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Pregnancy is associated with reactivation of latent infections of many protozoal and helminthic parasites. To facilitate in vivo studies on the process of transmammary transmission of hookworm infection to nursing newborns, we established an experimental model of infection of BALB/c mice with infective larvae of the canine nematode Ancylostoma caninum. To establish latency with a significant reservoir of tissue larvae and achieve acceptable pregnancy success rates, mice were subcutaneously infected at day 5 postimpregnation; similar larval distribution profiles were observed at the end of the gestational period for bred compared to correspondingly infected unbred animals. No larvae were detected in fetuses or neonatal pups. Significant numbers of larvae were not detected in mammary tissue during the periparturient or postpartum lactational periods although about 8% of a dam's reservoir of tissue larvae was transferred to her nursing pups; this suggests that larvae reaching the mammary glands are rapidly transmitted through the milk sinuses, as was documented by histopathological analyses. Comparison of BALB/c with C57BL/6 mice that typically display divergent immune responses to infection showed no difference in tissue larval burden or in numbers transferred to pups. A hypothesis for the molecular mechanism of larval reactivation and transmission is discussed.

It was investigated whether there is a linear correlation between the number of applied infective larvae of Ancylostoma caninum and the number of larvae excreted by bitches with the milk. The investigations were carried out with nine bitches that were infected percutaneously each with 5,000, 10,000 or 20,000 third stage larvae of Ancylostoma caninum at the day of conception. A clear linear correlation between the number of applied infective larvae of Ancylostoma caninum and the number of larvae excreted with the milk could be demonstrated only for the first week of lactation. Regarding the total investigated period of 28 days only a tendency towards such a correlation between infective dosage and excretion of larvae with the milk could be found.

The infectivity and migratory pattern of Ancylostoma ceylanicum infective larvae (L3) were investigated in hamsters infected by various routes. Following oral administration 40-70% of L3 attained maturity and there was no tissue migration. Following subcutaneous inoculation a small number (1-1.2%) of L3 attained maturity in the intestine after completing the broncho-oesophageal journey. Larvae which penetrated the skin also became adult in the intestine. Most of the larvae entering parenterally remained at the site of infection and in the tracheal region for more than 100 days without undergoing any development, other than desheathment. Those transmitted orally to naive hamsters developed in the normal way. Larvae inoculated parenterally into female hamsters were able to infect offspring in milk, but could not cross the placental barrier.