African horse sickness (AHS) is a highly infectious and deadly disease that affects all breeds of horses, mules, and donkeys. It is caused by the African horse sickness virus, which is a member of the Orbivirus genus and the Reoviridae family. Zebras, a type of wildlife equine species, are resistant to the disease. The virus is spread by the Culicoides midge, which acts as the vector host.
Horses cannot contract AHS directly from other horses through contact, but rather through the bite of an infected midge. These midges become infected by feeding on infected equine species, creating a cycle of transmission. The midges are most active during the warm, rainy season, particularly at sunrise and sunset, and do not survive cold weather. This means that most animals become infected during the warmer months, when the midges are most prevalent.
AHS has three forms: the lung form, the heart form, and the mixed form. The lung form, also known as the dunkop form, is characterized by a very high fever (up to 41 degrees), difficulty breathing, frothy discharge from the nose, and sudden death. The mortality rate for this form is 90%. The heart form, or dikkop form, is characterized by fever, swelling of the head and eyes, and in severe cases, the entire head swelling. Other symptoms may include the inability to swallow and colic, and terminal signs include bleeding in the mouth and eyes. The onset of death for this form is slower, occurring 4 to 8 days after the fever has started, and the mortality rate is 50%. The mixed form includes symptoms of both the dunkop and dikkop forms.
If you suspect that your horse may have AHS, it is important to contact a veterinarian for testing and confirmation. AHS is a controlled disease, and by law, owners are required to notify the local State Veterinarian of suspected cases. It is essential that blood samples be taken from the horse during the fever stage of the disease in order to confirm the diagnosis through laboratory testing.
There is currently no cure for AHS, so prevention is the most effective way to protect your horse from contracting the disease. One way to prevent AHS is through vaccination. Three vaccines are currently available: a polyvalent vaccine, a monovalent vaccine, and a monovalent inactivated vaccine. These vaccines can help protect uninfected horses from contracting the virus. It is important to note that vaccination may not provide complete protection and that booster shots may be necessary to maintain immunity.
Insecticides can also be used to kill the midges and prevent transmission. Habitat destruction, such as removing standing water where midges breed, can also help reduce their population. Keeping stables clean and dry can also help limit the number of midges present. Using insect repellents and keeping horses in the stable during peak midge activity (early mornings and late afternoons) can also help prevent bites.
It is always advisable to consult a veterinarian for any concerns about your horse's health. Early detection of AHS can be crucial in saving a horse's life, so it is important to be aware of your horse's behavior and any potential symptoms. Remember that prevention is the best course of action when it comes to AHS, so make sure to take steps to protect your horse from contracting the virus. It is also important to be mindful of the potential for transmission of the disease through insect vectors. If your horse has been in an area where AHS is present, it is crucial to take precautions to prevent the infected midges from spreading the disease to other horses.