Differential diagnosis of equine cestodosis based on E/S and somatic Anoplocephala perfoliata and Anoplocephala magna antigens

The tapeworm responsible for equine colic, Anoplocephala perfoliata, is considered the most common intestinal tapeworm of horses worldwide. However, there is evidence that Anoplocephala magna has a similar prevalence in North America and Spain, and possibly in other countries, highlighting the need for diagnostic methods capable of distinguishing between these two species. Currently, immunodiagnosis of A. perfoliata is based on the identification of the 12/13 kDa excretory/secretory (E/S) A. perfoliata immunoreactive antigen, which while apparently specific, has never been tested in sera from A. magna-positive horses. Accordingly, we evaluated the specificity of 12/13 kDa E/S A. perfoliata antigen for the first time by testing this crude antigen against A. magna-positive sera in Western blot. In addition, we characterized a somatic (Som) crude antigen of A. perfoliata and for the first time, the E/S and Som crude antigens of A. magna, evaluating their potential utility for the differential serodiagnosis of equine anoplocephalosis in sera from horses of known parasitic status. SDS-PAGE revealed major low MW bands at: 14 and 12 kDa for E/S and Som-A. magna; 14 and 11 kDa for E/S A. perfoliata; and 11 and 10 kDa for Som-A. perfoliata. Protein regions at 12-14 kDa (E/S A. perfoliata), 10-15 kDa (Som-A. perfoliata) and 10-12 kDa (Som-A. magna) were recognized by Anoplocephala-positive sera at the genus but not the species level. These findings demonstrate cross-reactivity of these unpurified antigenic components, precluding their use in differential diagnosis between A. perfoliata and A. magna. Although these results do not directly indicate cross reactivity at the purified 12/13 kDa component of the E/S A. perfoliata antigen, it is possible that current immunodiagnostic methods based on this component might not accurately differentiate between these two tapeworm species, suggesting erroneous diagnosis of A. perfoliata in areas where A. magna is present.