Implications of Host Genetic Variation on the Risk and Prevalence of Infectious Diseases Transmitted Through the Environment

Abstract

Previous studies have shown that host genetic heterogeneity in the response to infectious challenge can affect the emergence risk and the severity of diseases transmitted through direct contact between individuals. However, there is substantial uncertainty about the degree and direction of influence owing to different definitions of genetic variation, most of which are not in line with the current understanding of the genetic architecture of disease traits. Also, the relevance of previous results for diseases transmitted through environmental sources is unclear. In this article a compartmental genetic–epidemiological model was developed to quantify the impact of host genetic diversity on epidemiological characteristics of diseases transmitted through a contaminated environment. The model was parameterized for footrot in sheep. Genetic variation was defined through continuous distributions with varying shape and degree of dispersion for different disease traits. The model predicts a strong impact of genetic heterogeneity on the disease risk and its progression and severity, as well as on observable host phenotypes, when dispersion in key epidemiological parameters is high. The impact of host variation depends on the disease trait for which variation occurs and on environmental conditions affecting pathogen survival. In particular, compared to homogeneous populations with the same average susceptibility, disease risk and severity are substantially higher in populations containing a large proportion of highly susceptible individuals, and the differences are strongest when environmental contamination is low. The implications of our results for the recording and analysis of disease data and for predicting response to selection are discussed.

A Flexible Spatial Framework for Modeling Spread of Pathogens in Animals with Biosurveillance and Disease Control Applications

“…There are many things that impact the spread of an infectious disease epidemic in animals that include host genetics [60] and the environment [61]-with potential implications for impacting disease spread associated with climate change [62]. However, using appropriately scaled models to match the data collected from previous epidemics and observed disease characteristics can help alleviate the impacts of these micro impacts on overall simulations.…”

On the definition and utilization of heritable variation among hosts in reproduction ratio R0 for infectious diseases

“…Schliekelman (2007) seems to be the first who used rigorous mathematical modelling to investigate the impact of kin selection on the frequency of mutant alleles conferring resistance to the host. Moreover, despite the evidence of heterogeneity in infectivity (Woolhouse et al, 1997;Lloyd-Smith et al, 2005;Doeschl-Wilson et al, 2011), little attention has been given to the effect of kin selection on the frequency of alleles affecting infectivity in the host population. Our simulations show that, at least in theory, kin selection can greatly accelerate the evolution of R 0 , because it utilizes the indirect genetic variance in both susceptibility and infectivity in the host population.…”

MHC class II diversity of koala (Phascolarctos cinereus) populations across their range

“…A novel pathogen could potentially threaten entire populations that lack the necessary MHCII diversity to adapt (O'Brien and Evermann, 1988;Doeschl-Wilson et al, 2011). Climate change, combined with anthropogenic factors, may increase the risk of arthropod-borne diseases (Gubler et al, 2001) and, if this increases exposure of southern populations of koalas to arthropod vectors, their potential to become reservoirs for zoonotic pathogens may increase.…”

“…In particular, chlamydiosis is the most common infectious disease of koalas, inducing proliferative conjunctivitis and urogenital tract disease (Cockram and Jackson, 1974;Obendorf, 1981), and is present in most koala populations, besides some offshore islands (Martin and Handasyde, 1999). Second, host genetic diversity may be important for population-wide defense against new pathogens and emerging diseases (Yates et al, 2006;Doeschl-Wilson et al, 2011). Koalas with low genetic diversity could become potential reservoirs for emerging pathogens and therefore a biosecurity risk to livestock and human populations as a result of increased habitat overlap from anthropogenic or environmental changes (Daszak et al, 2000).…”