First description of Theiler’s disease-associated virus infection and epidemiological investigation of equine pegivirus and equine hepacivirus coinfection in Brazil.

This research investigated the prevalence and risk factors of three viral diseases – Equine Pegivirus (EPgV), Theiler’s disease-associated virus (TDAV) and equine hepacivirus (EqHV) – in Brazilian horses. The study found that these viruses are widely distributed, with specific risk factors identified, marking the first report of TDAV-infected horses outside of the USA.

Introduction and Methodology

• The researchers wanted to gain insight into the distribution, potential risk factors, presence of liver damage, and genetic variability of EPgV and TDAV in Brazil. To accomplish this, they conducted a cross-sectional study using a simultaneous detection assay and assessed for the occurrence of EqHV coinfection in different horse cohorts.
• The study examined 500 serum samples from horses across the country. The research also aimed to identify the presence of liver damage and any possible risk factors associated with the viruses.

Results and Findings

• The results indicated that TDAV was present in 1.6% of samples, EPgV in 14.2%, and EPgV and EqHV jointly in 18.3%. Affected horses were from four different Brazilian states: Espírito Santo, Mato Grosso do Sul, Minas Gerais, and Rio de Janeiro.
• In 40.4% of EPgV-infected horses, some physiological alterations indicative of liver damage were found, and for two horses, it came with a current liver injury. It was determined that younger horses (5 years old and below) and those raised under intensive farming conditions had higher rates of infection, standing 2.7 and 4.9 times higher chances, respectively.
• EPgV and EqHV coinfections were less likely in horses older than 5 years when compared to younger ones. TDAV-positive horses were detected in various horse categories, with no sign of physiological alterations.
• Nucleotide sequencing found significant similarities (≥88% identity) in virus isolates from this study compared to previous ones, indicating widespread conservation. Tree topology analysis revealed two distinct clades (isolated descendants of a unique ancestor) for both EPgV and TDAV NS3 partial sequences.

Conclusion

• This research found EPgV infections to be common in Brazil, with horses frequently experiencing subclinical viremia (presence of viruses in the blood). It also highlighted that horse management practices can influence the spread of the virus.
• This study is the first to report TDAV-infected horses outside USA, indicating subclinical viremia in a geographically distant region. Both EPgV and TDAV show similar circulating isolates worldwide, contributing to the larger body of research working to understand these viruses’ epidemiology and pathogenesis.