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Volume 16, Number 5—May 2010

Letter

Serologic Survey of Hantavirus Infection, Brazilian Amazon

Suggested citation for this article

To the Editor: Since the etiology of hantavirus cardiopulmonary syndrome (HCPS) was recognized in 1993 in the United States (1), various hantaviruses have been associated with the syndrome in South America (2,3). Depending on the viral genotype involved, hantavirus infection can take a wide variety of forms, from asymptomatic or oligosymptomatic to the classic clinical form (4,5).

The first cases of HCPS in Brazil were reported in the state of São Paulo in 1993 (6,7). In 2000, an outbreak of HCPS was reported in the municipality of Anajatuba in the state of Maranhão in the Maranhão western lowlands, a microregion in the Brazilian Amazon (8,9). An ecologic study in this region identified antibodies against hantaviruses in wild rodents (Oligoryzomys fornesi and Holochilus sciureus). Analysis of RNA from the viruses isolated from these 2 rodent species showed 2 new hantaviruses, which were named Anajatuba and Rio Mearim, respectively (10).

The Maranhão western lowlands is a swampy region that consists of 21 municipalities and ≈400,000 inhabitants. A cross-sectional study was conducted from August 2004 through September 2006 to identify exposures and activities associated with hantavirus infection. A convenience sample comprising 6 of the 21 municipalities in the region was selected: Pinheiro in the north, Vitória do Mearim in the south, São Bento and São João Batista in the east, and Penalva and Viana in the west. In each municipality, a village in the countryside was randomly chosen. All members of those communities were invited to participate. Persons who agreed to take part in the study were interviewed, and a standardized questionnaire was used to collect demographic information. Participants provided blood samples after giving written informed consent. ELISA to detect immunoglobulin (Ig) G antibodies against hantaviruses was performed in the Arbovirology and Hemorrhagic Fevers Department at the Evandro Chagas Institute (Belém, PA, Brazil) by using antigen from the Sin Nombre virus supplied by the Centers for Disease Control and Prevention (Atlanta, GA, USA). Samples were initially screened at 1:100, and all positive results were confirmed in a serial dilution (starting at 1:400) test. Positive samples were those with titers >400 (10).

Odds ratios (ORs) were estimated by logistic regression. Variables with p<0.20 in the univariate analysis were subjected to multivariate analysis.

Our study comprised 1,386 persons. The seroprevalence of antihantavirus antibodies in the 6 municipalities was 4.7% (65/1,389), distributed as follows: São João Batista, 2.6% (8/307); São Bento, 3.1% (6/195); Penalva, 3.5% (5/145); Pinheiro, 4.8% (13/273); Viana, 5.6% (9/160); and Vitória do Mearim, 7.8% (24/309). Most persons interviewed were farmers and illiterate and lived in rammed-earth huts. Killing rats in the fields was reported by 24.3% (337/1,389). According to univariate analysis, seeing rats in the dwelling or in the field, having killed rats in the dwelling or in the fields, being a farmer, being male, and being >20 years of age were associated with IgG against hantaviruses. No association was found between storage of grain inside a dwelling or presence of natural predators of rodents, e.g., domestic cats and snakes such as the red-tailed boa, and antibodies against hantaviruses (Table).

Because of colinearity between rat exposure variables, only “having killed rats in the field” was submitted to adjusted analysis. In the multivariate analysis, being >20 years of age and having killed rats in the field remained associated with hantavirus infection. In the model that did not consider sex and age, being a farmer (OR 2.63, 95% confidence interval [CI] 1.56%–4.41%) and having killed rats in the field (OR 2.30, 95% CI 1.38%–3.84%) were independently associated with hantavirus infection.

Hantavirus infection is endemic to the Maranhão western lowlands. It has characteristics of an occupational infection associated with agricultural work, but age mostly explained the effect of being a farmer (OR for being a farmer 1.29, 95% CI 0.74%–2.24%, adjusted for sex and age). Exposure to rodents appeared to occur both in fields and dwellings.

Although serologic evidence indicated that hantaviruses were circulating in the 6 municipalities studied, no cases of HCPS were reported in any of them. This finding suggests that either only mild or asymptomatic cases were occurring and that these were not recognized as HCPS or that cases of hantavirus were not being detected and reported. However, in a study in 2000 in Anajatuba in a cohort of 234 persons who did not initially have IgG against hantaviruses, 4 seroconversions to IgG against these viruses were detected; 2 of these infections were asymptomatic and 2 were self-limiting febrile illnesses that occurred after 24 months of follow-up (9). The present study reinforces the suspicion that mild or atypical cases are occurring in this region and may be the main reason classical hantavirus infection has not been identified.

Wellington S. Mendes1, Antônio A.M. da Silva, Romerito F. Neiva, Nicolle M. Costa, Maressa S. de Assis, Priscila M.O. Vidigal, Maria da G. L. Leite, Elizabeth S.T. da Rosa, Daniele B. de A. Medeiros, Darlene de B. Simith, and Pedro F. da C. VasconcelosComments to Author 
Author affiliations: Federal University of Maranhão, São Luís, Brazil (W.S. Mendes, A.A.M. da Silva, R.M. Neiva, N.M. Costa, M.S. de Assis, P.M.O. Vidigal); Maranhão State Department of Health, São Luís (M.G.L. Leite); Evandro Chagas Institute, Belém, Brazil (E.S.T. Rosa, D.B. Medeiros, D.B. Simith, P.F.C. Vasconcelos)

Acknowledgments

This paper is dedicated to Wellington S. Mendes. We thank Henrique Jorge Santos for assistance with the investigation.

This research was supported by Fundação de Amparo à Pesquisa do Estado do Maranhão and Conselho Nacional de Desenvolvimento Científico e Tecnológico/Ministério da Ciência e Tecnologia, Brazil (grants 301047/2008-1 and 573739/2008-0).

References

  1. Centers for Disease Control and Prevention. Outbreak of acute illness—northwestern United States. MMWR Morb Mortal Wkly Rep. 1993;42:4214.PubMed
  2. Pan American Health Organization. Hantavirus en las Americas: guia para el diagnostico, el tratamiento, la prevencion y el control. Washington: The Organization; 1999.
  3. Padula PJ, Colavecchia SB, Martinez VP, Gonzalez Della Valle MO, Edelstein A, Miguel SD, Genetic diversity, distribution, and serological features of hantavirus infection in five countries in South America. J Clin Microbiol. 2000;38:302935.PubMed
  4. McCaughey C, Hart CA. Hantaviruses. J Med Microbiol. 2000;49:58799.PubMed
  5. Butler JC, Peters CJ. Hantaviruses and hantavirus pulmonary syndrome. Clin Infect Dis. 1994;19:38795.PubMed
  6. Johnson AM, Sousa LTM, Ferreira IR, Pereira LE, Ksiasek TG, Rollin PE, Genetic investigation of novel hantaviruses causing fatal HPS in Brazil. J Med Virol. 1999;59:52735. DOIPubMed
  7. Silva MV, Vasconcelos MJ, Hidalgo NTR, Veiga AP, Canzian M, Marotto PC, Hantavirus pulmonary syndrome. Report of the first three cases in São Paulo, Brazil. Rev Inst Med Trop Sao Paulo. 1997;39:2314. DOIPubMed
  8. Mendes WS, Aragão NJL, Santos HJ, Raposo L, Vasconcelos PFC, Rosa EST, Hantavirus pulmonary syndrome in Anajatuba, Maranhão, Brasil. Rev Inst Med Trop Sao Paulo. 2001;43:23740. DOIPubMed
  9. Mendes WS, Silva AAS, Aragão LFC, Aragão NJL, Raposo ML, Elkhoury MR, Seroprevalence and risk factors for infection by hantavirus in Anajatuba, Maranhão, Brazil. Emerg Infect Dis. 2004;10:14968.PubMed
  10. Rosa EST, Mills JN, Padula PJ, Elkhoury MR, Ksiazek TG, Mendes WS, Newly recognized hantaviruses associated with hantavirus pulmonary syndrome in northern Brazil: partial genetic characterization of viruses and serologic implication of likely reservoirs. Vector Borne Zoonotic Dis. 2005;5:119. DOIPubMed

Table

Suggested citation for this article: Mendes WS, da Silva AAM, Neiva RF, Costa NM, de Assis MS, Vidigal PMO, et al. Serologic survey of hantavirus infection, Brazilian Amazon [letter]. Emerg Infect Dis [serial on the Internet]. 2010 May [date cited]. http://wwwnc.cdc.gov/eid/article/16/5/09-0766.htm

DOI: 10.3201/eid1605.090766

1Deceased

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Table of Contents – Volume 16, Number 5—May 2010

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Pedro F. da C. Vasconcelos, Departamento de Arbovirologia e Febres Hemorrágicas, Instituto Evandro Chagas, Rodovia BR316, Km 7, 67030-000, Ananindeua, Brazil





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