The sport of rodeo requires animals to cross state lines, which often results in potential exposure to sick horses. Therefore, it is vital to stay updated on recent disease outbreaks.
Viral diseases are the LARGEST concern for infectious disease outbreaks. A vaccine can protect a horse from showing clinical signs (being sick) or allow their body to adequately fight the infection before it causes negative health issues, but it should be noted that NO vaccine is 100% effective.
Recently, in Wyoming there was an outbreak of the neurological form of "Rhino" virus. This caused numerous barrel races, rodeo practices, public, and private arenas to shut down for 3-6 weeks.
Equine herpesvirus type 1 (EHV-1) and equine herpesvirus type 4 (EHV-4) infect the respiratory tract. Clinical infection is characterized by fever, lethargy, anorexia (not eating), nasal discharge, cough, and mandibular lymphadenopathy (swollen lymph nodes under the jaw). Some horses will show no clinical signs and be silent carries of the virus.
Infection of the respiratory tract with EHV-1 and EHV-4 typically first occurs in foals in the first weeks or months of life, but recurrent infections are seen in young horses entering training, especially when horses from different sources are commingled.
Both EHV-1/4 are transmitted primarily by the respiratory route, indirect/direct contact with nasal secretions, and by contact with aborted fetuses and placenta.
Like herpesviruses of other species, these viruses establish latent (no clinical signs) infection in the majority of horses. These horses become asymptomatic carriers of one or both viruses. Such horses may shed the virus at a later time when stressed. Pregnant mares, if infected, may abort if stressed.
Existence of a carrier state seriously compromises efforts to control these diseases and explains why outbreaks of EHV-1 or EHV-4 can occur in closed populations of horses.
In case of a current outbreak:
- The simplest approach is to vaccinate all horses in the exposure area—independent of their vaccination history. If horses are known to be un-vaccinated, the single dose may still produce some protection.
- If previously un-vaccinated or unknown, it's recommended to vaccinate a series of 3 vaccines of the inactivated EHV-1/EHF-4 or modified-life EHV-1 vaccine, at 4-6 weeks apart.
- It is essential to understand that strict quarantine, isolation, and monitoring protocols are more effective at controlling outbreaks than any vaccination protocol.