1. The wild−domestic interface
Interfaces between populations are important in infectious disease
epidemiology because they are spatiotemporal points of contact at which
transmission of microbes between populations could occur, leading to
spill-over events and potentially, the emergence of infectious diseases
(Magouras et al., 2020). Understanding the characteristics of such
interfaces, how contacts and microbe transmission occurs, and can be
influenced is critical to prevent disease spread (Hassell et al., 2017).
The wildlife−domestic interface represents risks of transmission of
microbes between wild and domestic animals. Because such interfaces
involve domestic animals, they are usually anthropogenic, occurring when
people and their activities encroach on wildlife habitat (for example,
agriculture (Jori et al. (2021) or deurbanization (Ward et al., 2004)),
people bring wildlife into built environments (for example, wildlife
farming and markets; Brookes et al. (2022); Wikramanayake et al.
(2021)), or wildlife become adapted to built environments (Bradley &
Altizer, 2007).
Established wildlife−domestic interfaces for infectious disease spread
include rabies virus between wild and domestic dog populations (Lushasi
et al., 2021), Japanese encephalitis virus between waterbirds, pigs and
poultry (Mulvey et al., 2021; Walsh et al., 2022), and tuberculosis
between badgers and cattle (Chambers et al., 2014). These examples
demonstrate the diversity of reservoir and other host species, as well
as ecological landscapes in which interfaces occur. The need to
understand interfaces involving wildlife and how disease transmission
events occur has become more important over the previous few decades as
increased anthropogenic pressure on wildlife populations and their
habitats have intensified the risk of microbe transmission, resulting in
increased frequency of emergence of infectious diseases (Cunningham et
al., 2017). Recent – and well-defined – wildlife-domestic interfaces
include those at which henipaviruses have emerged, including Hendra
virus from bats to horses and Nipah virus from bats to pigs (Field et
al., 2007); but there are also less well-defined or unknown interfaces
in which a disease of animal origin might have arisen from wildlife with
a domestic livestock or farmed wildlife intermediate. Examples of the
latter include SARS and COVID-19 (SARS-CoV and SARS-coV2, respectively)
in which wildlife and interfaces with farmed animals at markets are
implicated but the specific interfaces (for example, which species were
involved) are unknown (Shi & Hu, 2008; Worobey et al.).
Disease spread models can provide insights about the circumstances in
which wildlife−domestic interfaces become important, and factors that
could limit the transmission between populations at these interfaces. A
critical limitation of such models is that they are dependent on
adequate data to produce meaningful and useful predictions. Recent
reviews demonstrate that the data required for such models or about
specific interfaces can be limited (Brookes et al., 2022; Gabriele-Rivet
et al., 2019). Defining such interfaces in terms of the species and
pathogens involved, and the extent of the interface (for example,
spatially and temporally, the abundance or density of species involved,
and the prevalence of potential pathogens) are minimum requirements, but
fundamental to useful models is quantification of the probability or
rate of effective contact such that microbe transmission could occur
between individuals.
In the following sections, we review the concepts of infectious disease
epidemiology in the context of disease spread models, then illustrate
the types of data required using the example of rabies modelling in
northern Australia and the quantification of contacts that would be
required to determine rabies spread between wild and domestic dog
populations.