Page 594 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Reproductive system: 2.2 The male reproductive tr act 569

VetBooks.ir Management occurs at any stage of gestation with little to no
premonitory signs. Mares infected in late gesta-
Stallions should be sexually rested until the lesions
are fully healed. Care must be taken to prevent iat-
rogenic transmission. Secondary bacterial infections tion give birth to weak foals exhibiting a severe
interstitial pneumonia.
are treated with appropriate topical medications.
Differential diagnosis
Prognosis Other respiratory infections, including influenza,
The prognosis is excellent. EHV-1 or -4, equine adenovirus. Other causes of
abortion should be considered including Leptospira
EQUINE VIRAL ARTERITIS and EHV-1 or -4.

Definition/overview Diagnosis
The single-stranded RNA arterivirus, equine arte- Detection of the virus in farms experiencing clini-
ritis virus, causes EVA, which is readily spread cal respiratory illness and abortion can be achieved
by respiratory and venereal routes. Stallions may using serology, virus isolation or PCR. Submission
become permanent carriers. It has a worldwide dis- of aborted fetuses and membranes will assist in con-
tribution, but outbreaks are rare. EVA is endemic firming the diagnosis. Proper laboratory confirma-
in Standardbreds in many countries and the serop- tion of a diagnosis assists the clinician in providing
revalence of infection among Warmblood stallions advice as to appropriate vaccination and control
is very high in many European countries. measures. In the stallion, diagnosis of the persistent
shedding state is made via detection of equine arteri-
Aetiology/pathophysiology tis virus in the semen or by demonstrating serocon-
EVA is readily transmitted by respiratory and vene- version in a mare after breeding.
real routes. The venereal route of transmission is via
acutely and chronically infected stallions shedding Management
equine arteritis virus in the sperm-rich fraction of Acutely infected animals should be treated with
the ejaculate. Mares acutely infected by either route appropriate supportive care. There is currently
usually seroconvert within 28 days and shed virus no treatment to eliminate shedding in chronically
in body secretions. EVA can also be transmitted via infected stallions, other than castration. To prevent
embryo transfer, from an infected embryo donor infection, stallions should be tested for antibodies to
mare to the recipient. equine arteritis virus before commencing a breed-
The reason some stallions fail to clear the infection ing career. Annual vaccination will prevent infec-
and become chronic carriers of the virus within the tion. Mares being bred to infected stallions should
ampullary glands is not well understood. Recently, a be vaccinated 3 weeks prior to breeding and must
genetic difference in the CD3 T-lymphocyte pheno- be isolated from pregnant mares for at least 21 days
type of carrier stallions compared with non-carriers after vaccination. Currently, a modified live vac-
has been demonstrated. cine is available in North America, but only a killed
vaccine is available in Europe. Vaccines should be
Clinical presentation used according to the manufacturers’ recommenda-
Asymptomatic infection is common in stallions, tion. Since serological testing cannot differentiate
geldings and non-pregnant mares. In symptom- between natural infection and a vaccinate, pre-
atic cases, signs last 1–10 days and include fever, vaccination titres should be documented before
depression, anorexia, limb and scrotal oedema, vaccination of colts to allow international transport.
conjunctivitis and lacrimation, nasal and ocular Stallions with EVA-positive semen can be used for
discharge, and skin rash. A CBC reveals a leu- breeding purposes provided strict isolation practices
copenia. In stallions, scrotal oedema and fever are upheld, strict hygiene in the collection room is
may cause a decline in semen quality. In preg- followed to prevent cross-contamination and they
nant mares, abortion of a partially autolysed fetus are only bred to vaccinated mares.