Larval migration in oral and parenteral Toxocara pteropodis infections and a comparison with T. canis dispersal in the flying fox, Pteropus poliocephalus

When eggs of T. pteropodis were fed in large doses to juveniles of a definitive host, Pteropus poliocephalus, larvae hatched throughout the gastrointestinal tract. The majority penetrated the mucosa of the distal half of the intestine, to reach the liver via the portal circulation. A few entered the lymphatics to eventually reach the liver by passing through the lungs and migrating tracheally or continuing in the systemic circulation. Patent infections did not develop. Eggs inoculated subcutaneously also hatched and larvae again reached the liver, travelling via the circulation through the lungs and often other tissues; again, some underwent tracheal migration. Infective larvae of T. canis, identical in size with T. pteropodis, passed through the liver and lungs and dispersed mainly to skeletal muscles, but with time gradually accumulated in the brain. These findings indicate that Toxocara larval distribution is not primarily influenced by larval dimensions but reflects goal-directed behaviour.