OUTBREAK OF UPPER RESPIRATORY TRACT INFECTION IN ICELANDIC HORSES
An epidemic of upper
respiratory tract infection has now been affecting the Icelandic Horse
population in Iceland for three months. It is characterized by nasal
discharge, dry coughing and laryngitis (swollen throat). The first cases
were reported in early April 2010. In the following days it became
apparent that the disease was already wide spread and that an epidemic
could not be avoided.
The infection is now over for
the majority of the riding horses, but it is still ongoing in herds
that were not stabled during the winter.
Symptoms: The first symptoms are serous nasal discharge
which in many cases developes in to mucopurulent disharge . Some times a
mild conjuctivitis is also seen. Dry coughing is common and the most
obvious symptom. Temperature remains normal in most of the horses.
Laryngoscopy has revealed laryngitis and in some cases mild affection of
the upper thrachea. The duration of the clinical signs vary from 2 -10
weeks, most commonly 4-6 weeks.
Epidemiology: The morbitity seems to be 100% although the
clinical symptoms vary. This indicates that the horse population has no
or very little immunity to the infectious agent. No mortality has been
associated with the disease. The incubation time varies from 1-4 weeks,
depending on the infection load. Most often the transmission occurs by
direct contact with infected horses, but indirect contamination is also
common. Free-roaming herds without the possibility of contact with other
horses and only minimal contact with humans have also been infected.
Laboratory tests: Cultivation and testing by PCR for Streptococcus equi subsp. Equi has
been negative but Streptococcus equi subsp. Zooepidemicus has been
cultivated from nasal swabs in almost all coughing horses and all horses
with mucopurulent nasal discharge. It is considered that the clinical
symptoms are mainly due to the bacterial infection. Characterization of
the bacterial strain is ongoing and comparison with strains previously
isolated in Iceland will be made.
In spite of extensive virological
investigations no viruses previously known to affect the respiratory
tract of horses have been connected to the present epidemic.
Nasal swabs have been tested by PCR
for the following agents: Equine alfaherpesvirus type 1 and 4 (EHV-1 and
4), Equine gammaherpesvirus 2 and 5 (EHV- 2 and 5), Equine arteritis
virus (EAV), Equine adenovirus type 1 (EadV-1), pan-influenzavirus A,
Equine influenza A, pan-Reovirus, Equine rhinitis virus A (ERAV),
Equine rhinovirus type 3 (ErhV-3), parainfluenzavirus type 3.
Paired blood samples have been tested
for an increase in antibodies for the following viruses: EHV-1 ,
EHV-4, EHV-2 and 5, EAV, Equine influenza A2, Equine reovirus type 1, 2
and 3, ERAV, ERBV.
The cultivation of unknown viruses in
cell cultures is still ongoing in various cell lines. Equine
gammaherpesvirus has been isolated both from healthy and from clinically
affected horses.
No significant changes are seen in
haematology except for an increase of neutrophiles following bacterial
infection.
Measures: Due to the mild symptoms,
long incubation time, high density of horses and frequent transport of
horses between stables and different parts of the country, the disease
was already wide spread when first reported by clinical practitioners.
Therefore, no measures were taken by the Icelandic Food and Veterinary Authority to restrict further spread of the disease.
Horse owners were advised to minimize
the contact with horses in other stables as much as possible and to
cancel competitions and shows. They were further advised to reduce the
infection load within the stables by feeding the horses outdoors and
to put them on pasture as soon as possible. Disinfection of the stables
has also been recommended.
Export of horses was stopped in the
beginning of May as the District Veterinary Officer in charge of export
certification was no longer able to distinguish between infected and
uninfected stables and herds. That decision will be reevaluated in
August.
Conclusion: From the beginning, the
disease was characterized as a mild infection of the upper respiratory
tract although it has turned out to be more prolonged than expected. It
has paralyzed the whole horse industry for almost three months and
caused a serious economical problems. There have, however, only been few
examples of complications that can be related to the disease and the
horses generally gain full recovery. Equestrian activity are now
resuming under the supervision of the Icelandic Food and Veterinary
Authority.
Further information:
Export of horses from Iceland is scheduled to recommence September 15th - 20.08.10
Outbreak of an upper respiratory tract infection in Icelandic horses - 28.05.10
Disinfection of riding clothes and equipment