Evidence, nature, and implications of the constitutive resistance to Trichinella spiralis in gallinaceous birds.

White Leghorn chickens and mice were orally infected with Trichinella spiralis larvae and their digestive tracts were examined for parasites at postinfection hours (PIH) 5 and 10, and at postinfection days (PID) 1, 2, 4, 6, and 8. Evacuated feces were examined at PIH 5 and 10 and at PID 1, and blood was examined at PID 4, 6, and 8. With the exception of trichinae in the digestive tract (9 at PIH 5 and 2 at PIH 10), parasites were not recovered from chickens. All mice had abundant parasites in the digestive tract and a few parasites in the blood; however, parasites were not found in blood or feces at PID 4. In vitro incubation of infective larvae (4 hours at 37 C) in an extract of glandular stomach or in a combination of extracts from the small intestine, pancreas, and bile of chickens caused visible alterations in 42% to 64% of the larvae and caused total loss of larval infectivity for mice. Sequential incubation in both fluids caused damage in 91% to 97% of the larvae. The same experiments with mouse extracts caused damage in only 8% to 26% of the larvae and infectivity of the larvae for mice was not reduced noticeably. Digestion of infective T spiralis larvae is an important constitutive mechanism of resistance in chickens that probably precludes the transmission of the infection by gallinaceous birds in nature.