Age-dependent infectivity of orally transferred juvenile Fasciola hepatica.

Juvenile Fasciola hepatica is infective when administered orally. To determine whether the age of juveniles is a factor in infectivity by oral transfer, experimental mice were challenged orally with immature F. hepatica that had been grown in donor mice for 12, 14, 16, and 18 days. Experimental mice were examined for infections 12 16 days after the oral transfers. The infection success in experimental mice decreased with the age of juveniles. The worm recovery also decreased according to the age of juveniles. None of the juveniles was infective when grown for longer than 11 days. Once infected, orally transferred worms continued to grow. Juvenile age was a significant factor in determining the infectivity of orally transferred juvenile F. hepatica.