Leptospira interrogans in Rodents from Cape Verde

Introduction

Leptospirosis is an important zoonotic disease with a worldwide distribution (Levett 2001) caused by spirochetes belonging to the genus Leptospira (order Spirochaetales) (Farr 1995). Both animals and humans acquire the infection through contact with water or soil contaminated with the urine of infected animals or by direct contact with these animals (Levett 2001, Adler and de la Pena Moctezuma 2010). In most cases, leptospirosis in humans is a nonspecific self-limiting febrile illness, but some patients can develop a severe form that includes a severe pulmonary hemorrhagic syndrome and renal failure with a high mortality (Plank and Dean 2000).

A large variety of wild and domestic mammals have been described as Leptospira reservoirs, but rodents are believed to be the main reservoirs (Cosson et al. 2014). This fact highlights the importance of alien rodent control by humans and native predators on island habitats in the context of pest and disease control. In Cape Verde islands, serological tests for leptospirosis have shown the presence of antibodies against Leptospira spp. both in humans and domestic animals, although antibodies were not found in wild living mammals (Sebek et al. 1989). The seroprevalence found by Sebek et al. (1989) was 7.2% in humans and 3.1% in domestic animals. Considering these facts, the aim of this study was to analyze the presence of Leptospira in rodents in Cape Verde, detecting natural foci of leptospirosis, and to genetically characterize Leptospira spp. circulating within Santiago, to identify the severity of the diseases that they could be causing.

Materials and Methods

The study was carried out in Santiago Island, Cape Verde, in 2012–2013. A total of 62 wild rodents (36 Rattus rattus and 26 Mus domesticus) were captured at urban, Praia, and rural, Sao Domingos and Assomada, areas of the island. Animals were euthanized and urinary bladders were collected and preserved in absolute ethanol.

The lipL32 gene, which is present only in pathogenic leptospires, was amplified following Levett et al. (2005). Amplifications were performed in a Labnet thermocycler (Labnet International, Berkshire, United Kingdom). Nucleotide sequences were obtained at Macrogen, Inc. (Seoul, Korea), and the obtained sequences were analyzed by BLAST (http://blast.ncbi.nlm.nih.gov/Blast.cgi). A phylogenetic tree was constructed by the neighbor-joining method by employing the Kimura two-parameter model in MEGA 6 software (www.megasoftware.net/).

The χ ² test was used to determine statistical differences in the prevalence of Leptospira spp. among host species and islands.

Results

Sixteen samples were positive for pathogenic Leptospira spp. Therefore, the overall prevalence detected was 25.8% (95% CI: 16.6–37.9). The prevalence was higher in M. domesticus (34.6%; 95% CI: 19.4–53.8) than in R. rattus (19.4%; 95% CI: 9.75–35), but without significant differences. Rodents with Leptospira were found in the three localities analyzed with similar prevalences (Table 1), no significant differences were found. Ten identical sequences were successfully obtained, four from R. rattus from Sao Domingos (3) and Praia (1), and six from M. domesticus from Sao Domingos (5) and Assomada (1). Sequences were submitted to the GenBank database, under the accession numbers KT821084 for R. rattus and KT821085 for M. domesticus. The BLAST analyses showed 99% identity of this lipL32 sequence with different serovars of Leptospira interrogans published in GenBank. The neighbor-joining phylogenetic tree placed these sequences in the L. interrogans clade, which was separated from the rest of pathogenic Leptospira species (87% bootstrap) (data not shown).

Discussion

These results indicate a wide distribution of Leptospira in the environment and the role of rodents as important reservoir hosts in the epidemiology of leptospirosis in Cape Verde. Both rats and mice were infected with the same Leptospira species, contrarily to what we observed in the close archipelago the Canary Islands, where rats were infected by L. interrogans and mice by Leptospira borgpetersenii (Foronda et al. 2011).

Although leptospires have a worldwide distribution, these bacteria survive longest periods in tropical and subtropical areas (Levett 2001) as Cape Verde. The zoonotic potential of this finding is underlined by the fact that the species found in this study, L. interrogans, has been associated with the most severe form of leptospirosis, the Weil's disease (Vijayachari et al. 2008), that can be fatal (Plank and Dean 2000). Furthermore, the ability of L. interrogans to survive in a variety of different environments is higher than that showed by other Leptospira species, such as L. borgpetersenii (Bulach et al. 2006). In contrast, the socioeconomic constraints affecting Cape Verde may imply an increase of the number of Leptospira-infected rodents and human-rodent contacts. In this sense, it is common to see people walking barefoot in the sampling areas, which increases the risk of being infected. Taking all together, this study suggests that rodents could play an important role in the transmission of human leptospirosis in Cape Verde. However, further studies are needed to increase the knowledge about the distribution of Leptospira spp. in the other islands of Cape Verde and to identify other possible circulating species.

Conclusions

Pathogenic L. interrogans was identified in two species of rodents with a wide distribution in Cape Verde, highlighting a serious health risk for the population.