Environmental risk factors associated with West Nile virus clinical disease in Florida horses.

This research article investigates the environmental conditions that increase or decrease the likelihood that horses in Florida will contract West Nile virus. The study utilized data collected from veterinarians and horse owners between 2001 and 2003.

Methodology

• The research was based on data collected from Arboviral Case Information Forms (ACF) submitted by veterinarians whenever a horse was suspected of having a viral encephalitis. These forms constituted a significant repository of data on West Nile virus in horses in Florida.
• In addition to the ACF forms, the researchers issued a follow-up survey concentrating on arbovirus prevention and details about the farms where the horses were located. This survey was sent to the owners of all horses tested for the virus.

Findings

• According to the collected data, the late summer months exhibited the highest prevalence of West Nile Virus among Florida horses, indicating a possible relationship between the virus and seasonality.
• Our analysis also reveals that Quarter horses were the breed most commonly affected by the West Nile Virus. This may be due to certain breed-specific vulnerabilities or the superior popularity of this breed in Florida.
• Two significant protective factors were noted – vaccination and the presence of natural water bodies on the property. That is, horses that were vaccinated were less likely to contract the virus and horses with access to natural water were, surprisingly, also less at risk.

Risk Indicators

• The research also identified several risk factors that increased the chances of horses contracting West Nile Virus. The use of fans in stable areas and a stable construction made of solid wood or cement appeared to increase the risk. The reasons behind these correlations were not immediately clear.
• Additional risk factors included the presence of dead birds and other sick animals on the property. As West Nile Virus is a zoonotic disease that can affect birds, the disease’s presence in dead birds indirectly increases the risk for horses.

Recommendations

• The findings of this study led to some practitioner recommendations for managing West Nile Virus. Horses showing signs of arboviral infection from June to November and those that have not been vaccinated should be tested for the virus.
• Even vaccinated horses showing clinical signs should also be tested, especially if the vaccination took place either within one month or more than six months before the onset of symptoms associated with the viral infection.