Anthropogenic Influence on Prevalence of 2 Amphibian Pathogens

To the Editor: Although the relationship between the emergence of zoonotic diseases and human infl u-enced landscapes is accepted (1–3), the relationship between human-in-fl uenced landscapes and wildlife disease is less so. Evidence does support correlations between human activities and environmental conditions affecting wildlife disease emergence (2,3). These studies assume relationships between component(s) of human habitat modifi cation and the virulence of disease, and derive estimates of viru-lence from counts of the visibly diseased or those that have seroconverted (3). This explains only part of the host and pathogen dynamic; it seems reasonable to extend the relationship to include prevalence of infection. Data supporting this extension are lacking. Here we present data from a study examining the correlations between human infl uences on habitat and prevalence of 2 amphibian pathogens (Batrachochytrium dendrobatidis and ranavirus FV3) in populations of Rana clamitans in central and northeastern Ontario, Canada. We sampled an average of 25 animals (standard deviation ± 6.16) from 11 populations during summer 2005. We washed equipment in bleach and air-dried equipment between visits and sites. All animals were kept individually to avoid cross-contamination , euthanized with MS22, and assessed for infection using molecular diagnostics. We tested for ranavirus infection of livers by amplifying the major capsid protein using standard PCR (4). We tested for infection with B. dendrobatidis by using a quantitative real-time PCR (5). Prevalence for each pathogen was estimated as the proportion of animals testing positive at a pond. Site coordinates were determined by using global positioning satellite (GPS), and 4 quantitative measures of human habitat modifi cation were also assessed. GPS coordinates were used to map sites and to measure distance to the nearest road, industrial activity (agriculture, mine, paper mill), and human habitation; all measurements were in meters. We further assigned a qualitative measure of human infl u-ence on each breeding pond by assigning ponds to each of the following categories: 1) human presence without human habitat modifi cation or extensive disturbance; 2) recreational activities (fi shing, boating); 3) property development (housing or commercial buildings); 4) agricultural activity; and 5) industrial activity. Each of the 5 categories was assigned a 0/1 score; scores for each pond were summed 1–5 (by defi nition no site scored 0 due to sampling strategy) to derive the fi nal measure of human infl uence. We modeled the relationship between prevalence and human habitat modification or infl uence using general linear …