Parasites, ecology, epidemiology and climate change.

This post was originally written on September 14, 2011.

I had envisaged that this blog would be full of all kinds of interesting sciency things, but it’s quite difficult for me to find time to sit down and do much more than report on fun news items. So I’ve made some time and I thought it might be nice to review a recent paper on some of my favourite topics – wildlife parasitology and climate change. I saw this paper in the June edition of Trends in Parasitology and it’s been sitting on my desk for a while now, waiting for me to review it.

Davidson et al. (2011) Arctic parasitology: why should we care? Trends Parasitol. 27, 238-244.

The Arctic, as a region, is extremely fragile with the majority of species that occur there being highly specialized and adapted to the difficult conditions. The combination of highly adapted species in a very narrow climate envelope means that the region is going to feel the effects of a changing climate faster than most others. Antarctica is in a similar sticky situation in terms of temperatures, warming and increasing vulnerability, but the difference between the Arctic and Antarctica is that the former supports a human population too. The effects of a changing Arctic climate will have implications for human and veterinary health, and this is why we should care.

I liked this paper because it stuck to three main themes with its impacts of climate change: on waterborne transmission of parasites, on food security and parasites and on parasitic threats to Arctic wildlife.

From a public health perspective, one of the most important aspects of climate change in the Arctic is the change in distribution of waterborne parasites such as Giardia and Cryptosporidium, which may be able to increase in transmission due to warmer conditions. Increased runoff due to snowmelt and altered distributions of hosts will potentially expose more communities to infection with waterborne parasites.

Food security is a big issue for communities that use permafrost as a storage method and have minimal food-inspection practices. Many parasites can be transmitted from undercooked or improperly handled meat, or in meat that has been preserved using methods other than cooking. The authors list the parasites they think will be at highest risk to humans via food-borne routes. These include the protozoan Toxoplasma gondii, the cestodes Echinococcusspp (hydatids) and Diphyllobothrium spp, and the nematodes Anisakis spp and other anisakids, and Trichinella spp. These parasites are important because changes to the environment will affect the transmission and prevalence of these parasites and may result in more people becoming infected. Coupled with altered food practices, such as improperly cooled meat due to permafrost melting, and this could get quite serious.

Shifts in transmission rates of parasites and emergence of novel pathogens are the main issues faced from a wildlife perspective. Conditions in the Arctic are changing so quickly relative to the rest of the world that it is possible to see these shifts occurring already. My favourite case study was included in this review, which made me happy. The lifecycle of a nematode of muskoxen, the superbly-named Umingmakstrongylus pallikuukensis, has been demonstrated to have shifted from a cycle that takes two years, to now taking only one year. This is presumably due to increases in average temperatures, which supports faster development of the nematodes and availability of intermediate hosts (Kutz et al. 2005). Another important threat is that posed by range expansions of parasites to include immunologically naïve populations. This is demonstrated by a nematode in reindeer, Setaria tundrae, which has expanded its distribution in Finland. The pathology caused by parasites in immunologically naïve individuals can result in serious outbreaks of disease in populations.

One final concern raised is that the parasites of Arctic animals need very similar climatic envelopes in which to survive, so may actually be at the same, if not greater, risk of extinction as their hosts. The ability of Arctic parasites to adapt to a changing climate will be a fascinating study in parasite ecology, and will provide insight into the mechanisms that drive parasite diversification.

Additional reference: Kutz et al. (2005) Global warming is changing the dynamics of Arctic host-parasite associations. Proc. R. Soc. B 272, 2571-2576.

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