title: Infectious risk factors and clinical indicators for tracheal mucus in British National Hunt racehorses.
abstract: BACKGROUND
  Many studies of respiratory disease in racehorses have focused on a combination of increased tracheal mucus and airway neutrophilia. Examination of each component separately should provide further insight into this condition.
  
  
  OBJECTIVE
  To identify infectious risk factors for endoscopically visible tracheal mucus in National Hunt racehorses.
  
  
  METHODS
  A 2 year prospective longitudinal study.
  
  
  METHODS
  Monthly quantitative bacteriological examinations of tracheal wash samples and viral serological examinations were conducted. Risk factors for 'small amounts of mucus' (mucus score = 1/3) and 'increased mucus' (score ≥2/3) were identified.
  
  
  RESULTS
  There were increased odds of small amounts of mucus when both Streptococcus zooepidemicus and nonhaemolytic streptococci (NHS) were isolated (odds ratio [OR] 2.6; 95% confidence interval [CI] 1.5-4.6; P<0.001) but not when either species was isolated in the absence of the other. Increased odds of increased mucus were associated with the isolation of either S. zooepidemicus (OR 5.6; 95% CI 1.2-25.9; P = 0.03) or NHS (OR 3.7; 95% CI 1.2-11.6; P = 0.02), with an increased effect when both were isolated together (OR 12.5; 95% CI 3.7-41.6; P<0.001). Approximately 6-fold increased odds of small amounts of mucus were associated with the first 3 months in training (OR 6.3; 95% CI 2.0-19.4; P<0.001) and 3-fold increased odds of increased mucus associated with the first 6 months in training (OR 2.9; 95% CI 1.3-6.4; P = 0.01). Coughing at exercise and increased serous nasal discharge were specific but insensitive indicators of increased mucus.
  
  
  CONCLUSIONS
  Associations with S. zooepidemicus corroborate previous research, but an independent effect of NHS has not previously been reported. The possibility that there are individual pathogenic species within this group should be considered. Further work is required to identify S. zooepidemicus subtypes and NHS species associated with disease. Closer monitoring of the respiratory health of horses entering training for the first time is likely to be valuable.
authors.affiliation: Department of Production and Population Health, Royal Veterinary College, North Mymms, Hatfield, Hertfordshire, UK.
authors.forename: J M
authors.initials: JM
authors.lastname: Cardwell
authors.forename: K C
authors.initials: KC
authors.lastname: Smith
authors.forename: J L N
authors.initials: JL
authors.lastname: Wood
authors.forename: J R
authors.initials: JR
authors.lastname: Newton
mesh_terms: D000818:Animals; D006734:Horse Diseases / Q000453:epidemiology / Q000382:microbiology*; D006736:Horses; D009093:Mucus / Q000382:microbiology*; D016017:Odds Ratio; D012141:Respiratory Tract Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D012307:Risk Factors; D013177:Sports; D014132:Trachea / Q000382:microbiology*; D006113:United Kingdom / Q000453:epidemiology
keywords: airway; horse; inflammation; mucus; tracheal