BACKGROUND: Leishmania parasites cause leishmaniasis in humans and animals 
worldwide. These parasites are transmitted by phlebotomine sand flies, which 
become infected upon feeding on an infected mammalian host. We assessed the 
occurrence of Leishmania infection in small mammals in an area of cutaneous and 
visceral leishmaniasis endemicity.
METHODS: A total of 180 small mammals were trapped in 2003 and 2006 in a rural 
area in north-eastern Brazil. Spleen and skin samples from these animals were 
assessed by two PCR protocols, one targeting Leishmania (Viannia) spp. and other 
Leishmania (Leishmania) infantum. Additionally, serum samples were tested by an 
immunochromatographic test with rK39 as antigen.
RESULTS: Overall, 23.2% (38/164) of the animals were positive to L. (V.) spp. 
and 8.8% (14/160) to L. (L.) infantum). Five animals of four species (Didelphis 
albiventris, Nectomys squamipes, Rattus rattus and Holochilus sciureus) were 
positive by both PCR protocols, an overall co-infection rate of 2.5%. By 
serology, 5% (7/139) of the animals were positive, but all of them were 
PCR-negative. An isolate obtained from a water rat (N. squamipes) was 
characterized as L. (V.) braziliensis (zymodeme Z-74).
CONCLUSIONS: This study reinforces the involvement of different small mammals 
(e.g., N. squamipes, R. rattus and H. scieurus) in the transmission cycles of L. 
(V.) braziliensis and L. (L.) infantum in north-eastern Brazil. The finding of 
L. (V.) braziliensis infection in black rats suggests a rapid process of 
adaptation of a New World Leishmania species to an Old World rodent and raises 
interesting questions regarding the co-evolution of these parasites and their 
vertebrate hosts.