Detection and phylogenetic relationship of Neorickettsia risticii in horses from Southern Rio Grande do Sul, Brazil.
Authors: Silva J G, Martins K R, Rahal N M, Schuch L F D, Cunha R C, Meireles M C A
Journal: Journal of equine veterinary science
Summary
# Potomac Horse Fever in Southern Brazil: Genetic Characterisation Resolves Diagnostic Uncertainty Potomac Horse Fever, caused by the intracellular bacterium *Neorickettsia risticii*, represents a significant risk to equine operations in wetland environments, particularly during warm seasons when the pathogen's trematode vectors and freshwater snail hosts are most active. Silva and colleagues addressed a critical gap in Brazilian surveillance by genetically sequencing *N. risticii* isolates from horses in Rio Grande do Sul and establishing their phylogenetic position relative to known strains, building on earlier serological and PCR detection work that had confirmed the organism's presence but left its genetic identity unclear. The researchers' molecular characterisation not only confirmed *N. risticii* circulation in southern Brazilian herds but provided essential data on strain diversity and evolutionary relationships, clarifying whether local isolates represent established North American lineages or represent distinct South American variants. These findings have direct implications for vaccination strategy selection and epidemiological forecasting, enabling practitioners in endemic regions to make evidence-based decisions about disease prevention protocols and to anticipate seasonal risk periods with greater precision. For farriers, veterinarians, and stud managers operating in or importing horses from southern Brazil, understanding the confirmed genetic profile of circulating strains supports more targeted biosecurity measures and highlights the importance of recognising acute diarrhoeal disease clusters during warmer months as potential PHF outbreaks warranting rapid diagnostic confirmation.
Read the full abstract on PubMed
Practical Takeaways
- •Veterinarians in southern Brazil should maintain clinical awareness of PHF as an endemic disease in horses, particularly during warmer months and in horses with access to wetland areas
- •Confirmation of N. risticii presence through genetic characterization enables more accurate diagnosis and understanding of local strain variants
- •Prevention strategies should focus on reducing exposure to freshwater snails and digenetic trematodes in endemic regions
Key Findings
- •Neorickettsia risticii was detected in horse herds from southern Rio Grande do Sul, Brazil using serology and PCR
- •Genetic sequencing and phylogenetic classification of the pathogen were successfully characterized for the first time in this population
- •The disease exhibits endemic and seasonal patterns primarily affecting horses in wetlands during warmer months across multiple continents