African horse sickness
Australia has not recorded any outbreaks of African horse sickness, which is caused by an insect-transmitted virus.
African horse sickness (AHS) is endemic or occurs in all parts of Africa south of the Sahara but epidemics have spread further north to Egypt, the Middle East and Spain. Thailand is currently experiencing an outbreak of AHS thought to have entered the country via imported zebra, which do not show clinical signs. The outbreak is being contained by vaccination and by excluding insects from stables.
Horses and mules are highly susceptible and often die following infection. Dogs show severe disease if infected.
There are several forms of the disease. The specific signs of AHS reflect the effects of the virus on the lungs, or on the heart and circulatory system, or a combination of both.
Signs of African horse sickness
Lung form signs include:
- sudden fever with temperature to 41°C, panting, copious amounts of frothy nasal discharge
- standing with forelegs apart, ears drooping, nostrils dilated, head extended and very sweaty
- death within 4–24 hours.
Similar signs are seen in dogs.
Heart and circulatory form signs include:
- less acute with fever 39–41°C persisting for 3–4 days before swelling above and behind the eyes (the swelling may cause the eyes to close and bulge)
- later pinpoint haemorrhages of the membrane over the white of the eye and the inside of the eyelid (conjunctiva)
- swelling of the lips, cheeks, tongue and throat area
- swelling of the neck, brisket, lower chest and abdomen.
Swelling gradually subsides over a week or so in horses that recover.
Combination of lung and heart form signs include:
- temperature may be above 40°C for a day or two
- inflammation of the conjunctivae (whites of the eyes and inside of eyelid), breathing difficulty and increased pulse rate before a rapid recovery.