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Livestock Parasites in a Warmer World
Reference
Wall, R. and Ellse, L.S. 2011. Climate change and livestock parasites: integrated management of sheep blowfly strike in a warmer environment. Global Change Biology 17: 1770-1777.

Background
The authors say there is a widespread assumption that "a generally warmer environment will result in higher parasite abundance and increased disease incidence," but they note that "such extrapolations require a more careful consideration of the range of subtle interactions, for example in human behavior, which may occur within an entire parasite/host system (Randolph et al., 2008; Sumilo et al., 2009)."

What was done
Focusing on cutaneous myiasis (blowfly strike) in sheep, Wall and Ellse employed a stochastic simulation model "to examine the changes in the seasonal incidence of ovine cutaneous myiasis on farms in the United Kingdom and the likely effects of changes in husbandry and control strategies" in the face of projected changes in climate. And in doing so, they make a special point of noting that "the ability of this model to successfully account for observed patterns of strike has been confirmed previously by comparison of predicted with observed strike incidence patterns observed on 370 farms in England and Wales," citing the work of Wall et al. (2002).

What was learned
The two UK researchers say "the simulations show that the range of elevated temperatures predicted by current climate change scenarios result in an elongated blowfly season with earlier spring emergence and a higher cumulative incidence of strike," and that "overall, higher temperatures increased strike incidence disproportionately in ewes in early summer, but had relatively less direct effect on the pattern of lamb strike incidence," noting that "a 3°C increase in average temperature approximately doubles the cumulative incidence of strike in lambs but results in four times more strikes in ewes." However ...

What it means
... as expressed in the concluding words of Wall and Ellse's abstract, "the simulations suggest that integrated changes in husbandry practices are likely to be able to manage expected increases in strike, given the range of climate changes currently predicted." And as they elucidate in the body of their text, "modest changes in husbandry practices should be able to manage expected increases in strike, under the range of climate changes currently predicted," demonstrating that "consideration of the likely impact of climate change must take into account animal management practices as well as parasite biology (Morgan and Wall, 2009)."

References
Morgan, E.R. and Wall, R. 2009. Climate change and parasitic disease: farmer mitigation? Trends in Parasitology 25: 308-313.

Randolph, S.E., Asokliene, L., Avsic-Zupanc, T., Bormane, A., Burri, C., Gern, L., Golovljova, I., Hubalek, Z., Knap, N., Kondrusik, M., Kupca, A., Pejcoch, M., Vasilenko, V. and ˇygutiene, M. 2008. Variable spikes in tick-borne encephalitis incidence in 2006 independent of variable tick abundance but related to weather. Parasites and Vectors 1: 10.1186/1756-3305-1-44.

Sumilo, D., Bormane, A., Vasilenko, V., Golovljova, I., Asokliene, L., Zygutiene, M. and Randolph, S. 2009. Upsurge of tick-borne encephalitis in the Baltic States at the time of political transition, independent of changes in public health practices. Clinical Microbiology and Infection 15: 75-80.

Wall, R., Cruickshank, I., Smith, K.E., French, N.P. and Holme, A.S. 2002. Development and validation of a simulation model for sheep blowfly strike. Medical and Veterinary Entomology 16: 335-346.

Reviewed 8 June 2011