Plasma pepsinogen, inhibited larval development, and abomasal lesions in experimental infections of calves with Ostertagia ostertagi

Abstract

Single doses of Ostertagia ostertagi, followed in 42 days by multiple increasing doses in calves, were monitored by fecal egg counts and plasma pepsinogen. The level of plasma pepsinogen increase was related to the increase in graded levels of inoculation and to the fecal egg counts. Plasma pepsinogen in uninfected controls remained below 1 IU/L. Plasma pepsinogen in all calves reached levels greater than 5 IU/L at 48 days of the extended inoculation period, although fecal egg counts remained low in the previously inoculated calves. The previously infected calves had a higher proportion of early fourth-stage larvae, while larger adult worm burdens were found in the previously uninfected calves. Early fourth-stage larvae were observed in extra-glandular sites, notably between the glandular epithelium and basement membrane or within the lamina propria. An immunological response of the host was suggested by the lymphoid cell infiltration in the mucosa. This host immune response may account for the greater larval inhibition exhibited by the previously infected calves.