The location of parasites within their hosts: the behavioural component in the larval migration of Nippostrongylus bras1l1ensis in the tissues of the rat

The role of larval behaviour in successful completion of tissue migration is briefly discussed and it is related to the passive carriage of larvae along the ‘pipes and tubes’ of the host. Larvae of N. brasiliensis were injected into selected portions of the circulatory system and following periods of 5–60 min they were recovered from the blood, liver and lungs. Larvae were also immobilised in 0·4% piperazine, a dosage which permitted recovery in about 60 min. The dispersion of treated larvae was compared with that untreated controls. It was found that larvae were carried very rapidly in the blood stream and that they became lodged in the first capillary bed that they entered. They could not pass through capillary beds without movements (and/or secretions). A decreased number of adults developed after larvae were introduced via a series of routes which required the larvae to pass through an increasing number of ‘hurdles’ to migration.