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, 276 (1675), 3911-9

Hosts as Ecological Traps for the Vector of Lyme Disease

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Hosts as Ecological Traps for the Vector of Lyme Disease

F Keesing et al. Proc Biol Sci.

Abstract

Vectors of infectious diseases are generally thought to be regulated by abiotic conditions such as climate or the availability of specific hosts or habitats. In this study we tested whether blacklegged ticks, the vectors of Lyme disease, granulocytic anaplasmosis and babesiosis can be regulated by the species of vertebrate hosts on which they obligately feed. By subjecting field-caught hosts to parasitism by larval blacklegged ticks, we found that some host species (e.g. opossums, squirrels) that are abundantly parasitized in nature kill 83-96% of the ticks that attempt to attach and feed, while other species are more permissive of tick feeding. Given natural tick burdens we document on these hosts, we show that some hosts can kill thousands of ticks per hectare. These results indicate that the abundance of tick vectors can be regulated by the identity of the hosts upon which these vectors feed. By simulating the removal of hosts from intact communities using empirical models, we show that the loss of biodiversity may exacerbate disease risk by increasing both vector numbers and vector infection rates with a zoonotic pathogen.

Figures

Figure 1.
Figure 1.
The proportion of larval ticks that fed successfully (+s.e.m.) on six species that are common hosts for larval blacklegged ticks (Ixodes scapularis) in upstate New York, USA. Hosts were captured in the field and held in the laboratory until ticks naturally feeding on them had fed to repletion and dropped off. Hosts were then reinfested with 100 larval ticks and monitored to determine the proportion of those ticks that fed successfully. Lowercase letters indicate results that were significantly different (one-way ANOVA; p < 0.05).
Figure 2.
Figure 2.
The percentage change in the density of infected nymphal ticks as host species (see legend) were removed individually from our model. Ticks that would have fed on the removed host species were redistributed on the remaining hosts: (a) 0 per cent; (b) 33 per cent; (c) 67 per cent; and (d) 100 per cent. Bars above zero indicate an increase in LD risk, while those below zero indicate a reduction in risk. Brown, no veeries; orange, no opossums; light green, no catbirds; dark green, no squirrels; aqua, no chipmunks; dark blue, no mice.
Figure 3.
Figure 3.
The density of infected nymphal ticks (DIN) per hectare as host species were removed sequentially from our model, when the ticks that would have fed on missing hosts were redistributed among remaining hosts from 0 to 100 per cent. Species were removed from the model in an order determined by empirical observations of the sequence of species loss in fragmented forest habitats. Veeries were removed first, followed by opossums, squirrels, chipmunks and then catbirds; white-footed mice were present in all communities (see main text). In habitats with two or more species lost, DIN was higher if ticks were redistributed on the remaining hosts, and greater rates of redistribution resulted in higher DIN values. Black line, intact; dotted orange lines, remove one species; continuous orange line, remove two species; dark green, remove three species; blue, remove four species; light green, remove five species.

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