Epidemiology and control of frontier malaria in Brazil: lessons from community-based studies in rural Amazonia

Abstract

We describe the epidemiology of malaria in a frontier agricultural settlement in Brazilian Amazonia. We analysed the incidence of slide-confirmed symptomatic infections diagnosed between 2001 and 2006 in a cohort of 531 individuals (2281.53 person-years of follow-up) and parasite prevalence data derived from four cross-sectional surveys. Overall, the incidence rates of Plasmodium vivax and P. falciparum were 20.6/100 and 6.8/100 person-years at risk, respectively, with a marked decline in the incidence of both species (81.4 and 56.8%, respectively) observed between 2001 and 2006. PCR revealed 5.4-fold more infections than conventional microscopy in population-wide cross-sectional surveys carried out between 2004 and 2006 (average prevalence, 11.3 vs. 2.0%). Only 27.2% of PCR-positive (but 73.3% of slide-positive) individuals had symptoms when enrolled, indicating that asymptomatic carriage of low-grade parasitaemias is a common phenomenon in frontier settlements. A circular cluster comprising 22.3% of the households, all situated in the area of most recent occupation, comprised 69.1% of all malaria infections diagnosed during the follow-up, with malaria incidence decreasing exponentially with distance from the cluster centre. By targeting one-quarter of the households, with selective indoor spraying or other house-protection measures, malaria incidence could be reduced by more than two-thirds in this community.

The Global Public Health Significance of Plasmodium vivax

“…Relatively low parasite densities in blood (arising from its strict preference for reticulocytes) may lead to high rates of false-negative diagnoses by microscopy or rapid diagnostic tests (RDTs) (Mueller et al, 2009a). Microscopic diagnoses very often underestimate the true prevalence of P. vivax in blood in both high-and low-transmission settings (Mueller et al, 2009b;da Silva et al, 2010;Harris et al, 2010;Katsuragawa et al, 2010;Steenkeste et al, 2010). Further details regarding the diagnosis of P. vivax may be found in a review elsewhere in this thematic volume of Advances in Parasitology (Chapter 4, Volume 80).…”

Single-Nucleotide Polymorphism and Copy Number Variation of the Multidrug Resistance-1 Locus of Plasmodium vivax: Local and Global Patterns

“…Samples from Granada (n = 139) were collected from symptomatic and asymptomatic persons enrolled into prospective cohort studies conducted in this site during 2004-2006, [17][18][19] and those from Acrelâ ndia (n = 15) and Plá cido de Castro (n = 61) were collected from febrile patients attending the malaria clinics in these towns during 2008-2011. 20 Samples from Remansinho (n = 105) were collected from asymptomatic and symptomatic persons participating in an ongoing prospective cohort study of malaria risk factors.…”

New approaches for integrated and cost-effective malaria vector control

“…A total of 634 questionnaire interviews and 12 FGDs and IIs each which were performed in treatment and untreated control arms, indicated, that those programs could benefit from equally treating Culex and Aedes larval sources, since community members were not able to discriminate between different mosquito species and attribute a corresponding risk 35 . The success of larviciding programs heavily depends on community acceptance and their willingness of getting involved [36][37][38] . Support, financially, through labor, or by granting access to private compounds, is more likely to be offered by the communities if people can witness an immediate relief in mosquito nuisance.…”