IMMUNOEPIDEMIOLOGY OF THE EQUINE TAPEWORM ANOPLOCEPHALA-PERFOLIATA - AGE-INTENSITY PROFILE AND AGE-DEPENDENCY OF ANTIBODY SUBTYPE RESPONSES

The equine intestinal cestode Anoplocephala perfoliata has been the su bject of recent epidemiological and immunological studies because of i ts suspected association with intestinal disease in the horse. We have previously shown that the IgG(T) subtype antibody response to the 12/ 13 kDa component of the parasite excretory/secretory (E/S) antigen is positively correlated with parasite intensity. In this study, we utili ze that correlation to examine the changes in natural infection intens ity with age. Infection intensity based on IgG(T) responses showed a t riphasic age-dependency pattern with peak mean worm burden in the 6 mo nths-2 years age group, falling to a lower plateau level from 3 to 15 years, and rising again in older age groups. Anti-E/S total IgG was fo und to have a convex age-dependency curve, with maximal response in th e 6 months-2 years old age group. IgG(a) showed a triphasic response s imilar to the age-intensity profile of IgG(T); IgG(c) showed steadily increasing levels of antibody with age. The IgG(b) age-dependency prof ile was intermediate between IgG(a) and IgG(c). Age-specific correlati on coeficients between anti-12/13 kDa IgG(T) (as a measure of infectio n intensity) and IgG(a) and IgG(b) revealed statistically significant values for many age groups. The relative importance of exposure to inf ection and the development of acquired immunity as determinants of the observed age-intensity pattern is considered.