Endoscopic and virological observations on respiratory disease in a group of young Thoroughbred horses in training.

A group of racehorses in training was examined on several occasions with a fibreoptic endoscope and monitored for viral infection. Only equine herpes virus-2 (EHV-2) infection was detected. Pharyngeal lymphoid hyperplasia (PLH) was present in all horses and decreased in severity with age. There was no association between PLH severity and antibody titres to EHV-1, or with the isolation of EHV-2. Finishing position in races was not affected by PLH severity. Exercise induced pulmonary haemorrhage (EIPH) was evident on 23 out of 49 (47 per cent) examinations after maximal speed training exercise. Eighteen out of 19 (95 per cent) horses examined on at least two occasions had EIPH but its occurrence was not predictable. Observable mucoid or mucopurulent exudate was present in the trachea in 60 out of 118 (50 per cent) examinations and the amount seen was increased following exercise.

Isolation of Streptococcus pneumoniae from the respiratory tract of horses.

Streptococcus pneumoniae was isolated from nasopharyngeal swabs and tracheal washings taken from Thoroughbred horses in training at three of four separate stables that were sampled during investigations into respiratory disease. The growth of Strep pneumoniae in culture was enhanced by an environment enriched with carbon dioxide. In one stable, five of 15 horses that were sampled repeatedly were found to carry the organism for at least four months. There was an apparent association between lower respiratory tract inflammatory disease and heavy growths (10(6) to 10(8) colony forming units/ml) predominantly of Strep pneumoniae or of that organism together with large numbers of Strep zooepidemicus obtained from tracheal washings. Twelve strains of Strep pneumoniae isolated from three stables were all of capsule Type 3. Only one strain, which was of capsule Type 9, was isolated from nose and throat swabs taken from 32 staff working in one of the stables and suggested an absence of cross infection between horses and their handlers in this instance.

Streptococci and Pasteurella spp. associated with disease of the equine lower respiratory tract.

The likelihood of finding evidence of inflammation in 551 tracheal washes collected endoscopically from 278 Thoroughbred racehorses increased with the number of bacterial colony forming units (cfu) per ml of wash (P < 0.001). The aerobic bacteria Streptococcus zooepidemicus, Pasteurella/Actinobacillus-like species and Streptococcus pneumoniae were significantly associated with lower airway inflammation whereas coagulase-negative Staphylococcus spp., alpha-haemolytic Streptococcus spp., Acinetobacter spp., Bacillus spp., Escherichia coli, Pseudomonas aeruginosa, non-haemolytic Streptococcus spp. and Enterobacteriaceae were not; Bordetella bronchiseptica was not isolated. Lower airway inflammation was particularly associated with bacteria in horses < or = 3 years of age. S. zooepidemicus, S. pneumoniae and Pasteurella/Actinobacillus-like species were isolated from 167 of 551 washes, either alone or in combination.

Progressive haematoma of the maxillary sinus in a horse.

A nine-and-a-half-year-old three quarters thoroughbred gelding was presented with unilateral epistaxis. The cause was a destructive, progressive haematoma in the left maxillary sinus. In all previous reports of progressive haematomata in the equine nasal cavity, the site of origin has been the ethmoidal labyrinth. Surgical removal of the progressive haematoma resulted in an apparent cure.

An outbreak of respiratory disease in horses associated with Mycoplasma felis infection.

Lower respiratory tract disease developed in a group of racehorses in training between two and six years of age. Disease was observed in 22 of 25 horses for which full records were available. Seroconversion to Mycoplasma felis was demonstrated by indirect haemagglutination assay in 19 of 22 paired sera and high titres (> or = 64) were found in convalescent sera from the three remaining horses. Evidence of respiratory viral infection was confined to seroconversions to equine herpesvirus-4 in two of the horses. Tracheal wash samples, taken from four horses with visibly increased tracheal mucopus, contained more than 10(4) colony forming units/ml M felis and high proportions of neutrophils. This is the first description of an outbreak of lower respiratory tract disease in horses in training associated with M felis infection.

Respiratory disease in thoroughbred horses in training: the relationships between disease and viruses, bacteria and environment.

A longitudinal study of respiratory disease in racehorses was carried out to assess its relative associations with different infectious agents and to examine any role that the environmental conditions might play. The relationships between coughing, nasal discharge, pyrexia and lower respiratory tract disease were also examined to provide information for improving clinical diagnosis, particularly of disease of the lower respiratory tract. Lower airway disease was closely associated with infection with Streptococcus zooepidemicus. It was also found that equine herpesvirus seroconversions and S pneumoniae infections were independently associated with the development of nasal discharge. Coughing was a specific, but insensitive measure of lower respiratory tract disease (specificity 84 per cent, sensitivity 38 per cent). However, horses that coughed were very likely to have had lower airway disease for more than one month. Horses housed on straw in loose boxes were twice as likely to suffer from lower airway disease as those kept on shredded paper in American barns. The study was not large enough to assess the significance of rarer infections but it did improve the definition of the problem of respiratory disease in racehorses and revealed some of the trends in the associations between viruses, bacteria and the environment in respiratory disease.