Epidemiological and immunological studies of sweet itch in horses in Israel.

A survey of sweet itch in horses in Israel based on a questionnaire to owners reported that 158 of 723 horses (21.8 per cent) had sweet itch lesions. The results indicated that the likelihood of a horse acquiring sweet itch decreased with increasing altitude but no definite association with rainfall zones was evident. Variation in the density of the horse population, however, obscured these observations. In the population surveyed, stallions were more sensitive than mares and pale horses appeared to be less sensitive than dark ones, but the sample size of this latter group was much smaller. Intradermal injection of extracts of Culicoides imicola and Stomoxys calcitrans gave immediate reactions in sensitive horses but delayed reactions were observed only with extracts of C imicola. Sensitivity to extracts of C circumscriptus was also evident in allergic horses. Antibodies to extracts of Culicoides species and Stomoxys species were demonstrable in the serum of normal and allergic horses by the ELISA technique.