equis - Articles
Respiratory: EHV infection
Synonym(s): EHV-1, EHV-4
Introduction
- Five equine herpesviruses Equine herpesvirus have been identified, each with a different clinical presentation; EHV-1, 2, 3, 4 and 5.
- Cause: rhinopneumonitis.
- Signs: pyrexia, depression serous → mucopurulent nasal discharge; rarely secondary bacterial bronchopneumonia.
- Diagnosis: virus isolation; serology; histopathology.
- Treatment: control secondary bacterial infection; quarantine newly introduced or stressed animals; vaccination.
- See also Abortion: EHV 1 Abortion: EHV-1 , CNS: myeloencephalopathy CNS: myeloencephalopathy - EHV , Lung: multinodular fibrosis Lung: multinodular fibrosis .
- Prognosis: good.
Presenting signs
- Upper respiratory tract disease (EHV-4, EHV-1, EHV-2).
- Ataxia, posterior paresis (EHV-1).
- Lymphoid follicular hyperplasia (EHV-2).
- Foal pneumonia (EHV-1, EHV-2, EHV-4) Lung: pneumonia - interstitial (foals) .
- Interstitial pneumonia (EHV-5) Lung: pneumonia - interstitial (foals) .
Acute presentation
- Cough.
- Nasal discharge.
- Depression.
- Fever.
Geographic incidence
- Worldwide: EHV-1, EHV-2, EHV-4.
- USA, Europe, including the UK: EHV-3, EHV-5.
Age predisposition
- Young (EHV-1, 2 or 4 respiratory disease).
- Neonate (EHV-1 systemic infection).
- Older adults (EHV-5).
Breed/Species predisposition
- More common in groups of young, naive horses, such as TB racehorses.
Cost considerations
- Respiratory tract disease in horses in training or competitive work.
- Time out of work.
- Diagnostic testing.
Special risks
- Genral anesthesia not suitable for horses showing signs of respiratory compromise.
Pathogenesis
Etiology
- Equine herpesviruses Equine herpesvirus :
- EHV-1: causes abortion Abortion: EHV-1 , respiratory tract disease and neurological disease Abortion: EHV-1 .
- EHV-2: associated with upper respiratory disease, pharyngeal lymphoid hyperplasia Pharynx: lymphoid hyperplasia , pharyngitis and pneumonia in foals Lung: pneumonia - interstitial (foals) although its exact role is unproven.
- EHV-3 is the cause of equine coital exanthema Reproduction: coital exanthema - EHV 3 .
- EHV-4 (formally EHV-1 subtype 2): also associated with respiratory tract disease Respiratory: EHV infection .
- EVH-5 has been linked to fibrotic type of interstitial pneumonia Lung: multinodular fibrosis .
Predisposing factors
General- Young age.
- Stress.
- Season (autumn/winter).
Specific
- Waning maternally derived immunity.
- Reactivation of latent infection.
Pathophysiology
- Spread by close contact or aerosol transmission → primary replication, usually in respiratory epithelium → viremia → localization in predilection site, eg lymphoid tissue, epithelium → latent infections may develop in neural or lymphoid tissues → recrudescence under conditions of stress.
- Replication in respiratory tract → viremia → respiratory tract infection.
- Damage to endothelium of central nervous system vasculature → myeloencephalitis → ataxia, posterior paresis.
- Vasculitis affecting placenta or direct viremic spread to foal → abortion.
EHV-2
- Ubiquitous, therefore difficult to prove pathogenicity.
- Associated with pharyngeal lymphoid hyperplasia Pharynx: lymphoid hyperplasia , pharyngeal ulceration, and respiratory tract disease.
EHV-4
- Primary replication in respiratory epithelium → viremia → pyrexia and malaise → relocalization in respiratory tract → epithelial necrosis, congestion, and petechiation → nasal discharge and conjunctivitis.
- May localize in lymphocytes → necrosis of germinal centers of lymph nodes and reactive hyperplasia → local lymphadenopathy.
- May cause bronchitis or interstitial pneumonia in young animals.
- Secondary bacterial infection → mucopurulent nasal discharge, pneumonia.
EHV-5
- Recently described form of fibrotic interstitial lung disease, pathogenesis still unclear.
- Chronic respiratory disease and weight loss in older horses.
Timecourse
- Primary viral replication and viremia over initial 2-5 days.
- Course of acute disease may last several weeks.
- Latent infections may persist for life of animal.
Epidemiology
- Horses: 50% seropositive to EHV-1; almost 100% of adults seropositive to EHV-2.
- Subclinically or latently infected horses may act as reservoirs of infection.
- Virus transmitted by direct or indirect contact or erosol (EHV-3 transmitted venereally).
- Short-lived immunity (2-6 months), although mares which have aborted rarely abort again.
Diagnosis
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Treatment
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Prevention
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Outcomes
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Further Reading
Publications
Refereed papers
- Recent references from PubMed and VetMedResource.
- Dunowska M (2016) How common is equine herpesvirus type 1 infection? Vet Rec 178 (3), 67-69 PubMed.
- Bazanow B A et al (2014) Abortogenic viruses in horses. Equine Vet Educ 26 (1), 48-55 VetMedResource.
- Soare T, Leeming G, Morgan R et al (2011) Equine multinodular pulmonary fibrosis in horses in the UK. Vet Rec 169 (12), 313 PubMed.
- Pusterla N et al (2011) Surveillance programme for important equine infectious respiratory pathogens in the USA. Vet Rec 169 (1), 12 PubMed.
- Kydd J H, Slater J, Osterrieder N, Antezak D F & Lunn D P (2010) Report of the second Havermeyer EHV-1 workshop, Steamboat Springs, Colorado, USA, September 2008. Equine Vet J 42 (6), 572-575 PubMed.
- Wong D M, Maxwell L K & Wilkins P (2010) Use of antiviral medications against equine herpes virus associated disorders. Equine Vet Educ 22 (5), 244-252 VetMedResource.
- Pusterla N & Mapes S (2008) Evaluation of an air tester for the sampling of aerosolised equine herpersvirus type 1. Vet Rec 163 (10), 306-308 PubMed.
- Luce R et al (2007) Equine herpesvirus-1-specific interferon gamma (IFNy) synthesis by peripheral blood mononuclear cells in Throughbred horses. Equine Vet J 39 (3), 202-209 PubMed.
- Foote C E, Love D N, Gilkerson J R & Whalley J M (2004) Detection of EHV-1 and EHV-4 DNA in unweaned Thoroughbred foals from vaccinated mares on a large stud farm. Equine Vet J 36 (4), 341-345 PubMed.
- Wilson W D (1997) Equine herpesvirus 1 myeloencephalopathy. Vet Clin N Am Equine Pract 13 (1), 53 PubMed.
- Smith K C (1997) Herpes viral abortion in domestic animals. Vet J 153 (3), 253-268 PubMed.
- Donaldson M T & Sweeney C R (1997) Equine herpes virus myeloencephalopathy. Comp Cont Educ Pract Vet 19 (7), 864 VetMedResource.
- Whitwell K E & Blunden A S (1992) Pathologic findings in horses dying during an outbreak of the paralytic form of equid herpesvirus type 1 (EHV-1) infection. Equine Vet J 24 (1), 13-19 PubMed.
Other sources of information
- Horserace Betting Levy Board (2016) Codes of Practice. 5th Floor, 21 Bloomsbury Street, London WC1B 3HF, UK. Tel: +44 (0)207 333 0043; Fax: +44 (0)207 333 0041; Email: enquiries@hblb.org.uk; Website: http://codes.hblb.org.uk.
Further Information
- The Webinar Vet - Equine Infectious Disease and their diagnosis and treatment
- The Webinar Vet - The Equine Neurological Examination and Recent Outbreaks