Host immunity against newborn Trichinella spiralis larvae of different ages.

The infectivity of newborn Trichinella spiralis larvae of different ages was studied in normal rats. Newborn larvae collected after incubation of adult worms in vitro for 2, 12, or 24 hr were injected intravenously (i.v.) into normal AO rats in 3 separate recipient groups. All recipient rats developed strikingly similar numbers of muscle larvae 20 days later. The susceptibility to immunity by newborn larvae of different ages was also studied. No difference was found when degree of protection was compared by assessing muscle larvae burden or peritoneal anti-newborn larvae effects after injection of newborn larvae of different ages either i.v. or intraperitoneally into immunized recipient rats. We conclude that newborn larvae of any age up to 24 hr have similar infectivity in normal rats and are equally susceptible to anti-newborn larvae immunity in vivo.