In autumn 2006, Finnish meat inspection data revealed lesions in tendons, muscles and ligaments of bovine hind legs leading to partial condemnation of carcasses. In gross pathological examination at Finnish Food Safety Authority Evira, Oulu (now Fish and Wildlife Health) Research Unit, Onchocerca sp. (Filarioidea; Onchocercidae) nematodes were detected in lesions. Due to this, a pilot study was made in order to find out what filarioid nematodes do occur in cattle, horses and sheep in Finland.
Ventral skin biopsies from 209 dairy cattle and 42 horses, as well as blood samples from 209 cattle, 146 horses and 193 sheep, were collected from different parts of Finland and examined for microfilariae. Visceral organs and other tissues from 33 cattle with parasitic lesions were studied histopathologically.
Onchocerca sp. microfilariae (mf), 240 μm long, range 225–260 μm, 5.4 μm thick, were found in 37% of the skin biopsies of cattle. All blood samples from cattle, horses and sheep and skin biopsies from horses were negative for mf. Ventral skin microfilaria prevalence in cattle was higher in southern Finland than in the North (p = 0.001). Animal age and sampling time was not associated with mf prevalence. The infection was evenly distributed among young and older animals. Macroscopic lesions on tissues included greenish-grey discolouration and often oedema. In most of the lesions, small pale nodules were seen on the fasciae. Histopathologic examination of the samples revealed mild to intense infiltration with eosinophilic granulocytes and multifocal nodular lymphoplasmacytic aggregations were seen. In some samples, there were granulomatotic lesions with central necrotic tissue and cell detritus, surrounded by eosinophilic granulocytes, lympho-, plasma- and histiocytes and some multinucleated giant cells. Around living nematodes no or only weak inflammatory changes were observed.
Onchocerca sp. infection in cattle was found to be common in Finland, but the amount of pathological changes leading to condemnation of infected parts is low compared to the mf prevalence. Pronounced pathological changes are distinct but rare and mild changes are difficult to distinguish. No other filarioid nematodes were observed from the animals and it appears that horses and sheep may be free from filarioid nematodes in Finland.