Virus and its relationship to the "poor performance" syndrome.

Racehorses perform badly for many different reasons. Trainers often expect clinicians to determine the cause in individual cases and, more especially, where most of the immates of the stable are apparently affected by loss of form. Clinical examinations may reveal signs including fever, serous nasal discharge and the occasional cough. Haematology and blood biochemistry are commonly used aids to diagnosis in the field and may be helpful, but there is a need for facilities for virological investigations to be made readily available for use by clinicans as an adjunct to more commonplace laboratory techniques. This paper presents the background to a serious and widely publicised problem experienced by racing stables in the UK in recent years and, in discussing its epidemiology, lays emphasis on upper respiratory tract (URT) disease caused by viruses. It is suggested that, if the incidence of URT disease could be reduced, there would be a corresponding diminution of the "poor performance" syndrome. The inter-relationship of viral diagnosis, epidemiology and research is discussed in terms of methology, interpreting results and limits of present day knowledge.