Difference between revisions of "African Horse Sickness"

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== Introduction ==
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[[Image:Lung oedema in African horse sickness.jpg|thumb|right|200px|<small><center>Lung oedema in African horse sickness (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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This is a serious viral disease transmitted by [[Ceratopogonidae|midges]] causing systemic signs and often death in the horse. It is a worldwide disease but is currently not found in the UK and is notifiable here. However, with global warming, the midge breeding area is growing and there are worries that in the future the disease will occur here. It affects horses, donkeys and mules and also is present subclinically in zebras and african donkeys. These can be a reservoir of infection for the disease. The disease has only been found in Africa, but since 1987 has recurred in Spain and Portugal.
  
====Antigenicity====
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There are nine serotypes of African Horse Sickness. The vectors for the disease are [[Ceratopogonidae|'''midges''']]. The virus oscillates between horses and midges. It replicates in the salivary glands of biting midges, and occurs where they breed.
*9 serotypes
 
  
====Hosts====
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The virus is pantropic and infects the endothelium and myocardium. It enters via the bloodstream from a midge bite and then disseminates throughout the body.
*Clinical: horses, mules, donkeys
 
*Subclinical: african donkeys, zebras
 
  
====Pathogenesis====
 
*Virus oscillates between horses and midges
 
**Replicates in the salivary glands of biting midges, and occurs where they breed
 
*'''Pantropic''' virus: infects endothelium and myocardium
 
*'''Peracute''': causes sudden death with pyrexia before the onset of clinical signs
 
*Two forms:
 
**'''Acute cardac-pneumonic form''':
 
***Interlobular pulmonary oedema
 
***Pericarditis
 
***Hemorrhage and oedema of the viscera
 
***Death within 5 days
 
**'''Subacute cardiac form''':
 
***Milder clinical signs but still a high mortality rate
 
  
====Diagnosis====
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== Clinical Signs==
*Clinical signs
 
*Differential: Equine Arteritis Virus (EAV)
 
**EAV causes oedema in the legs, which AHS does NOT
 
*Suckling mouse inoculation
 
*Virus serotype identification
 
*Serology
 
*RT-PCR will be used in future outbreaks
 
  
====Control====
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'''Peracute''': causes sudden death with pyrexia before the onset of clinical signs.  
Control measures are largely preventative:
 
*Slaughter or immediate isolation of sick animals
 
*Mandatory and immediate vaccination with appropriate serotype
 
*Restricted movement of susceptible animals
 
**Protection zones and Surveillance zones set in place around outbreaks
 
*Control of vector: ectoparasiticides, etc.
 
  
====Current Relevance====
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'''Acute cardiac-pneumonic form''':causes signs such as interlobular [[Pulmonary Oedema|pulmonary oedema]], [[pericarditis]], hemorrhage and [[Oedema|oedema]] of the viscera. Death usually occurs within 5 days.
*Once only found in Africa, but since 1987 has recurred in Spain and Portugal
 
*Not present currently in the UK but global warming may expand midge breeding grounds
 
  
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'''Subacute cardiac form''': causes milder clinical signs but still a high mortality rate.
  
  
[[Image:Lung oedema in African horse sickness.jpg|right|thumb|100px|<small><center>Lung oedema in African horse sickness (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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== Diagnosis==
  
*Caused by [[Orbiviruses|orbivirus]], family reoviridae
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Clinical signs are quite presumptive and would lead you to be concerned of a severe viral infection and inflict necessary precautions such as isolation etc. Definitive diagnosis should be made via elimination of differential diagnoses such as [[Equine Arteritis Virus]] (EAV). EAV causes oedema in the legs, which AHS does NOT.
*Respiratory distress or cardiovascular failure
 
*Rapid death due to massive [[Lungs Circulatory - Pathology#Pulmonary oedema|pulmonary oedema]]
 
*[[Pleural Cavity & Membranes Degenerative - Pathology#Hydrothorax|Hydrothorax]] may also develop
 
*Large amounts of froth present in airways
 
  
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Samples should be taken for virus serotype identification and serology.
  
[[Category:Orbiviruses]][[Category:Horse Viruses]][[Category:To_Do_-_Clinical/Viruses]]
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[[Category:Respiratory_Viral_Infections]]
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== Treatment and Control ==
[[Category:Respiratory Diseases - Horse]]
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In countries where the disease is not endemic, e.g. the UK, then humane destruction of the horse will be required.
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Control measures are largely preventative and include slaughter or immediate isolation of sick animals, mandatory and immediate vaccination with appropriate serotype, restricted movement of susceptible animals and protection zones and surveillance zones set in place around outbreaks. The control of the vector with ectoparasiticides, etc is also very important.
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== References ==
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Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) Equine Internal Medicine (Third Edition), Saunders. <br>Reed, S.M, Bayly, W.M, Sellon, D.C. (2004) Equine Internal Medicine (Second Edition) Saunders. <br>Robinson, N.E., Sprayberry, K.A. (2009) Current Therapy in Equine Medicine (Sixth Edition) Saunders Elsevier<br>Rose, R. J. and Hodgson, D. R. (2000) Manual of Equine Practice (Second Edition) Sauders. <br>
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{{review}}
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[[Category:Orbiviruses]] [[Category:Horse_Viruses]] [[Category:Expert_Review - Horse]] [[Category:Respiratory_Viral_Infections]] [[Category:Respiratory_Diseases_-_Horse]]

Latest revision as of 16:54, 31 July 2012


Introduction

Lung oedema in African horse sickness (Image sourced from Bristol Biomed Image Archive with permission)

This is a serious viral disease transmitted by midges causing systemic signs and often death in the horse. It is a worldwide disease but is currently not found in the UK and is notifiable here. However, with global warming, the midge breeding area is growing and there are worries that in the future the disease will occur here. It affects horses, donkeys and mules and also is present subclinically in zebras and african donkeys. These can be a reservoir of infection for the disease. The disease has only been found in Africa, but since 1987 has recurred in Spain and Portugal.

There are nine serotypes of African Horse Sickness. The vectors for the disease are midges. The virus oscillates between horses and midges. It replicates in the salivary glands of biting midges, and occurs where they breed.

The virus is pantropic and infects the endothelium and myocardium. It enters via the bloodstream from a midge bite and then disseminates throughout the body.


Clinical Signs

Peracute: causes sudden death with pyrexia before the onset of clinical signs.

Acute cardiac-pneumonic form:causes signs such as interlobular pulmonary oedema, pericarditis, hemorrhage and oedema of the viscera. Death usually occurs within 5 days.

Subacute cardiac form: causes milder clinical signs but still a high mortality rate.


Diagnosis

Clinical signs are quite presumptive and would lead you to be concerned of a severe viral infection and inflict necessary precautions such as isolation etc. Definitive diagnosis should be made via elimination of differential diagnoses such as Equine Arteritis Virus (EAV). EAV causes oedema in the legs, which AHS does NOT.

Samples should be taken for virus serotype identification and serology.


Treatment and Control

In countries where the disease is not endemic, e.g. the UK, then humane destruction of the horse will be required.

Control measures are largely preventative and include slaughter or immediate isolation of sick animals, mandatory and immediate vaccination with appropriate serotype, restricted movement of susceptible animals and protection zones and surveillance zones set in place around outbreaks. The control of the vector with ectoparasiticides, etc is also very important.


References

Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) Equine Internal Medicine (Third Edition), Saunders.
Reed, S.M, Bayly, W.M, Sellon, D.C. (2004) Equine Internal Medicine (Second Edition) Saunders.
Robinson, N.E., Sprayberry, K.A. (2009) Current Therapy in Equine Medicine (Sixth Edition) Saunders Elsevier
Rose, R. J. and Hodgson, D. R. (2000) Manual of Equine Practice (Second Edition) Sauders.




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