PARASITES AND DISEASE
Disease, defined by Jakob-Hoff et al. (2014a), constitutes ‘Any impairment of the normal structural or physiological state of a living organism resulting from its physiological response to a hazard.’ A hazard is defined as a biological, chemical or physical agent, or a condition of an animal or animal product with the potential to cause an adverse health effect.
Hazards include parasites (as defined below) and non-infectious agents such as toxins and trauma. Parasites are agents that live on or within a host and that survive at the expense of the host regardless of whether disease follows or not. This includes microparasites (viruses, bacteria, fungi, protozoa) and macroparasites (helminths, parasitic arthropods) (Jakob-Hoff et al. 2014a). Pathogens are described as any diseasecausing parasite (Jakob-Hoff et al. 2014a).When novel host-parasite interactions occur as a consequence of translocation the impact on populations can vary from negligible to severe. For example, the introduction of squirrelpox virus carried asymptomatically by the North American grey squirrel (Sciurus carolinensis) to the United Kingdom caused fatal disease in native red squirrels (S. vulgaris), contributing to the species’ decline (Sainsbury et al. 2008). Similar cases have been seen with the translocation of native animals within Australia from one area to another. For example, a papillomatosis and carcinomatosis syndrome in western barred bandicoots (Perameles bougainville) in WA has been associated with the bandicoot papillomatosis carcinomatosis virus type 1 (BPCV1). BPCV1 was likely introduced into mainland western barred bandicoot populations through the introduction of infected western barred bandicoots from Red Cliff on Bernier Island (Woolford et al. 2009).
1.1 Translocation and parasites
Translocation of any living organism includes not only the individual but the movement of a complete biological package: the host and all of its associated organisms (Davidson and Nettles 1992; Sainsbury and Vaughan- Higgins 2012).
Disease occurs naturally in all populations; however, hosts can have long evolutionary associations with certain parasites without causing disease (Hudson et al. 2002). Translocation can induce changes in these host-parasite dynamics, increasing the risk of disease (Kock et al. 2010). This may occur as a result of one or more of the following:• translocated species may introduce novel parasites that may cause disease in immunologically naive hosts at the destination site
• translocated species may lack immunity or resistance and be challenged by novel parasites in the destination environment
• managed care or transport can lead to stress, resulting in immunosuppression and increased disease susceptibility, including to commensal parasites (Dickens et al. 2010; Kock et al. 2010; Ewen et al. 2012a)
• translocated animals may contract a parasite during transport, which may then cause disease in translocated or recipient populations (Sainsbury and Vaughan-Higgins 2012).
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