Epidemiological features of malaria at Jau National Park,Amazonas, Brazil
Cross-sectional surveys were performed in the Jau National Park (Parque Nacional do Jau, PNJ), state of Amazonas, Brazil, to investigate the levels of malaria endemicity and the prevalence and risk factors for clinical disease. PNJ is inhabited by native riverine populations settled on the banks of Unini and Jau rivers. Malaria transmission in the area occurs year-round, with peaks in February-March and August-September. Each visit to the study area took about three months; the first was carried out between November 2002 and January 2003 and the second between May 2003 and July 2003. The first visit included two cross-sectional studies, with interviews, physical examination and colection of blood samples (the riverine populations were surveyed during the journeys upstream and downstream the Unini and Jau rivers), while the second visit included a single cross-sectional survey during the upstream journey and a brief re-assessment of malaria-related morbidity during the downstream journey. The current analysis deals with data on: (a) cumulative exposure to malaria, (b) current malaria morbidity and presence of splenomegaly, (c) prevalence of malaria infection as detected by conventional microscopy and polymerase chain reaction (PCR), (d) presence and levels of antibodies to Plasmodium falciparum and P. vivax, as detected by indirect antibody fluorescent test (IFAT) with whole parasites and enzyme-linked immunosorbent assay (ELISA) with recombinant antigens corresponding to the 19-kDa C-terminal fragment of the merozoite surface protein-1 (MSP119) of both species. Results of a preliminary survey of the local anopheline fauna were analyzed as well. A total of 540 subjects (372 living on the banks of Unini river and 168 living on the banks of Jaú river), aged between 3 months and 77 years, were present in at least one of the three cross-sectional surveys. Males predominated over females (1.25:1). 77% of them had a history of one or more past malaria infections (71.5% with laboratory confirmation), ranging between 1 and 31 past episodes (median, 2). The splenic index in children aged 2-9 years ranged between 9.2 and 13.6% in different cross-sectional surveys. The overall prevalence of malaria infection was 14.4% (ranging from 8.7 to 20.6% in different cross-sectional surveys), with a not significant higher prevalence (p=0.058) in Unini river communities (15.4%) than in Jau river communities (10.3%); more than two thirds of all infections were detected by PCR alone. P.vivax was found in 74.7% of infections, P.falciparum in 26.6% and P.malariae in 0.3%. The prevalence of infection decreased with age; when compared to those in adults aged gt;30 years, prevalences were 8.1, 6.1, 4.7 and 3.1 times higher in subjects aged lt;1, 1-5, 6-10 and 11-20 years, respectively. Splenomegaly and anemia were respectively 3 and 2.6 times more prevalent among infected subjects, when compared to non-infected ones. 60.8% of all malaria infections were diagnosed in asymptomatic subjects; of 104 subjects without symptoms at the time of diagnosis, 11 became ill between 2 days and 5 months later (8 of them during the first 23 days of follow-up). Only 22 asymptomatic infections were detected by conventional microscopy. The proportion of ymptomless:symptomatic infections was greater in women, regardless of age, and asymptomatic subjects were significantly older (median age, 10 years) than symptomatic ones (median age, 5 years). IgG antibodies to both P.vivax and P.falciparum, as detected by IFAT, were detected in83.2% and 71.7% subjects, respectively, but geometric mean titers were low (72.5 and 54.6). Most subjects had IgG antibodies to PvMSP119 (67% in the first visit to the area and 64% in the second visit) and to PfMSP119 (respectively 52% and 51.7%). Significantly higher levels of antibodies to PvMSP-1 were measured in subjects with current P.vivax infections, as compared to non-infected ones, but no association was found between the presence and levels of antibodies to either antigen and the presence or absence of symptoms. Our preliminary entomological data suggest that An. darlingi is the main local malaria vector, with biting activity peaking between 6 and 11 pm. This biting pattern suggests the use of bednets as a possible measure for preventing malaria in the area. Other possible control measures include: (a) screening of community houses and schools where nocturnal activities are held, (b)periodical cross-sectional surveys of the whole population, regardless of the presence of symptoms, for diagnosing asymptomatic infections by conventional microscopy, (c) training of local health agents in malaria diagnosis and treatment, for prompt intervention in symptomatic infections.
Advisor:José Rodrigues Coura; Marcelo Urbano Ferreira
School:Faculdades Oswaldo Cruz
Source Type:Master's Thesis
Jau National Park
Date of Publication:11/18/2005