Evaluation of Rickettsia sp. strain Atlantic Rainforest as a protective agent against Rickettsia rickettsii infections, agent of Brazilian spotted fever

Abstract

Brazilian spotted fever (BSF), a disease caused by the bacterium Rickettsia rickettsii and transmitted by the bite of Amblyomma sculptum and Amblyomma aureolatum ticks, has a fatality rate of 20 to 40% in Brazil. Studies published by the Brazilian Ministry of Health (BMH) in 2014, show a 28.9% fatality rate in the 734 confirmed cases of BSF during 2007 to 2012. In 2010, a new rickettsia, named Rickettsia sp. strain Atlantic rainforest, was discovered in Brazil. This agent causes a milder disease in humans with no lethal cases reported to date, being the tick Amblyomma ovale appointed as vector. Recent studies conducted in the United States and Costa Rica showed that guinea pigs (Cavia porcellus) previously inoculated with Rickettsia amblyommii, a rickettsia of yet not well understood pathogenicity, were protected against infection by R. rickettsii. Based on these findings, this study aims to assess the cross-protective of Rickettsia sp. strain Atlantic rainforest in naturally infected (via parasitism by infected ticks) guinea pigs (C. porcellus) against a secondary infection with R. rickettsii. This study will be a pioneer in Brazil, and will contribute important data for active surveillance of BSF, when we think in relation to man displacement flow between areas at risk of infection by strain Atlantic rainforest and R. rickettsii, and the possible protection that dogs could have during a challenge with R. rickettsii, when previously infected with Rickettsia sp. strain Atlantic rainforest, since these dogs could act as amplifiers hosts of R. rickettsii. Finally, this work could open perspectives on the use of a vaccine against Rocky Mountain spotted fever in dogs, based on infection with Rickettsia sp. Atlantic rainforest, which could be of great relevance to public health. (AU)