Impacts of biodiversity on the emergence and transmission of infectious diseases, Keesing et al. 2010

Compendium Volume 4 Number 1 July 2020

This paper contextualizes reduced transmission of infectious disease as one of the many ecosystem services provided by biodiversity. Changes in biodiversity affect infectious disease transmission by changing the abundance of the host and/or vector; the loss of non-host species may increase the density of host species, increasing the encounter rates between pathogen and host.

Often, the species that remain when biodiversity is lost are those which are better pathogen hosts, while the lost species tend to be more resistant to infectious disease.

In several case studies, the species most likely to be lost from ecological communities as diversity declines are those most likely to reduce pathogen transmission [Keesing 2010: 648].

For example, the white-footed mouse, which are high-quality hosts both for the bacteria causing Lyme Disease and for the tick vectors, are abundant in both biodiverse systems and impoverished systems, while opossums, a poorer host for the Lyme bacterium that also kill/eat most ticks attempting to feed on them, do poorly in lower-biodiversity conditions.

Therefore, as biodiversity is lost, the host with a strong buffering effect – the opossum – disappears, while the host with a strong amplifying effect – the mouse – remains [Keesing 2010: 650].

There may be a causal link between a species’ susceptibility to biodiversity loss and its quality as a disease host. Among vertebrates,

resilience in the face of disturbances that cause biodiversity loss, such as habitat destruction and fragmentation, is facilitated by life history features such as high reproductive output and intrinsic rates of increase. Vertebrates with these features tend to invest minimally in some aspects of adaptive immunity; we hypothesize that this may make them more competent hosts for pathogens and vectors [Keesing 2010: 650].

Biodiversity also affects the emergence of infectious disease, such as the evolution of a new strain of pathogen in the same host (due to antibiotic resistance, for example), and the spillover to a new host species. Pathogen establishment in humans from other animal hosts is related to mammal species richness (a larger source pool), and land-use change (such as deforestation), which increases contact between humans and pathogen hosts. The pathogen then becomes an epidemic due to the new host species’ density (domesticated animals and humans).

The authors recommend preserving biodiversity by protecting natural habitat, while also preserving microbial diversity within organisms by limiting the use of antimicrobial agents. A diverse microbiome within an organism serves as a buffer against pathogens.

Keesing, F., et al., 2010, Impacts of biodiversity on the emergence and transmission of infectious diseases, Nature 468,

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