High Seroprevalence for Rickettsia rickettsii in Equines Suggests Risk of Human Infection in Silent Areas for the Brazilian Spotted Fever.

Celso Eduardo Souza,Adriano Pinter,Luciana Bonato Camargo,Maria Rita Donalisio,Xue-Jie Yu

doi:10.1371/journal.pone.0153303

Celso Eduardo Souza, Adriano Pinter + Show 3 more

Open Access

https://doi.org/10.1371/journal.pone.0153303

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Journal: PloS one	Publication Date: Apr 11, 2016
Citations: 18	License type: CC BY 4.0

Affiliation: Universidade Estadual de Campinas

Abstract

Equines play a role in the epidemiology of Brazilian spotted fever (BSF) since they are a primary host for the tick Amblyomma sculptum. We studied the seroprevalence for three species of Rickettsia in equines in four endemic (with human cases) and in four non-endemic areas (no human cases) in the Piracicaba River Basin, São Paulo, Brazil. A serological survey of 504 equines was performed: around 63 animals were sampled in each area and tested through indirect immunofluorescence assay for R. rickettsii, R. parkeri, and R. bellii in 2012–2013. Blood samples were seropositive for 183 equines (36.3%) in which 73 (39.9%) were from non-endemic areas. In the studied sites equines were highly exposed to Rickettsia infection ranging from 6.1% to 54.7%, with Geometric Mean Titers greater in endemic area (p = 0.012). Results suggest that Rickettsia may be more widespread than the surveillance of BSF has detected. These results highlight the need to include data on the seroprevalence of sentinel animals to improve human diagnoses and surveillance in areas with no reported human cases.

Highlights

Brazilian spotted fever (BSF) is the most important rickettsial disease in Brazil [1]
The aim of this research is to study the seroprevalence of antibodies to R. rickettsii, R. bellii and R. parkeri in equines in endemic and nonendemic areas of the Piracicaba River Basin, state of São Paulo and to compare the seroprevalence of anti-rickettsial antibodies with the incidence of human BSF cases in this region
Noteworthy high Rickettsia rickettsii seropositivity was detected in equines that live in areas without reported human cases, especially in Bragança Paulista and Rio Claro, 53% and 43.5% respectively

Summary

Introduction

Brazilian spotted fever (BSF) is the most important rickettsial disease in Brazil [1]. BSF is an acute infectious disease whose etiological agent Rickettsia rickettsii is transmitted to humans and to other animals by several different tick’ species, including Amblyomma sculptum, the main vectors of BSF in the country. Capybara (Hidrochoerus hidrochaeris) is one of the primary hosts of A. sculptum and is abundant in endemic areas for BSF [2]. Capybaras were reported as a competent amplifier host for R. rickettsii and the most important tick host in Spotted Fever transmission areas where A. sculptum is the vector to humans [3]. Other wild animal tested as an amplifier hosts was the opossum (Didelphis sp.) which showed a minor competence [4] [5].

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