Brazilian spotted fever serological investigation among equids at the Guarapiranga Dam area in the city of São Paulo, Brazil

Abstract

The Guarapiranga Dam region, in the metropolitan area of São Paulo, has been an endemic area for Brazilian spotted fever (BSF), a tick-borne disease caused by the bacterium Rickettsia rickettsii. In this particular area, R. rickettsii is known to be transmitted to humans by Amblyomma aureolatum, a typical dog tick that is not associated with horses. In other BSF-endemic areas, R. rickettsii transmission is associated with Amblyomma sculptum, a tick species that typically infest capybaras and horses. The Guarapiranga Dam bears abundant populations of capybaras and horses; however, since nothing is known about a possible cycle of transmission of R. rickettsii by A. sculptum in this area, this study evaluated such transmission by performing a serosurvey of horses living in the Guarapiranga Dam region. A total of 206 equids living in the margins of the Guarapiranga Dam were serologically tested for antibodies reactive to five Rickettsia species, four of the spotted fever group (R. rickettsii, R. parkeri, R. amblyommatis, R. rhipicephali) and one basal group species, R. bellii. Overall, 171 (83%) equids reacted positively to at least one Rickettsia species. A total of 160 (78%), 123 (60%), 80 (39%), 72 (35%), and 71 (34%), equid sera reacted to R. bellii, R. rickettsii, R. parkeri, R. rhipicephali, and R. amblyommatis, respectively, with endpoint titers ranging from 64 to 1024 for R. bellii, and 64 to 512 for the remaining four Rickettsia species. Endpoint titers to R. bellii (median: 256) was significantly higher (P<0.05) than the endpoint titers to the other four Rickettsia species, for which the median values varied from 64 to 128. A total of 65 (32%) equid sera showed endpoint titers to R. bellii at least 4-fold higher than those to any of the other four antigens, indicating that they have been exposed to R. bellii or a very closely related species. Our results provide serological evidence that the sampled equids were not frequently exposed to R. rickettsii-infected ticks. Since horses are a highly suitable sentinel for R. rickettsii transmission by A. sculptum, we conclude that this tick species has no epidemiological role in the transmission of R. rickettsii in the BSF-endemic area of the Guarapiranga Dam in the metropolitan area of São Paulo Municipality.

Coupling spatial statistics with social network analysis to estimate distinct risk areas of disease circulation to improve risk‐based surveillance

“…One reason for a lack of studies that include the explicit effect of barriers in animal disease epidemiology may be associated with the challenges of model implementation, which have been resolved by Bakka et al (2019). The relevance of non-stationary field approaches in animal disease epidemiology is mainly targeted at diseases that disseminate locally, such as West Nile virus (Siqueira et al, 2022), Brazilian spotted fever (Moraes Filho et al, 2019), and piroplasmosis (Minervino et al, 2020).…”

“…(2019). The relevance of non‐stationary field approaches in animal disease epidemiology is mainly targeted at diseases that disseminate locally, such as West Nile virus (Siqueira et al., 2022), Brazilian spotted fever (Moraes Filho et al., 2019), and piroplasmosis (Minervino et al., 2020).…”

Rickettsial infection in equids, opossums and ticks in the municipality of Monte Mor, state of São Paulo, Brazil

“…Even in regions where there have never been cases of BSF or where cases have not occurred for a long time, such as Monte Mor, which has only had one case (reported in 2005), serological tests on horses have great value for active surveillance of BSF (Souza et al, 2016). On the other hand, horses are not good sentinels in places where the vector is probably not A. sculptum (Cunha et al, 2014;Oliveira et al, 2019).…”