Page 479 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

454 CHAPTER 2

VetBooks.ir EQUINE HERPESVIRUS TYPE 4 stallions should be identified and treatment consid-
ered before testing to confirm them to be free from
Abortion can be caused by EHV-4, but these cases
are less common and appear to be sporadic rather
horses are in stud farm quarantine will establish the
than abortion storms. infection. Serological testing of blood samples while
status of mares prior to breeding with known dis-
EQUINE VIRAL ARTERITIS ease-free stallions or their semen. In an outbreak,
Definition/overview all in-contact mares and stallions should be tested
EVA occurs worldwide and is the subject of govern- and isolated for 3 weeks post recovery. All infected
ment controls in various countries. It occurs sporad- materials should be destroyed and disinfection of all
ically in the UK (notifiable disease), but is common equipment and living areas carried out. A modified
elsewhere in the world, including the USA. live virus vaccine is available under license in the
UK, Ireland, France, Germany and certain states in
Aetiology/pathophysiology the USA, but with different national restrictions on
EVA virus is spread to the mare from aerosol con- use in other countries. Blood testing for seronega-
tact with the respiratory form of the disease, venere- tivity prior to vaccination is essential as vaccinated
ally from a carrier stallion or via insemination with and infected/previously infected horses cannot be
infected semen. The products of an abortion are also distinguished by blood test alone. Virus isolation on
infectious. The disease leads to a vasculitis in a vari- semen samples can be performed to prove the status
ety of tissues. The incubation period is reasonably of stallions that return positive on a blood test.
rapid (3–8 days). In groups of animals the morbidity
rate can be quite high, but the mortality rate is low. BACTERIAL ABORTION
Definition/overview
Clinical presentation A large number of bacterial species can cause abor-
There is considerable variation in the range and tions in mares and some clinicians consider this the
severity of the clinical signs: pyrexia, depression most important cause of abortion.
and anorexia; nasal discharge; oedema of the limbs
and ventral abdomen; conjunctival swelling; skin Aetiology/pathophysiology
plaques; and abortion. Bacteria can be introduced at breeding, ascend
through the cervix (most common) or spread hae-
Diagnosis matogenously. Cervical incompetence and/or pneu-
Diagnosis of the disease can be difficult, especially movagina can predispose the mare to an ascending
prior to abortion. Virus isolation from the aborted bacterial infection and abortion. A placentitis devel-
fetus, nasal discharges of the mare and semen from ops and the chorionic surface becomes brown and
the breeding stallion are helpful. Paired serology oedematous, with possibly an overlying exudate. The
testing can be used to confirm exposure of the mare bacterial infection may spread to the fetus itself and
to the virus and indirectly identify carrier stallions. infect and damage a range of organs. Abortion occurs
False positives occur post vaccination. following fetal death either from septicaemia or by
progressive placentitis and subsequent placental insuf-
Management ficiency. The most likely aetiological agents for bacte-
Treatment is supportive and most animals recover. rial abortion are Streptococcus spp. (which are the most
Prevention includes the use of vaccination if per- common), Escherichia. coli, Pseudomonas spp., Klebsiella
mitted and careful management practices. The pre- spp., and Staphylococcus spp. Haematogenously spread
breeding testing of all mares and stallions is highly organisms include Salmonella spp., Streptococcus zooepi-
recommended and is a requirement in some coun- demicus and Leptospira spp. A form of non-cervical
tries and by some breed societies before any breed- placentitis, which affects the body of the chorion and
ing takes place. The test is valid for the breeding the base of the horns and is associated with a nocar-
year in which it is taken. The use of infected car- dioform organism, has been reported in the USA,
rier stallions should be avoided if possible, and such particularly in Kentucky.