Epidemic down under
Gainesville, Fla. — As government restrictions ease in Australia following a massive outbreak of equine influenza last August, officials are still investigating the cause of the outbreak.
E. Paul J. Gibbs, BVSc, PhD, FRCVS, professor of virology in the College of Veterinary Medicine at the University of Florida, reports Australia's outbreak offers many lessons for veterinarians in the United States.
As part of his job, he tracks epidemic diseases in livestock populations around the world and assesses their potential to impact the United States. DVM Newsmagazine recently asked him a series of questions about the outbreak and what can be learned from it.DVM: What was unique about the situation in Australia last year that made the occurrence of equine influenza (EI) there reach epidemic proportions?
Dr. Gibbs: This epidemic, which affected many thousands of horses in New South Wales and Queensland, occurred in a population that had no previous exposure to EI virus. Australia has been remarkably effective in keeping out major diseases of livestock and horses through quarantine rather than through vaccination.
Prior to August of 2007, EI had never occurred in Australia and no vaccination had ever been used in horses that did not travel out of the country.
It appears that a shuttle stallion, imported in August 2007 as one of a group from Ireland, Japan, England, and the United States, was infected with EIV. Although an outbreak of EI in Japan had brought racing in that country to a standstill during the first weeks of August, it has not yet been determined whether Japan was the source of the virus.
The disease was first identified in the Eastern Creek quarantine facility outside Sydney. Then a few days later, EI was recognized in riding stables in central Sydney. This caused great consternation because it was assumed that the virus had escaped from quarantine even though the imported horses were still in quarantine.
Many originally thought the virus had originated from a "break" at the quarantine building itself. However, the imported horses had been flown into the country, and the celebrity status of some of them had attracted keen attention at the airport. Maybe the quarantine procedures at the airport were not as tight as they should have been. A government inquiry is in progress to determine exactly how the virus entered the country.
Once EI had been recognized in the local horse population, quarantine of the affected premises and a total ban on all horse movement between farms across Australia was quickly instigated to limit further spread.
However, it was soon discovered that the virus had been circulating in horses that had attended a show about a week prior to its discovery in the riding stables in Sydney. So the epidemic had been seeded widely before the disease was recognized. The Australian government has pursued a policy of eradication of the disease, but control of this epidemic has been a major challenge for the nation's equine industry and veterinarians.
DVM: Review which animals are at the highest risk for EI and how the disease is spread. What do these factors mean for the care and movement of animals as part of the normal course of business?
Dr. Gibbs: All breeds of horses and other equidae are susceptible to EI virus. The disease rarely kills adult horses, but you commonly see more severe disease and secondary infections in older horses and young foals. EI can be lethal for foals.
EI viruses can be transmitted quickly and easily between horses in stables via the respiratory route. It spreads by aerosols over short distances. EI is relatively stable over short periods, especially if the weather is cool. In some areas, due to the density of the horse population, the virus was jumping across fence lines, from farm to farm.
Fomite transmission is considered important, because the virus can remain viable on contaminated tack, vehicles, etc. for several hours and probably even days in cool weather. It may be that people were inadvertently carrying virus farm to farm.
Because veterinarians initially hoped to contain the disease without using vaccines, it was important to identify infected horses quickly, quarantine them and thereby break the chain of transmission.
The states of Victoria, South Australia, Queensland and New South Wales canceled racing extensively. For a period of time, horse movement was at a standstill across most of Australia; those who moved horses without authorization could be prosecuted.