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African horse sickness virus

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by

Melvyn Quan

on 12 May 2016

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Transcript of African horse sickness virus

Reoviridae
African horse sickness virus
Epidemiology
Clinical signs
peracute "dunkop"/pulmonary
Control
Culicoides imicola
Thomas Perry
District surgeon at Graaff-Reinet
1819
Epidemics
James Backhouse
missionary
1838
History of AHS
“If the animal is rode during the Sickness, or urged by driving or otherwise to any degree of speed, he falls at once, literally suffocated by the quantity of frothy matter which fills his trachea and issues in abundance from his nostrils”.
Epidemics every 20-30 years
Warm phase of the El Niño/Southern Oscillation phenomenon
1854/1855 outbreak
65 000 horses, 40% of the entire horse population of the Cape of Good Hope
£525 000
Horses that survived - "salted", worth 6-10X more
“When a horse takes the sickness, or at least shows indications of it, thirty-six hours will terminate the matter one way or the other; if the unfortunate animal is alive after that, experienced persons would pronounce an opinion, or express a hope, that the creature was going to salt”.
Breed in damp soil rich in organic matter
Widespread
Associated with rain
Active at night
Tend to not enter buildings
Virogenesis in the midge - 8 days
Stabling
Fans
Netting on windows and door impregnated with insecticide
topical insecticide/repellents on the horse
high-lying areas
Initial mutiplication - regional lymph node
Primary viraemia
Target organs - lung, heart, spleen
Replication - microvascular endothelial cells, monocyte-macrophages
vasculitis - oedema
Secondary viraemia
up to 21 days in horses
up to 40 days in zebras
Clinical signs
Virus isolation - heparin blood
RT-PCR - EDTA
Serology - serum
Organs - lung, spleen on ice for isolation/PCR, or formalin for IHC
Unvaccinated horses, foals, dogs
Fever
Very rapid onset of severe dyspnoea
Sometimes frothy discharge from nostrils
Rapid deaths (< 24 h)
Less than 5% recover
Lung oedema, hydrothorax
“At day-break, one of our horses exhibited symptoms of a fatal disease, called in this Colony, The Sickness. His eyelids were swollen and the blood vessels of his mouth and tongue were in a state of congestion. He appeared to be in perfect health last night when tied to the wagon wheel to secure him from Hyenas which are numerous here. The disease usually comes on suddenly and runs its course quickly. On being loosed, he began to browse, but had difficulty in swallowing: he was bled without delay and dosed with Calomel and Tartarized Antimony. After this, he neighed cheerfully to his companion, went to him on an adjacent hill, where he lay down; he soon rose again, and began to eat, but quickly lay down, and then struggled and died. His death took place about an hour after the symptoms of “The Sickness” were first noticed; before night, his carcase was nearly consumed by Vultures and by the dogs of the Hottentots. Thus quickly is a horse finished in Africa!
T.B. Bayley, 1856
Not contagious
Stabling
Avoid low lying areas
AHS “could be traced, almost without exception, to the deleterious influence of the night air”.
“The distemper was everywhere most destructive in the low grounds and along the watershed of each district; the fatal miasma seeming to be held in suspension during the day, and to descend again at night with the heavy dews”.
Discovery
1900
1955
1944
before 1900: dew, grass, cobwebs
McFadyean: transmitted the disease with a bacterial-free filtrate of blood
Confirmed by Theiler and Nocard
Conclusion: cause was a virus
Aetiology
1903
McFadyean
Horses protected in mosquito proof enclosures
Winged night insects
1905
1905: 1st vaccine developed by Arnold Theiler
Simultaneous inoculation of virus and hyperimmune serum from salted horses
Used till 1933
1931
Alexander
Attenuation of AHSV through passage of virus in mouse brains
Propagation of virus in chicken embryos
Culicoides
Serotypes
Theiler - 1st to suggest that there was a plurality of “immunologically distinct strains” of AHSV
Alexander and McIntosh - 7 serotypes (1955)
Howell - 9 serotypes (1962)
1963
Propagation of AHSV in tissue culture
large plaques avirulent
1969
Double-stranded RNA
10 segments
1993
PCR
2009
2010
Recombinant vaccine
Real-time PCR
Aetiology
Reoviridae
Orbivirus
10 segments of dsRNA
receptor-mediated endocytosis
300 000 deaths!
1960
Recent outbreaks
Environment
Host
Vector
Heavy rains followed by warm, dry spells
late summer
frost
Horse
70-95% mortality
Mule
50-70% mortality
Donkey
Resistant
Zebra
Resistant
Dog
Susceptible
not a carrier!
Onderstepoort
2000
C. bolitinos
Cuilcoides bolitinos
Breed in cattle, buffalo, wildebeest dung
Cooler areas
Not dependent on rainfall
Enters buildings
du Toit
Pathogenesis
subacute "dikkop"/cardiac
acute mixed
horsesickness fever form
lung oedema
oedema of fat in coronary groove
hydropericardium
epidcardial haemmorhages
endocardial haemmorhages
congestion of glandular part of the stomach
both "pulmonary" and "cardiac" forms present
mortality rate - 70%
subcutaneous oedema of head and neck
mortality rate - 50%
mucosal petechiae
swollen supra-orbital fossae
oedema of the conjunctiva
Subcutaneous and intermuscular oedema
vaccinated horses, donkeys, zebra
Fever only clinical signs
subclinical infections
Diagnosis/Control
Diagnosis
Differential diagnoses
Equine encephalosis
Oedema - purpura haemorrhagica and equine viral arteritis, swelling in AHS does not extend to legs
Piroplasmosis
Control
No specific treatment
Rest
Vaccination - bottle 1 and 3 weeks later bottle 2, repeat annually late winter, early spring
Bottle 1 - serotypes 1, 3, 4
Bottle 2 - serotypes 2, 6, 7, 8
Cross reaction between 1 and 2, 3 and 7, 5 and 8, 6 and 9
Doctor!
Which samples should be submitted for AHS diagnosis?
What is a CT value and does a positive PCR assay confirm that my horse has AHS?
My horse has been vaccinated every year with the AHS vaccine yet still got AHS.
Can my horse be worked after vaccination?
Neighbours have moved zebras onto their properties and now my horses have AHS.
A horse in the yard has AHS and I’m worried that it will infect the other horses
I want to move my horse into the AHS controlled area – what do I need to do?
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