Abstract
BackgroundAnopheles darlingi is the major malaria vector in countries located in the Amazon region. Anopheles aquasalis and Anopheles albitarsis s.l. are also proven vectors in this region. Anopheles nuneztovari s.l. and Anopheles triannulatus s.l. were found infected with Plasmodium vivax; however, their status as vectors is not yet well defined. Knowledge of susceptibility of Amazon anopheline populations to Plasmodium infection is necessary to better understand their vector capacity. Laboratory colonization of An. darlingi, the main Amazon vector, has proven to be difficult and presently An. aquasalis is the only available autonomous colony.MethodsLarvae of An. darlingi, An. albitarsis s.l., An. nuneztovari s.l. and An. triannulatus s.l. were collected in the field and reared until adult stage. Adults of An. aquasalis were obtained from a well-established colony. Mosquitoes were blood-fed using a membrane-feeding device containing infected blood from malarial patients.The infection of the distinct Anopheles species was evaluated by the impact variance of the following parameters: (a) parasitaemia density; (b) blood serum inactivation of the infective bloodmeal; (c) influence of gametocyte number on infection rates and number of oocysts. The goal of this work was to compare the susceptibility to P. vivax of four field-collected Anopheles species with colonized An. aquasalis.ResultsAll Anopheles species tested were susceptible to P. vivax infection, nevertheless the proportion of infected mosquitoes and the infection intensity measured by oocyst number varied significantly among species. Inactivation of the blood serum prior to mosquito feeding increased infection rates in An. darlingi and An. triannulatus s.l., but was diminished in An. albitarsis s.l. and An. aquasalis. There was a positive correlation between gametocyte density and the infection rate in all tests (Z = −8.37; p < 0.001) but varied among the mosquito species. Anopheles albitarsis s.l., An. aquasalis and An. nuneztovari s.l. had higher infection rates than An. darlingi.ConclusionAll field-collected Anopheles species, as well as colonized An. aquasalis are susceptible to experimental P. vivax infections by membrane feeding assays. Anopheles darlingi, An. albitarsis s.l. and An. aquasalis are very susceptible to P. vivax infection. However, colonized An. aquasalis mosquitoes showed the higher infection intensity represented by infection rate and oocyst numbers. This study is the first to characterize experimental development of Plasmodium infections in Amazon Anopheles vectors and also to endorse that P. vivax infection of colonized An. aquasalis is a feasible laboratory model.
Highlights
Anopheles darlingi is the major malaria vector in countries located in the Amazon region
An. darlingi and An. triannulatus s.l. fed the most rapidly with 64% of individuals fed to repletion in 40 minutes
Anopheles darlingi had a significantly higher infection rate compared with An. triannulatus s.l. (G = 13.1, GL = 1, p = 0.001) (Figure 1)
Summary
Anopheles darlingi is the major malaria vector in countries located in the Amazon region. Malaria threatens almost one third of the world population in 103 tropical countries, resulting in 207 million of clinical cases and 627,000 deaths in 2012 [1]. In the Americas, 21 countries are affected by malaria, with approximately 1.1 million cases in 2010, most of which occurred in the Amazon basin, which covers 40% of South American territory. In Brazil, 84% of registered malaria cases are caused by P. vivax [2]. The consequences of this increase in distribution are higher exposure and increased infection, adding to difficulties in controlling the disease. P. vivax malaria is generally considered to be relatively benign, there are numerous reports of complex cases with severe clinical complications and deaths [3,4,5,6,7,8,9,10]
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