Relevance of Indirect Transmission for Wildlife Disease Surveillance

Abstract

Epidemiological models of infectious diseases are essential tools in support of risk assessment, surveillance design, and contingency planning in public and animal health. Direct pathogen transmission from host to host is an essential process of each host–pathogen system and respective epidemiological modeling concepts. It is widely accepted that numerous diseases involve indirect transmission (IT) through pathogens shed by infectious hosts to their environment. However, epidemiological models largely do not represent pathogen persistence outside the host explicitly. We hypothesize that this simplification might bias management-related model predictions for disease agents that can persist outside their host for a certain time span. We adapted an individual-based, spatially explicit epidemiological model that can mimic both transmission processes. One version explicitly simulated indirect pathogen transmission through a contaminated environment. The second version simulated direct host-to-host transmission only. We aligned the model variants by the transmission potential per infectious host (i.e., basic reproductive number R0) and the spatial transmission kernel of the infection to allow unbiased comparison of predictions. The quantitative model results are provided for the example of surveillance plans for early detection of foot-and-mouth disease in wild boar, a social host. We applied systematic sampling strategies on the serological status of randomly selected host individuals in both models. We compared between the model variants the time to detection and the area affected prior to detection, measures that strongly influence mitigation costs. Moreover, the ideal sampling strategy to detect the infection in a given time frame was compared between both models. We found the simplified, direct transmission model to underestimate necessary sample size by up to one order of magnitude but to overestimate the area put under control measures. Thus, the model predictions underestimated surveillance efforts but overestimated mitigation costs. We discuss parameterization of IT models and related knowledge gaps. We conclude that the explicit incorporation of IT mechanisms in epidemiological modeling may reward by adapting surveillance and mitigation efforts.

The Risk of Foot and Mouth Disease Transmission Posed by Public Access to the Countryside During an Outbreak

“…If susceptible livestock are exposed to FMDV they may become infected. The likelihood that exposure of susceptible livestock to FMDV in the environment results in infection is not well-characterized (51), but is likely to vary by species, the virus dose exposed to and transmission route. When considering the infection of susceptible livestock via contaminated environment, the transmission route could be aerosol or oral.…”

Spores and soil from six sides: interdisciplinarity and the environmental biology of anthrax (Bacillus anthracis)

“…In this respect, it is interesting to note that B. subtilis recently has been shown to protect plants against bacterial pathogens in the plant rhizosphere, and that the protective effect requires biofilm formation (Beauregard et al, 2013;Chen et al, 2013). Although knowledge is lacking about a potential role for B. anthracis biofilm formation, in the rhizosphere or during infection, the bacterium is capable of biofilm formation in vitro (Lee et al, 2007).…”

“…As many pathogens like plague utilize several transmission strategies, and may not rely primarily on environmental transmission (see Fig. 1), modelling efforts for many pathogens may miss important dynamics if they exclude the occasional environmental route (Tien & Earn, 2010;Lange, Kramer-Schadt & Thulke, 2016;Mata, Greenwood & Tyson, 2017;McCallum et al, 2017).…”

Domestic Dogs and Wild Foxes Interactions in a Wildlife-Domestic Interface of North-Central Chile: Implications for Multi-Host Pathogen Transmission

“…Direct interactions involve spatial and temporal co-occurrence and often a specific behavioral interaction, while indirect interactions only require spatial co-occurrence of reservoir and susceptible hosts within a certain time window ( 3 ). The second may determine indirect cross-species transmission of several environmentally-resistant pathogens (including viruses, bacteria, and macro parasites), where the interacting hosts would be exposed to the contaminated environments they share ( 4 – 6 ).…”