African horse sickness is an acute or subacute disease of horses caused by orbivirus. It is transmitted by various biting insects. The disease affects horses severely and causes edema, hemorrhaging, and accumulation of fluids. Symptoms range from mild fever to severe respiratory distress and death. Diagnosis involves isolating the virus from blood or tissues in cell cultures or eggs. There is no cure, but control relies on vaccination, quarantining sick animals, and reducing insect vectors.

1. AFRICAN HORSE SICKNESS
Dr Ashish Tanwer
Teaching Associate
V. C.C, C.V.A.S Bikaner

2. INTRODUCTION :-
• African Horse Sickness (AHS) is an acute or sub acute, febrile, arthropod borne
disease of horses characterized by oedema of subcutaneous tissues, lungs,
hemorrhages of internal organs and accumulation of serous fluids in the body
cavities.
• This disease is caused by orbi virus belonging to the family Reo viridae which is
a double stranded RNA virus.
• Horses of all breeds are highly susceptible to natural infection.
• Mules and zebras are less Affected and donkeys are generally resistant. The
disease occurs principally in Southern, Eastern and Central Africa.
• From there it spreads to Syria, Lebanon, Israel and other parts of Middle East.

4. • It has been recorded in Afghanistan, West Pakistan, Turkey and Iraq
•It is a seasonal disease, common in late summer in warm, humid, low lying
marshy districts. This disease is not directly contagious.
• Various nocturnal biting insects including mosquitoes are the most important
vectors of infection in Africa.
• Culicoides species of mosquito and insects belonging to Tabanidae family and
genus stomoxys have been incriminated in outbreaks in Turkey.
• Many serotypes have been described. In Africa 9 distinct serotypes are
recognized and considerable variation in virulence amongst individual strains
within each immunological type occurs.

5. • On the other hand only a single antigenic type involved in the Asian
outbreak in 1961. Almost all strains grow in the in the yolk Sac of fertile eggs.
• Virus can be propagated in cell cultures of many different types. Monkey cell
lines are most susceptible.
•In Rhesus kidney cultures the characteristic CPE is rounding and shrinkage
of infected cells which remain attached to the glass.

7. CLINICAL MANIFESTATIONS :-
• Incubation period is 6-9 days. 4 different clinical forms of illness were
described.
 Very mild form - only rise in temperature to 41°C.
 Acute or pulmonary form (DUNKOP) - In this there is severe
dyspnoea, pyrexia and coughing with abundant frothy discharge from the
nostrils. This form is common in virulent outbreaks and mostly the
affected horses die.
 Sub acute form (DIKKOP) – It is characterized by remarkable swelling
of head, neck and supra-orbital fossa associated with cardiac dyspnoea.
This form usually occurs when the immunity has been broken down by a
natural infection or in animals inoculated with mild strains of virus. This
form is much milder than the acute form and the affected animals
recover.
 Mixed form - Combination of pulmonary form and cardiac form. Heart
is affected.
• Mortality : In virulent form it is as high as 90% in horses and lower in mules.
In milder outbreaks mortality is 25%.

8. LESIONS AND DIAGNOSIS
Lesions :-
• Varies depending upon the severity of the case.
• In acute pulmonary form - extensive oedema of lungs and thorax may contain
several litres of fluid.
• In more chronic cardiac form there is oedematous infiltration of
subcutaneous tissue, sub- serosal tissue and other tissues together with gross
accumulation of fluid in the pericardial sac.

10. Diagnosis :-
• Samples to be collected
Live animals: Blood from affected animal should be
collected during early febrile phase
 Dead animals: Spleen
• Based on clinical signs and by post mortem findings.
• For virus isolation, the tissues of choice for diagnosis are spleen,
lung, and lymph nodes, collected at necropsy.
• Sample preparations can be inoculated in cell cultures, such as
baby hamster kidney-21 (BHK21), monkey stable (MS) or African
green monkey kidney (Vero), intravenously in embryonated eggs,
and intracerebrally in newborn mice.

12. • Several enzyme-linked immunosorbent assays (ELISAs) for the
rapid detection of African horse sickness virus (AHSV) antigen in
spleen tissues and supernatant from infected cells have been
developed.
• Identification of AHSV RNA has also been achieved using a reverse-
transcription polymerase chain reaction method.
• Virus isolates can be serotyped by a type-specific serological test
such as virus neutralisation (VN) and by reverse-transcription
polymerase chain reaction and sequencing.
• Serological tests-complement fixation test, ELISA, immunoblotting
and VN.

14. CONTROL :-
• Vector control
• Quarantine of affected animals
• Vaccination
• Recently freeze dried live attenuated neurotropic mouse brain virus
vaccine has been proved useful and polyvalent vaccines from 7 or 8
antigenically distinct serotypes appear to be safe and highly effective
against all field strains.
• Regular annual immunization is advocated.
• Tissue culture adapted virus, Hamster or Monkey kidney cell culture
vaccines are widely used in Africa and Middle East.

15. Thanks