Herpesvirus

Herpesvirus


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Basic Information image



Definition




• Equine herpesviruses (EHVs) are ubiquitous enveloped DNA viruses that have a major economic and welfare impact on the horse industry worldwide.


• Nine EHVs have been characterized. Five (EHV-1 to EHV-5) infect domestic horses, and two (EHV-6 and EHV-9) are associated with infections in wild Equids, including asses and zebra.


• EHV-1 through EHV-5 may be further classified into viral subfamilies on the basis of their genetic sequence:


image α-Herpesviridae: EHV-1, EHV-3, and EHV-4

image γ-Herpesviridae: EHV-2 and EHV-5

• In domestic horses, EHV-1 is associated with respiratory disease, abortion, and neurologic disease.


• EHV-2 has not been convincingly associated with pathology in horses as a primary etiologic agent, but some evidence suggests that it may be associated with keratoconjunctivitis in young horses and superficial keratopathies in adult horses.


• EHV-3 causes coital exanthema, a venereal disease of stallions and mares (see “Venereal Diseases in the Stallion: Viruses,” in this section).


• EHV-4 is associated primarily with respiratory tract disease in horses.


• EHV-5 is epidemiologically associated with pulmonary nodular fibrosis in adult horses.



Synonym(s)




• EHV-1


image Equine rhinopneumonitis

image Viral abortion

image Neurologic herpes

image Equine herpesvirus myeloencephalopathy (EHM)

• EHV-3: Coital exanthema


• EHV-4: Equine rhinopneumonitis


• EHV-5: Pulmonary nodular fibrosis



Epidemiology



Species, Age, Sex




• Most adult horses have serologic evidence of exposure to EHVs.


• The neurologic form of disease appears to be more common in adult horses.



Risk Factors




• Areas of high comingling of horses: Racetracks, show grounds, veterinary hospitals


• Stress or immunosuppression: Transport, hospitalization, training, showing, weaning, high doses of corticosteroids



Geography and Seasonality




• Worldwide


• Highest incidence of EHV-1 neurologic disease in late winter, spring, and early summer with concomitant outbreaks of respiratory disease or abortion.



Clinical Presentation



Disease Forms/Subtypes




• Respiratory disease


image Usually EHV-4, occasionally EHV-1

image Typically causes a self-limiting upper respiratory disease

image In neonates or immunocompromised young animals, may cause a severe viral pneumonitis with secondary bacterial pneumonia

• Abortion


image Almost always EHV-1

image EHV-4 with single cases rather than outbreaks (possibly indicating reactivation of latent infection)

• Neurologic disease: See “Myeloencephalitis, Equine Herpesvirus-1” in this section.


• Ocular disease


image Recurrent conjunctivitis ± corneal ulceration may be caused by EHV-1 or EHV-2.

image Uveitis has been described in association with EHV-1.

image Keratitis has been described in association with EHV-2.

• Multinodular pulmonary fibrosis: EHV-5 has been associated with this disorder and may be a cofactor or primary etiologic agent.



History, Chief Complaint


Horses may present with one or more of the following common complaints:



• Inappetence, fever, nasal discharge


• Mare in late gestation with sudden abortion or expulsion of placenta


• Multiple abortions on the premises


• Acute-onset neurologic deficits in one or more horses with some horses febrile


• Weak foal that is not thriving


• Persistent keratitis or keratoconjunctivitis


• Adult horse with weeks-long history of intermittent fever, weight loss, coughing, or tachypnea



Physical Exam Findings




• Respiratory disease


image Depression, anorexia

image Fever from 101° to 106° F that may be biphasic peaking at 24 to 48 hours after infection and again on days 6 to 7

image Serous nasal discharge changing to mucopurulent

image Conjunctivitis

image Serous ocular discharge

image Progressive lymphadenopathy of mandibular and retropharyngeal lymph nodes

image Coughing may or may not be evident (less consistent than with equine influenza)

image Occasional limb edema, diarrhea, colic

• Viral pneumonitis of neonates


image Fever, marked depression

image Tachypnea

image Dyspnea, respiratory distress

image Abnormal lung sounds

image Petechia, icterus

• Abortion


image Abortion in the last third of pregnancy; refractory to abortion if infected less than 120 days’ gestation

image After abortion, mare may be normal or have respiratory disease or neurologic signs before abortion

image Typically no premonitory signs, with rapid expulsion of placenta

image After abortion, mares generally breed successfully and foal normally.

image May result in birth of stillborn or very weak foals that die shortly after birth

image Stallions may develop scrotal edema, loss of libido, reduction in sperm quality, and shedding of infectious virus in semen.

image Foals may be stillborn or born weak and die

• Neurologic disease: See “Myeloencephalitis, Equine Herpesvirus-1” in this section


• Infectious keratitis


image Blepharospasm, serous epiphora

image Chemosis, conjunctival hyperemia

image Superficial punctuate or dendritic lesions

image Recurrent cases may have corneal vascularization.

• Multinodular pulmonary fibrosis


image Weight loss, poor body condition

image Fever

image Cough, nasal discharge

image Tachypnea, respiratory disease


Etiology and Pathophysiology




• Principal reservoir of infection is latently infected horses.


image An estimated 80% to 90% of horses are latently infected with EHV-1 or EHV-4 by 2 years of age.

image Foals are exposed and may become latently infected as early as 1 to 2 weeks of age (from their dam or other adult horses).

image Latently infected horses serve as a source of virus for spread to other foals.

image Reactivation of latent virus may occur with any stressful situation, including transport, handling, rehousing, or weaning.

image Reactivation of latent virus in adult horses often causes viral shedding without clinical signs.
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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Herpesvirus

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