Leishmania infantum in wild rodents: reservoirs or just irrelevant incidental hosts?

Wild rodents constitute a very large biomass of potential reservoirs for Leishmania spp. Therefore, an epidemiological study was carried out in a well-known focus of canine leishmaniasis from southern Spain, with the objective of detecting and characterizing Leishmania infantum infection in wild rodents. Blood, liver, spleen, bone marrow, and skin from 37 rodents (24 Apodemus sylvaticus, 9 Rattus rattus, and 4 Mus musculus) were analyzed by optical microscopy, culture, and two different polymerase chain reactions. L. infantum DNA was found in 27% (10 out of 37) of the trapped rodents, in a variety of tissues: bone marrow, spleen, or healthy skin (ear lobe). High prevalences of L. infantum infection were found in the three investigated rodent species. The presence of other trypanosomatids was also evidenced. These rodent species are abundant, widely distributed in Europe, and have a long enough lifespan to overcome the low sandfly activity season. They live in a suitable habitat for sandflies and serve as blood sources for these insects, which can become infected when induced to feed on Leishmania-infected animals. Whether they are reservoirs or just irrelevant incidental hosts, it is clear that the epidemiology of L. infantum is more complex than previously thought, and so is its control. The classic epidemiological cycle dog-sandfly-human is turning into a network of animal species that collaborate with the dog in the maintenance of the parasite under natural conditions and probably showing local differences.