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week3 reading - Fatal attraction in rats infected with...

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Unformatted text preview: Fatal attraction in rats infected with Toxoplasma gondii M. Berdoy 1,3* , J. P. Webster 2 and D. W. Macdonald 3 1 Oxford University Veterinary Services, Oxford OX1 3PT, UK 2 Wellcome Trust Centre for the Epidemiology of Infectious Disease, University of Oxford, Oxford OX1 3FY, UK 3 Wildlife Conservation Research Unit, Department of Zoology, University of Oxford, Oxford OX1 3PS, UK We tested the hypothesis that the parasite Toxoplasma gondii manipulates the behaviour of its intermediate rat host in order to increase its chance of being predated by cats, its feline de¢nitive host, thereby ensuring the completion of its life cycle. Here we report that, although rats have evolved anti-predator avoidance of areas with signs of cat presence, T. gondii ’s manipulation appears to alter the rat’s perception of cat predation risk, in some cases turning their innate aversion into an imprudent attraction. The selectivity of such behavioural changes suggests that this ubiquitous parasite subtly alters the brain of its intermediate host to enhance predation rate whilst leaving other behavioural categories and general health intact.This is in contrast to the gross impediments frequently characteristic of many other host^parasite systems. We discuss our results in terms of their potential implications both for the epidemiology of toxoplasmosis and the neurological basis of anxiety and cognitive processes in humans and other mammals. Keywords: Rattus norvegicus ; Toxoplasma gondii ; parasite manipulation; cat odours; anxiety; predation 1. INTRODUCTION According to the manipulation hypothesis, a parasite may alter the behaviour of its host for its own bene¢t, usually by enhancing its transmission rate. The hypothesis implies that such host behaviour modi¢cation represents a sophisticated product of parasite evolution aimed at host manipulation, rather than an accidental side-e¡ect of infection (Barnard & Behnke 1990; Poulin 1994). Para- sites that are transmitted through the food chain consti- tute classic examples of such manipulation: the parasite is immature in the intermediate host and must be eaten by a predatory de¢nitive host before it can reach maturity and complete its life cycle. Unfortunately, however, many studies have either attached little importance as to whether the host in question normally carries the parasite and/or studied hosts maintained under highly unnatural laboratory conditions. The transferability of such studies and their applicability to the epidemiology and evolution of disease in the wild may thus be open to question (Moore & Gotelli 1990; Webster et al. 2000). The host ^ parasite system Rattus norvegicus ^ Toxoplasma gondii provides a convenient model in which to examine such questions. T. gondii is an intracellular protozoan (Beverley 1976) capable of infecting all mammals. Its associate disease, toxoplasmosis, is of signi¢cant economic, veterinary and medical importance (Luft & Remington 1986; Schmidt & Roberts 1989) and...
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This note was uploaded on 10/28/2010 for the course BIEB 166 taught by Professor Nieh during the Spring '09 term at UCSD.

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week3 reading - Fatal attraction in rats infected with...

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