DR WAQAS NAWAZ PMAS Arid Agriculture University, Rawalpindi Pakistan

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It is highly infectious & deadly disease.
Host range:
 Horses
 Mules
 Donkeys
 Zebras
Etiology:
It is viral disease
Family-----Reoviridae
Genus-------Orbivirus
Species------ African Horse Sickness Virus
This disease can be caused by any of the nine serotypes of this virus. It is not directly contagious
but it is known to be spread by insect vectors.
History:
 First case was recorded in mid-1600s in Sahara Desert
 1987-90, AHS was diagnosed in Spain
 1989, in Portugal
 But it was eradicated by using slaughter policy, movement restrictions, vector eradication
& vaccination
Epidemiology:
 AHS is known to be endemic in Sub-Saharan Africa, and has spread to Morocco,
the Middle East, India and Pakistan.
 More recently, outbreaks have been reported in the Iberian Peninsula.
 AHS has never been reported in the Americas, eastern Asia or Australasia.
 Epidemiology is dependent on host-vector interaction, where cyclic disease outbreaks
coincide with high numbers of competent vectors.
 The most important vector for AHS in endemic areas is the biting midge Culicoides
imicola, which prefers warm, humid conditions. Larvae do not carry the virus and long,
cold winters are sufficient to break epidemics in non-endemic areas.
However, elephants, camels and dogs can be infected as
well, but often show no signs of the disease. Dogs
usually contract the disease after eating infected horse
meat, but there has been a recent report of the diseases
occurring in dogs with no known horse meat ingestion

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Transmission:
 This disease is spread by insect vectors.
 The biological vector of the virus is the Culicoides (midges) species.
 However, this disease can also be transmitted by species of mosquitoes including Culex
& Anopheles
 Some species of ticks such as Hyalomma and Rhipicephalus.
Clinical Signs:
Horses are the most susceptible host with close to 90% mortality of those affected,
followed by mules (50%) and donkeys (10%). AHS manifests itself in four different forms: the
pulmonary form, the cardiac form, a mild (horse sickness fever) form, and a mixed form.
1. Pulmonary form
The per-acute form of the disease is characterized by;
o High fever
o Depression
o Respiratory symptoms
The clinically affected animal has
o Trouble breathing
o Starts coughing
o Frothy fluid from nostril and mouth
o Show signs of pulmonary edema within four days.
o Serious lung congestion causes respiratory failure and results in death in < 24 hours.
This form of the disease has the highest mortality rate
2. Cardiac form
This sub-acute form of the disease has an incubation period longer than that of the pulmonary
form.
 Signs of disease start at day 7-12 after infection
 High fever is a common symptom
 Conjunctivitis, with abdominal pain
 Progressive dyspnea
 Additionally, edema is presented under the skin of the head and neck, most notably in
swelling of the supra-orbital fossae, palpebral conjunctiva and intermandibular space.
Mortality rate is between 50-70% and survivors recover in 7 days.

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3. Mild or horse sickness fever form
Mild to subclinical disease is seen in zebras and African donkeys. Infected animals may have;
 Low grade fever
 Congested mucous membrane.
The survival rate is 100%
4. Mixed form
Diagnosis is made at necropsy. Affected horses show signs of both the pulmonary and cardiac
forms of AHS.
Diagnosis:
Clinical signs
Postmortem lesions
Presence of vector
Lab tests confirmation is by;
o Virus Isolation
o PCR
o ELISA kits
o CFT
o Serological test is only useful for detecting recovered animals, as sick animals die
before they are able to mount effective immune responses
o IHA
o HA
o Blood chemistry
Treatment:
There is currently no treatment for AHS.
Control of an outbreak in an endemic region involves quarantine, vector control and vaccination.
To prevent this disease, the affected horses are usually slaughtered, and the uninfected horses are
vaccinated against the virus. Three vaccines currently exist, which include a polyvalent vaccine,
a monovalent vaccine and a monovalent inactivated vaccine. This disease can also be
prevented by destroying the insect vector habitats using insecticides.