Equine Influenza is an acute, highly contagious respiratory disease in horses. Although major epidemics of equine influenza have occured sporadically in many parts of the worl, 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.
The signs of influenza ususlly 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 manibles, 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 severrely ill horses may require weeks to months to recover fully, especially if they are not allowed to rest completely. Most uncomplicated cases recover fullu, but affected animals under stress, or ones not allowed to rest, may develope secondary pneumonia, a chronic cough, or infalammation of the heart muscle, sometimes resulting in death.
Clinical signs suggest a diagnosis of equine influenza. However, because horses are susceptible to several other respitatory infections, laboratory tests may be required for 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 antibiody titers.
Rest and supportive nursing care are important for uncomplicated recovery for equine influenza. Sick horses should be kept well ventilated stalls that are as dust free as possible. Medications to reduce fever may be needed if fever is as high (above 104 F). Antibiotics may be required if the fever lasts more than 3-4 days, the nasal discharge becomes mucopurulent, or pneumonia develops. Rest is absolutely essentia; and should continue for some time after clinical signs have resolved completely.
Prevention is by far the best approach to controling equine influenza. Vaccination, begining at an early age, with adequate boostering and frequent revaccination, will provide protection against the infection or reduce the severity of signs if disease does occur. Reqired 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 recognised in that animal. New horses brought into that stable or farm should be quarantined for up to 6 weeks to avaid the possibility of introducing equine influenza.