Parasitic diseases can have a significant impact on wildlife. This is a major concern, particularly for the conservation of threatened species.2 Parasites can cause wildlife populations to decline either temporarily or permanently.3 For example, about 14 species of frogs in Australian rainforests are thought to have become extinct because of the parasitic fungal disease, chytridiomycosis.4
There are at least as many species of parasites as there are other organisms.5,6 Parasites are an important part of biodiversity and a healthy ecosystem. This means that there is no simple way to deal with parasite infections.
Research has primarily focused on parasitic diseases that threaten humans or domestic animals.7 Insufficient attention has been given to the potential impacts of parasitic diseases on wildlife.
Humans and domestic animals can spread parasites to wildlife. This is expected to increase as wildlife interact more with humans and domestic animals due to urban expansion and land clearing. Recent advances in science have meant that researchers are now gaining an insight into diseases spread to wildlife from people and domestic animals.
Wildlife as a source of parasite infection
Wildlife are often seen as the cause of parasitic diseases that spread to humans or livestock. In many cases though, there is evidence that these parasitic diseases were originally introduced to wildlife populations by humans. Examples include Giardia (think ‘Bali Belly’), sarcoptic mange (scabies) and Echinococcus granulosus, a tapeworm parasite (‘hydatids’).
Impact of parasite infection on wildlife
Wildlife conservation efforts often neglect the potential impacts of parasites on wildlife populations. Humans know very little about the ecological relationships between parasites and hosts and their impact on wildlife health. Some targeted investigations have produced valuable and often unexpected data. Examples are investigations into Leishmania, Trypanosoma and Toxoplasma in Australia.
Another major concern to wildlife is the unintentional introduction of diseases through the relocation or release of captive bred animals. 24 Wildlife living in areas where the release occurs may not have been exposed to the same diseases and might not have any immunity.24 For example, parasites introduced by exotic fish species, such as anchor worm, also poses a threat to native fishes. This can occur when exotic fish, such as goldfish, are released into waterways.25
Parasites have conservation value
While parasites can be a threat to wildlife, they also have conservation value. Parasites are important components of ecosystems and can alter the stability of food webs.39,40 Parasites may influence the behaviour of individual hosts,41 regulate population sizes of the host by changing birth and death rates42 and act as ecosystem engineers.43 Therefore, reducing the parasite population and losing parasite species may have important impacts on ecosystem function and affect biodiversity. 44,45
When species become extinct, this often causes the extinction of many parasite species, especially those that are specific to a particular host.44,46,47 Researchers generally have incomplete knowledge about parasite species that exist in these hosts.48,49 In many cases it is not known how many parasites species are lost through extinction. For example, a study into freshwater fishes of south-western Australia found 44 parasite species. All but two of these species appeared to be native and most were previously unknown to science.49=
Treatment of parasitic infection is essential where there is a threat to endangered wildlife. In some cases however, parasites may be important to the health of individual animals to develop immunity, or to the health of a wildlife population or the broader ecosystem. 1
The number of threatened species is increasing throughout the world. This is being exacerbated by human encroachment into wildlife habitats, land degradation and climate change.1 Understanding the diversity and ecology of parasites in ecosystems, and the relationship between hosts and parasites, is very important for wildlife conservation.
1Thompson, R.C.A., Lymbery, A.J. and Smith, A. (2010) Parasites, emerging disease and wildlife conservation. International Journal for Parasitology, 40 (10). pp. 1163-1170.
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2 Hudson et al., 1992, 1998; Tompkins and Begon, 1999; Daszak et al., 2000; Albon et al., 2002; Newey and Thirgood, 2004; Hawlena et al., 2007; Møller and Nielsen, 2007; Pedersen et al., 2007; Aguirre and Tabor, 2008; Burthe et al., 2008.
3 Daszak et al., 2000; Harvell et al., 2002; Smith et al., 2006.
4 Retallick et al., 2004.
5 Price, P.W., 1980.
6 Toft, C.A. 1986.
7 e.g. McCallum and Dobson, 1995; Holmes, 1996; Daszak et al., 2000; Rhyan and Spraker, 2010
8 Thompson, R.C.A. 2004.
9 Appelbee, A.J., Thompson, R.C., Olson, M.E., 2005.
10 Kutz, S.J., Thompson, R.C.A. and Polley, L., 2009.
11 Thompson, R.C.A., Colwell, D.D., Shury, T., Appelbee, A.J., Read, C., Njiru, Z., Olson., M.E. 2009a.
12 Adams, P.J., Monis, P.T., Elliot, A.D., Thompson, R.C.A., 2004.
13 Moro, D., Lawson, M.A., Hobbs, R.P., Thompson, R.C.A., 2003.
14 Thompson, R. C. A., Kutz, S. J. and Smith, A., 2009b.
15 Sulaiman, I. M., Fayer, R., Bern, C., Gilman, R. H., Trout, J. M., Schantz, P. M., Das, P., Lal, A. A. and Xiao, L., 2003.
16 Dixon, B.R., Parrington, L.J., Parenteau, M., Leclair, D., Santín, M., Fayer, R., 2008.
17 Kutz, S.J., Thompson, R.A., Polley, L., Kandola, K., Nagy, J.., Wielinga, C.M., Elkin,B.T., 2008.
18 Teichroeb, J.A., Kutz, S.J., Parkar, U., Thompson, R.C.A., Sicotte, P., 2009.
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20 Jenkins, D.J., Romig, T., Thompson, R.C.A., 2005.
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28 Stark, D., Pett, S., Marriott, D., Harkness, J., 2006.
29 Thompson, R.C.A., Owen, I.L., Puana, I., Banks, D., Davis, T.M.E., Reid, S.A., 2003.
30 Konecny, P., Stark, D.J., 2007.
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32 Cox, F. E. G., 2001.
33Brown, M. J. F., Loosli, R., Schmid-Hempel, P. 2003.
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35 Arrea, G. C., Carmona, M. C., Bermudez, O. M. G. and Abrahams, E., 1998.
36 McCallum, H., Dobson, A., 2002.
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38 Pedersen, A. B., Grieves, T. J., 2008.
39 Hudson, P.J, Dobson, A.P., Lafferty, K.D., 2006.
40 Lafferty, K.D., 2008.
41 Lefèvre, T., Lebarbenchon, C., Gauthier-Clerc, M., Missé, D., Poulin, R., Thomas, F., 2009.
42 Møller, A.P., 2005.
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48 Colwell, D.D., Otranto, D., Stevens, J.R., 2008.
49 Lymbery, A.J., Hassan, M., Morgan, D.L., Beatty, S.J., Doupé, R.G., 2010.
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55 Ashburner 1978; Hall 1983; Callinan 1988; Rowland & Ingram 1991; Dove 2000; Bond 2004.
56 Morgan et al (2004)
57 Bauer 1991; Kennedy 1993; Arthington & McKenzie 1997; Levy 2004.