here - Australian College of Veterinary Scientists

and this and other uncontrolled trials using alum-precipitated vaccine having very
similar rates of success compared with aqueous vaccines (~60-70% of cases showing
good to excellent/greater than 50% improvement).
There is controversy regarding the benefits of ASIT using insect extracts. A
randomised, double-blinded, placebo-controlled clinical trial of ASIT for Culicoides
hypersensitive horses involving 14 horses over a 6-month period demonstrated no
difference between verum and placebo treated groups (Barbet 1990). However, a
later Canadian open study conducted over 1-2 years with a crude Culicoides extract
injected into 10 horses severely affected by disease resulted in a reduction of clinical
signs in 9/10 (90%) in the first year. Of the eight horses treated during the second
year, three were free of clinical signs at the end of the year(37.5%), three showed
much less severe signs(37.5%), and two (25%) showed moderate reduction in clinical
signs (Anderson et al 1996).
In a retrospective study of 43 horses with allergic skin disease, of which 33 had been
on immunotherapy for a minimum of 4 months the following data were reported
(Rosenkrantz 1992): 10 horses showed pruritus only, 14 were urticarial and 9 had
pruritus and urticaria. Good-to-excellent responses to ASIT were reported in 60% of
the pruritic horses, 71% of the urticaria cases and 66% of the horses with both
urticaria and pruritus. Another study (Fadok 1996) showed that in horses that were
purely atopic 5/7 (71.4%) were greater than 50% improved and 7/13 (53.8%)
atopic and insect-allergic horses were greater than 50% improved, whereas 3 of 4
(75%) insect-only allergic horses had no response to immunotherapy.
A subsequent study of symptomatic horses with positive intradermal responses to
insect and environmental allergens evaluated the efficacy of insect hyposensitisation
compared to insect and environmental hyposensitisation in a double-blinded,
placebo-controlled study (Rosenkrantz et al 1998). Clinical scores were ascribed for
pruritus, excoriations, scale-crust and alopecia) ranging from 1-10 for affected
regions of the body and mean scores ascribed. Cases were re-evaluated after 3
months and those that had received placebo were allowed to receive verum
treatment, and subsequently horses in the insect-only treatment group were
permitted to convert to insect + environmental ASIT. Analysis of clinical scores
after the initial 3 months treatment showed no statistically significant difference
between the placebo and verum treated groups with either formulation of
immunotherapy. However, when the pre-treatment and post-treatment scores for
individual horses were analysed, there was a significant difference in verum treated
animals compared to the placebo groups. Similarly, when the placebo groups were
changed to verum treatments, statistically significant changes in scores were
achieved. There was no significance in changing from insect only to insect +
environmental ASIT. Minor reactions characterised by swelling at the injection site
was observed in six of 27 horses receiving ASIT, but all reactions subsided in 24-72
hours.
ACVSC Proceedings Dermatology Chapter Science Week 2005 39