Country Vet - Equine Influenza

Equine influenza is an OIE listed disease of horses caused by a Type A influenza virus of the family Orthomyxoviridae.

There are two subtypes, H3N8 and H7N7, which are not cross protective. The H7N7 subtype occurs only rarely and has not been recorded in European horse populations for many years. Antigenic drift in the H3N8 subtype has given rise to European and American lineages. A South American sub-lineage is becoming increasingly dominant in North America and was responsible for outbreaks in United Kingdom and

South Africa

in 2003.

Worldwide.Endemic in Europe, Canada, USA, Scandinavia and South America.Periodic epidemics in other areas are associated with import of infected horses, the most recent being in

South Africa

at the end of 2003.Only Australia and

New Zealand

and few isolated islands have never had an outbreak. Japan, Hong Kong, Singapore and Macau are currently virus free but continue to vaccinate.

All Equidae are susceptible. Canine influenza due to the H3N8 subtype has recently been identified in greyhounds in

USA

. The dogs may have been infected by eating horse meat.

Equine influenza can cause explosive outbreaks of fever with persistent coughing and nasal discharge, depression and anorexia in unvaccinated horse populations. Signs in vaccinated horses are less severe. Clinical signs resolve in 1-3 weeks.While morbidity is high, mortality is usually low unless horses are stressed or sick for other reasons. Occasional deaths occur in young foals.

The incubation period is 2 - 3 days and horses remain infectious for about 8 days.There is no long term carrier state but mild or subclinical disease in recently infected horses which are vaccinated may escape notice.

Transmission occurs by direct contact between coughing horses via respiratory route.Coughing horses can propel virus laden aerosol up to 35 m.The disease is spread between premises and internationally by movement of infected horses.

The virus can survives in the environment for up to 36 hours so spread by fomites e.g. people, contaminated equipment and transport vehicles is also important.

Isolation/quarantine periods greater than incubation/virus excretion periods

All-in/all-out post quarantine period of 14 days after arrival in Australia

Post arrival quarantine for 14 days provides:

assurance that even if an infected horse is imported, provided an 'all-in, all-out' quarantine policy is practised, the horse will not be shedding virus when it is released.
an opportunity to investigate any respiratory disease arising in imported horses before horses are released into the general population

Threats

Remember vaccination does NOT prevent infection but may mask signs of disease
Greatest threat is a recently exposed, vaccinated, imported horse
Antigenic drift - vaccine strains may not be protective, need regular updating
Antigenic shift - emergence of new strain from wild birds but unusual
Post arrival quarantine breakdown in Australia
People movement

Impact of an outbreak in Australia

Cancellation of all horse events including racing for up to 3 months
Catastrophic consequential economic loss
Additional industry costs for control and vaccination

Control

An AUSVETPLAN has been developed for equine influenza (EI) and is available on-line at http://www.aahc.com.au/ausvetplan/index.htm .The document is currently under review.

The strategy is to control and (hopefully) eradicate EI by minimising spread of virus by:

- stringent quarantine and movement controls

- decontamination of people, equipment, vehicles and premises, and

- strategic vaccination of susceptible horse populations at high risk.

To be eradicated swiftly and successfully, EI would have to be detected almost immediately after entry to Australia. An immediate standstill on all horse movements would need to be implemented.

Equine Influenza

Equine Influenza - For the current situation in your state see www.outbreak.gov.au