Clinical and serological evaluation of capybaras (Hydrochoerus hydrochaeris) successively exposed to an Amblyomma sculptum-derived strain of Rickettsia rickettsii

Alejandro Ramírez-Hernández,Maria Carolina De Azevedo Serpa,Alessandra Castro Rodrigues,Lina C Binder,Andrea Fogaça,Celso Eduardo Souza,Francisco Uchoa,Marcelo B Labruna,Matias P J Szabó

doi:10.1038/s41598-020-57607-5

Alejandro Ramírez-Hernández, Maria Carolina De Azevedo Serpa + Show 7 more

Open Access

https://doi.org/10.1038/s41598-020-57607-5

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Abstract

Brazilian spotted fever (BSF), caused by Rickettsia rickettsii, is the most lethal tick-borne disease in the western hemisphere. In Brazil, Amblyomma sculptum ticks are the main vector. Capybaras (Hydrochoerus hydrochaeris), the largest living rodents of the world (adults weighing up to 100 Kg), have been recognized as amplifying hosts of R. rickettsii for A. sculptum in BSF-endemic areas; i.e., once primarily infected, capybaras develop bacteremia for a few days, when feeding ticks acquire rickettsial infection. We conducted experimental infections of five capybaras with an A. sculptum-derived strain of R. rickettsii and performed clinical and bacteremia evaluation during primary and subsequent infections. Bacteremia was detected in all capybaras during primary infection, but not in subsequent infections. All animals seroconverted to R. rickettsii (titres range: 64–32,768), and remained seropositive throughout the study. Primary infection resulted in clinical spotted fever illness in four capybaras, of which two had a fatal outcome. Subsequent infections in seropositive capybaras resulted in no clinical signs. Capybaras developed a sustained immune response that prevented a second bacteremia. This condition may imply a high reproduction rate of capybaras in BSF-endemic areas, in order to continuously generate capybaras susceptible to bacteremia during primary infection.

Highlights

Brazilian spotted fever (BSF), caused by Rickettsia rickettsii, is the most lethal tick-borne disease in the western hemisphere
The bacterium Rickettsia rickettsii is the etiological agent of Rocky Mountain spotted fever, known in Brazil as Brazilian spotted fever (BSF), a disease that has been registered in different American countries including Canada, United States, Mexico, Costa Rica, Panama, Colombia and Argentina[1,2]
No rickettsial DNA was detected in the blood of capybaras 1 and 4 during primary infection (Fig. 8)

Summary

Introduction

Brazilian spotted fever (BSF), caused by Rickettsia rickettsii, is the most lethal tick-borne disease in the western hemisphere. The bacterium Rickettsia rickettsii is the etiological agent of Rocky Mountain spotted fever, known in Brazil as Brazilian spotted fever (BSF), a disease that has been registered in different American countries including Canada, United States, Mexico, Costa Rica, Panama, Colombia and Argentina[1,2] This bacterium is transmitted by different tick species throughout Americas [i.e., Dermacentor variabilis, Dermacentor andersoni, Rhipicephalus sanguineus sensu lato (s.l.), Amblyomma cajennense species complex, and Amblyomma aureolatum]2. In the two previous studies performed with capybaras[11,12], authors used R. rickettsii strains that were not of capybara or A. sculptum origin, which could have resulted in less realistic results It was never tested if a capybara could develop bacteremia after a primary infection, a condition of great importance for the epidemiology of BSF. We aimed to evaluate the clinical and serological profile of these capybaras during primary and subsequent infections via tick parasitism, and the occurrence of bacteremia during all infection challenges

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