Patterns of milk transmission of Strongyloides ratti.

Eight days after mother rats were injected with 4000 infective larvae of Strongyloides ratti at different stages of lactation the numbers of adult worms in their intestines were uniformly low (less than 3% of the dose) compared with unmated controls (mean = 25%). Those in their litters varied from 12% on day 5 to a maximum of 47% on day 17 post partum. These data, which do not correlate with lactational performance, imply that parasite movements in lactating rats are controlled by qualitative, not quantitative, consequences of humoral events. The numbers of worms in litters are concluded to be the result of the interaction of dynamic determinants of larval routes in the mother and changes in the suitability of the neonatal gut as an environment for worm development. The timing of events leading to milk-borne infection is defined. Injected larvae were closely synchronized in their movements, which were completed in 36 h. Larvae experimentally diverted into the mother's tissues during her first lactation were not available for the infection of a second litter.