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Volume 27, Number 9—September 2021
Dispatch

Ecologic Determinants of West Nile Virus Seroprevalence among Equids, Brazil

Edmilson F. de Oliveira-Filho1, Carlo Fischer1, Beatrice Sarah Berneck, Ianei O. Carneiro, Arne Kühne, Angelica C. de Almeida Campos, Jorge R.L. Ribas, Eduardo Martins Netto, Carlos Roberto Franke, Sebastian Ulbert, and Jan Felix DrexlerComments to Author 
Author affiliations: Charité-Universitätsmedizin Berlin, Berlin, Germany (E.F. de Oliveira-Filho, C. Fischer, A. Kühne, A.C. de Almeida Campos, J.F. Drexler); Fraunhofer Institute for Cell Therapy and Immunology, Leipzig, Germany (B.S. Berneck, S. Ulbert); Federal University of Bahia, Salvador, Brazil (I.O. Carneiro, E.M. Netto, C.R. Franke); Bahia State Agricultural Defense Agency, Salvador (J.R.L. Ribas); Sechenov University, Moscow, Russia (J.F. Drexler); German Centre for Infection Research, Berlin (J.F. Drexler)

Main Article

Figure 2

WNV seroprevalence among equids, Brazil. A) ELISA absorbance values displayed as sample to cutoff ratio, as previously described (2). We increased the ELISA cutoff by 10% above which samples were considered positive to maximize specificity because the ELISA was not originally validated for horses in Latin America, which are infected by more Japanese encephalitis serocomplex viruses compared with horses in Europe. Dotted orange line represents the 1.1 positivity cutoff. B) Reciprocal PRNT90 titers for WNV and other flaviviruses. Statistical significance levels were inferred by using the Kruskal-Wallis test. Bars indicate mean. Graph created by using Prism (GraphPad software, https://www.graphpad.com). C) Distinction of heterotypic serum samples based on the endpoint titers of various flaviviruses. Triangles indicated endpoint titers >4-fold. D) Effects of forests and forest loss on WNV seropositivity and seronegativity among equids in municipalities, Brazil. Natural forest is made up of introduced or native tree or vegetation that have reproduced naturally, without help or (human) intervention. Primary forest is made up of intact and nonintact natural forest and refers to areas that reached the final stage of succession during 2013–2018. Data on primary and natural forest were retrieved from Global Forest Watch (http://www.globalforestwatch.org). Right y-axis represents number of total number of equids tested for seroprevalence. Horizontal bars indicate means. Areas below dotted line had no forest loss. BSQV, Bussuquara virus; CPCV, Cacipacoré virus; ha, hectare (10,000 m2); PRNT90, 90% plaque-reduction neutralization test; ROCV, Rocio virus; SLEV, Saint Louis encephalitis virus; WNV, West Nile virus.

Figure 2. WNV seroprevalence among equids, Brazil. A) ELISA absorbance values displayed as sample to cutoff ratio, as previously described (2). We increased the ELISA cutoff by 10% above which samples were considered positive to maximize specificity because the ELISA was not originally validated for horses in Latin America, which are infected by more Japanese encephalitis serocomplex viruses compared with horses in Europe. Dotted orange line represents the 1.1 positivity cutoff. B) Reciprocal PRNT90 titers for WNV and other flaviviruses. Statistical significance levels were inferred by using the Kruskal-Wallis test. Bars indicate mean. Graph created by using Prism (GraphPad software, https://www.graphpad.com). C) Distinction of heterotypic serum samples based on the endpoint titers of various flaviviruses. Triangles indicated endpoint titers >4-fold. D) Effects of forests and forest loss on WNV seropositivity and seronegativity among equids in municipalities, Brazil. Natural forest is made up of introduced or native tree or vegetation that have reproduced naturally, without help or (human) intervention. Primary forest is made up of intact and nonintact natural forest and refers to areas that reached the final stage of succession during 2013–2018. Data on primary and natural forest were retrieved from Global Forest Watch (http://www.globalforestwatch.org). Right y-axis represents number of total number of equids tested for seroprevalence. Horizontal bars indicate means. Areas below dotted line had no forest loss. BSQV, Bussuquara virus; CPCV, Cacipacoré virus; ha, hectare (10,000 m2); PRNT90, 90% plaque-reduction neutralization test; ROCV, Rocio virus; SLEV, Saint Louis encephalitis virus; WNV, West Nile virus.

Main Article

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1These first authors contributed equally to this article.

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