Diseases and parasites can affect the mortality of wild forest reindeer, both directly and indirectly. Their general condition may be reduced so that they become more susceptible to other sources of disease, as well as to large predators.
Climate change promotes the spread of parasites normally considered tropical into the North. These include, for example, the insect-mediated parasites of the Filarioidea superfamily.
The Setaria tundra nematode caused extensive and rapidly spreading mass illness in reindeer in the period 2003-2005. The parasite may have had an effect on the sharp decline of the wild forest reindeer population, since an estimated quarter of all wild forest reindeer were infected. The parasite is especially severe in calves. Wild forest reindeer can also act as symptom-free carriers and distributors of the parasite.
The early twenty-first century saw the spread of the lymphatic nematode (Rumenfilaria andersoni) which according to studies was found to occur in about half of the Suomenselkä population and as much as 71% of the Kainuu population. The summers of 2002 and 2003 were unusually warm in Finland, and warm summers favour the parasite life cycle and make disease outbreaks possible.
The deer fly (Lipoptena cervi) uses the wild forest reindeer as a host. Animals with deer fly parasites experience stress, shake their bodies vigorously, and rub their fur with their antlers and hooves. Extensive damage to the coat increases energy use, causes heat loss, and harms the animal's welfare. Skin changes leave the wild forest reindeer open to a variety of infections.
Photo: Wear and tear on the coat caused by deer fly can be seen as escaping heat in this picture.
Wild forest reindeer
Scientific name: Rangifer tarandus fennicus
Range and numbers:
In Finland, 800 individuals in Kainuu, 2000 individuals in Suomenselkä and about 20 individuals in Seitseminen and Lauhanvuori National Parks (reintroduced populations).
In Russian Karelia up to 2,400. See range map.
Conservation status in Finland (2019): Near Threatened (NT)