Fact Sheet - African Horse Sickness

What is African horse sickness?

African horse sickness (AHS) is an insect-borne disease that affects 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.

AHS causes fever and impairment of the respiratory and/or circulatory systems. The severity of the disease can range from a mild fever to sudden death. The sickness can have a sudden onset and is often fatal.

Is AHS a risk to human health?

No. There is no evidence of risk to humans.

What are the clinical signs of AHS?

Clinical signs are typically seen five to seven days after infection. The first signs of AHS are fever, followed by redness of the inside surface of the eyelids.

The disease can then progress to one of the following forms.

Pulmonary Form: Sudden onset of fever. This is followed by acute respiratory distress, coughing, sweating and foam in the nostrils. Death happens quickly.

Cardiac Form: Fever lasts three to six days. 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 can die due to heart failure. If the disease is not fatal, the swelling will gradually subside after three to eight days.

Mixed Form: This is a mixture of the pulmonary and cardiac forms. It is usually diagnosed only after a horse is dead.

Mild Form (AHS Fever): This mildest form is often overlooked. The animal may have a fever that fluctuates, but other clinical signs are not apparent. Rapid recovery often occurs after a one or two days.

Where is AHS found?

As its name indicates, AHS is endemic in the central tropical regions of Africa. On occasion, the disease has extended into Egypt, the Middle East and the southern Arabian Peninsula.

AHS has never been found in Canada.

How is AHS transmitted and spread?

AHS is not transmitted directly from one horse to another. It is spread mainly by insects. These can include small insects such as midges or "no-see-ums." The insects carry the virus after biting an infected horse.

AHS often occurs in Africa in late summer and early autumn when weather conditions are favourable for insect breeding.

The virus can only survive through continuous cycles of transmission between its hosts-horses and insects. It does not survive in the environment outside of the host.

Dogs can also become infected after eating infected horsemeat. However, dogs are not believed to be capable of transmitting the disease.

How is AHS diagnosed?

Diagnosis is based on clinical signs and lesions. A characteristic sign of AHS is swelling in the indentation above the animal's eyes.

The history of the animal is taken into account. That includes its exposure to recently imported horses and to the insect population. The only way to confirm AHS, however, is through laboratory testing.

How is AHS treated?

There is no specific treatment for this disease. Vaccines are routinely used for control in countries where AHS occurs naturally.

What is done to protect Canadian livestock from AHS?

The Canadian Food Inspection Agency (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 port-of-entry inspections done either by the Canada Border Services Agency or the CFIA.

AHS is a reportable disease under the Health of Animals Act, and all cases must be reported to the Canadian Food Inspection Agency (CFIA).

How would the CFIA respond to an outbreak of AHS in Canada?

Canada's emergency response strategy to an outbreak of AHS would be to:

  • eradicate the disease; and
  • re-establish Canada's disease-free status as quickly as possible.

In an effort to eradicate AHS, the CFIA would use its "stamping out" policy, which includes:

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

In some cases, the disease is not detected before the virus becomes widespread in the insect population that is carrying it. In these cases, the strategy could be modified to include vaccinating animals who may be at more risk of becoming infected.

Owners whose animals are ordered destroyed may be eligible for compensation.

Additional information

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