Serological evidence of Rickettsia in horses from a semi-arid Brazilian region

Serosurvey of spotted fever group Rickettsia in equids from western Pará, Amazon, Brazil

From a previous large epidemiological survey, we randomly selected 474 serum samples (463 horses and 11 mules) distributed among four municipalities of Pará state, Amazon region, Brazil, and from three types: farm animal, urban carthorse, and sport horse. Samples were tested by indirect fluorescence antibody test (IFAT ≥ 64) for antibodies reactive to spotted fever group (SFG) rickettsiae using Rickettsia rickettsii as crude antigens. From the 474 equids tested, 149 (31.4%) had ticks attached during sampling, belonging mostly to the species Dermacentor nitens. The overall seroprevalence for SFG rickettsiae was 31.4% (95% confidence interval: 27.3-35.9%) with 149 seropositive animals out of 474 screened. Notably, 77 equids (16.2%) had high endpoint titers ranging from 512 to 16,384, indicating that they had been exposed to SFG rickettsiae not long before sampling. Animal type affected rickettsial seroprevalence, with significantly higher values among farm horses when compared with urban and sport animals. Presence of dogs and tick infestation were negatively associated with equid seropositivity to R. rickettsii. This is the first report of SFG rickettsiae-reactive antibodies in equids from Pará state, Brazilian Amazon.

Recent Advances in the Immunologic Method Applied to Tick-Borne Diseases in Brazil

Zoonotic-origin infectious diseases are one of the major concerns of human and veterinary health systems. Ticks, as vectors of several zoonotic diseases, are ranked second only to mosquitoes as vectors. Many ticks’ transmitted infections are still endemic in the Americas, Europe, and Africa and represent approximately 17% of their infectious diseases population. Although our scientific capacity to identify and diagnose diseases is increasing, it remains a challenge in the case of tick-borne conditions. For example, in 2017, 160 cases of the Brazilian Spotted Fever (BSF, a tick-borne illness) were confirmed, alarming the notifiable diseases information system. Conversely, Brazilian borreliosis and ehrlichiosis do not require notification. Still, an increasing number of cases in humans and dogs have been reported in southeast and northeastern Brazil. Immunological methods applied to human and dog tick-borne diseases (TBD) show low sensitivity and specificity, cross-reactions, and false IgM positivity. Thus, the diagnosis and management of TBD are hampered by the personal tools and indirect markers used. Therefore, specific and rapid methods urgently need to be developed to diagnose the various types of tick-borne bacterial diseases. This review presents a brief historical perspective on the evolution of serological assays and recent advances in diagnostic tests for TBD (ehrlichiosis, BSF, and borreliosis) in humans and dogs, mainly applied in Brazil. Additionally, this review covers the emerging technologies available in diagnosing TBD, including biosensors, and discusses their potential for future use as gold standards in diagnosing these diseases.