Domestic dogs in indigenous Amazonian communities: Key players in Leptospira cycling and transmission?

Abstract

Background: Leptospirosis is the world's most common zoonotic disease. Mitigation and control rely on pathogen identification and understanding the roles of potential reservoirs in cycling and transmission. Underreporting and misdiagnosis obscure the magnitude of the problem and confound efforts to understand key epidemiological components. Difficulties in culturing hamper the use of serological diagnostics and delay the development of DNA detection methods. As a result, especially in complex ecosystems, we know very little about the importance of different mammalian host species in cycling and transmission to humans.

Methodology/principal findings: We sampled dogs from five indigenous Kichwa communities living in the Yasuní National Park in the Ecuadorian Amazon basin. Blood and urine samples from domestic dogs were collected to assess the exposure of these animals to Leptospira and to identify the circulating species. Microscopic Agglutination Tests with a panel of 22 different serovars showed anti-leptospira antibodies in 36 sampled dogs (75%), and 7 serogroups were detected. Two DNA-based detection assays revealed pathogenic Leptospira DNA in 18 of 19 dog urine samples (94.7%). Amplicon sequencing and phylogenetic analysis of 16S rRNA and SecY genes from 15 urine samples revealed genetic diversity within two of three different Leptospira species: noguchii (n = 7), santarosai (n = 7), and interrogans (n = 1).

Conclusions/significance: The high prevalence of antibodies and Leptospira DNA provides strong evidence for high rates of past and current infections. Such high prevalence has not been previously reported for dogs. These dogs live in the peridomestic environment in close contact with humans, yet they are free-ranging animals that interact with wildlife. This complex web of interactions may explain the diverse types of pathogenic Leptospira observed in this study. Our results suggest that domestic dogs are likely to play an important role in the cycling and transmission of Leptospira. Future studies in areas with complex ecoepidemiology will enable better parsing of the significance of genotypic, environmental, and host characteristics.

Fig 1. Geographic location of study sites in the Yasuní Biosphere Reserve.

The five Kichwa communities that were sampled are shown as grey dots: Pompeya (lat:-0.44148, long:-76.60161), Indillama (lat:-0.44281, long:-76.5184), Nueva Providencia (lat:-0.48804, long:-76.48771), Sani Isla (lat:-0.48152, long:-76.27553), and San Roque (lat:-0.45611, long:-76.20086). Dark gray color shows the boundaries for the Yasuní National Park, and the lighter gray color indicates the park buffer zone. Maps were created using ArcGIS software by ESRI (https://www.esri.com/en-us/home) ArcGIS and ArcMap are the intellectual property of ESRI and are used herein under license. Copyright Esri. All rights reserved. Base layer was obtained from: (https://wcs-global.maps.arcgis.com/ - Reserva de Biósfera Yasuní) and (https://www.portal30x30.com - Áreas Protegidas Ecuador SNAP).

Fig 2. Molecular phylogenetic analysis of a 466 bp fragment obtained by concatenating a 266 bp fragment of the 16S rRNA and a 200 bp fragment of the SecY genes.

Bootstrap values (500 replicates) > 0.90 are indicated with “*”. The tree was rooted with sequences from Leptonema illini DSM 21528 (not depicted on the tree). The samples sequenced from this project are indicated by green text.