Serosurvey of antibodies against spotted fever group Rickettsia spp. in horse farms in Northern Paraná, Brazil.

This research article documents a study on the prevalence of Brazilian spotted fever (BSF) rickettsia infections among horses in certain parts of Brazil. The researchers tested the horses’ blood serum for antibodies against Rickettsia rickettsii and Rickettsia parkeri, two species of bacteria believed to cause BSF, finding that a notable percentage of the horses may have been exposed to these microbes.

Study Context and Goal

• The study was carried out to assess the prevalence of Brazilian spotted fever, a disease predominantly caused by the bacterium Rickettsia rickettsii, in horses from six farms located in Londrina County, Paraná, Southern Brazil.
• This area is significant as Brazilian spotted fever had not been previously reported there. Despite this, the study aimed to determine if horses in the region had developed antibodies for the disease – a sign of prior exposure.

Methodology

• A total of 273 horses from farms in the municipalities of Cambé, Santa Fé, Guaraci, and Londrina were tested.
• The researchers used an indirect immunofluorescence assay (IFA) to test the horse’s sera. This test detects and measures the presence of specific antibodies that work against the BSF-causing bacteria R. rickettsii and R. parkeri in the horse’s blood serum.
• Samples that showed titers (measurement of the concentration of an antibody in the blood) equal to or more significant than 64 were considered positive, suggesting exposure to the bacteria.

Results

• Of the 273 sera tested, 15 (5.5%) reacted to R. rickettsii and 5 (1.8%) to R. parkeri, providing evidence of prior exposure to these bacteria.
• Seropositive animals were found in five out of the six farms studied, with the seropositivity rate ranging from 0 to 13%.
• The titers ranged from 64 to 512, and the highest titer, 512, was found in four samples. This high titer points to a substantial immune response and potentially a high level of exposure to the bacteria.
• Nine animals presented a reaction to R. rickettsii with titers four-fold higher than R. parkeri, suggesting a significant exposure to R. rickettsii.

Conclusion

• The findings suggest that horses from the studied farms in Northern Paraná may have been exposed to Rickettsia bacteria that were either identical or closely related to R. rickettsii.
• This exposure infers a risk of Brazilian spotted fever in areas previously thought to be free of the disease, which can help guide future preventative and management strategies for the disease in these areas.