Asymptomatic Plasmodium infection in a residual malaria transmission area in the Atlantic Forest region: Implications for elimination

Abstract

Introduction: Elimination of malaria in areas of interrupted transmission warrants careful case assessment to avoid the reintroduction of this disease. Occasional malaria cases are reported among visitors of the Atlantic Forest area of Brazil, while data on residents of this area are scarce. Methods: A sectional study was carried out to examine 324 individuals living in a municipality where autochthonous cases were detected. Results: Asymptomatic Plasmodium infections were detected in 2.8% of the individuals by polymerase chain reaction (PCR), with one case of P. falciparum (0.3%), two cases of P. vivax (0.6%), and six cases of P. malariae (1.9%). The thick blood smears were negative in all individuals. Serological tests performed in 314 subjects were reactive in 11.1%, with 3.5% for P. falciparum and 7.7% for P. vivax. A subsample of 42 reactive individuals for any Plasmodium species showed P. malariae in 30.9% of specimens. Individuals who entered the Atlantic Forest region were 2.7 times more likely to exhibit reactive serology for P. vivax compared with individuals who did not enter this region (p<0.05). Children <15 years had a higher chance of reactive serology for P. falciparum and P. vivax than individuals ≥15 years of age (p<0.05). Individuals living in the Paraiso district had a higher chance of reactive serology for P. vivax compared to other districts (p<0.05). No associations were found between sex, past exposure to malaria, or serological response to antibodies of any Plasmodium species. Conclusions: The implications of these results for the elimination of malaria were discussed.

Howler monkeys are the reservoir of malaria parasites causing zoonotic infections in the Atlantic forest of Rio de Janeiro

“…Costal slope of Serra do Mar has much more sites coveted by urban people to settle hidden weekend home in the forest and visited sights by ecotourists and hikers than the continental one. As explained, the autochthonous human cases in the Atlantic forest in RJ has been reported mainly in non-residents [1,2,19]. Together, the environmental, entomological, ecological and epidemiological characteristics seem to indicate costal slope of Serra do Mar as the place to acquire malaria of simian origin.…”

“…In reality, P. simium was only identified by molecular tests and DNAmt sequencing as the causative agent in the 2015-2016 malaria outbreak in RJ, whose patients were essentially non-residents of foci [2]. Nevertheless, six human asymptomatic infection by P. malariae were detected by PCR in residents of Guapimirim in RJ, in 2011 [19], and a subsample of reactive local individuals for any plasmodial species revealed antibodies against erythrocytic antigens of P. malariae in 30.9%. The hypothesis of infection of NHP origin due to P. brasilianum was raised because there was no index case of introduced or imported human case of P. malariae in Guapimirim, and because the cases had close contact with the Atlantic forest [19].…”

“…Nevertheless, six human asymptomatic infection by P. malariae were detected by PCR in residents of Guapimirim in RJ, in 2011 [19], and a subsample of reactive local individuals for any plasmodial species revealed antibodies against erythrocytic antigens of P. malariae in 30.9%. The hypothesis of infection of NHP origin due to P. brasilianum was raised because there was no index case of introduced or imported human case of P. malariae in Guapimirim, and because the cases had close contact with the Atlantic forest [19]. It is well known that P. brasilianum is a widespread and common simian malaria parasite in the Amazon [5,14,42] and that it is experimentally infective to humans, either by inoculation of parasitized monkey blood or by the bite of infected mosquitoes [9].…”

“…Noteworthy, most of the P. simium - and P. brasilianum/malariae - infected howlers (73%) were from forest coastal slope of Serra do Mar, where all autochthonous human malaria cases have been acquired [2,19]. At least two main premises may explain this apparently geographical coincidence and distinct distribution of simian and human malarias.…”

“…Consequently, the hypothesis of simian origin in these RJ malaria cases has been raised [5,7]. In response, multidisciplinary studies including clinical, epidemiological, parasitological, and molecular approaches have been conducted in RJ [2,4,19]. More recently, molecular studies of parasites infecting humans and four howlers clearly demonstrated that they shared the same P. simium parasite.…”