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African Horse Sickness

What is African horse sickness?

African horse sickness (AHS) is an insect-borne disease affecting horses and related species such as mules, donkeys, and zebras. Horses are most severely affected by the disease. AHS is caused by the AHS virus, of which there are nine different strains. Any of the strains can cause disease with severity ranging from a mild fever to sudden death. AHS causes fever and impairment of the respiratory and/or circulatory systems. The sickness can have a sudden onset and is highly fatal.

Do we have this disease in Canada?

AHS is not present in Canada. As its name indicates, AHS is endemic to the central tropical regions of Africa. A few outbreaks have occurred outside Africa, such as in the Near and Middle East (1959-63), in Spain (1966, 1987-90) and in Portugal (1989).

Is there a human health risk associated with this disease?

No. There is no evidence that humans can become infected with the AHS virus.

How is AHS transmitted and spread?

AHS is not transmitted directly from one horse to another. It is spread mainly by vectors, including small biting insects such as midges or "no-see-em’s." The insects carry the virus after biting an infected horse. AHS often occurs in Africa in late summer and early autumn when climatic conditions are favourable for insect breeding. The virus can only survive through continuous and uninterrupted cycles of transmission between its hosts—horses and insects. It does not survive in the environment outside a host. Dogs can also become infected with AHS after eating infected horsemeat; however, this method of transmission of AHS has not been observed in any other animals.

What are the clinical signs of this disease?

The first signs of AHS are fever, followed by redness of the inside surface of the eyelids. The disease can then progress in one of the following forms:

• Pulmonary Form: Sudden onset of fever, followed by acute respiratory distress, coughing, sweating and foam in the nostrils. Death occurs rapidly.
• Cardiac Form: Fever lasts three to six days and swelling of the head and neck occurs due to fluid collecting beneath the skin. There may be restlessness, signs of abdominal pain, and depression. The animal dies due to heart failure. If the disease is not fatal, the swelling will gradually subside after three to eight days.
• Mixed Form: This form represents a mixture of the pulmonary and cardiac forms and is most often diagnosed post-mortem.
• Mild Form (AHS Fever): This is the mildest form and is often overlooked. The animal may have a fever that fluctuates, but other clinical signs are not apparent. Rapid recovery often occurs after a day or two.

How is AHS diagnosed?

Diagnosis of AHS is based on the appearance of clinical signs and lesions. A history consistent with insect transmission is also taken into account. Diagnosis must be confirmed by laboratory tests that detect the virus in blood samples taken from horses during the fever stage of the disease.

Are there any treatments for AHS?

There is no specific treatment for this disease. Vaccines may be used to prevent the disease in countries where AHS is naturally occurring.

How can the Canadian Food Inspection Agency (CFIA) prevent the entry of this disease into Canada?

African horse sickness is a reportable disease under the Health of Animals Act. This means that all suspected cases must be reported to the CFIA. All reported suspect cases are immediately investigated by inspectors from the agency. The CFIA imposes strict regulations on the import of animals and animal products from countries where AHS is known to occur. These regulations are enforced through CFIA port-of-entry inspections.

Canada’s emergency response strategy in the event of an outbreak of a foreign animal disease is to eradicate the disease and re-establish the country’s disease-free status as quickly as possible. In an effort to eradicate AHS, the CFIA would employ its "stamping out" policy, which would include:

• the humane destruction of all infected and exposed animals;
• surveillance and tracing of potentially infected or exposed animals;
• strict quarantine and animal movement controls;
• strict decontamination of infected premises; and
• zoning to define infected and disease-free areas.

How to get more information?

Contact your Canadian Food Inspection Agency Area Office:

You can find your local Canadian Food Inspection Agency District Office on the CFIA Web site or by consulting the blue pages of your local phone directory.

September 2003
P0307E-03