Special Veterinary Pathology

AFRICAN HORSE SICKNESS

Synonym: AHS, EQUINE PLAGUE

Definition

• 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

Etiology

• Double Stranded RNA virus – Orbivirus

Incidence

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

Susceptibility

• Horses, mules and donkeys

Transmission

• By Culicoides mosquitoes

Pathogenesis

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

Four forms

• Acute pulmonary form
• Subacute cardiac form
• Mixed form
• Mild form

Acute Pulmonary form: (DUNKOP form)

• Fever, dyspnea, coughing
• Frothy nasal discharge – pulmonary oedema
• Profuse sweating & nasal discharge
• Death

Subacute 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

Lesions

Pulmonary form: Hydrothorax

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

Cardiac form

• Hydropericardium, ascites
• Haemorrhages of myocardium
• Necrosis of myocardium
• Congestion of GI mucosa
• Enlarged & congested liver
• Haemorrhagic lymph nodes – depletion of lymphocytes
• Edema around pharynx – paralysis of oesophagus

Diagnosis

• Clinical signs & lesions
• Intracerebral inoculation into mice and then conducting neutralization test using a known antiserum
• Neutralization test