Serodiagnosis of haemonchosis with a somatic antigen (Hc26) in several breeds of sheep

Sera from 53 sheep belonging to Castellano, Churro, Manchego, and Merino br eeds were analyzed to test the diagnostic value of a 26-kD antigen from adu lt Haemonchus contortus at prepatency and early and late patency of experim ental haemonchosis. Animals that received zero, 1, or 2 infections with the parasite were tested. In addition, sera from 20 experimentally infected an d 10 noninfected Texel sheep were used to test the antigen. Sera from 37 in fected animals at prepatency as well as at patency in primary and secondary infection were found positive with the 26-kD antigen. However, sera from 1 0 animals with the lowest worm burdens (second infection) did not recognize the antigen during early patency (day 28 postinfection). IgG1 was the only isotype implicated in antigen recognition because IgG2, IgA, and IgM, in t he same sera, showed no reactivity with the peptide. Antigen specificity wa s confirmed because hyperimmune sera against infective larvae and adult sta ges of the most common gastrointestinal nematodes found in natural infectio ns in sheep (Trichostrongylus colubriformis and Teladorsagia circumcincta) did not recognize this peptide. The antigen was recognized only by anti-adu lt H. contortus hyperimmune sera and appeared to be absent in the L3 parasi te stage. In addition, the partial N-terminal amino acid sequence of the di agnostic peptide is reported.