Selected content from the Animal Health and Production Compendium (© CAB International 2013). Distributed under license by African Union – Interafrican Bureau for Animal Resources.
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Identity Pathogen/s Overview Distribution Distribution Map for Africa Distribution Table for Africa Hosts/Species Affected Host Animals Pathology Diagnosis Disease Course Disease Treatment Table Vaccines Prevention and Control References Links to Websites OIE Reference Experts and Laboratories Images
Preferred Scientific Name
African horse sickness
African horse sickness virus.
African horse sickness is a highly infectious, non-contagious, insect-transmitted disease affecting all species of Equidae. It is characterized by respiratory and circulatory damage.
This disease is on the list of diseases notifiable to the World Organisation for Animal Health (OIE). Please see the AHPC library for further information on this disease from OIE, including the International Animal Health Code and the Manual of Standards for Diagnostic Tests and Vaccines. Also see the website: www.oie.int.
It is endemic in the central tropical regions of Africa and regularly spreads to Southern Africa and occasionally to Northern Africa. 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.
During 2011, a total of 627 outbreaks of AHS were reported to AU-IBAR by 6 countries, compared to 305 outbreaks reported from 5 countries in 2010 and 15 outbreaks reported from 7 countries in 2009. Although the disease has been reported over the past years in five of the affected countries, the appearance of AHS in Somalia is regarded as a new epidemiological event. The highest numbers of AHS outbreaks were reported from South Africa with 447 outbreaks followed by Ethiopia with 167 reported outbreaks. Overall a total of 2754 horses were affected with AHS with 1013 reported mortalities representing a 36.8% case fatality rate. The highest numbers of outbreaks were reported in the month of March with 255 outbreaks (AU-IBAR, 2011).
= Present, no further details = Widespread = Localised
= Confined and subject to quarantine = Occasional or few reports
= Evidence of pathogen = Last reported... = Presence unconfirmed
|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 information may be available for individual references may be available in the Animal Health and Production Compendium. A table for worldwide distribution can also be found in the Animal Health and Production Compendium.|
|Country||Distribution||Last Reported||Origin||First Reported||Invasive||References||Notes|
|Algeria||Last reported||1966||OIE, 2012|
|Angola||No information available||OIE, 2009|
|Benin||Disease not reported||OIE, 2009|
|Botswana||Disease not reported||OIE, 2009|
|Burkina Faso||No information available||OIE, 2009|
|Burundi||Disease not reported||OIE, 2012|
|Cameroon||Disease not reported||OIE, 2012|
|Cape Verde||Last reported||2001||OIE Handistatus, 2005|
|Central Africa||Widespread||Mellor & Boorman, 1995|
|Central African Republic||Disease not reported||OIE, 2012|
|Chad||No information available||OIE, 2012|
|Congo||No information available||OIE, 2009|
|Congo Democratic Republic||Disease not reported||OIE Handistatus, 2005|
|Côte d'Ivoire||Disease not reported||OIE Handistatus, 2005|
|Djibouti||Disease never reported||OIE, 2012|
|Egypt||Disease not reported||OIE, 2009|
|Gabon||No information available||OIE, 2009|
|Ghana||Last reported||2010||OIE, 2012|
|Guinea||No information available||OIE, 2009|
|Guinea-Bissau||No information available||OIE, 2009|
|Kenya||Disease not reported||OIE, 2012|
|Lesotho||Last reported||2011||OIE, 2012|
|Libya||Last reported||1964||OIE, 2012|
|Madagascar||Disease never reported||OIE, 2012|
|Malawi||Disease not reported||OIE, 2009|
|Mali||No information available||OIE, 2009|
|Mauritius||Disease never reported||OIE, 2012|
|Morocco||Last reported||1991||OIE, 2012; Mellor & Boorman, 1995|
|Mozambique||Last reported||2006||OIE, 2012|
|Namibia||Last reported||2011||OIE, 2012|
|Nigeria||Disease not reported||OIE, 2009|
|North Africa||Present||Mellor & Boorman, 1995|
|Réunion||Disease never reported||OIE Handistatus, 2005|
|Rwanda||No information available||OIE, 2009|
|Sao Tome and Principe||Disease not reported||OIE Handistatus, 2005|
|Senegal||Last reported||2009||OIE, 2012|
|Seychelles||Disease not reported||OIE, 2012|
|Somalia||Last reported||2011||OIE, 2012|
|South Africa||Present||OIE, 2012; Mellor & Boorman, 1995|
|Sudan||Disease not reported||OIE, 2009|
|Swaziland||Present||OIE, 2012; OIE, 2004a|
|Tanzania||Last reported||2006||OIE, 2012|
|Togo||No information available||OIE, 2009|
|Tunisia||Last reported||1966||OIE, 2012|
|Uganda||Disease never reported||OIE, 2012|
|Zambia||No information available||NULL||OIE, 2012; OIE, 2004b|
|Zimbabwe||Last reported||2004||OIE, 2012|
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).
Usual hosts of the disease include horses, mules, donkeys and zebra. Other occasional hosts include elephants, camels, and dogs (after eating infected blood or horsemeat).
|Camelus bactrianus (Bactrian camel)||Domesticated host|
|Camelus dromedarius (dromedary camel)||Domesticated host|
|Canis familiaris (dogs)||Domesticated host, Wild host|
|Equus asinus (donkeys)||Domesticated host, Wild host|
|Equus caballus (horses)||Domesticated host, Wild host|
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.
Differential diagnosis should include Anthrax, equine infectious anaemia, equine viral arteritis, trypanosomosis, equine encephalosis, piroplasmosis and purpura haemorrhagica.
Virus isolation can be achieved by suckling mice or cell cultures. Virus identification is carried out using ELISA, virus neutralisation (Serotyping) and PCR. Serological diagnosis is carried out using ELISA, complement fixation tests and immunoblotting.
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.
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.
|Drug||Dosage, administration and withdrawal times||Life stages||Adverse affects||Drug resistance||Type|
|African horse sickness virus vaccine||A polyvalent and monovalent live vaccine are most used. Minimum immunization of 1000 PFU/dose. Two vaccinations, at 21 day intervals are recommended. Annual revaccination is advised.||All Stages||None have been reported.||No||Vaccine|
|Vaccine||Dosage, Administration and Withdrawal Times||Life Stages||Adverse Affects|
|African horse sickness virus vaccine||A polyvalent and monovalent live vaccine are most used. Minimum immunization of 1000 PFU/dose. Two vaccinations, at 21 day intervals are recommended. Annual revaccination is advised.||-Other: All Stages||None have been reported.|
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. Inactivated vaccines are not readily available. 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).
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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.
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(http://www.oie.int, accessed 5 June 2013)
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Date of report: 22/05/2013
© CAB International 2013. Distributed under license by African Union – Interafrican Bureau for Animal Resources.
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.