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African horse sickness

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Datasheet

African horse sickness

Summary

  • Last modified
  • 22 May 2020
  • Datasheet Type(s)
  • Animal Disease
  • Preferred Scientific Name
  • African horse sickness
  • Overview
  • African horse sickness (AHS) is a highly infectious, non-contagious, insect-transmitted disease affecting all species of Equidae. It is characterized by respiratory and circulatory damage.

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Pictures

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PictureTitleCaptionCopyright
A horse infected with African horse sickness virus (subacute, cardica form): oedema of the supraorbital fossa.
TitleSymptoms
CaptionA horse infected with African horse sickness virus (subacute, cardica form): oedema of the supraorbital fossa.
CopyrightPhilip Mellor/Institute for Animal Health, Pirbright, UK
A horse infected with African horse sickness virus (subacute, cardica form): oedema of the supraorbital fossa.
SymptomsA horse infected with African horse sickness virus (subacute, cardica form): oedema of the supraorbital fossa.Philip Mellor/Institute for Animal Health, Pirbright, UK
A horse infected with African horse sickness virus (acute, pulmonary form): excessive nasal discharge, which will be followed by death from anoxia.
TitleSymptoms
CaptionA horse infected with African horse sickness virus (acute, pulmonary form): excessive nasal discharge, which will be followed by death from anoxia.
CopyrightPhilip Mellor/Institute for Animal Health, Pirbright, UK
A horse infected with African horse sickness virus (acute, pulmonary form): excessive nasal discharge, which will be followed by death from anoxia.
SymptomsA horse infected with African horse sickness virus (acute, pulmonary form): excessive nasal discharge, which will be followed by death from anoxia.Philip Mellor/Institute for Animal Health, Pirbright, UK
Foam from the nares is due to pulmonary oedema.
TitleExternal symptoms
CaptionFoam from the nares is due to pulmonary oedema.
Copyright©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Foam from the nares is due to pulmonary oedema.
External symptomsFoam from the nares is due to pulmonary oedema.©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Depressed horse; note the bilateral supraorbital oedema.
TitleExternal symptoms
CaptionDepressed horse; note the bilateral supraorbital oedema.
Copyright©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Depressed horse; note the bilateral supraorbital oedema.
External symptomsDepressed horse; note the bilateral supraorbital oedema.©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Congestion and oedema of the conjunctiva. Congestion is a consistent clinical finding in AHS.
TitleExternal symptoms
CaptionCongestion and oedema of the conjunctiva. Congestion is a consistent clinical finding in AHS.
Copyright©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Congestion and oedema of the conjunctiva. Congestion is a consistent clinical finding in AHS.
External symptomsCongestion and oedema of the conjunctiva. Congestion is a consistent clinical finding in AHS.©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Excessive fluid in the thoracic cavity and pulmonary oedema; note the distended interlobular septa.
TitlePathology
CaptionExcessive fluid in the thoracic cavity and pulmonary oedema; note the distended interlobular septa.
Copyright©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Excessive fluid in the thoracic cavity and pulmonary oedema; note the distended interlobular septa.
PathologyExcessive fluid in the thoracic cavity and pulmonary oedema; note the distended interlobular septa.©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Cut surface of an oedematous lung; note the distended interlobular septa.
TitlePathology
CaptionCut surface of an oedematous lung; note the distended interlobular septa.
Copyright©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Cut surface of an oedematous lung; note the distended interlobular septa.
PathologyCut surface of an oedematous lung; note the distended interlobular septa.©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Petechial haemorrhages on the serosa are indicative of a viremic or septicemic condition.
TitlePathology
CaptionPetechial haemorrhages on the serosa are indicative of a viremic or septicemic condition.
Copyright©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Petechial haemorrhages on the serosa are indicative of a viremic or septicemic condition.
PathologyPetechial haemorrhages on the serosa are indicative of a viremic or septicemic condition.©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Petechial haemorrhages on the diaphragm are indicative of a viremic or septicemic condition.
TitlePathology
CaptionPetechial haemorrhages on the diaphragm are indicative of a viremic or septicemic condition.
Copyright©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Petechial haemorrhages on the diaphragm are indicative of a viremic or septicemic condition.
PathologyPetechial haemorrhages on the diaphragm are indicative of a viremic or septicemic condition.©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Pathology. Pericardium.
TitlePathology
CaptionPathology. Pericardium.
Copyright©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Pathology. Pericardium.
PathologyPathology. Pericardium.©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Supraorbital oedema.
TitleExternal symptoms
CaptionSupraorbital oedema.
Copyright©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Supraorbital oedema.
External symptomsSupraorbital oedema.©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Oedema in the intermuscular fascia of the neck may be the only lesion in AHS.
TitlePathology
CaptionOedema in the intermuscular fascia of the neck may be the only lesion in AHS.
Copyright©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Oedema in the intermuscular fascia of the neck may be the only lesion in AHS.
PathologyOedema in the intermuscular fascia of the neck may be the only lesion in AHS.©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)

Identity

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Preferred Scientific Name

  • African horse sickness

English acronym

  • AHS

Overview

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African horse sickness (AHS) is a highly infectious, non-contagious, insect-transmitted disease affecting all species of Equidae. It is characterized by respiratory and circulatory damage.

AHS is caused by African horse sickness virus (AHSV), a member of the family Reoviridae of the genus Orbivirus. AHSV is endemic in the central tropical regions of Africa and regularly spreads to Southern Africa and occasionally to Northern Africa. Infected animals or vectors can carry the virus into AHS-free regions. Outbreaks have occurred outside Africa, including in the Near and Middle East, Spain, Portugal and Morocco. In February 2020, ASH was reported in Thailand (OIE, 2020); the outbreak is the first that south-east Asia has ever experienced.

This disease is on the list of diseases notifiable to the World Organisation for Animal Health (OIE). For more information, see the website: www.oie.int.

Host Animals

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Animal nameContextLife stageSystem
Camelus bactrianus (Bactrian camel)Domesticated hostOther: All Stages
Camelus dromedarius (dromedary camel)Domesticated hostOther: All Stages
Canis familiaris (dogs)Domesticated host, Wild host
ElephantidaeWild host
EquidaeDomesticated host, Wild host
Equus asinus (donkeys)Domesticated host, Wild hostOther: All Stages
Equus burchelliiWild host
Equus caballus (horses)Domesticated host, Wild hostOther: All Stages
Equus zebraWild host
Equus zebra hartmannaeWild host
mulesDomesticated hostOther: All Stages

Hosts/Species Affected

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Usual hosts of the disease include horses, mules, donkeys and zebras. Other occasional hosts include elephants, camels, and dogs (after eating infected blood or horsemeat).

Zebras, which are often asymptomatic, are thought to be the natural reservoir hosts in most regions of Africa (Spickler, 2015).

Distribution

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African horse sickness virus is endemic in tropical and subtropical areas of Africa, south of the Sahara, from Senegal in the west to Ethiopia and Somalia in the east and extending as far south as South Africa (Zientara et al., 2015).

Outbreaks outside Africa in the Near and Middle East (1959-63), Spain (1966 (serotype 9), 1987-90 (serotype 4)), Portugal (1989, serotype 4) and Morocco (1989-91, serotype 4) have occurred.

The disease has a seasonal occurrence and its prevalence is influenced by climatic and other conditions that favour the breeding of its insect vectors. Recent northward expansion of the main African vector, Culicoides imicola, and Bluetongue virus (a similar Orbivirus) into the Mediterranean Basin of Europe now threatens that region and beyond to African horse sickness (Mellor, 1992; Mellor and Hamblin, 2004; Dufour et al., 2008; Calvo et al., 2009). Due to the similarities between bluetongue and African horse sickness viruses and their vectors, there are fears that if African horse sickness should appear again in Europe, it could spread as widely as Bluetongue virus.

In February 2020, ASH was reported in Thailand (OIE, 2020); the outbreak is the first that south-east Asia has ever experienced.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Last updated: 11 Mar 2020
Continent/Country/Region Distribution Last Reported Origin First Reported Invasive Reference Notes

Africa

BeninAbsent, No presence record(s)OIE (2009)
BotswanaAbsent, No presence record(s)OIE (2009)
BurundiAbsent, No presence record(s)OIE (2012)
CameroonAbsent, No presence record(s)OIE (2012)
Central African RepublicAbsent, No presence record(s)OIE (2012)
Congo, Democratic Republic of theAbsent, No presence record(s)OIE Handistatus (2005)
Côte d'IvoireAbsent, No presence record(s)OIE Handistatus (2005)
DjiboutiAbsent, No presence record(s)OIE (2012)
EgyptAbsent, No presence record(s)OIE (2009)
EritreaPresentOIE (2012)
EswatiniPresentOIE (2012); OIE Handistatus (2004)
EthiopiaPresentOIE (2012)
GambiaPresentOIE (2012)
KenyaAbsent, No presence record(s)OIE (2012)
MadagascarAbsent, No presence record(s)OIE (2012)
MalawiAbsent, No presence record(s)OIE (2009)
MauritiusAbsent, No presence record(s)OIE (2012)
MoroccoPresentMellor and Boorman (1995)
NigeriaAbsent, No presence record(s)OIE (2009)
RéunionAbsent, No presence record(s)OIE Handistatus (2005)
São Tomé and PríncipeAbsent, No presence record(s)OIE Handistatus (2005)
SeychellesAbsent, No presence record(s)OIE (2012)
South AfricaPresentOIE (2012); Mellor and Boorman (1995)
SudanAbsent, No presence record(s)OIE (2009)
UgandaAbsent, No presence record(s)OIE (2012)

Asia

ArmeniaAbsent, No presence record(s)OIE (2009)
AzerbaijanAbsent, No presence record(s)OIE (2009)
BahrainAbsent, No presence record(s)OIE (2009)
BangladeshAbsent, No presence record(s)OIE (2009)
BhutanAbsent, No presence record(s)OIE (2009)
BruneiAbsent, No presence record(s)OIE Handistatus (2005)
ChinaAbsent, No presence record(s)OIE (2009)
GeorgiaAbsent, No presence record(s)OIE Handistatus (2005)
IndiaAbsent, No presence record(s)OIE (2009)
IndonesiaAbsent, No presence record(s)OIE (2009)
IranAbsent, No presence record(s)OIE (2009)
IraqAbsent, No presence record(s)OIE (2009)
IsraelAbsent, No presence record(s)OIE (2009)
JapanAbsent, No presence record(s)OIE (2009)
JordanAbsent, No presence record(s)OIE (2009)
KazakhstanAbsent, No presence record(s)OIE (2009)
KuwaitAbsent, No presence record(s)OIE (2009)
KyrgyzstanAbsent, No presence record(s)OIE (2009)
LaosAbsent, No presence record(s)OIE (2009)
LebanonAbsent, No presence record(s)OIE (2009)
MalaysiaAbsent, No presence record(s)OIE (2009)
-Peninsular MalaysiaAbsent, No presence record(s)OIE Handistatus (2005)
-SabahAbsent, No presence record(s)OIE Handistatus (2005)
-SarawakAbsent, No presence record(s)OIE Handistatus (2005)
MongoliaAbsent, No presence record(s)OIE (2009)
MyanmarAbsent, No presence record(s)OIE (2009)
NepalAbsent, No presence record(s)OIE (2009)
North KoreaAbsent, No presence record(s)OIE Handistatus (2005)
OmanAbsent, No presence record(s)OIE (2009)
PakistanAbsent, No presence record(s)OIE (2009)
PhilippinesAbsent, No presence record(s)OIE (2009)
Saudi ArabiaAbsent, No presence record(s)OIE (2009)
SingaporeAbsent, No presence record(s)OIE (2009)
South KoreaAbsent, No presence record(s)OIE (2009)
Sri LankaAbsent, No presence record(s)OIE (2009)
SyriaAbsent, No presence record(s)OIE (2009)
TaiwanAbsent, No presence record(s)OIE Handistatus (2005)
TajikistanAbsent, No presence record(s)OIE (2009)
TurkmenistanAbsent, No presence record(s)OIE Handistatus (2005)
United Arab EmiratesAbsent, No presence record(s)OIE (2009)
UzbekistanAbsent, No presence record(s)OIE Handistatus (2005)
VietnamAbsent, No presence record(s)OIE (2009)

Europe

AndorraAbsent, No presence record(s)OIE Handistatus (2005)
AustriaAbsent, No presence record(s)OIE (2009)
BelarusAbsent, No presence record(s)OIE (2009)
BelgiumAbsent, No presence record(s)OIE (2009)
Bosnia and HerzegovinaAbsent, No presence record(s)OIE Handistatus (2005)
BulgariaAbsent, No presence record(s)OIE (2009)
CroatiaAbsent, No presence record(s)OIE (2009)
CyprusAbsent, No presence record(s)OIE (2009)
CzechiaAbsent, No presence record(s)OIE (2009)
DenmarkAbsent, No presence record(s)OIE (2009)
EstoniaAbsent, No presence record(s)OIE (2009)
Federal Republic of YugoslaviaAbsent, No presence record(s)OIE Handistatus (2005)
FinlandAbsent, No presence record(s)OIE (2009)
FranceAbsent, No presence record(s)OIE (2009)
GermanyAbsent, No presence record(s)OIE (2009)
GreeceAbsent, No presence record(s)OIE (2009)
HungaryAbsent, No presence record(s)OIE (2009)
IcelandAbsent, No presence record(s)OIE (2009)
IrelandAbsent, No presence record(s)OIE (2009)
Isle of ManAbsent, No presence record(s)OIE Handistatus (2005)
ItalyAbsent, No presence record(s)OIE (2009)
JerseyAbsent, No presence record(s)OIE Handistatus (2005)
LatviaAbsent, No presence record(s)OIE (2009)
LiechtensteinAbsent, No presence record(s)OIE (2009)
LithuaniaAbsent, No presence record(s)OIE (2009)
LuxembourgAbsent, No presence record(s)OIE (2009)
MaltaAbsent, No presence record(s)OIE (2009)
MoldovaAbsent, No presence record(s)OIE Handistatus (2005)
MontenegroAbsent, No presence record(s)OIE (2009)
NetherlandsAbsent, No presence record(s)OIE (2009)
North MacedoniaAbsent, No presence record(s)OIE (2009)
NorwayAbsent, No presence record(s)OIE (2009)
PolandAbsent, No presence record(s)OIE (2009)
PortugalAbsent, No presence record(s)1989OIE (2009); Mellor and Boorman (1995)Last reported: 198911
RomaniaAbsent, No presence record(s)OIE (2009)
RussiaAbsent, No presence record(s)OIE (2009)
SerbiaAbsent, No presence record(s)OIE (2009)
Serbia and MontenegroAbsent, No presence record(s)OIE Handistatus (2005)
SlovakiaAbsent, No presence record(s)OIE (2009)
SloveniaAbsent, No presence record(s)OIE (2009)
SpainAbsent, No presence record(s)1990OIE (2009); Mellor and Boorman (1995)Last reported: 199010
SwedenAbsent, No presence record(s)OIE (2009)
SwitzerlandAbsent, No presence record(s)OIE (2009)
UkraineAbsent, No presence record(s)OIE (2009)
United KingdomAbsent, No presence record(s)OIE (2009)
-Northern IrelandAbsent, No presence record(s)OIE Handistatus (2005)

North America

BarbadosAbsent, No presence record(s)OIE Handistatus (2005)
BelizeAbsent, No presence record(s)OIE (2009)
BermudaAbsent, No presence record(s)OIE Handistatus (2005)
British Virgin IslandsAbsent, No presence record(s)OIE Handistatus (2005)
CanadaAbsent, No presence record(s)OIE (2009)
Cayman IslandsAbsent, No presence record(s)OIE Handistatus (2005)
Costa RicaAbsent, No presence record(s)OIE (2009)
CubaAbsent, No presence record(s)OIE (2009)
CuraçaoAbsent, No presence record(s)OIE Handistatus (2005)
DominicaAbsent, No presence record(s)OIE Handistatus (2005)
Dominican RepublicAbsent, No presence record(s)OIE (2009)
El SalvadorAbsent, No presence record(s)OIE (2009)
GreenlandAbsent, No presence record(s)OIE (2009)
GuatemalaAbsent, No presence record(s)OIE (2009)
HaitiAbsent, No presence record(s)OIE (2009)
HondurasAbsent, No presence record(s)OIE (2009)
MartiniqueAbsent, No presence record(s)OIE (2009)
MexicoAbsent, No presence record(s)OIE (2009)
NicaraguaAbsent, No presence record(s)OIE (2009)
PanamaAbsent, No presence record(s)OIE (2009)
Saint Kitts and NevisAbsent, No presence record(s)OIE Handistatus (2005)
Saint Vincent and the GrenadinesAbsent, No presence record(s)OIE Handistatus (2005)
Trinidad and TobagoAbsent, No presence record(s)OIE Handistatus (2005)
United StatesAbsent, No presence record(s)OIE (2009)
-GeorgiaAbsent, No presence record(s)OIE (2009)

Oceania

AustraliaAbsent, No presence record(s)OIE (2009)
French PolynesiaAbsent, No presence record(s)OIE (2009)
New CaledoniaAbsent, No presence record(s)OIE (2009)
New ZealandAbsent, No presence record(s)OIE (2009)
SamoaAbsent, No presence record(s)OIE Handistatus (2005)
VanuatuAbsent, No presence record(s)OIE Handistatus (2005)

South America

ArgentinaAbsent, No presence record(s)OIE (2009)
BoliviaAbsent, No presence record(s)OIE (2009)
BrazilAbsent, No presence record(s)OIE (2009)
ChileAbsent, No presence record(s)OIE (2009)
ColombiaAbsent, No presence record(s)OIE (2009)
EcuadorAbsent, No presence record(s)OIE (2009)
Falkland IslandsAbsent, No presence record(s)OIE Handistatus (2005)
French GuianaAbsent, No presence record(s)OIE (2009)
GuyanaAbsent, No presence record(s)OIE Handistatus (2005)
ParaguayAbsent, No presence record(s)OIE Handistatus (2005)
PeruAbsent, No presence record(s)OIE (2009)
UruguayAbsent, No presence record(s)OIE (2009)
VenezuelaAbsent, No presence record(s)OIE (2009)

Pathology

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The pulmonary form of the disease gives oedematous lungs, with abundant serous fluid present in the pleural cavity and occasionally in the pericardium. Affected animals also get enlarged thoracic and abdominal lymph nodes. There are petechial haemorrhages in the mucosa and serosa of the small and large intestines and pericardium. The renal cortex becomes congested and hyperaemic glandular fundus of the stomach occurs.

In the cardiac form of the disease, haemorrhages in the epicardium, myocardium and endocardium can be seen along the coronary vessels and beneath the bicuspid and tricuspid valves.

Diagnosis

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Differential diagnosis should include anthrax, equine infectious anaemia, equine viral arteritis, trypanosomosis, equine encephalosis, piroplasmosis, purpura haemorrhagica and Hendra virus.

Laboratory diagnosis

Virus isolation can be achieved by suckling mice or cell cultures. Virus identification can be carried out using ELISA, virus neutralisation (serotyping) and PCR. Real-time or classical RT-PCR assays, which allow rapid virus identification and typing (in a few hours), have replaced serological techniques in most laboratories (Zientara et al., 2015).

Confirmatory diagnosis of AHS is better achieved through virus detection techniques than through serology, because many horses will die before the induction of AHSV antibodies, antibodies being detectable 10 to 14 days post infection. Furthermore, in areas where vaccination is routinely carried out, serological results can be difficult to interpret. However, serological surveys can provide confirmation of virus circulation in a specific region or country. Several serological techniques are specified by the World Organisation for Animal Health (OIE) for the purposes of animal trade including complement fixation test, serum neutralisation test and ELISA (Zientara et al., 2015).

List of Symptoms/Signs

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SignLife StagesType
Cardiovascular Signs / Tachycardia, rapid pulse, high heart rate Other:All Stages Sign
General Signs / Fever, pyrexia, hyperthermia Other:All Stages Sign
General Signs / Head, face, ears, jaw, nose, nasal, swelling, mass Other:All Stages Diagnosis
General Signs / Oral cavity, tongue swelling, mass in mouth Other:All Stages Diagnosis
General Signs / Orbital, periorbital, periocular, conjunctival swelling, eyeball mass Other:All Stages Diagnosis
Nervous Signs / Dullness, depression, lethargy, depressed, lethargic, listless Other:All Stages Sign
Ophthalmology Signs / Conjunctival, scleral, redness Other:All Stages Sign
Pain / Discomfort Signs / Colic, abdominal pain Other:All Stages Sign
Respiratory Signs / Coughing, coughs Other:All Stages Diagnosis
Respiratory Signs / Dyspnea, difficult, open mouth breathing, grunt, gasping Other:All Stages Diagnosis
Respiratory Signs / Increased respiratory rate, polypnea, tachypnea, hyperpnea Other:All Stages Diagnosis
Respiratory Signs / Mucoid nasal discharge, serous, watery Other:All Stages Diagnosis

Disease Course

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Mortality rates are 50-95% (horses), 50% (mules) and 10% (donkeys). There are four classical forms of AHS, pulmonary (acute), cardiac (subacute), mixed, and horse sickness fever (House, 1992).

The acute (pulmonary) form is characterized by a fever (40-41°C) after an incubation period of 3-5d. This is accompanied by dyspnoea when the respiratory rate may increase to 60-75 breaths/minute. Animals also experience spasmodic coughing, have dilated nostrils with frothy fluid oozing out and redness of the conjunctivae. Animals often die from anoxia within 1 week (more than 95% cases).

The subacute (cardiac) form is characterized by a fever (39-41°C) following an incubation period of 7-14 d. Infected animals also experience swelling of the supraorbital fossa, eyelids, facial tissues, neck, thorax, brisket and shoulders. The animal finally becomes restless and may show signs of colic before death from cardiac failure, usually within 1 week (50% of cases). In recovering cases, swelling gradually subsides within a period of 3-8 days.

The mixed form (cardiac and pulmonary) of the disease occurs frequently and has an incubation period of 5-7 d. It is characterized by mild pulmonary signs that do not progress, oedematous swellings and effusions. Again, in more than 80% of cases, death from cardiac failure occurs, usually within 1 week. In the subclinical form ('Horse sickness fever') a fever (40-40.5°C) occurs following an incubation period of 5-14 days and a general malaise for 1-2 days is observed. Conjunctivae may be slightly congested, the pulse rate increased, and a certain degree of anorexia and depression may be present. A fifth, nervous form of the disease may occur, but this is rare.

Lesions

In the pulmonary form of the disease, oedema of the lungs, hydropericardium, pleural effusion, oedema of thoracic lymph nodes and petechial haemorrhages in the pericardium occur. With the cardiac form, subcutaneous and intramuscular gelatinous oedema, epicardial and endocardial ecchymoses, myocarditis, haemorrhagic gastritis are observed.

Epidemiology

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AHSV is transmitted by Culicoides spp. that occur regularly in most countries of sub-Saharan Africa.

A proven vector of the disease is Culicoides imicola (Mellor and Boorman, 1995). Other Culicoides spp., notably C. bolitinos may also play a role in transmission (Venter et al., 2000; Meiswinkel and Paweska, 2003).

Other occasional modes of transmission are mosquitoes – Culex, Anopheles and Aedes spp.; ticks – Hyalomma, Rhipicephalus; and possibly biting flies – Stomoxys and Tabanus spp. (OIE, 2013).

The disease has a seasonal (late summer/autumn) and an epizootic cyclical incidence, with disease associated with drought followed by heavy rain. Major epizootics in southern Africa are strongly linked with warm (El Niño) phase of the El Niño/Southern Oscillation (ENSO) (OIE, 2013).

Impact: Economic

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AHS is one of the most lethal viral diseases of horses and it is one of the most economically devastating viral diseases of the equine industry (Sánchez-Vizcaíno et al., 2014). AHSV is a major threat to the equine sport and companion animal industries. This threat occurs both in endemic regions of AHSV transmission, where breeding and export of horses is a major trade (e.g. South Africa), and in regions at risk of epidemics from importation (e.g., Europe and the Middle East) (Carpenter et al., 2017).

In addition, morbidity and mortality from AHS within working equids may constrain the draft power these animals provide in low-income countries, thereby affecting food security, poverty alleviation, and gender equality (Carpenter et al., 2017).

The main routes of AHS introduction are movements of infected Equidae (i.e. trade and competitions), and spread of infected Culicoides midges by the wind (Sánchez-Vizcaíno et al., 2014). The expansion of Bluetongue virus in European countries and climate change have increased concern about the possibility of AHS dissemination outside endemic localizations, especially in European countries. Entry of AHSV into a country previously declared free of AHS is economically significant for the equine industry as it causes disease in animals and world trade restrictions (MacLachlan and Guthrie, 2010).

Disease control in endemic countries is largely by immunization with a live‐attenuated vaccine. However, the use of the vaccine has raised concerns with regard to reversion to virulence, gene segment reassortment between outbreak and vaccine strains and the absence of the ability to differentiate between infected and vaccinated animals (DIVA). There is a need to develop new, safe, efficacious and cost‐effective DIVA vaccines which would address the concerns about the currently used live vaccines, as well as being acceptable prophylactic or rapid response vaccines in the European and other emerging outbreak contexts (Dennis et al., 2018).

Zoonoses and Food Safety

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African horse sickness is not zoonotic.

Disease Treatment

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No efficient treatments are available.

Prevention and Control

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Disease prevention

Vaccines are used against African horse sickness in sub-Saharan Africa, where the disease is endemic. There are vaccines for all 9 serotypes of African horse sickness virus. These are either cell culture adapted or mouse brain attenuated and provide long-lasting protection. As there are concerns over the use of live vaccines, the development of efficacious vaccines, suitable for use in both endemic and non-endemic regions is an important focus of research (MacLachlan et al., 2007). No killed or subunit vaccines are currently manufactured commercially (Spickler, 2015).

Stabling equids in insect-proof housing, especially from dusk to dawn (when Culicoides are most active), can reduce the risk of infection. Vector control measures such as insect repellents and targeted applications of insecticides or larvicides might also be helpful. (Spickler, 2015).

Most non-endemic countries test and quarantine imported equids to prevent them from introducing AHSV (Spickler, 2015).

Disease control

When outbreaks occur in endemic areas, they have generally been controlled by vaccination and movement restrictions on equids (Spickler, 2015).

If a virus is introduced into a non-endemic region, control measures may include the establishment of quarantine zones and movement controls, vaccination campaigns, and possibly the euthanasia of infected animals, depending on the situation. (Spickler, 2015).

References

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African Union-Interafrican Bureau for Animal Resources, 2011. Panafrican Animal Health Yearbook 2011. Pan African Animal Health Yearbook, 2011:xiii + 90 pp. http://www.au-ibar.org/index.php?option=com_flexicontent&view=items&cid=71&id=109&Itemid=56&lang=en

Calvo JH, Calvete C, Martinez-Royo A, Estrada R, Miranda MA, Borras D, Sarto i Monteys V, Pages N, Delgado JA, Collantes F, Lucientes J, 2009. Variations in the mitochondrial cytochrome c oxidase subunit I gene indicate northward expanding populations of Culicoides imicola in Spain. Bulletin of Entomological Research, 99(6):583-591. http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=6545284&next=true&jid=BER&volumeId=99&issueId=06

Carpenter, S., Mellor, P. S., Fall, A. G., Garros, C., Venter, G. J., 2017. African horse sickness virus: history, transmission, and current status. Annual Review of Entomology, 62, 343-358. doi: 10.1146/annurev-ento-031616-035010

Coetzer JAW, Guthrie AJ, 2004. African horsesickness. In: Infectious Diseases of Livestock, Second Edition [ed. by Coetzer, J. A. W. \Tustin, R. C.]. Cape Town, South Africa: Oxford University Press, 1231-1246

Dardiri AH, Brown CC, 1989. African horse sickness update. In: 11th International Symposium of the World Association of Veterinary Microbiologists, Immunologists and Specialists in Infectious Diseases, Perugia, Mantova, Italy, October 2-6, 1989. 40131 Bologna, Italy: Società Editrice Esculapio, 287-289

Dennis, S. J., Meyers, A. E., Guthrie, A. J., Hitzeroth, I. I., Rybicki, E. P., 2018. Immunogenicity of plant-produced African horse sickness virus-like particles: implications for a novel vaccine. Plant Biotechnology Journal, 16(2), 442-450. doi: 10.1111/pbi.12783

Dufour B, Moutou F, Hattenberger AM, Rodhain F, 2008. Global change: impact, management, risk approach and health measures - the case of Europe. Revue Scientifique et Technique - Office International des Épizooties, 27(2):541-550

El-Husseini MM, Salama SA, Abdallah SK, Bakr HEA, Hassanein MM, 1986. Role of Culex pipiens L. in recovering latent African horse sickness virus from dogs. Journal of the Egyptian Society of Parasitology, 16(1):249-258

Hamblin C, Salt JS, Mellor PS, Graham SD, Smith PR, Wohlsein P, 1998. Donkeys as reservoirs of African horse sickness virus. In: African horse sickness [ed. by Mellor, P. S.\Baylis, M.\Hamblin, C.\Calisher, C. H.\Mertens, P. P. C.]. Vienna, Austria: Springer-Verlag, 37-47

House C, 1992. African Horse Sickness. In: Castro AE, Heuschele WP, eds., Veterinary Diagnostic Virology. Mosby Year Book, 165-159

MacLachlan NJ, Balasuriya UB, Davis NL, Collier M, Johnston RE, Ferraro GL, Guthrie AJ, 2007. Experiences with new generation vaccines against equine viral arteritis, West Nile disease and African horse sickness. Vaccine [4th International Veterinary Vaccines and Diagnostic Conference, Oslo, Norway, 25-29 June 2006.], 25(30):5577-5582. http://www.sciencedirect.com/science/journal/0264410X

MacLachlan, N. J., Guthrie, A. J., 2010. Re-emergence of bluetongue, African horse sickness, and other Orbivirus diseases. Veterinary Research, 41(6), 41:35. doi: 10.1051/vetres/2010007

Meiswinkel R, Paweska JT, 2003. Evidence for a new field Culicoides vector of African horse sickness in South Africa. Preventive Veterinary Medicine, 60(3):243-253

Mellor PS, 1992. Culicoides as potential orbivirus vectors in Europe. In: Bluetongue, African horse sickness, and related orbiviruses: Proceedings of the Second International Symposium [ed. by Walton, T. E.\Osburn, B. I.]. Boca Raton, Florida, USA: CRC Press, Inc., 278-283

Mellor PS, 1993. African horse sickness: transmission and epidemiology. Veterinary Research, 24(2):199-212

Mellor PS, Boorman J, 1995. The transmission and geographical spread of African horse sickness and bluetongue viruses. Annals of Tropical Medicine and Parasitology, 89(1):1-15; 6 pp. of ref

Mellor PS, Hamblin C, 2004. African horse sickness. Veterinary Research, 35(4):445-466

Meyden CHvan der, Erasmus BJ, Swanepoel R, Porzesky OW, 1992. Encephalitis and chorioretinitis associated with neurotropic African horsesickness virus infection in laboratory workers. Part I. Clinical and neurological observations. South African Medical Journal, 81(9):451-454

OIE Handistatus, 2002. World Animal Health Publication and Handistatus II (dataset for 2001). Paris, France: Office International des Epizooties

OIE Handistatus, 2003. World Animal Health Publication and Handistatus II (dataset for 2002). Paris, France: Office International des Epizooties

OIE Handistatus, 2004. World Animal Health Publication and Handistatus II (data set for 2003). Paris, France: Office International des Epizooties

OIE Handistatus, 2005. World Animal Health Publication and Handistatus II (data set for 2004). Paris, France: Office International des Epizooties

OIE, 2004. African horse sickness in Swaziland. Disease Information, 17(21)

OIE, 2004. African horse sickness in Zambia. Disease Information, 17(19)

OIE, 2009. World Animal Health Information Database - Version: 1.4. World Animal Health Information Database. Paris, France: World Organisation for Animal Health. http://www.oie.int

OIE, 2012. World Animal Health Information Database. Version 2. World Animal Health Information Database. Paris, France: World Organisation for Animal Health. http://www.oie.int/wahis_2/public/wahid.php/Wahidhome/Home

OIE, 2013. African horse sickness (updated April 2013). In: OIE Technical Disease Cards, Paris, France: World Organisation for Animal Health.https://www.oie.int/fileadmin/Home/eng/Animal_Health_in_the_World/docs/pdf/Disease_cards/AFRICAN_HORSE_SICKNESS.pdf

OIE, 2020. African horse sickness, Thailand. (Immediate notification) . In: World Animal Health Information System. Weekly Disease Information, 33(14) . Paris, France: World Organisation for Animal Health.https://www.oie.int/wahis_2/public/wahid.php/Reviewreport/Review?page_refer=MapFullEventReport&reportid=33768

Sailleau C, Hamblin C, Paweska JT, Zientara S, 2000. Identification and differentiation of the nine African horse sickness virus serotypes by RT-PCR amplification of the serotype-specific genome segment 2. Journal of General Virology, 81(3):831-837

Sánchez-Vizcaíno JM, 2004. Control and eradication of African horse sickness with vaccine. In: Control of infectious animal diseases by vaccination [ed. by Schudel, A.\Lombard, M.]. Basel, Switzerland: S Karger AG, 255-258

Sánchez-Vizcaíno, J. M., Martínez-Avilés, M., Sánchez-Matamoros, A., Rodríguez-Prieto, V., 2014. Emerging vector-borne diseases and the potential to prevent them spreading. CAB Reviews, 9(039), 1-13. doi: 10.1079/PAVSNNR20149039

Spickler, A. R., 2015. African Horse Sickness. Iowa, USA: Center for Food Security and Public Health (CFSPH), Iowa State University.http://www.cfsph.iastate.edu/DiseaseInfo/factsheets.php

Theiler A, 1906. Transmission of horse sickness into dogs. Report of the Government Veterinary Bacteriologist. 160-162

Venter GJ, Graham SD, Hamblin C, 2000. African horse sickness epidemiology: vector competence of South African Culicoides species for virus serotypes 3, 5 and 8. Medical and Veterinary Entomology, 14(3):245-250

Zientara, S., Weyer, C. T., Lecollinet, S., 2015. African horse sickness. Revue Scientifique et Technique - Office International des Épizooties, 34(2), 315-327. http://www.oie.int/publications-and-documentation/scientific-and-technical-review-free-access/list-of-issues/

Distribution References

Mellor P S, Boorman J, 1995. The transmission and geographical spread of African horse sickness and bluetongue viruses. Annals of Tropical Medicine and Parasitology. 89 (1), 1-15.

OIE Handistatus, 2004. World Animal Health Publication and Handistatus II (dataset for 2003)., Paris, France: Office International des Epizooties.

OIE Handistatus, 2005. World Animal Health Publication and Handistatus II (dataset for 2004)., Paris, France: Office International des Epizooties.

OIE, 2009. World Animal Health Information Database - Version: 1.4., Paris, France: World Organisation for Animal Health. https://www.oie.int/

OIE, 2012. World Animal Health Information Database. Version 2., Paris, France: World Organisation for Animal Health. https://www.oie.int/wahis_2/public/wahid.php/Wahidhome/Home

Links to Websites

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WebsiteURLComment
CFSPH: Animal Disease Informationhttp://www.cfsph.iastate.edu/DiseaseInfo/index.php"Animal Disease Information" provides links to various information sources, including fact sheets and images, on over 150 animal diseases of international significance.
EFSA. Scientific report on African Horse Sicknesshttp://www.efsa.europa.eu/en/scdocs/doc/4e.pdfScientific report submitted to EFSA prepared by Boinas, F., Calistria, P., Domingo, M., Martínez-Avilés, M., Martínez-López, B., Rodríguez-Sánchez, B. and Sánchez-Vizcaíno, J.M. on African Horse Sickness. (2009), 1-61
OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animalshttp://www.oie.int/en/international-standard-setting/terrestrial-manual/access-online/The Manual of Diagnostic Tests and Vaccines for Terrestrial Animals (Terrestrial Manual) aims to facilitate international trade in animals and animal products and to contribute to the improvement of animal health services world-wide. The principal target readership is laboratories carrying out veterinary diagnostic tests and surveillance, plus vaccine manufacturers and regulatory authorities in Member Countries. The objective is to provide internationally agreed diagnostic laboratory methods and requirements for the production and control of vaccines and other biological products.
OIE Technical Disease Cardshttp://www.oie.int/animal-health-in-the-world/technical-disease-cards/An updated compilation of 33 technical disease cards, containing summary information, mainly directed to a specialised scientific audience, including 32 OIE-listed priority diseases. USDA-APHIS (USA) are also credited with contributing to the maintenance of the cards.
South Africa, African horse sickness trusthttp://www.africanhorsesickness.co.za/Represents industry stakeholders, gathers research data from all suspected cases reported.
USAHA: Foreign Animal Diseases. Seventh Editionhttp://www.aphis.usda.gov/emergency_response/downloads/nahems/fad.pdfCopyright © 2008 by United States Animal Health Association ALL RIGHTS RESERVED. Library of Congress Catalogue Number 2008900990 ISBN 978-0-9659583-4-9. Publication with 472pp. aimed at providing information for practitioners within the USA to prevent and or mitigate the incursion of foreign animal diseases into that country. Contains general chapters on surveillance, diagnosis, etc. as well as 48 chapters covering individual diseases, mostly those notifiable to the OIE.

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