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Equine Viral Respiratory Diseases Viral causes of respiratory disease in the horse include strains of influenza, herpesviruses, EVA virus, rhinoviruses, adenoviruses, and parainfluenza viruses. The two most commonly observed clinical signs in horses with a viral respiratory disease are inappetance and depression. Other signs include a fever and a slight nasal discharge early in the disease. Within 24-48 hours, the discharge becomes more copious. The horse may develop a cough due to pharyngitis and/or laryngitis. Many cases of respiratory disease in the horse are associated with outbreaks, meaning several horses in a barn become sick. Furthermore, stress is a leading factor in infection. Horses in heavy training or stressful living environment are more prone to infection. The following are the main viruses associated with respiratory disease in the horse. Equine influenza This virus spreads rapidly, and is highly contagious, especially in areas with a high equine population, such as stables. This virus can be transmitted over a distance of 30 yards from one cough or snort. As with most of these viruses, the young are more at risk to develop illness (<2 yrs.). Clinical signs include fever, inappetance, nasal discharge, depression, coughing lethargy, and lung sounds may be harsh. If the disease is uncomplicated by secondary bacterial infections, clinical signs improve in 4-7 days, although a dry cough may persist for several weeks. If stress is not reduced for the horse, secondary complications such as bacterial pneumonia may occur. Equine Herpesvirus-4 EHV-4 is the major cause of acute respiratory disease in horses <2 years of age. Clinical signs are less severe, and morbidity is lower, in these horses than in those infected with equine influenza. Young foals show transient and mild signs; however, foals that are going through the stress of weaning develop more severe signs. Foals are weaned at a time when the maternal antibodies are waning, leaving the foal ill-equipped to fight viral infections. Latent infections are possible, and may reactivate later in life after periods of stress or administration of corticosteroids. Equine Herpesvirus-1 EHV-1 causes respiratory disease similar to EHV-4. In addition, it may cause abortion in mares infected within their last trimester. EHV-1 may also cause neurological dysfunction. Diagnosis In most cases of equine respiratory disease, specific diagnostics tests are not performed due to the self-limiting nature of the disease. However, serological diagnostics (blood test) may be performed. Treatment Most of the uncomplicated viral respiratory diseases run a natural course of 7-14 days with spontaneous resolution. Good nursing care, eliminating stress, and stopping training will aid minimizing complications. Antibiotics are not generally used unless there is evidence of a secondary bacterial infection or other complications. In some complicated cases, i.e. pneumonia, bronchodilators may be utilized. Prevention All infected animals must be isolated to prevent virus spread. Stress should be minimized, and the environment should be clean and well-ventilated. Vaccinating has been shown to decrease the severity of the clinical signs and shorten the duration of viral shedding. Therefore, decreasing the amount of virus shed will decrease the spread of the disease. The vaccinations currently used are the intranasal FLU vaccine (equine influenza) and Pneumobort-K (equine herpesvirus-1 and –4). |
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