Where the Wild Things Aren’t: Loss of Biodiversity, Emerging Infectious Diseases, and Implications for Diagnosticians, Granter 2016

This status-quo-challenging editorial is written for the American Society of Clinical Pathology, a group seemingly unrelated to the Bio4Climate community. The authors suggest that medical training in pathology over-emphasizes oncology at the expense of an adequate coverage of infectious disease, even though “between 1940 and 2004, a total of 335 human infectious diseases ‘emerged,’ and 60% of these were zoonotic” [Granter 2016: 645]. Having explained biodiversity loss as a factor driving disease rates, the authors make a plea for diagnosticians to become aware of the human health implications of environmental destruction.

Knowledge and prowess with infectious diseases for diagnosticians must be incorporated back into training with a reimagined lens crafted from the information we have gained by studying our environment, its destruction, and the ultimate resulting human infections. As loss of habitat, habitat fragmentation, and consequent biodiversity loss continue unabated, tools and skills will need to be in the hands of all diagnosticians if we hope to minimize the effect of these infections as they continually emerge [Granter 2016: 645].

This paper provides a particularly clear explanation of how biodiversity loss increases human infection risk.

The relationship between loss of biodiversity and human disease was first illustrated by Lyme disease. Its cause, the Borrelia burgdorferi bacterium, has the opportunity to encounter numerous vertebrate hosts – in one study estimated to be at least 125 species – in a diverse and healthy ecosystem. The potential hosts vary tremendously in their ability to harbor and transmit the bacteria, that is, their “reservoir competence.” Studies estimate the white-footed mouse infects more than 90% of ticks that complete their blood meal. While a few other hosts, such as eastern chipmunks and short-tailed shrews, are moderately competent, most tick hosts are marginally competent or dead-end hosts that are highly unlikely to transmit the infection. Since the white-footed mouse tends to thrive in impoverished ecosystems lacking biodiversity, infected ticks and, consequently, risk of human infection show a strong negative relationship with biodiversity. Because a diverse ecosystem with a range of vertebrate hosts – including many incompetent and dead-end hosts – “dilutes” the representation of the white-footed mouse and reduces human infection risk, this phenomenon has been termed the dilution effect [Granter 2016: 644].