Conspicuous impacts of inconspicuous hosts on the Lyme disease epidemic

Abstract

Emerging zoonotic pathogens are a constant threat to human health throughout the world. Control strategies to protect public health regularly fail, due in part to the tendency to focus on a single host species assumed to be the primary reservoir for a pathogen. Here, we present evidence that a diverse set of species can play an important role in determining disease risk to humans using Lyme disease as a model. Hosttargeted public health strategies to control the Lyme disease epidemic in North America have focused on interrupting Borrelia burgdorferi sensu stricto (ss) transmission between blacklegged ticks and the putative dominant reservoir species, white-footed mice. However, B. burgdorferi ss infects more than a dozen vertebrate species, any of which could transmit the pathogen to feeding ticks and increase the density of infected ticks and Lyme disease risk. Using genetic and ecological data, we demonstrate that mice are neither the primary host for ticks nor the primary reservoir for B. burgdorferi ss, feeding 10% of all ticks and 25% of B. burgdorferi-infected ticks. Inconspicuous shrews feed 35% of all ticks and 55% of infected ticks. Because several important host species influence Lyme disease risk, interventions directed at a multiple host species will be required to control this epidemic.

Plague outbreaks in prairie dog populations explained by percolation thresholds of alternate host abundance

“…Although the importance of percolation thresholds in disease systems has been established before (24), percolation thresholds in which alternate hosts are the key element determining outbreaks of disease in a primary host have not previously been reported. Many disease systems involve multiple hosts infected by generalist pathogens (for example, canine distemper virus in Serengeti carnivores and Lyme disease in small mammals) (29,30) and furthermore, involve species that occupy more or less discrete home ranges that induce spatial structure pertinent to disease transmission. Consequently, insights provided by percolation dynamics involving alternate hosts may be of crucial importance in understanding the complex disease dynamics of wildlife and zoonotic diseases.…”

Pangloss revisited: a critique of the dilution effect and the biodiversity-buffers-disease paradigm

“…Chipmunks actually produce almost as many infected engorged larvae or questing nymphs per hectare as do mice, while all non-mouse hosts together produce twice as many per hectare . Although these statistics change somewhat when other less commonly studied vertebrates, such as shrews, are included (Brisson et al 2008), nevertheless adding chipmunks (rather than replacing mice with chipmunks), even if they diverted some larvae from mice, would have little effect on the density of infected nymphs. A similar conclusion arises from experimental data from a large forested area of Connecticut, independent of detailed knowledge of each host species; mice evidently contributed only about half the infected nymphs, with the rest coming from alternative host species (Tsao et al 2004).…”

“…In conclusion, Lyme borreliosis is one of the most robust and biodiverse zoonotic disease systems known, even in the New World (Brisson et al 2008) with its more limited genetic and phenotypic diversity of B. burgdorferi s.l. than in the Old World (Kurtenbach et al 2006) where a number of tick species act as vectors amongst a wide variety of competent vertebrate transmission host species .…”

Spatial Dynamics of Lyme Disease: A Review

“…Lyme disease in North America is caused by the spirochete bacterium, Borrelia burgdorferi, which is vectored between hosts by Ixodes scapularis in eastern and central regions and Ixodes pacificus in the west. There are many potential reservoir hosts, mostly small mammals and birds, but the dominant hosts are rodents (e.g., white-footed mice, Peromyscus leucopus; eastern chipmunks, Tamias striatus; western gray squirrels, Sciurus griseus; and dusky-footed woodrats, Neotoma fuscipes) and shrews (e.g., Blarina brevicauda and Sorex cinereus) (Mather et al, 1989;Lane and Brown, 1991;Lane, 1992, 1996;LoGiudice et al, 2003;Lane et al, 2005;Brisson et al, 2008). Humans become infected when bitten by a tick that was previously infected while feeding on an infected host.…”