Biodiversity and Disease Risk: the Case of Lyme Disease

TLDR

Biodiversity is valued for its medicinal and research benefits, yet the idea that species diversity itself can reduce disease exposure is underexplored; in Lyme disease, many ticks remain uninfected because some hosts, like the white‑footed mouse, are highly competent reservoirs, and the interaction between host competence and tick specialization shapes disease risk. The study proposes a conceptual model linking high vertebrate species richness and evenness to reduced Lyme disease exposure risk. The model posits that greater host diversity dilutes the white‑footed mouse’s transmission ability by diverting tick feeding to less competent reservoirs. Empirical analyses along the U.S.

Abstract

Abstract: Utilitarian arguments concerning the value of biodiversity often include the benefits of animals, plants, and microbes as sources of medicines and as laboratory models of disease. The concept that species diversity per se may influence risk of exposure to disease has not been well developed, however. We present a conceptual model of how high species richness and evenness in communities of terrestrial vertebrates may reduce risk of exposure to Lyme disease, a spirochetal ( Borrelia burgdorferi ) disease transmitted by ixodid tick vectors. Many ticks never become infected because some hosts are highly inefficient at transmitting spirochete infections to feeding ticks. In North America, the most competent reservoir host for the Lyme disease agent is the white‐footed mouse ( Peromyscus leucopus ), a species that is widespread and locally abundant. We suggest that increases in species diversity within host communities may dilute the power of white‐footed mice to infect ticks by causing more ticks to feed on inefficient disease reservoirs. High species diversity therefore is expected to result in lower prevalence of infection in ticks and consequently in lower risk of human exposure to Lyme disease. Analyses of states and multistate regions along the east coast of the United States demonstrated significant negative correlations between species richness of terrestrial small mammals (orders Rodentia, Insectivora, and Lagomorpha), a key group of hosts for ticks, and per capita numbers of reported Lyme disease cases, which supports our “ dilution effect ” hypothesis. We contrasted these findings to what might be expected when vectors acquire disease agents efficiently from many hosts, in which case infection prevalence of ticks may increase with increasing diversity hosts. A positive correlation between per capita Lyme disease cases and species richness of ground‐dwelling birds supported this hypothesis, which we call the “ rescue effect .” "The reservoir competence of hosts within vertebrate communities and the degree of specialization by ticks on particular hosts will strongly influence the relationship between species diversity and the risk of exposure to the many vector‐borne diseases that plague humans.