title: Comparison of results for intradermal testing between clinically normal horses and horses affected with recurrent airway obstruction.
abstract: OBJECTIVE
  To evaluate differences in response to ID injection of histamine, phytohemagglutinin (PHA), and Aspergillus organisms between clinically normal horses and horses with recurrent airway obstruction (RAO).
  
  
  METHODS
  5 healthy adult horses and 5 adult horses with RAO.
  
  
  METHODS
  Intradermal testing (IDT) was performed on the neck with 2 positive control substances (histamine and PHA) and a mixture comprising 5 Aspergillus species. Four concentrations of each test substance plus a negative control substance were used. Equal volumes (0.1 mL) of each test substance were prepared to yield 15 syringes ([4 concentrations of each test substance plus 1 negative control substance] times 3 test substances) for each side of each horse (ie, 30 syringes/horse). Intradermal injections were administered; diameter of wheals was recorded 0.5, 4, and 24 hours after injection.
  
  
  RESULTS
  Hypersensitive responses to ID injection of histamine were detected 0.5 hours after injection, and a delay in wheal formation after ID injection of Aspergillus mixture 24 hours after injection was detected in RAO-affected horses but was not observed in clinically normal horses. No differences were detected between the 2 groups after ID injection of PHA.
  
  
  CONCLUSIONS
  RAO-affected horses are hypersensitive to histamine, suggesting that RAO is associated with a heightened vascular response to histamine. Higher concentrations of Aspergillus mixture may be needed to detect horses that are sensitive to this group of antigens. Wheal reactions to Aspergillus may be a delayed response, suggesting that IDT results should be evaluated 0.5, 4, and 24 hours after ID injection.
authors.affiliation: Department of Large Animal Clinical Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic and State University, Blacksburg, VA 24061-0442, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Wong
authors.forename: Virginia A
authors.initials: VA
authors.lastname: Buechner-Maxwell
authors.forename: Thomas O
authors.initials: TO
authors.lastname: Manning
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Ward
mesh_terms: D000402:Airway Obstruction / Q000276:immunology / Q000662:veterinary*; D000818:Animals; D001230:Aspergillus / Q000276:immunology; D005260:Female; D006632:Histamine / Q000008:administration & dosage*; D006734:Horse Diseases / Q000276:immunology*; D006736:Horses; D006967:Hypersensitivity / Q000175:diagnosis / Q000662:veterinary; D007428:Intradermal Tests / Q000662:veterinary*; D008297:Male; D010835:Phytohemagglutinins / Q000008:administration & dosage*; D012008:Recurrence
chemical_list: D010835:Phytohemagglutinins; D006632:Histamine