EQUINE INFLUENZA

Diagnosis, Treatment, and Prevention

Equine influenza is an acute, highly contagious respiratory disease in horses. Although major epidemics of equine influenza have occurred sporadically in many parts of the world, this viral disease appears to be present in the United States at all times.

Today equine influenza can spread quickly over long distances for two reasons: (1) horses are now commonly transported via trailer and airplane to all parts of the country; and (2) the illness may not be apparent for several days, even though a horse is infected and contagious. Vaccinated horses may show only mild clinical signs of sickness, which owners and trainers can miss.

CLINICAL SIGNS

The signs of equine influenza usually start suddenly, with an affected horse abruptly developing a high fever. A dry, harsh cough begins early in the infection and may last for weeks. The nasal discharge initially is watery and scant, but usually becomes yellow and heavy, due to secondary bacterial infection. A sick horse may have watery eyes, enlarged lymph nodes between the mandibles, edema and stiffness in the legs, and breathing difficulty. Depression, weakness, and loss of appetite are common. Horses with relatively mild cases of equine influenza usually recover in a week or so, but severely ill horses may require weeks to months to recover fully, especially if they are not allowed to rest completely. Most uncomplicated cases recover fully, but affected animals under stress, or ones not allowed to rest, may develop secondary pneumonia, a chronic cough, or inflammation of the heart muscle, sometimes resulting in death.

DIAGNOSIS

Clinical signs suggest a diagnosis of equine influenza. However, because horses are susceptible to several other respiratory infections, laboratory tests may be required for a definite diagnosis. Samples for testing, whether serum (for antibody levels) or nose and throat swabs (for viral isolation), must be taken early in the disease. A second serum sample will be required several weeks later to demonstrate a rise in antibody titers.

TREATMENT

Rest and supportive nursing care are important for uncomplicated recovery from equine influenza. Sick horses should be kept in well-ventilated stalls that are as dust-free as possible. Medications to reduce fever may be needed if the fever is high (above 104? F). Antibiotics may be required if the fever lasts more than three to four days, the nasal discharge becomes mucopurulent, or pneumonia develops. Rest is absolutelv essential and should continue for some time after clinical signs have resolved completely.

PREVENTION

Prevention is by far the best approach to controlling equine influenza. Vaccination, beginning at an early age, with adequate boostering and frequent revaccination, provides protection against infection or reduces the severity of signs if disease does occur. Required frequency of revaccination depends on factors which vary from farm to farm and horse to horse.

Good management practices can also reduce the damage caused by an influenza outbreak. Early recognition and immediate isolation of sick horses reduce exposure of other horses to the virus. Any training or work done by individual horses should be stopped as soon as clinical signs are recognized in that animal. New horses brought into a stable or farm should be quarantined for up to six weeks to avoid the possibility of introducing equine influenza.