Visceral larva migrans: migratory pattern of Toxocara canis in pigs

The migratory pattern of Toxocara canis was investigated following infectio n of pigs with 60 000 infective eggs. Groups of six pigs were slaughtered a t 7, 14 and 28 days after infection (p.i.), and the number of larvae in sel ected organs and muscles was determined by digestion. A group of uninfected pigs was used as negative controls for blood parameters and weight gain. T oxocara canis migrated well in the pig, although the relative numbers of la rvae recovered decreased significantly during the experiment. On day 7 p.i. , high numbers of larvae were recovered from the lymph nodes around the sma ll 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 lar vae were recovered from the lungs and the lymph nodes around the small inte stine, 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. N o 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 gra nulomas was observed in the kidneys. Finally, a strong specific antibody re sponse towards T. canis L2/L3 ES products was observed from day 14 p.i. unt il termination of the experiment, and the maximum eosinophil response was o bserved 14 days p.i. The pig is a useful non-primate model for human viscer al larva migrans, since T. canis migrate well and induce a strong immunolog ical 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 t he larvae. (C) 1999 Australian Society for Parasitology Inc. Published by E lsevier Science Ltd. All rights reserved.