Viral Disease - African Horse Sickness


AHS, Equine plague


AHS is a highly fatal viral disease of horse, mules and donkey caused by orbivirus characterized by either pulmonary involvement or cardiac involvement or both


Double Stranded RNA virus - Orbivirus


The disease was originally present in South Africa, but in recent years, it has crossed the boundaries of other countries. In 1960, India has seen many outbreaks

Susceptible animals

Horses, mules and donkeys


By Culicoides mosquito


Orbivirus is a viscerotropic virus and is found in all tissues and fluids in the body

Four forms

Acute pulmonary form

Sub-acute cardiac form

Mixed form

Mild form

Acute Pulmonary form: (DUNKOP form)

Fever, dyspnea, coughing

Frothy nasal discharge - pulmonary oedema

Profuse sweating & nasal discharge --Death

Sub-acute Cardiac form (DIKKOP FORM)

Progressive fever

Progressive edema of lips, eyelids, neck and chest

Swollen, cyanotic tongue with petechiae

Paralysis of esophagus - unable to swallow

Cardiac failure - pulmonary oedema, hydropericardium and endocarditis---Death

Mixed form

Both pulmonary & cardiac form present

Mild from

No symptoms, mild fever, anorexia, dyspnea, mild conjunctivitis


Pulmonary form


Pulmonary edema -frothy exudate in bronchi, trachea, pharynx & nasal passages

Cardiac form

Hydro pericardium, ascites

Haemorrhages of myocardium

Necrosis of myocardium

Congestion of GI mucosa

Enlarged & congested liver

Hemorrhagic lymph nodes - depletion of lymphocytes

Edema around pharynx - paralysis of esophagus


Clinical signs & lesions

Intracerebral inoculation

Neutralization test

Differential diagnosis

The fulminant disease in groups of horses is characteristic, although acute intoxication by monensin, salinomycin, or similar compounds can produce similar signs.

Individual horses affected with purpura hemorrhagica and groups of horses affected with equine viral arteritis can have signs similar to horses with AHS.

Piroplasmosis (B. caballi or T. eqw) and trypanosomiasis cause fever and depression.

Anthrax can cause acute deaths in solitary horses or groups of horses.

Samples for confirmation of diagnosis

Virology - chilled spleen, lung, lymph node (PCR, VI)

Histology - fixed lung, heart.


There is no specific treatment for AHS.

Supportive care and treatment of complication of the disease should be provided.


The principles of control in enzootic areas are vaccination and reduction of exposure of horses to biting insects, whereas in non-enzootic areas the aim is to prevent introduction of the disease, and eradication if it is introduced.

The objectives of a control program for African horse sickness are:

  • » Prevention of introduction of infection by clinically ill or inapparently infected animals
  • » Slaughter of viraemic animals where animal welfare and economic considerations permit this course of action
  • » Management changes to reduce exposure to midge
  • » Vector control
  • » Induction of active immunity in animals at risk of disease.

Recently Discussed Topics

Blog Archive