Equine flu is a highly contagious viral disease which can affect all equine species, including donkeys. Transmission occurs by inhalation of respiratory secretions, most commonly via nose-to-nose contact. Shedding of the virus in nasal secretions begins as soon as 24 hours after infection and can continue for up to 10 days. Depending on the prevailing weather conditions, the virus can be windborne over distances of up to 8 km. Transmission can also occur via tack, grooming equipment, machinery, water, feed and human contact.
Animals of any age, breed or sex can be affected and the disease is not seasonal. In the presence of the virus, spread of infection is exacerbated where large numbers of horses are kept in close proximity. Animals with low levels of immunity, such as young, stressed or unvaccinated horses, are particularly susceptible.
Clinical signs of equine flu vary greatly, and are affected by the general health of the infected animal and the immune status. Vaccinated horses usually develop few or no clinical signs following infection but they can infect other horses as a result of virus excretion.
Although outbreaks of equine flu can affect large numbers of the equine population, it rarely causes severe illness and fatalities are very rare. Those that do occur are usually associated with secondary bacterial infection. The earliest clinical signs of infection include: a rapid increase in temperature, nasal discharge, harsh dry cough, depression, inappetence and enlarged lymph nodes in the head and neck region. These signs usually resolve within 2 – 5 days although secondary bacterial infection may delay recovery for weeks or even months. Secondary infection should be suspected if clinical signs, particularly increased temperature and nasal discharge, persist for longer than 5 days.
In order to contain an outbreak, early diagnosis is vital. If horses display the clinical signs described above, especially if they are know to have been in contact with infected horses, veterinary advice should be sought immediately. Nasopharyngeal swabs or paired serum samples will be used to confirm or eliminate a diagnosis. Treatment consists largely of supportive care. Affected horses will require good quality feed, dust-free bedding and clean water to which electrolyte solutions may be added. They should be rested for a period of at least 3 weeks; those that return to work too quickly are more susceptible to secondary complications. The attending veterinarian may prescribe antibiotics if a horse is thought to be at risk of secondary bacterial infection.
To decrease the risk of influenza, strict adherence to a vaccination programme is essential, both to protect individual animals and also to control the spread of disease within a population. High levels of vaccination will reduce the susceptible population and diminish the likelihood of large scale outbreaks. A variety of influenza vaccines are available on prescription either as a single component or in combination with tetanus vaccines. The duration of immunity of these vaccines is variable and veterinary advice should be sought with regard to the most efficacious products and vaccination schedule.