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SUMMARYThe migration in mice of 20, 50 and 90 krad. 60Co-irradiated Schistosoma mansoni larvae, biosynthetically radio-isotope labelled with [75Se]-selenomethionine, was evaluated by autoradiography of compressed tissues and compared to the migration of non-irradiated 75Se-labelled larvae. The migration of 20 krad. -irradiated schistosomula between skin and lungs was slightly delayed but otherwise paralleled the migration of normal, non-irradiated schistosomula during the first 8 days following exposure. By day 8 over 90% of both non-irradiated and 20 krad. -irradiated organises were located in the lungs. In contrast to non-irradiated organisms, however, only a small proportion of 20 krad. organisms migrated to the liver. The delay in migration between skin and lungs was more pronounced with 50 krad. -irradiated schistosomula. Nevertheless, 45–93% of 50 krad. -irradiated organisms migrated to the lungs by 8 days post-exposure. Over 90% of the 50 krad. larvae detected in the mouse on day 21 were in the lungs; no more than an occasional 50 krad.-irradiated organism was ever detected in the liver. In three experiments, over 85% of the 90 krad. -irradiated organisms were retained in the skin; in a fourth experiment about half of the 90 krad. -irradiated organisms migrated as far as the lungs. As with 50 krad. organisms, only an occasional 90 krad. organism was ever detected in the liver. Removal of the skin exposure site within the first 4 days of immunization with either 50 or 90 krad. -irradiated cercariae completely blocked the induction of resistance. Removal between the 4th and 6th days gave variable results. Mice had to be in contact with the irradiated larvae for a minimum of 8–11 days to stimulate a level of resistance comparable to that of mice whose immunization site was not removed.

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Abstract. Real-time quantitative polymerase chain reaction (qPCR) testing for Mycobacterium avium subspecies paratuberculosis (MAP) in fecal samples is a rapid alternative to culture on Herrold egg yolk medium (HEYM), the traditional antemortem reference test for MAP. Although the sensitivity and specificity of these 2 tests have been estimated based on dichotomized test results, the correlation between real-time qPCR threshold cycle (Ct) values and colony-forming units (CFU) on HEYM for fresh and thawed samples has not been evaluated. The objectives of the present study were to estimate the correlation and association between Ct and CFU in fresh and thawed pooled fecal and environmental samples. Results of HEYM culture of 1,997 pooled fecal samples from cows in 14 herds, and 802 environmental samples from 109 dairies nationwide were negatively (inversely) correlated with their respective real-time qPCR results. The Spearman's rank correlation between Ct and CFU was good (20.66) in fresh and thawed pooled fecal samples, and excellent (20.76) and good (20.61) in fresh and thawed environmental samples, respectively. The correlation varied from good (20.53) to excellent (20.90) depending on the number of samples in a fecal pool. Truncated regression models indicated a significant negative association between Ct and CFU in fecal pools and environmental samples. The use of real-time qPCR instead of HEYM can yield rapid, quantitative estimates of MAP load and allow for incorporation of real-time qPCR results of pooled and environmental samples in testing strategies to identify dairy cow groups with the highest MAP shedding.