is the assumption that detecting and targeting these individuals for radical treatment, as opposed to using mass drug administration approaches, would be an efficient and effective tactic.…”