Role of wild rabbits as reservoirs of leishmaniasis in a non-epidemic Mediterranean hot spot in Spain.

There is limited information regarding the role of wild mammals in the transmission dynamics of Leishmania infantum. A potential human leishmaniasis hot spot was detected in southern Spain that could not be explained solely by canine leishmaniasis prevalence. The aim of this work was to analyse the involvement of wild rabbits as the main factor affecting this Mediterranean hot spot. A survey of wild rabbits, dogs and sand flies was conducted in the human cases environment. A nearby region without clinical leishmaniasis cases was used as reference control. 51 wild rabbits shot by hunters were analysed by molecular techniques. 1100 sand flies were captured and morphologically identified. Blood collected from patients' relatives/ neighbours (n = 9) and dogs (n = 66) was used for molecular analysis and serology. In Mediterranean leishmaniasis hot spots such as Montefrío municipality (average incidence of 16.8 human cases per 100,000 inhabitants/year), wild rabbits (n = 40) support high L. infantum infection rates (100%) and heavy parasite burdens (average value: 503 parasites/mg) in apparently normal ear skin directly accessible to sand flies, enabling the existence of heavily parasitized Phlebotomus perniciosus females (12.5% prevalence). The prevalence of infection and median parasite load were very low among rabbits captured in Huéscar (n = 11), a human clinical leishmaniasis-free area for the last 18 years. P. perniciosus was the most abundant Phlebotomus species in all the domestic/peridomestic microhabitats sampled, both indoors and outdoors. Accordingly, leishmaniasis is clustering in space and time at this local scale represented by Montefrío due to the proximity of two competent host reservoirs (dogs and heavily parasitized wild rabbits) associated with overlapping sylvatic and domestic transmission cycles through the main vector, P. perniciosus. We highlight the usefulness of determining the prevalence of infection and parasite burden in wild rabbits as a control leishmaniasis measure with the advantage that the use of the ear offers.

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.