Small Mammals as Carriers/Hosts of Leptospira spp. in the Western Amazon Forest

Abstract

Leptospira is a bacteria that causes leptospirosis and is transmitted through water, soil, or mud that is contaminated by the urine of infected animals. Although it is mainly associated with the urban environment, Leptospires also circulate in rural and wild environments. This study aimed to investigate the role of small mammals in leptospirosis epidemiology in the western Amazon, Brazil. In total, 103 animals from 23 species belonging to the orders Didelphimorphia and Rodentia were captured. Blood, kidney, and urine samples were collected and Microscopic Agglutination Test (MAT), lipL32 PCR, secY sequencing, and culturing were conducted. MAT was reactive on 1/15 sera, and no bacterial isolate was obtained. PCR yielded 44.7% positive samples from 16 species. Twenty samples were genetically characterized and identified as L. interrogans (n = 12), L. noguchii (n = 4), and L. santarosai (n = 4). No statistical association was found between the prevalence of infection by Leptospira spp. in small mammals within carrier/hosts species, orders, study area, and forest strata. Our results indicate a high prevalence of pathogenic Leptospira spp. in several rodent and marsupial species and report the first evidence of Leptospira spp. carrier/hosts in the Brazilian Western Amazon.

Keywords: Amazon; marsupial; small mammal; sylvatic leptospirosis; wild rodent.

Figure 1

The four study areas located in the state of Acre. Floresta do Seringal Cachoeira (FSC): a continuous and conserved primary forest, Reserva Florestal Humaitá (RFH): a wide fragment of a primary rain forest, Floresta do Parque Zoobotânico (FPZ): an urban small fragment, and Floresta Experimental Catuaba (FEC): a secondary forest with agriculture.

Figure 2

Small mammals (A: Didelphimorphia; B: Rodentia) included in the present study according to study area (shown by different colors as indicated in the figure). Samples positive for pathogenic Leptospira, detected by lipL32 gene amplification, are indicated by a (+) sign. Columns at right show prevelance values for each host. Pathogenic Leptospira prevalence on Didelphimorphia (C) and Rodentia (D) of each collection site are also presented. *Species with first Leptospira DNA detection. **Species already described as carrier hosts of Leptospira by Bunnell at al. (29) and Cortez et al. (30). Species for which all samples were negative for Leptospira have no asterisk. Study areas located in the state of Acre: Floresta do Seringal Cachoeira (FSC), Reserva Florestal Humaitá (RFH), Floresta do Parque Zoobotânico (PPZ), and Floresta Experimental Catuaba (FEC).

Figure 3

Maximum likelihood phylogenetic tree inferred from partial secY gene sequences (410 bp) of L. interrogans, L. noguchii, and L. santarosai from this study (bold and underlined) and GenBank sequences from other carrier/hosts (accession numbers are shown). Hosts are indicated by vectors and geographical locations by colors, as indicated in the figure. Numbers at nodes are bootstrap values >50%. Leptospira biflexa strain “Patoc” is the outgroup taxa.