Protection from parasite-induced weight loss by the vaccination of calves with excretory-secretory products of larval Oesophagostomum radiatum

Excretory-secretory products (ESP) were collected from in vitro maintained Oesophagostomum radiatum larvae during the period in which the larvae molt from the third to fourth larval stage. The ESP were used to immunize 13 uninfected calves which were subsequently challenged with 1.7×10 4 infective O. radiatum larvae. Worm recoveries from immunized calves were reduced 23% compared to 12 unimmunized controls, while the number of intestinal nodules was 72% greater compared to unimmunized controls; however, neither difference was statistically significant. Immunized calves had enhanced serum IgG and IgA anti-ESP antibody responses upon challenge. No differences in serum IgG 2 or IgM antibody or cellular immune responsiveness, as determined by in vitro antigen-induced lymphocyte proliferation, were seen. Vaccination with ESP did significantly protect calves from the weight loss seen in non-immunized calves. Unimmunized calves ceased gaining weight ∼5 weeks after challenge and by 10 weeks after challenge had lost an average of 4 lbs. per calf. Over the same time interval (i.e., 5–10 weeks after challenge), the immunized calves gained an average of 23 lbs. per calf. These results strongly suggest that vaccination with ESP conferred an advantage to calves that is not correlated solely with the number of worms developing from challenge infection.