Detection of Plasmodium falciparum and Plasmodium vivax subclinical infection in non-endemic region: implications for blood transfusion and malaria epidemiology

Abstract

BackgroundIn Brazil, malaria is endemic in the Amazon River basin and non-endemic in the extra-Amazon region, which includes areas of São Paulo state. In this state, a number of autochthonous cases of malaria occur annually, and the prevalence of subclinical infection is unknown. Asymptomatic infections may remain undetected, maintaining transmission of the pathogen, including by blood transfusion. In these report it has been described subclinical Plasmodium infection in blood donors from a blood transfusion centre in São Paulo, Brazil.MethodsIn this cross-sectional study, representative samples of blood were obtained from 1,108 healthy blood donors at the Fundação Pró-Sangue Hemocentro de São Paulo, the main blood transfusion centre in São Paulo. Malaria exposure was defined by the home region (exposed: forest region; non-exposed: non-forest region). Real-time PCR was used to detect Plasmodium falciparum and Plasmodium vivax. Subclinical malaria cases were geo-referenced.ResultsEighty-four (7.41%) blood donors tested positive for Plasmodium; 57 of these were infected by P. falciparum, 25 by P. vivax, and 2 by both. The prevalence of P. falciparum and P. vivax was 5.14 and 2.26, respectively. The overall prevalence ratio (PR) was 3.23 (95% confidence interval (CI) 2.03, 5.13); P. falciparum PR was 16.11 (95% CI 5.87, 44.21) and P. vivax PR was 0.47 (95% CI 0.2, 1.12). Plasmodium falciparum subclinical malaria infection in the Atlantic Forest domain was present in the mountain regions while P. vivax infection was observed in cities from forest-surrounded areas.ConclusionsThe presence of Plasmodium in healthy blood donors from a region known as non-endemic, which is important in the context of transfusion biosafety, was described. Infected recipients may become asymptomatic carriers and a reservoir for parasites, maintaining their transmission. Furthermore, P. falciparum PR was positively associated with the forest environment, and P. vivax was associated with forest fragmentation.

Finding connections in the unexpected detection of Plasmodium vivax and Plasmodium falciparum DNA in asymptomatic blood donors: a fact in the Atlantic Forest

“…Finally, the third evidence comes from the confirmation of twenty-four randomly drawn P. falciparum positive blood samples retested by nested-PCR at the Laboratório de Pesquisa em Malária, Instituto Oswaldo Cruz, Fiocruz, according to the protocol of Zalis et al [17]. Consequently, in view of the results reported by Maselli et al [1] and the recent data quoted above, it seems evident that the dynamics of malaria in the Atlantic Forest is poorly known and needs further investigations, including studies relative to mosquito vectors and other determinants of the transmission, i.e., infectiveness and pathogenicity of the Plasmodium lineages that are circulating in the region, duration of infection in untreated individuals, duration of sporogony and gametocytogony, as discussed by Wernsdorfer [18]. …”

Spotlight on Plasmodium falciparum evolutionary system in the southeastern Atlantic forest

“…Individuals had few clinical symptoms and sub-microscopic P. falciparum infections in Central America (Elbadry et al 2015) and Africa (Tiedje et al 2017), meaning that transmission is still occurring despite anti-malarial interventions. Sub-clinical P. falciparum infections in Maselli et al (2014) are yet more complex, because 100% of tested individuals had no symptoms. The pathways that malaria transmission systems create to resist against anti-malaria interventions should be less looked from a medical view and more studied from an evolutionary perspective.…”

“…This adaptation was discussed by and exemplified by Molina-Cruz et al (2016). An adaptation would be selected in the environment if P. falciparum could not cause symptoms in human hosts (as evidentiated in Maselli et al 2014); because then it would be invisible to the surveillance system, which is based mainly on symptomatic malaria individuals. For instance, São Paulo State has not reported any autochthonous case of P. falciparum in the southeastern Atlantic forest since 1980 (Couto et al 2010, São Paulo 2017.…”

“…While P. falciparum should not circulate among monkeys and humans, a novel system of P. falciparum transmission is taking place in the southeastern Atlantic forest. In such malaria transmission system, two mechanisms may be contributing to the P. falciparum circulation: 1) Elevated host tolerance (asymptomatic infected humans; Maselli et al 2014), 2) Inefficient vector adaptation (low number of P. falciparum sporozoites in An. cruzii; Laporta et al 2015, Figure 1).…”

Malaria epidemiology in the State of Piauí, Northeastern Brazil: a retrospective study with secondary data

“…Although few extra-Amazonian cases occur, they nevertheless represent an extremely important problem because they occur in regions in which the disease is poorly understood by both the population and health personnel (8) (9) (10) . This lack of understanding can delay diagnosis, increase the case fatality rate, and allow the persistence of parasitemic individuals in nonendemic areas.…”