Transplacental migration of Toxocara canis larvae in experimentally infected mice.

In experimentally infected, nonpregnant mice the larvae of Toxocara canis were not found in the uterus at any time. In mice infected at 1 week, but not at 2 weeks, before gestation, larvae were found in the uterus but not in either the placenta or fetus. In mice infected during pregnancy, larvae were found in the uterus and placenta from the 9th day and in the fetus from the 11th day of pregnancy, more abundantly when infected at the middle than at the earlier stages. Examination of microsections revealed larvae in both maternal sinusoidal spaces and fetal blood vessels of the placenta; though mechanical damage to the tissues and the debris of tissues were sometimes seen, larva-associated inflammation in these tissues were not observed. The results suggest that in the pregnant mouse the migration of T. canis larvae is influenced by the developmental stages of the placenta.