Association between anthropization and rodent reservoirs of zoonotic pathogens in Northwestern Mexico.

The world is facing a major pulse of ecological and social changes that may favor the risk of zoonotic outbreaks. Such risk facilitation may occur through the modification of the host's community diversity and structure, leading to an increase in pathogen reservoirs and the contact rate between these reservoirs and humans. Here, we examined whether anthropization alters the relative abundance and richness of zoonotic reservoir and non-reservoir rodents in three Socio-Ecological Systems. We hypothesized that anthropization increases the relative abundance and richness of rodent reservoirs while decreasing non-reservoir species. We first developed an Anthropization index based on 15 quantitative socio-ecological variables classified into five groups: 1) Vegetation type, 2) Urbanization degree, 3) Water quality, 4) Potential contaminant sources, and 5) Others. We then monitored rodent communities in three regions of Northwestern Mexico (Baja California, Chihuahua, and Sonora). A total of 683 rodents of 14 genera and 27 species were captured, nine of which have been identified as reservoirs of zoonotic pathogens (359 individuals, 53%). In all regions, we found that as anthropization increased, the relative abundance of reservoir rodents increased; in contrast, the relative abundance of non-reservoir rodents decreased. In Sonora, reservoir richness increased with increasing anthropization, while in Baja California and Chihuahua non-reservoir richness decreased as anthropization increased. We also found a significant positive relationship between the anthropization degree and the abundance of house mice (Mus musculus) and deer mice (Peromyscus maniculatus), the most abundant reservoir species in the study. These findings support the hypothesis that reservoir species of zoonotic pathogens increase their abundance in disturbed environments, which may increase the risk of pathogen exposure to humans, while anthropization creates an environmental filtering that promotes the local extinction of non-reservoir species

GLMM’s prediction plots of the effect of anthropization on the RA of rodents.

(A) Predicted probabilities for reservoir species and (B) predicted probabilities for non-reservoir species in BC+CHI. Grey shadows represent CI 95%.</p

Variables contribution plot.

Contribution of the six variables that contributed the most in PC1. The red dashed line indicates the expected average contribution. (TIFF)</p

Results of the GLMMs to test for the association between RA and richness of reservoir and non-reservoir species.

The model output includes the estimates for the fixed and random effects. Numbers in bold indicate significant values.</p

Map of Northwestern Mexico and the study sites.

The buffers that correspond to Baja California are shown in green, Sonora in purple, and Chihuahua in cyan. Boxes represent sites characterized by predominant native (A) vegetation, (B) cropland or livestock, and (C) urban/peri-urban areas. Reprinted from the OpenStreetMap vector basemap hosted by Environmental Systems Research Institute (Esri) and provided under a CC BY 4.0 license (Map data © OpenStreetMap contributors, Map layer by Esri 2019).</p

Anthropization variables.

We evaluated 15 variables classified into five groups. Most of the variables were derived from repositories and databases.</p

Overdispersion evaluation for GLMM with Poisson distribution.

Overdispersion evaluation for GLMM with Poisson distribution.</p

PCA-Biplot of variables and sites.

The small symbols represent the sites in each region and are contained in an ellipse, representing the 95% Confidence Intervals (CI) for each region. The larger, centered symbols in each ellipse represent the average of the scores for each region.</p

S1 File -

Database of a) site coordinates, b) Anthropization Index variables, c) anthropization degree of sites, and d) rodent monitoring. (XLSX)</p

GLMM’s prediction plot of rodent richness.

Predicted counts of the association between anthropization and non-reservoir richness in BC+CHI. Grey shadows represent CI 95%.</p