Abstract
Catastrophic declines in African great ape populations due to disease outbreaks have been reported in recent years, yet we rarely hear of similar disease impacts for the more solitary Asian great apes, or for smaller primates. We used an age-structured model of different primate social systems to illustrate that interactions between social structure and demography create ‘dynamic constraints’ on the pathogens that can establish and persist in primate host species with different social systems. We showed that this varies by disease transmission mode. Sexually transmitted infections (STIs) require high rates of transmissibility to persist within a primate population. In particular, for a unimale social system, STIs require extremely high rates of transmissibility for persistence, and remain at extremely low prevalence in small primates, but this is less constrained in longer-lived, larger-bodied primates. In contrast, aerosol transmitted infections (ATIs) spread and persist at high prevalence in medium and large primates with moderate transmissibility;, establishment and persistence in small-bodied primates require higher relative rates of transmissibility. Intragroup contact structure – the social network - creates different constraints for different transmission modes, and our model underscores the importance of intragroup contacts on infection prior to intergroup movement in a structured population. When alpha males dominate sexual encounters, the resulting disease transmission dynamics differ from when social interactions are dominated by mother-infant grooming events, for example. This has important repercussions for pathogen spread across populations. Our framework reveals essential social and demographic characteristics of primates that predispose them to different disease risks that will be important for disease management and conservation planning for protected primate populations.
Highlights
Recent catastrophic declines in African gorilla and chimpanzee populations have illustrated the impact that infectious disease can have on wild populations [1,2,3,4], yet we rarely hear of similar disease impacts to Asian great apes, or to smaller primates
Our model revealed a non-intuitive trend: as population turnover decreased, there was a general trend of increasing R0
If infection leads to mortality, higher R0 can lead to faster ‘burn out’ of hosts, whereas lower R0 (1.25.R0.1.0) can promote low-level, long term persistence [45,46]. Transient dynamics of this type in a metapopulation are relevant to management of pathogen outbreaks in populations of endangered primate species; our analysis suggests that slowing the spread of infection is more important than waiting for an endpoint, or natural die-off; as this might take a significant period of time
Summary
Recent catastrophic declines in African gorilla and chimpanzee populations have illustrated the impact that infectious disease can have on wild populations [1,2,3,4], yet we rarely hear of similar disease impacts to Asian great apes, or to smaller primates. We developed an age-structured model framework for different primate species to examine how the interaction between social system and demography predisposes them to invasion by a potentially lethal pathogen that produces no immunity, such as a novel spillover pathogen like Ebola [3] or circulating human respiratory pathogens [1]. We hypothesize that a combination of social structure and demography predispose some primates to greater disease impact, and that pathogen transmission mode is central to this. We hypothesize that large primates with complex group structures (social systems that involve more than a mating pair and their respective offspring, as in solitary and monogamous systems) are more likely to sustain pathogens with frequency dependent transmission, than will smaller primates with similar group structures, or large primates with simpler, less polygamous, social structures
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