Heterogeneity in pathogen transmission: mechanisms and methodology

Abstract

Summary1. Heterogeneity in the ability of hosts to transmit pathogens is among the most fundamental concepts in disease dynamics and has major implications for disease control strategies. 2. The number of secondary infections produced by an infected individual is a function of three components: an individual's infectiousness, the rate at which it contacts susceptible individuals and the duration of infection. Individual-level variation can emerge in each of these components through a combination of behavioural and physiological mechanisms. 3. In this review, we describe mechanisms that promote variation in the number of individuals to which an individual transmits a pathogen, emphasizing insights that can be gained by understanding which components of transmission (infectiousness, contact rate, infection duration) are primarily affected. We also discuss how behavioural and physiological processes generate transmission heterogeneities across multiple scales, from individual-level variation to heterogeneity among species. 4. Strategies for quantifying each transmission component are presented, and we discuss why studies focusing on only one component of the infection process may be misleading. 5. To conclude, we describe how future research focusing on variation in transmission across all three components can provide a more holistic view of heterogeneity in pathogen transmission.

Host behaviour–parasite feedback: an essential link between animal behaviour and disease ecology

“…Parasites have recently been discussed as potential state variables that can feedback on and maintain variation in animal personality [53,54]; and animal personalities are especially promising candidates for generating feedback with parasites because they can readily create between-individual heterogeneities in the acquisition and spread of parasites [55]. In terms of parasite acquisition, bolder individuals may be more likely to encounter conspecifics or environmental sources of infection, increasing their risk of acquiring a broad suite of parasite types.…”

Covariation between the physiological and behavioral components of pathogen transmission: host heterogeneity determines epidemic outcomes

“…In disease ecology, however, the focus has largely been on variability in contact rate (β c ) (VanderWaal andEzenwa 2016, White et al 2017a), while individual heterogeneity in physiology, plasticity in behavior in response to infection, and possible covariation between behavioral and immune competence have been somewhat neglected (Barron et al 2015). The role that physiological immunity might play in superspreading has not been fully elucidated Altizer 2011, VanderWaal and, but there is evidence that some individuals are particularly vulnerable to infection (super-receivers) or particularly adept at transmitting the pathogen to others due to high infection load or shedding rates (super-shedders) (Cattadori et al 2007, Zohdy et al 2012.…”

Changes in physiological stress and behaviour in semi-free-ranging red-capped mangabeys ( Cercocebus torquatus ) following antiparasitic treatment

“…Defence strategies against parasitic diseases include avoidance (behavioural mechanisms that reduce risk of exposure), resistance (immune response that reduces pathogen burden) and tolerance (multiple mechanisms that reduce susceptibility to fitness costs by limiting damage caused by the pathogen) [8]. Investment in avoidance and tolerance strategies, compared with resistance, has important implications for host infectiousness [9].…”