Infrequency of asymptomatic malaria in an endemic area in Amazonas, Brazil

Abstract

A malaria survey was conducted in an area of high transmission (Costa Marques, Rondonia, Brazil) to determine the prevalence of asymptomatic parasitemia and its clinical significance. Most of the people surveyed were immigrants who had lived in the endemic area < 5 years. The people had easy access to free diagnostic and treatment services at the Malaria Clinic in the town of Costa Marques. The prevalence of plasmodial parasitemia in 344 people was 22%. There were 36 individuals with asymptomatic infections among the 77 parasitemic patients. During the two days following the initial examination, 19 ofthe 36 individuals: with asymptomatic infections developed malaria. Among the 17 patients who remained asymptomatic for > 2 days, 4 had only gametocytes, 1 had taken inadequate anti-malarial treatment, 3 were under treatment and 2 moved. Six asymptomatic patients denied the use of anti-malarial drugs and they developed malaria 3-6 days after the initial parasitological diagnosis. The final patient remained asymptomatic during the 7 day observation period. He had a history of > 40 malaria attacks and denied the use of antimalarial treatment. With the exception of the latter all of the other asymptomatic patients, were either in the incubation period or had been treated It is concluded that asymptomatic malaria is rare in the Costa Marques area and that it is necessary to treat all individuals with plasmodial parasitemia.

Association of the IgG response to Plasmodium falciparum merozoite protein (C-terminal 19 kD) with clinical immunity to malaria in the Brazilian Amazon region.

“…Asymptomatic cases of malaria have been considered rare in Brazil. 17,30 However, a study of miners in the state of Mato Grosso showed that 14% of the malaria cases were asymptomatic based on clinical examination and blood smear microscopy for diagnosis. 31 We also observed that 11% of the malaria cases presently studied in 531 miners from Apiacas followed-up for two months and who had parasitemia caused by P. falciparum or P. vivax were asymptomatic.…”

Antibodies anti Bloodstream and Circumsporozoite Antigens (Plasmodium vivax and Plasmodium malariae/P. brasilianum) in Areas of Very Low Malaria Endemicity in Brazil

“…In Brazil, there is evidence that asymptomatic or oligosymptomatic malaria cases may also occur in certain endemic areas (Prata et al 1988, Silva et al 1993, Malafronte et al 1994. Arruda et al (1989) in a seroepidemiological study of malaria in several Indian tribes in Brazil, found a high prevalence of anti-plasmodial antibodies, while parasites were only rarely found in their blood.…”

A Reduced Risk of Infection with Plasmodium vivax and Clinical Protection against Malaria Are Associated with Antibodies against the N Terminus but Not the C Terminus of Merozoite Surface Protein 1

“…Previous studies done in these epidemiological settings showed that Plasmodium infection was always associated with symptoms, and clinical protection was not observed (27). However, through a cross-sectional and longitudinal study among native Amazon residents of the riverine community of Portuchuelo in Rondônia, located in the western Brazilian Amazon, the occurrence of symptomless Plasmodium vivax-infected individuals was reported (1,6).…”