Experimental infection of horses with Rickettsia rickettsii

Abstract

BackgroundRickettsia rickettsii is vectored by ticks, and some vertebrate hosts can be sources of infection to ticks during bacteremic periods. In Brazil, the main vector for R. rickettsii is the tick Amblyomma sculptum, a member of the A. cajennense complex. Horses, in turn, are one of the major hosts for A. sculptum. In this study, horses experimentally infected with R. rickettsii were assessed for clinical changes and their capability to transmit the infection to A. sculptum ticks.MethodsFour horses were infected with R. rickettsii through either intraperitoneal injection or infestation with R. rickettsii-infected A. sculptum ticks. Simultaneously, the animals were infested with non-infected A. sculptum ticks. The horses were monitored for 30 days by clinical examination, hematological and biochemical tests, real-time PCR of blood for the detection of Rickettsia, and inoculation of blood in guinea pigs. IgG antibody titers were followed until the horses have shown seronegativity or until the end of the experiment. Uninfected ticks that fed on horses were subjected to real-time PCR and/or were fed on susceptible rabbits.ResultsThe horses showed no clinical, hematological or blood biochemical alterations, and bacteremia was not detected by real-time PCR or by inoculation of horse blood into guinea pigs. Anti-R. rickettsii antibodies were detected in horses from 10 days to 2 years after infection. Uninfected ticks, after feeding on infected horses, showed 2.1 % positivity in real-time PCR, but failed to transmit the infection to rabbits at a next feeding stage.ConclusionsRickettsia rickettsii-infected horses did not manifest illness and are not competent amplifier hosts of R. rickettsii for A. sculptum ticks.

Serological survey of Rickettsia in equids from Vale do Paraíba, São Paulo, Brazil, and their tick identification and molecular investigation of Rickettsia

“…Some samples obtained from all collection sites presented titers for a given antigen at least four times higher when compared to the values found for the other four etiologic agents analyzed, which is defined as most probable homologous antigen (PHA) (Ueno et al, 2016). For the other animals, it was not possible to determine which was the most probable infecting agent, since they presented similar values for the five antigens analyzed.…”

“…Equines are animals that can play a fundamental role in the epidemiological chain of BSF because they have free movement and can disseminate infected ticks, spreading the disease to different regions (Cardoso et al, 2006;Medeiros et al, 2013). Ueno et al (2016) evaluated horses after either intravenous inoculation of R. rickettsii or infestation by R. rickettsii-infected ticks, demonstrating that, in both cases, this bacteria was able to infect horses, inducing immune response, but without bacteremia and clinical manifestations of the disease. These experimentally infected horses were not a source of infection for the uninfected ticks that had fed on them during R. rickettsii infection.…”

“…These experimentally infected horses were not a source of infection for the uninfected ticks that had fed on them during R. rickettsii infection. Therefore, Ueno et al (2016) demonstrated that although horses were not amplifying hosts of R. rickettsii for ticks, these animals are efficient sentinels for the epidemiological surveillance of rickettsial diseases, since they develop an effective and lasting humoral immune response after R. rickettsii infection.…”

Rickettsiosis

“…However, they do develop anti-rickettsia antibodies. Studies also conclude that equines are not good amplifiers of rickettsia, suggesting that they do not play our role as a natural amplifier of these microorganisms (30). Future studies must address the role of domestic animals in good transmission dynamics of rickettsiosis, including the possibility of some animals to serve as reservoirs, amplifiers, or both (34).…”

Preliminary Detection of Rickettsiae Using PCR Targeting OmpA Gene Among Dogs and Horses in Cairo, Egypt

“…In a study in North America, R. rickettsii-experimentally infected horses showed fever and had rickettsemia for only one day. R. rickettsii-infected horses did not present other clinical signs of the disease, but they reported high titers of IgG antibodies with long-lasting persistence [15].…”