EcoHealth 7, 7–13, 2010 DOI: 10.1007/s10393-010-0308-z Short Communication 2010 The Author(s). This article is published with open access at Springerlink.com Climate Change Promotes the Emergence of Serious Disease Outbreaks of Filarioid Nematodes Sauli Laaksonen,1 Jyrki Pusenius,2 Jouko Kumpula,3 Ari Vena¨la¨inen,4 Raine Kortet,5 Antti Oksanen,1 and Eric Hoberg6 1Finnish Food Safety Authority Evira (FINPAR), P.O. Box 517, FI-90101 Oulu, Finland 2Finnish Game and Fisheries Research Institute, FI-80100 Joensuu, Finland 3Finnish Game and Fisheries Research Institute, FI-99910 Kaamanen, Finland 4Finnish Meteorological Institute, P.O. Box 503, FI-00101 Helsinki, Finland 5Department of Biology, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland 6US National Parasite Collection, ARS, USDA, Animal Parasitic Diseases Laboratory, BARC East 1180, 10300 Baltimore Avenue, Beltsville, MD 20705 Abstract: Filarioid parasites represent major health hazards with important medical, veterinary, and economic implications, and considerable potential to affect the everyday lives of tens of millions of people globally (World Health Organization, 2007). Scenarios for climate change vary latitudinally and regionally and involve direct and indirect linkages for increasing temperature and the dissemination, ampliﬁcation, and invasiveness of vector-borne parasites. High latitude regions are especially inﬂuenced by global climate change and thus may be prone to altered associations and dynamics for complex host-pathogen assemblages and emergence of disease with cascading effects on ecosystem structure. Although the potential for substantial ecological per- turbation has been identiﬁed, few empirical observations have emanated from systems across the Holarctic. Coincidental with decades of warming, and anomalies of high temperature and humidity in the sub-Arctic region of Fennoscandia, the mosquito-borne ﬁlarioid nematode Setaria tundra is now associated with emerging epidemic disease resulting in substantial morbidity and mortality for reindeer and moose. We describe a host- parasite system that involves reindeer, arthropods, and nematodes, which may contribute as a factor to ongoing declines documented for this ungulate species across northern ecosystems. We demonstrate that mean summer temperatures exceeding 14 C drive the emergence of disease due to S. tundra. An association between climate and emergence of ﬁlarioid parasites is a challenge to ecosystem services with direct effects on public health, sustainability of free-ranging and domestic ungulates, and ultimately food security for subsistence cultures at high latitudes. Keywords: global warming, ﬁlarioid nematodes, vector-borne diseases, emerging diseases, reindeer popula- tions, sub-Arctic Published online: April 27, 2010 Correspondence to: Sauli Laaksonen, e-mail: sauli.laaksonen@evira.ﬁ INTRODUCTION Setaria tundra, a species of ﬁlarioid nematode, has caused three documented disease outbreaks among cervids in