Host and Vector Animals affected are, all breeds of horses (mortality rate of 70-90%), mules and donkeys. Wild life Equine species (Zebras) are resistant to the disease. How do horses contract the disease? AHS does not spread directly from one horse to another, but is transmitted by the Culicoides midge, which becomes infected when feeding on other infected equidae. It occurs mostly in the warm, rainy season when midges are plentiful, and disappears after frost, when the midges die. Most animals become infected in the period associated with sunset and sunrise, when the midges are most active. Symptoms The disease manifests in three ways, namely the lung form, the heart form and the mixed form. The lung (dunkop) form is characterised in the following manner: very high fever (up to 41 degrees). difficulty in breathing, with mouth open and head hanging down. frothy discharge may pour from the nose. sudden onset of death. very high death rate (90%). The heart (dikkop) form is characterised in the following manner: fever, followed by swelling of the head and eyes. in severe cases, the entire head swells (“dikkop”). loss of ability to swallow and possible colic symptoms may occur. terminal signs include bleeding (of pinpoint size) in the membranes of the mouth and eyes. Slower onset of death, occurring 4 to 8 days after the fever has started. Lower death rate (50%). The mixed form is characterised by symptoms of both the dunkop and dikkop forms of the disease. Diagnosis and Notification The symptoms described above may assist with an initial diagnosis of AHS. This diagnosis can only be confirmed by identifying the virus in a laboratory. It is, therefore, essential that blood samples be taken from the horse during the fever stage of the disease for analysis. As AHS is a controlled disease, horse owners are obliged by law to notify the local State Veterinarian of suspected cases.