Malaria Vectors, Epidemiology, and the Re-Emergence ofAnopheles darlingiin Belém, Pará, Brazil

Abstract

An evaluation of malaria transmission and epidemiology in the Amazonian city of Belém over the last 70 years shows that (1) Anopheles darlingi, reported to be eradicated in 1968, reappeared in the mid 1990s, with a marked increase in abundance between 1997 to 1999 in two of three districts sampled; (2) An. darlingi and An. aquasalis are each implicated in current malaria transmission in different districts of the city; (3) mosquito species diversity (in Anopheles subgenus Nyssorhynchus) has increased from two in the 1930s to six in the 1940s to 10 in the 1990s; (4) there is no overall correlation between malaria case incidence and human population size from 1940 to 1996 in Belém; (5) however, the total number of malaria cases has increased significantly since the late 1970s and over the short term from 1993 to 1999; and (6) interestingly, the short term increases are due solely to cases of Plasmodium vivax infection; cases of P. falciparum malaria are declining (significantly for Pará state only). The reappearance of An. darlingi may be a result of the continued expansion of Belém into the surrounding forest in the 1990s. In the absence of preventative measures, we predict an increase in local outbreaks of malaria in the DAENT and DAICO districts where the population sizes of An. darlingi are increasing.

The importance of Anopheles albitarsis E and An. darlingi in human malaria transmission in Boa Vista, state of Roraima, Brazil

“…Thick blood smears also underestimate the prevalence of P. malariae in humans (Scopel et al 2004). These findings suggest that accurate diagnosis of P. malariae should be a higher priority because this parasite results in low, but significant levels of morbidity in humans (Collins et al 2004), there has been a recent resurgence in human cases in Pará (Póvoa et al 2003) as well as in Suriname (PAHO 2002) and misdiagnosis may mean that the wrong antimalarial treatment is given (Scopel et al 2004). Because our collections identified An.…”

Can mosquitoes help to unravel the community structure of Plasmodium species?

“…In the 1930s, they were estimated to represent 40% (P. vivax) and 60% (P. falciparum) of the human malaria cases in Pará state (Brazil) [27], and similar proportions were observed in the 1980s in Brazil [28]. In a recent article by Póvoa et al…”

“…In the 1930s, they were estimated to represent 40% (P. vivax) and 60% (P. falciparum) of the human malaria cases in Pará state (Brazil) [27], and similar proportions were observed in the 1980s in Brazil [28]. In a recent article by Póvoa et al [28], Anopheles darlingi is described as re-emerging in Brazil in Belem and Pará , leading to an increase in the number of malaria cases, all species confounded. It is striking that this increase in malaria incidence is due to P. vivax (and, to a much lesser extent, P. malariae), whereas the incidence of P. falciparum is decreasing.…”

“…the P. vivax infections were 'cryptic'). However, even if mixed infections in humans were underestimated, as shown recently [31,32], their proportions would remain extremely low [28]. Moreover, if P. vivax co-infections were to reduce P. falciparum infection pathology, as recently suggested [3,5], treatment would inadvertently focus on P. falciparum unispecies infections.…”

“…This reflects fundamental differences in the biology of the two species, such as faster sporogonic development, the existence of latent hypnozoite liver stages and the rapid production of gametocytes in P. vivax. In the area of Brazil that was studied by Póvoa et al [28], transmission is seasonal and, therefore, it is likely that the parasites persist in a human infectious reservoir from which they must infect the first mosquitoes of the season. Such seasonality would initially give P. vivax the advantage because it infects mosquitoes first, and P. vivax gametocyte densities might dominate those of P. falciparum in mixed infections that have remained from the previous transmission season (i.e.…”