Visceral larva migrans: migratory pattern of Toxocara canis in pigs.

The migratory pattern of Toxocara canis was investigated following infection of pigs with 60000 infective eggs. Groups of six pigs were slaughtered at 7, 14 and 28 days after infection (p.i.), and the number of larvae in selected organs and muscles was determined by digestion. A group of uninfected pigs was used as negative controls for blood parameters and weight gain. Toxocara canis migrated well in the pig, although the relative numbers of larvae recovered decreased significantly during the experiment. On day 7 p.i., high numbers of larvae were recovered from the lymph nodes around the small intestine and to some extent also from the lymph nodes around the large intestine, and from the lungs and the liver. On day 14, the majority of larvae were recovered from the lungs and the lymph nodes around the small intestine, and by day 28 p.i. most larvae were found in the lungs. Larvae were recovered from the brain on days 14 and 21, with a maximum on day 14 p.i. No larvae were found in the eyes. Severe pathological changes were observed in the liver and lungs, especially on day 14 p.i.; also, development of granulomas was observed in the kidneys. Finally, a strong specific antibody response towards T. canis L2/L3 ES products was observed from day 14 p.i. until termination of the experiment, and the maximum eosinophil response was observed 14 days p.i. The pig is a useful non-primate model for human visceral larva migrans, since T. canis migrate well and induce a strong immunological response in the pig. However, the importance of the pig as a paratenic host is probably minor, because of the relatively early death of most of the larvae.