66. African horse sickness, equine encephalosis.

Question 1

African Horse sickness History/Occurrence?

Answer 1

African horse sickness - NOTIFIABLE

• Vector transmitted disease of equids with acute, febrile, endothelia damages, oedema, haemorrhages,
• pulmonary & cardiac disorders ʹ circulatory problems of the lungs ʹ HIGH MORTALITY

History, occurrence

• First description on epizootics in central & S. Africa (1569)
• Present in several parts of Africa (mainly in S. Africa)
• Introductions to other regions: 1959-63 (ZOO!) Turkey, Saudi Arabia, Iran, India; 1966, 1987-90
• Spain, 1989 Portugal

Question 2

Causative agent/ Epizootiology African horse Sickness?

Answer 2

Causative agent:

• African horse sickness virus (AHSV), Orbivirus genus, Reoviridae
• Orbivirus, at least 9 serotyoes, diverse virulence
• Susceptibility: equids: horse, donkey, zebra; rarely other sp: elephant, camel, dog, ferret

Epizootiology

• Arthropod vectors
• Midges/gnats (Culicoides spp), biological vectors
• Mosquitoes (Culicidae), more mechanical vector
• Rarely ticks (Hyaloma, Ripicephalus), more mechanical vector
• Natural reservoirs: probably zebras (less susceptible)
• Viraemia: horse ʹ 4-8 (18) days; zebra, donkey: 28 days
• Infected horses shed virus through semen, urine, discharges too
• Infection of carnivores ʹ consumption of infected horse meat, blood or organs

Question 3

African horse sickness Pathogenesis?

Answer 3

Pathogenesis:

• Vector injects
• Primary virus multiplication in the lymphatic tissue
• Viraemia ʹ lymphatic & BV endothel damage (LUNG & SC TISSUE)
• Oedema, haemorrhages ʹ pulmonary oedema, cardiopathy ʹ death
• Mortality: horse 70-96%, mule 50%, donkey 10%, zebra survives

Question 4

African horse sickness Clinical signs?

Answer 4

Clinical signs:

• after 5-7 (2-14) days incubation
• Peracute, pulmonary form
• Fever (40-41oC) general weakness, sweating, red conjunctiva
• Dyspnoea (60-75/min), foamy nasal discharge, coughing
• Sudden death (w/in 24h)
• Acute, respiratory form ʹ fever (40-41oC), respiratory signs, death w/in 1 week
• Subacute, cardiac, oedematic form (the most frequent)
• Fever (39-41oC for 3-6 days)
• Oedema around the eyes, lips, head, tongue, throat (Hippo head͟)
• Later neck, chest oedema
• In final stage haemorrhage in the conjunctiva & on underside of the tongue
• The horse dies of cardiac dysfunction 4-8 days after the onset of the signs
• If survives, oedema disappears w/in 3-8 days
• Mixed form (respiratory & cardiac) ʹ fever (40-41oC), milder respiratory signs, oedema,mortality
• Chronic, febrile form
• Recurrent fever (in the mornings lower, in the afternoons higher max 40oC)
• Rarely other signs, reddish conjunctiva
• Mainly in donkeys, zebras, immune horses (vaccine/recovered)

Question 5

Pathology, Histopathology?

Answer 5

Pathology, histopathology

• Pulmonary oedema, hydrothorax, hyperaemia
• Oedema under the skin & in the CT
• Haemorrhages in the mucosa, hyperaemic visceral organs
• Fibrinous exudate in the thoracic cavity
• Haemorrhages on the serosal surfaces, kidney cortex, on the spleen
• Epi- & endocardial haemorrhage

Question 6

Diagnosis?

Answer 6

Diagnosis

• Clinical signs, pathology, epizootiology ʹ suspicion
• Communicable disease ʹ laboratory diagnosis is necessary
• Virus isolation ʹ suckling mouse brain, BHK, vero cells
• Reverse-transcription polymerase chain reaction, PCR, Ag-ELISA
• Serology ʹ ELISA, (CF, AGID, VN)

Question 7

African horse sickness Differential diagnosis?

Answer 7

Differential diagnosis

• (mainly based on case history)
• Equine infectious anaemia ʹ
• chronic, anaemia, decreasing condition
• Equine viral arteritis ʹ usually milder, typically abortions
• Babesiosis ʹ anaemia, icterus
• Anthrax ʹ pathology (Spleen), mild resp signs

Question 8

African horse sickness Prevention & Control?

Answer 8

Prevention & control

• ASH-free countries
• Avoiding introduction
• Restriction on equine (zebra!) importation from endemic countries
• Or permissions, min 30 days QT, serological & virological investigations
• Insecticide treatment against ectoparasites
• Dogs are potential carriers!
• Outbreak control
• Sanitary prophylaxis & supplementary treatment
• Restriction, slaughtering of affected animals, insect control
• Vaccinations in the safety zone ʹ with (live attenuated or) inactivated, type-specific
• vaccine 2x
• Long term surveillance, monitoring
• Endemic countries ʹ vaccine ʹ attenuated, polyvalent vaccines (produced in mouse brain or in cell
• cultures) ʹ protection for a few years

Question 9

Equine encephalosis?

Answer 9

Equine encephalosis

• (not notifiable)
• History, occurrence: - first detection in S. Africa, usually in the southern countries of Africa, but in Israel too (in 2009)
• Causative agent: orbivirus, culicoides vector
• Susceptibility: equines (gorse, donkey, zebra), elephant
• Pathogenesis: similar to AHS, BV damages
• Clinical signs, pathology
• 3-10 days incubation
• Frequently asymptomatic (donkey, mule)
• Fever for 1-5 days, restlessness, loss of appetite
• Oedema of the lips & eyelids, elevated pulse, CNS signs (oedema of brain)
• Abortion, typically in the first 5-6 months of pregnancy
• Inflammations of the mucosa & BVs
• Enteritis, liver dystrophy
• Recover in 1 ʹ 3 weeks
• Encephalosis = neuron damage but no signs of inflammation (unlike encephalitis which is due to
• inflammation)
• Diagnosis: virus isolation, RT-PCR, serology: ELISA, DDX: AHS!
• Prevention no vaccine! Epidemiological measures