“Evirafilaria”, a new species and genus of parasitic nematode in Finland – nematodes transmitted by insects researched at Evira’s Fish and Wildlife Health Research Unit
The Filarioidea nematodes are parasites of the subcutaneous tissues and body cavities. Their main hosts are all the vertebrates except fishes. The parasites of the superfamily have a great significance on the health and the economy of animals and humans worldwide.
The Filarioidea nematodes are transmitted by haematophagous arthropods. The Filarioidea parasites produce the first stage larvae (microfilariae) in the blood or tissue of the definitive host. The microfilariae are taken up in the blood meal of the insect vector, where the larvae develop via two moults into the infective third stage and move to a new definitive host with the next blood meal. The larva develops into an adult after two more moults in the definitive host where it lives, the female worm becomes fertilised and starts to produce microfilariae. Their intermediate hosts and vectors are different arthropods sucking blood from vertebrates, such as horseflies, mosquitoes, lice, louse-flies, black flies, mites and ticks.
A recent example of the effects of the parasites is the peritonitis epidemic that flared up among reindeer in 2003, which was followed by slaughter losses and substantial economic losses to reindeer herding. The cause of the epidemic was shown to be the nematode Setaria tundra that lives in the reindeer’s peritoneal cavity. A study carried out by Evira found that the parasite is transmitted in Finland by a mosquito, mainly the Aedes spp. The disease outbreak spread between 2003 and 2005 to Northern Lapland. Fortunately it seems like the reindeer after the cool summer of 2008 have gotten rid of this nuisance. The previous severe outbreak happened in 1973.
Setaria tundra infection has been found in the survey carried out on reindeer but also in other cervids. It is especially common in the wild forest reindeer and roe deer which are thought to be the reservoirs of the parasite in the wild. The research has shown that a genetically different type of the parasite S. tundra caused a similar epidemic in moose (European elk) in 1989 in Northern Finland.
During the survey on vector-borne parasites transmitted by insects a species of nematode new to Finland was found in December 2006. The still officially unnamed large (the female is about 17 cm and the male about 6 cm) parasite "Evirafilaria" lives in the lymphatic system of cervids. This parasite is found in Finland in reindeer and also in moose (in our material about 7 %), in wild forest reindeer (in Kainuu 48 %, in Suomenselkä 71 %) and in white-tailed deer (22 %). Based on the morphological and genetic research, the parasite belongs to the Filarioidea nematodes.
Nematodes in the lymphatic vessels have not previously been found in cervids worldwide. By its life cycle and ability to tolerate parasitic medication, the parasite reminds of the parasites that cause elephantiasis in humans (Brugia spp.). Structurally the parasite is similar to the nematode Rumenfilaria andersoni found in elk in Canada.
So far the research has shown that the parasite became common in 2003-2005, similarly to the parasite S. tundra. The parasite produces great amounts of about 0.2 mm long microfilariae into the bloodstream of the cervid, of which the largest measured concentrations have been about 60 000/ml blood. The local pathological changes caused by the parasite can be seen with the eye, but there is not yet exact information on the effect of the parasite on the health of cervids. The work in order to clarify this and the vector insect of the parasite are continuing at Evira's Fish and Wildlife Health Research Unit in Oulu.
Also a third nematode transmitted by insects (Onchocerca tarsicola) and the changes caused by it has increased in our cervids during the last few years. It has been reported that its close relations are becoming common also in cattle. The parasite causes colony-like formations on the muscle- and synovial membrane and clinical inflammation of the mucous bursa and joint capsule. According to the preliminary research carried out at Evira, the parasite is spread in Finland by black flies (Simuliidae).
The research carried out recently indicates that the parasites, that previously have been considered to be mainly tropical, would benefit from the current global warming, which can set the scene for the spread of new and harmful vector-transmitted diseases into the North. The rising temperatures can for example affect the number of vector insects, the areas where they occur, the feeding frequencies and speed up the development of the parasites to the infective stage in the vectors.
In connection with the outbreak of Setaria tundra it was found, based on the research carried out by Evira, that the meat of the reindeer infected by the parasites was faultless as to its hygiene and taste. The meat inspection stops altered pieces from ending up as food for humans.
For more information, please contact:
Researcher Sauli Laaksonen, Fish and Wildlife Health Research Unit,
tel. +358 50 469 1471, sauli.laaksonen evira.fi