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.

About a month into the epidemic, when there were several thousand farms affected, vaccination began in the affected areas under strict veterinary control. There were strong arguments both for and against vaccination as well as questions about the need for repeated vaccination. Concerns were raised whether vaccinated horses with subclinical disease could maintain the virus.

When the first shuttle stallions were quarantined, the initial concern was loss of service fees. Then there was no racing for almost six months; money was lost by trainers and owners. The government lost revenue from the lack of betting. The epidemic has cost many millions of dollars. Horse racing is considered an Australian national pastime – the Melbourne Cup is equivalent to the (Kentucky) Derby. At one time there was concern that it might be canceled. However, EI did not spread to the state of Victoria and the race was held.

DVM: Which measures usually prove to be the most effective in treating affected animals and containing outbreaks of equine influenza? What are the challenges associated with such measures?

Dr. Gibbs: There really isn't very much you can do for a horse with EI. Think about it as you would with people: rest is the most important feature. Given supportive care, the horse will recover. In some cases, usually young foals and older horses, a secon-

dary bacterial infection may lead to pneumonia. In that circumstance, antibiotics will be used.

Because EI is not communicable to humans, a draconian approach to disease control involving slaughter of horses is not necessary. The most effective means to contain outbreaks of EI is quarantine. Movement of animals must be restricted — widely to begin with and then boundaries fine-tuned — based on political authority and the number of outbreaks in infected areas. These boundaries can move frequently, even daily.

A good thing is that horses infected with EI do not become carriers. The disease will burn itself out if there is no susceptible population to maintain transmission of the virus. Right now, it appears to have burned itself out. There have been no reported clinical cases of EI since the end of December. This is excellent news.

I understand that the Australian authorities hope to announce by the middle of March that Australia is provisionally free of EI and by the end of the year that they have eradicated the disease.

DVM: When faced with an epidemic of any equine illness, what do you recommend as the most effective means of communicating accurate and up-to-date information to members of the community?

Dr. Gibbs: It's important to use all modern means of communication to get information out — the Web, cell phones, as well as traditional print and the local and national press. Australia is like the United States in that there is a system where states are responsible for communication. They picked up the ball and ran with it. Local papers ran stories every day. The effect of EI on the racing community was national news.

Australia's use of Web technology for this purpose improved quickly when they got going. They produced Web sites, put up maps and published where to get more information. Town-hall meetings were organized to explain the vaccination program.

DVM: What can practitioners in this country learn from what happened in Australia?

Dr. Gibbs: It is conceivable that a completely new type of EI could emerge, against which the current vaccines are ineffective. If this were the case, an epidemic could ensue in the unprotected horse populations of any nation that could parallel the recent experience in Australia.

Practitioners, not only in this country but around the world, should remember that spread of influenza viruses occurs very rapidly.

Equine influenza spread widely in Australia through the commingling of infected animals at shows and similar events before the disease was recognized in the country.

It is always of critical importance to identify quickly all infected horses and their contacts if the chain of transmission is to be broken.