Date Published: December 11, 2014
Publisher: Public Library of Science
Author(s): Renata Cássia-Pires, Mariana C. Boité, Paulo S. D’Andrea, Heitor M. Herrera, Elisa Cupolillo, Ana Maria Jansen, André Luiz R. Roque, Gabriele Schönian. http://doi.org/10.1371/journal.pntd.0003389
Abstract: BackgroundCaviomorph rodents, some of the oldest Leishmania spp. hosts, are widely dispersed in Brazil. Despite both experimental and field studies having suggested that these rodents are potential reservoirs of Leishmania parasites, not more than 88 specimens were analyzed in the few studies of natural infection. Our hypothesis was that caviomorph rodents are inserted in the transmission cycles of Leishmania in different regions, more so than is currently recognized.MethodologyWe investigated the Leishmania infection in spleen fragments of 373 caviomorph rodents from 20 different species collected in five Brazilian biomes in a period of 13 years. PCR reactions targeting kDNA of Leishmania sp. were used to diagnose infection, while Leishmania species identification was performed by DNA sequencing of the amplified products obtained in the HSP70 (234) targeting. Serology by IFAT was performed on the available serum of these rodents.Principal findingsIn 13 caviomorph rodents, DNA sequencing analyses allowed the identification of 4 species of the subgenus L. (Viannia): L. shawi, L. guyanensis, L. naiffi, and L. braziliensis; and 1 species of the subgenus L. (Leishmania): L. infantum. These include the description of parasite species in areas not previously included in their known distribution: L. shawi in Thrichomys inermis from Northeastern Brazil and L. naiffi in T. fosteri from Western Brazil. From the four other positive rodents, two were positive for HSP70 (234) targeting but did not generate sequences that enabled the species identification, and another two were positive only in kDNA targeting.Conclusions/SignificanceThe infection rate demonstrated by the serology (51.3%) points out that the natural Leishmania infection in caviomorph rodents is much higher than that observed in the molecular diagnosis (4.6%), highlighting that, in terms of the host species responsible for maintaining Leishmania species in the wild, our current knowledge represents only the “tip of the iceberg.”
Partial Text: More than 30 species within the Leishmania genus (Trypanosomatidae, Trypanosomatida) are recognized, including both extremely specific as well as generalist species transmitted by a variety of Phlebotomine vectors worldwide – In fact, several Leishmania species are multi-host parasites that infect mammal species of different orders, including humans –. The diversity of Leishmania species, mammal hosts and environments in which the transmission occurs reveals a complex system. Leishmaniasis has an important impact on public health since it results in a spectrum of debilitating diseases, which can progress to very severe, even fatal cases. In Brazil, human cutaneous leishmaniasis is associated with at least six different species of the subgenus Leishmania (Viannia) besides Leishmania (Leishmania) amazonensis, while the visceral form is exclusively associated with Leishmania (L.) infantum–.
We found 17 caviomorph rodents (4.6%) positive in the PCR directed to Leishmania sp. kDNA. From these, 15 samples were also positive when tested for HSP70 (234) primers, two directly after the PCR and 13 only after the re-amplification of the product obtained in the first PCR reaction (Fig. 1). DNA sequencing analyses allowed the identification of −4 species of the subgenus Leishmania (Viannia) and −1 species of the subgenus Leishmania (Leishmania) in samples of 13 caviomorph rodents (Fig. 2, Table 2). In five situations, the DNA sequence analysis revealed identity values above 95% for more than one Leishmania species and we opted not to define one of them as the etiological agent. A single sample (one Thrichomys laurentius from Piauí) displayed different DNA sequences that presented high values of similarity with distinct species of Leishmania in two consecutive reactions. This was considered as result of a hybrid population or mixed infection. Leishmania infection was observed in five caviomorph rodent species captured in two municipalities belonging to Pantanal and in two belonging to Caatinga biomes (Fig. 2). In the Pantanal, 7 animals were positive for Leishmania spp and the identification of the Leishmania species was possible in 4 of them: one T. fosteri captured in Corumbá, was found infected by L. (V). naiffi while L. (L). infantum was found infecting one Dasyprocta azarae and two Clyomys laticeps in Aquidauna and Corumbá, respectively. Also in Corumbá, we were unable to identify the Leishmania species infecting one T. fosteri because the analysis of the parasite DNA sequence revealed similarity with two Leishmania species (L. (V). naiffi and L. (V). braziliensis).
A clear expansion of leishmaniasis around the country has been observed in the last decades , –. From the different reasons already proposed to explain this expansion, a common point is the recognition that we still have poor knowledge of some aspects of the biology and epidemiology of Leishmania species, which, in the end, result in inefficient control strategies. The mammalian hosts of most Leishmania species are still poorly understood, which reinforces the need for studies that verify the distribution of these parasites in other mammalian taxa beyond those classically reported as reservoirs. Caviomorph rodents comprise an enormous group of species that exploit different habitats, and also include some species already domesticated by humans, such as the chinchilla and the guinea pig (Cavia spp.) .