Page 704 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Respir atory system: 3.3 Medical conditions of the upper respir atory tr act 679

VetBooks.ir occurs, the expelled fetus is generally autolysed. stallions are tested for antibodies before breeding.
The disease can be controlled by vaccination but,
Carrier stallions are clinically normal and show nor-
because of the notifiable status, the vaccine can only
mal libido and fertility.
be used under the supervision of regulatory agencies
Differential diagnosis in many countries. Veterinary certification of vacci-
All other causes of infectious respiratory disease and nation is usually required (to distinguish vaccinated
abortion, especially EHV-1 infections, should be horses from infected and convalescent horses) and it
considered. is therefore important that the horse is confirmed
seronegative before vaccination. EVA-positive stal-
Diagnosis lions and mares can still be used for breeding, albeit
The clinical features of EVA disease are not pathog- following strict rules.
nomonic, although an outbreak of respiratory dis-
ease associated with marked conjunctivitis, oedema Prognosis
and infertility or abortion is highly suggestive. The prognosis is good for recovery from clinical dis-
Leucopenia with lymphopenia followed by leuco- ease, but EVA causes major economic loss because of
cytosis with lymphocytosis on recovery is sugges- breeding failure through early embryonic death and
tive of a viral infection but is not diagnostic of EVA abortion.
infection. Confirmation of diagnosis requires dem-
onstration of virus, virus antigens or virus nucleic OTHER VIRAL INFECTIONS
acids in a nasal swab or semen samples. A rising virus
neutralising antibody titre on paired serum samples Adenovirus
taken 10–14 days apart is diagnostic. Many laborato- Adenovirus infections are common, based on
ries perform EVA PCR on nasal swabs as part of an serology, but are believed to cause subclinical disease
equine URT disease PCR panel. only. Clinical disease caused by an adenovirus has
only been seen in immunocompromised animals,
Management specifically in Arabian foals with severe combined
The disease is notifiable in many countries and sus- immunodeficiency (SCID), in the form of broncho-
pected or confirmed cases must be reported. Clinical pneumonia. The clinical significance of adenovirus
cases should be isolated and maintained with strict infections in young horses in training is uncertain
barrier conditions until no new clinical EVA cases are and there are currently no data to suggest that infec-
observed for 3–4 weeks. Affected horses require little tion impacts on training, causes poor performance
veterinary attention, as clinical disease is often mild or predisposes to other, more serious, respiratory
and self-limiting or subclinical. NSAIDs can be used disease.
to control pyrexia and improve welfare. Antibiotics
are usually not required and other respiratory medi- Rhinovirus
cines (e.g. mucolytics) are not indicated. The virus The equine rhinoviruses are divided into equine
is easily inactivated by many disinfectants, including rhinitis A virus (ERAV), equine rhinitis B virus
1% bleach, 70% ethanol, iodine-based disinfectants, type 1 (ERBV1) and equine rhinitis B virus type
quaternary ammonium disinfectants, peroxygen dis- 2 (ERBV2). They are globally widespread and are
infectants and phenolics. serologically very common in horses. Horses typi-
Prevention and control of EVA in many countries cally become infected during their younger years,
is based on testing and exclusion, restriction of move- while being trained and raced. These viruses are
ment of affected horses or quarantine. For example, believed to be able to cause URT disease and fever,
in the UK horses imported from a country where clinically undistinguishable from the other respira-
EVA is known or suspected to occur are isolated on tory viruses. However, in many cases disease will
arrival for 21 days. Blood samples taken on arrival be subclinical. Their role in the development of
and 14 days later are tested for antibodies. Mares and inflammatory airway disease is currently unknown.