here - Australian College of Veterinary Scientists

Allergen Positive reactions
Mosquito (Culicidae) 2/11
Blackfly (Simulidae) 3/11
Horsefly (Tabanidae) 2/11
Culicoides spp 6/13
10-fold dilution 6/13 (1)
100-fold dilution 4/13
Delayed reactions in parentheses and underlined
All horses showed at least two immediate positive reactions; in some cases reactions
were not evident until the 4-hour time point. Twelve horses showed delayed
(>24hour) reactions, not necessarily preceded by immediate or late-immediate
reactions. Two horses reacted to all allergens tested; in both cases the negative
control did not produce a wheal reaction, nor did application of mechanical pressure,
ruling out dermatographism as the cause of the multiple reactions. Reactions to mite
extracts were common; only 2 horses (8.3%) showed no reactions to any mite
species. Dust mite reactions were seen in 20/24 (83.3%); 58.3% reacted to both dust
and forage mites, 25% to dust mites alone. Two horses reacted to forage mites but
not dust mites. Housedust reactions were also common, occurring in 81% of cases.
Reactions to epithelial extracts were also frequent; 54.2% reacted to human dander,
33.3% to sheep and 12.5% to cats; in all of the latter cases there were yard cats that
had access to the stables and tack rooms and often slept on rugs or in the stables.
Feather reactions were also quite common (37.5%), including two delayed reactions;
two cases improved dramatically following removal of birds nests and preventing
further access of birds, with complete resolution of skin disease without any other
interventions.
The majority of cases showed reactions to pollens; 10/24 (41.7%) did not. Weed
pollen reactions were the most common - seen in 13 horses (54.2%), with nine
(37.5%) having reactions to tree pollens and five (20.8%) to grasses. In a number of
cases the history suggested that exposure to grass and weed pollens in meadow hay
were relevant. A few positive reactions to each of the moulds were noted. A
considerable number of cases showed reactions to cereal smuts – 41.7% to barley
smut, 41.7% to oat smut and 34.8% to wheat smut.
Six horses developed immediate and delayed reactions to biting insects, particularly
Culicoides. Horses with reactions to mosquito, blackfly and horsefly extracts were also
positive to Culicoides. All of these cases had a history of clinical signs consistent with
“sweet itch”, but all showed additional symptoms that were not typical of summer
recurrent seasonal hypersensitivity. Together with two further cases that had
consistent history and clinical signs but were not tested with insect extracts, these
horses were considered to be suffering from both atopic dermatitis and insect bite
hypersensitivity (33.3% of cases).
Reference:
Littlewood JD, Paterson S, & Shaw SC. (1998) Atopy-like skin disease in the horse. Advances
in Veterinary Dermatology 3, p563
ACVSC Proceedings Dermatology Chapter Science Week 2005 35