here - Australian College of Veterinary Scientists

18
Intradermal Testing (IDT) in Horses:
The Australian Perspective
Applications of IDT in Australia
ACVSC Proceedings Dermatology Chapter Science Week 2005
Tina Baxter
Intradermal testing (IDT) is probably an underutilized diagnostic tool in Australia.
The incidence of atopy in Australian horses has not been documented. ‘Skin disease’
or ‘itch’ is a common presentation - approximately 20% of horse owners surveyed
recently in Queensland reported their horses had a ‘skin problem’ (28) - and the
majority of these had clinical presentations that were consistent with insect bite
hypersensitivity. As the exact trigger of the skin disease was not identified in these
cases, there may be a poor clinical distinction between insect related hypersensitivity
and atopic dermatitis.
More importantly, intradermal testing has applications in diseases other than atopic
dermatitis, both here and overseas, and the following notes are equally relevant in
performing the test for horses with insect bite hypersensitivity (including Queensland
itch), recurrent urticaria, head shaking, chronic obstructive pulmonary disease and
other airway diseases (reactive airway disease) where an allergic basis is suspected
(7,12, 14, 16, 25). While Type I hypersensitivity is not the only contributing factor in
these diseases, information gained from intradermal testing in these cases can only be
of benefit. In a survey of aged horses, an estimate of 22% of horses had respiratory
disease and the majority of these are thought to have an allergic pathogenesis (28).
Possible reasons for the relative paucity of equine cases undergoing intradermal
allergy testing include:
The test requires time, skill and experience to perform, such that it is usually
performed only by specialists in dermatology
Much of the information and experience in IDT available to specialists in
dermatology is based on small animals. Clinic facilities and personal
preference of the dermatologist may preclude the handling of horses
The allergens used in the test have a limited shelf life, so regular tests need to
be performed to make the purchase of the allergens worthwhile and ensure
the cost of the test to the individual owner remains reasonable
Referral requires effort on the owners part to travel (in some cases significant
distances from country regions of Australia) to the nearest major centre
Costs and time to the owner: the average cost to the owner for IDT and
consultation are around$500 to $650; costs of travel and time are additional