The Survival of Migratory and Post-Migratory Stages of Litomosoides carinii in White Rats

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Abstract
One-year-old white rats are highly resistant to an infection with Litomosoides carinii produced by a subcutaneous introduction of known numbers of infective larvae. In infections of 7 to 45 days, an average of only 2% of these larvae completed migration from skin to pleural (or peritoneal) cavity as compared to 42% for similar cotton rat infections. White rat resistance to migrating larvae was bypassed by allowing migration in normal hosts, and transferring late third-stage larvae (or fourth and fifth-stage worms) into peritoneal cavities of white rats. Transferred worms survived and developed for periods of 9 to 28 days approximately as well in white rats as in cotton rats. In longer infections (several months) transferred worms developed to sexual maturity and produced microfilariae which developed normally in mites into infective larvae. These larvae showed no adaptation for survival in white rats. The survival of transferred (especially female) worms in these longer infections was reduced in white rats. Encapsulation of transferred worms in white rats was not apparent in short infections (9 days), but was common (especially for female worms) as the infection period increased (28 days to several months). Encapsulation was rare in control cotton rat infections.
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