Vertical transmission may play a greater role in the spread of Leishmania infantum in synanthropic Mus musculus rodents than previously believed.

Vertical transmission of Leishmania infantum was demonstrated in domestic mice captured close to the home of a patient with leishmaniasis. Leishmania infantum DNA was detected in 88.9% of synanthropic Mus musculus adult rodents and 29.2% of their unborn foetuses. Mother-to-infant transmission was observed in all females whose gestational stage was sufficiently advanced to allow foetal analysis (foetal length 2-2.5 cm). The infection rate in foetal samples ranged from 11.1% to 50.0%, with parasite loads of up to 6,481 parasites/5 mg tissue. A low density of Phlebotomus perniciosus was also found (0.2 specimen/CDC trap). Six infected mice captured in March were only 1.5 months old and could thus not have had contact with the vector. Vertical transmission thus appears to play a greater role in the spread of leishmaniasis than previously thought, particularly since rodents are natural hosts for the parasite and are prolific in nature.