African Horse Sickness Fact Sheet
What is African horse sickness?
African horse sickness (AHS) is an insect-borne virus that affects horses and related species such as mules, donkeys and zebras. The disease affects horses most severely.
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?
There is no evidence of risk to humans.
What are the clinical signs of AHS?
Horses usually show clinical signs 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 (Lung) Form: Sudden onset of fever. This is followed by difficulty breathing, coughing, sweating and foam in the nostrils. Death follows quickly.
- Cardiac (Heart) 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 lethargy. Heart failure can be fatal. If the disease is not fatal, the swelling will gradually subside after three to eight days.
- Mixed Form: This is a mixture of the lung and heart forms and is usually diagnosed only after the horse has died.
- Mild Form (AHS Fever): This mildest form is often overlooked. The animal may have a fever that fluctuates, but there are no other clinical signs. Mild cases of AHS usually see the animal recover in one or two days.
Where is AHS found?
As its name suggests, AHS occurs naturally in the central tropical regions of Africa. In the past, it has extended into Egypt, the Middle East and the southern Arabian Peninsula.
No cases of AHS have been reported 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.
Zebras usually do not show signs of AHS. However, they may act as a source of infection for insects, which then infect horses.
AHS-infected horsemeat, if consumed, can infect dogs. Some dogs infected with AHS virus will show no clinical signs, while others will have a fever and may have difficulty breathing which can cause death. However, infected dogs cannot transmit AHS.
The AHS virus can survive in blood and some tissues collected from infected animals for a long period of time particularly if chilled or frozen. Strict biosecurity measures should be in place around infected premises. More information on biosecurity can be found on the CFIA Animal Biosecurity webpage.
How is AHS diagnosed?
Suspicion of AHS may be based on clinical exam findings, post-mortem examination and the possibility of exposure to horses, mules, donkeys or zebras from an area known to have AHS in a season when insects are active.
The only way to definitively diagnose AHS 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. All suspected cases must be reported to the Canadian Food Inspection Agency (CFIA) for immediate investigation by inspectors.
How would the CFIA respond to an outbreak of AHS in Canada?
Canada's emergency response strategy to an outbreak of AHS is to:
- eliminate the disease; and
- re-establish Canada's disease-free status as quickly as possible.
In an effort to eliminate AHS, the CFIA may use some or all of the following disease control methods:
- the humane euthanasia 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 cleaning and disinfection 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 to be euthanized may be eligible for compensation.
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