Assessment of asymptomatic Plasmodium spp. infection by detection of parasite DNA in residents of an extra-Amazonian region of Brazil

Malaria Journal

Helder Ricas Rezende¹  Antonio Ralph Medeiros-Sousa²  Angelica Espinosa Miranda³  Julyana Cerqueira Buery³  Blima Fux³  Crispim Cerutti Junior³  Filomena E. C. de Alencar³  Lícia Natal Fernandes⁴  Rosely dos Santos Malafronte⁴  Ana Maria Ribeiro de Castro Duarte⁵ 

[1] Entomology and Malacology Unit, Espírito Santo State Department of Health (SESA);Faculty of Public Health, University of São Paulo;Graduate Programme in Infectious Diseases, Federal University of Espírito Santo;Protozoology Laboratory, Institute of Tropical Medicine, University of São Paulo;Superintendency for the Control of Endemic Diseases (SUCEN), São Paulo State Department of Health;

关键词: Malaria;    Plasmodium vivax;    Plasmodium malariae;    Asymptomatic carrier;    PCR;   

DOI  :  10.1186/s12936-018-2263-z

来源: DOAJ

【 摘 要 】

Abstract Background The hypotheses put forward to explain the malaria transmission cycle in extra-Amazonian Brazil, an area of very low malaria incidence, are based on either a zoonotic scenario involving simian malaria, or a scenario in which asymptomatic carriers play an important role. Objectives To determine the incidence of asymptomatic infection by detecting Plasmodium spp. DNA and its role in residual malaria transmission in a non-Amazonian region of Brazil. Methods Upon the report of the first malaria case in 2010 in the Atlantic Forest region of the state of Espírito Santo, inhabitants within a 2 km radius were invited to participate in a follow-up study. After providing signed informed consent forms, inhabitants filled out a questionnaire and gave blood samples for PCR, and thick and thin smears. Follow-up visits were performed every 3 months over a 21 month period, when new samples were collected and information was updated. Results Ninety-two individuals were initially included for follow-up. At the first collection, all of them were clearly asymptomatic. One individual was positive for Plasmodium vivax, one for Plasmodium malariae and one for both P. vivax and P. malariae, corresponding to a prevalence of 3.4% (2.3% for each species). During follow-up, four new PCR-positive cases (two for each species) were recorded, corresponding to an incidence of 2.5 infections per 100 person-years or 1.25 infections per 100 person-years for each species. A mathematical transmission model was applied, using a low frequency of human carriers and the vector density in the region, and calculated based on previous studies in the same locality whose results were subjected to a linear regression. This analysis suggests that the transmission chain is unlikely to be based solely on human carriers, regardless of whether they are symptomatic or not. Conclusion The low incidence of cases and the low frequency of asymptomatic malaria carriers investigated make it unlikely that the transmission chain in the region is based solely on human hosts, as cases are isolated one from another by hundreds of kilometers and frequently by long periods of time, reinforcing instead the hypothesis of zoonotic transmission.

【 授权许可】

Unknown