Comparison of results for intradermal testing between clinically normal horses and horses affected with recurrent airway obstruction.
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.
Wong
David M
DM
Department of Large Animal Clinical Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic and State University, Blacksburg, VA 24061-0442, USA.
Buechner-Maxwell
Virginia A
VA
Manning
Thomas O
TO
Ward
Daniel L
DL
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
D010835:Phytohemagglutinins; D006632:Histamine