Difference between revisions of "Equine Infectious Anemia"

Revision as of 12:34, 29 August 2010

Also known as: EIA, Swamp Fever

Description

Equine Infectious Anemia (EIA) is an exotic viral disease affecting horses, donkeys and mules characterised by immuned-mediated haemolytic anemia. It is caused by Equine Infectious Anemia Virus (EIAV), an equid-specific lentivirus in the retrovirus family that is closely to related to HIV in humans.

Signalment

All equids are susceptible to EIA but donkeys and mules appear to be less severely affected. No breed, age or sex predilection has been reported.

Pathogenesis

EIA occurs worldwide but most commonly in countries with warm climates. The virus is usually transmitted via mechanical innoculation of blood from large biting flies such as horseflies (Tabanid spp) or stable flies (Stomoxys calcitrans). Transmission of the virus can also occur when a nursing foal ingests milk from a carrier mare or iatrogenically via contaminated needles.

Following coating of erthrocytes and thrombocytes by the virus and the development of a Type III immune complex reacion, lysis of erthrocytes occur. Infection with EIA results in an acute phase of infection followed by recurrent episodes that usually susbide after a period of time. Affected horses become persistently infected, lifelong carriers of the disease. EIA may be induced by stress, disease or immunosuppressive drugs.

Epidemiology

Notifiable in UK but endemic in parts of the US
Animals can be carriers for years despite being antibody-positive
Transfer is mechanical via vectors:
- Mosquitoes transfer infected macrophages
Also transferred via infected needles, semen and milk
Infected horses have lifetime latent infection of macrophages with recurring bouts of virus when immunocompromised

Clinical signs

The incubation period of the disease ranges from 10 to over 45 days and the clinical presentation is highly variable. A large number of affected horses do not display any clinical signs. Animals may be affected acutely, chronically or sub-clinically and clinical signs vary according to the stage of the disease. Inapparent carriers may be clinically normal. In the acute stages, clinical signs may include mucosal petechial haemorrhages, depression, fever, lethargy and inappetance. Horses that have been infected for thirty days or may display the characteristic signs of EIA including ventral and limb oedema, anemia, icterus, 'spiking' fever and cachexia.

Diagnosis

The 'gold standard' for diagnostic confirmation is an agar gel immunodiffusion test (the Coggins test) which detects serum antibodies against the EIA virus. The test is 95% accurate for the diagnosis of EIA but false positives may be obtained from foals that have absorbed colostrum from affected mares and false negatives may occur during acute stages of EIA. The Coggins test may be performed in combination with an ELISA in order to increase the test sensitivity.

Treatment

No specific treatment or vaccine for EIA is available and treatment is usually supportive. Infected horses should be isolated from other horses due to the risk of spread of disease. NSAIDs may be used to control pyrexia and inflammation and/. Corticosteroids are contraindicated due to the possibility of exacerbating viral replication and clinical disease.

Prognosis

Foals exposed to EIAV have a high fatality rate but generally horses recover from the disease, becoming lifelong inapparent carriers. Although occasionally some horses die from EIA, the majority become lifelong inapparent carriers.

References

Dwight, C., Hirsh, Y., Zee, Y. C. (1999) Veterinary Microbiology Wiley-Blackwell
Higgins, A., Snyder, J. R. (2006) The Equine Manual Elsevier Health Sciences
Jain, N. C. (1993) Essentials of Veterinary Haematology Wiley-Blackwell
Lavoie, J. P., Hinchcliff, K. W. (2009) 'Blackwell's Five-Minute Veterinary Consult: Equine

@@ Line 1: / Line 1: @@
-{{OpenPagesTop}}
+{{unfinished}}
-Also known as: '''''EIA, Swamp Fever
-==Introduction==
+Also known as: EIA, Swamp Fever
-Equine Infectious Anaemia (EIA) is an exotic viral disease affecting horses, donkeys and mules characterised by viraemia, anaemia and thrombocytopaenia. The disease is caused by Equine Infectious Anaemia Virus (EIAV), an equid-specific [[:Category:Lentiviruses|lentivirus]] in the [[:Category:Retroviridae|retrovirus]] family that is closely to related to HIV in humans. Cases of EIA in the UK are extremely rare and have previously occurred in horses that have travelled abroad or been imported from areas of endemic disease. In the UK the disease is notifiable and confirmed cases must be humanely destroyed.
+==Description==
+Equine Infectious Anemia (EIA) is an exotic viral disease affecting horses, donkeys and mules characterised by immuned-mediated haemolytic anemia. It is caused by Equine Infectious Anemia Virus (EIAV), an equid-specific lentivirus in the retrovirus family that is closely to related to HIV in humans.
 ==Signalment==
-All equids are susceptible to EIA but [[Equine Infectious Anaemia - Donkey|donkeys]] and mules appear to be less severely affected. No breed, age or sex predilection has been reported.
+All equids are susceptible to EIA but donkeys and mules appear to be less severely affected. No breed, age or sex predilection has been reported.
 ==Pathogenesis==
-EIA occurs worldwide but most commonly in countries with warm climates. The virus is usually transmitted via mechanical inoculation of blood via large biting flies such as [[Tabanidae|horseflies (''Tabanid'' spp)]] or stable flies (''[[Stomoxys calcitrans]]''). Additionally, transmission of the virus may occur through saliva, milk, body secretions or via contaminated needles and blood products. The virus may also be passed from pregnant mares to their foals across the placenta.
+EIA occurs worldwide but most commonly in countries with warm climates. The virus is usually transmitted via mechanical innoculation of blood from large biting flies such as horseflies (Tabanid spp) or stable flies (Stomoxys calcitrans). Transmission of the virus can also occur when a nursing foal ingests milk from a carrier mare or iatrogenically via contaminated needles.
-Viral replication occurs primarily in mature tissue macrophages located in the spleen. These macrophages act as the main source of high-titre viraemia during the course of the disease and also as a reservoir for infection during subclinical infection.
+Following coating of erthrocytes and thrombocytes by the virus and the development of a Type III immune complex reacion, lysis of erthrocytes occur. Infection with EIA results in an acute phase of infection followed by recurrent episodes that usually susbide after a period of time. Affected horses become persistently infected, lifelong carriers of the disease. EIA may be induced by stress, disease or immunosuppressive drugs.
-Infection in subclinically affected horses may be reactivated during times of stress, disease or during treatment with immunosuppressive drugs.
+====Epidemiology====
+*'''Notifiable''' in UK but '''endemic''' in parts of the US
+*Animals can be '''carriers''' for years despite being '''antibody-positive'''
+*Transfer is '''mechanical''' via '''vectors''':
+**'''Mosquitoes''' transfer infected '''macrophages
+*Also transferred via infected needles, semen and milk
+*Infected horses have '''lifetime latent infection of macrophages''' with recurring bouts of virus when '''immunocompromised'''
 ==Clinical signs==
-The incubation period of the disease ranges from 10 to over 45 days and the clinical presentation is highly variable. EIA occurs in acute and subacute forms in susceptible animals but more commonly assumes a chronic course. However, a large number of affected horses do not display any clinical signs and unapparent carriers may be clinically normal.
+The incubation period of the disease ranges from 10 to over 45 days and the clinical presentation is highly variable. A large number of affected horses do not display any clinical signs. Animals may be affected acutely, chronically or sub-clinically and clinical signs vary according to the stage of the disease. Inapparent carriers may be clinically normal. In the acute stages, clinical signs may include mucosal petechial haemorrhages, depression, fever, lethargy and inappetance. Horses that have been infected for thirty days or may display the characteristic signs of EIA including ventral and limb oedema, anemia, icterus, 'spiking' fever and cachexia.
-In the acute stages, clinical signs may include mucosal petechial and ecchymotic haemorrhages, depression, lymphadenopathy, fever, lethargy and inappetance. In rare cases the disease may result in sudden death. Horses that have been infected for thirty days may display the characteristic signs of EIA including ventral and limb oedema, anemia, bloody diarrhoea, icterus, pyrexia and cachexia.
 ==Diagnosis==
-The 'gold standard' for diagnostic confirmation is an '''agar gel immunodiffusion test (the Coggins test)''' which detects serum antibodies against the EIA virus. The test is 95% accurate for the diagnosis of EIA but false positives may be obtained from foals that have absorbed colostrum from affected mares and false negatives may occur during the acute stages of EIA. The Coggins test may be performed in combination with an '''[[ELISA]]''' or '''PCR''' test in order to increase the test sensitivity.
+The 'gold standard' for diagnostic confirmation is an agar gel immunodiffusion test (the Coggins test) which detects serum antibodies against the EIA virus. The test is 95% accurate for the diagnosis of EIA but false positives may be obtained from foals that have absorbed colostrum from affected mares and false negatives may occur during acute stages of EIA. The Coggins test may be performed in combination with an ELISA in order to increase the test sensitivity.
-Additionally, haematology may reveal a moderate to marked [[Regenerative and Non-Regenerative Anaemias|anaemia]], leukopaenia and [[Bilirubin|bilirubinaemia]]. Mild [[Platelet Abnormalities|thrombocytopaenia]] is common in the acute phase of infection.
 ==Treatment==
-No specific treatment or vaccine for EIA is available and strict procedures for affected horses are enforced in the UK. Until the presence of disease has been confirmed by a positive Coggins test, supportive treatment may be provided such as NSAIDs to reduce pyrexia and inflammation. Any horse that is suspected to be infected with EIA must be reported to the appropriate divisional veterinary manager of DEFRA. DEFRA policy is that horses with confirmed EIA must be slaughtered under Section 32 of the Animal Health Act 1981. Horses that have been in close contact with diseased animals must be kept in isolation for 90 days and tested on a monthly basis with regular veterinary assessment. After this period of testing, restrictions may be lifted if no disease is found.
+No specific treatment or vaccine for EIA is available and treatment is usually supportive. Infected horses should be isolated from other horses due to the risk of spread of disease. NSAIDs may be used to control pyrexia and inflammation and/. Corticosteroids are contraindicated due to the possibility of exacerbating viral replication and clinical disease.
-==Control==
-Although attenuated live vaccines are available in the United States, these are not in current use in the UK. Acutely affected horses carry high levels of virus in the blood and are a high risk source of infection to other horses so should be isolated immediately if EIA is suspected. All movement of horses on and off the premises must be prevented.
 ==Prognosis==
-Foals exposed to EIAV have a high fatality rate but generally horses recover from the disease, becoming lifelong inapparent carriers. Relapse of the disease may occur during times of stress or illness. The current UK control measures dictate that confirmed cases of EIA carry a grave prognosis.
+Foals exposed to EIAV have a high fatality rate but generally horses recover from the disease, becoming lifelong inapparent carriers. Although occasionally some horses die from EIA, the majority become lifelong inapparent carriers.
-{{Learning
-|literature search = [http://www.cabdirect.org/search.html?rowId=1&options1=AND&q1=((title:(%22swamp+fever%22))+OR+(title:(%22Equine+Infectious%22+)+AND+(title:(Anaemia)+OR+title:(Anemia)))+OR+(title:(EIA)))+AND+od:(horses)&occuring1=freetext&rowId=2&options2=AND&q2=&occuring2=freetext&rowId=3&options3=AND&q3=&occuring3=freetext&publishedstart=2000&publishedend=yyyy&calendarInput=yyyy-mm-dd&la=any&it=any&show=all&x=50&y=8 Equine Infectious Anaemia publications since 2000]
-}}
 ==References==
@@ Line 41: / Line 38: @@
 *Higgins, A., Snyder, J. R. (2006) '''The Equine Manual''' ''Elsevier Health Sciences''
 *Jain, N. C. (1993) '''Essentials of Veterinary Haematology''' ''Wiley-Blackwell''
-*Lavoie, J. P., Hinchcliff, K. W. (2009) '''Blackwell's Five-Minute Veterinary Consult: Equine''' ''John Wiley and Sons''
+*Lavoie, J. P., Hinchcliff, K. W. (2009) '''Blackwell's Five-Minute Veterinary Consult: Equine''
-{{review}}
-{{OpenPages}}
-{{Learning |Vetstream = [https://www.vetstream.com/equis/Content/Disease/dis00071.asp Equine Infectious Anemia]}}
 [[Category:Lentiviruses]][[Category:Horse Viruses]]
-[[Category:Lymphoreticular and Haematopoietic Diseases - Horse]]
+[[Category:To_Do_-_Clinical/Viruses]]
-[[Category:Anaemia|4]]
+[[Category:Cardiovascular_Disorders_-_Horse]]
+[[Category:Anaemia]]
-[[Category:Expert Review]]
+[[Category:To Do - Blood]][[Category:To Do - SophieIgnarski]]