Development of the large American liver fluke, Fascioloides magna, in white-tailed deer, cattle, and sheep.

The comparative development of Fascioloides magna in white-tailed deer, cattle and sheep has been studied. Flukes were recovered from 72% of 32 deer administered 40 to 500 metacercariae, from 82% of 11 cattle administered 10 to 500 metacercariae, and from 53% of 15 sheep administered 8 to 200 metacercariae. The percentage recovery of the flukes administered as metacercariae was 4.1% of 6,130 in deer, 5.7% of 2,510 in cattle, and 4.7% of 1,213 in sheep. Flukes were recovered only from livers of infected deer, while in cattle, 1 fluke was also found in the lungs of each of 2 animals. In sheep, all but 10 flukes were recovered from the livers; 6 were found in the lungs and 4 in the abdominal cavities. The black iron porphyrin pigment associated with F. magna infection was found to be most widespread in cattle and sheep, but was also a pathognomonic feature in deer. Growth of the fluke was similar in all 3 host species tested, but eggs were passed only from deer, the normal definitive host. In cattle, the eggs were retained in the liver, and F. magna was lethal to sheep before its own maturity was attained. In cattle and deer, flukes matured approximately 7 months after exposure, but immature migrating flukes were found 12 months after infection and apparently can remain in this retarded state for an undetermined period of time.