Rev 07/22/2024
Rhabditida
Onchocercidae
Female:
Male:
Ref: Buckland and Walker, 1969; Olos et al., 2021
Reported in Northern Europe, Hungary, Finland, Spreading through Europe with climate chage and larger populations of host species. As of 2021, reported from 15 European countries (Olos et al., 2021).
Setaria tundra has significant veterinary health importance in boreal regions of Europe as the causative agent of setariosis in cervids (reindeer, roe deer, moose and others: Rangifer tarandus, Capreolus capreolus, Alces alces) (Laaksonen et al., 2007).
Classic symptoms of setariosis include: fever, weight loss, and weakness; also, S. tundra may cause severe fibrinous perihepatitis and severe peritonitis, to which calves are particularly vulnerable (Olos et al., 2021).
In Finland, there have been severe outbreaks of S. tundra among semi-domestic reindeer. The prevalence and level of infection are very high in reindeer calves, resulting in substantial economic losses to the reindeer herders. Adult domestic reindeer and wild forest reindeer are considered as the main source of infection, via the mosquito vectors, for the calves (Laaksonen et al., 2009).
The significance of the nematode as a human parasite is still unknown.
The focus of annual infections of reindeer in Finland has moved northwards approximately 100 km each year associated with global warming and movenemnt of reindeer herding areas (Laaksonen et al., 2009)..
Transmitted by mosquitoes (Kemenesi et al., 2015)
Two hosts to complete the life cycle, an intermediate host (often an arthropd) and a primary host (usually a vertebrate). The juvenile stages occur in the intermediate host and the reproductive adult in the definitive (primary) host.
Adults of S. tundra live in the peritoneal cavity of ther definitive hosts (wild cervids). L2 and L3 larvae (microfilariae) are ingested by mosquitoes while feeding on blood of the definitiver host. Nematode larvae develop in the insect's thorax and abdomen then migrate to the salivary glands where the microfilariae develop to the L3 infective larvae, about 1.5 mm in length. The larvae are transmitted to the definitive hosts during the salivation process that precedes ingestion of a new blood meal by the mosquito. In the definitive host, larvae develop to stage L4 during a period of around 4 months and finally to L5 adults. Almost certainly, adult of S. tundra can live in the definitive host for at least a year, probably longer, producing microfilariae released into the blood of the host (Olos et al., 2021)..
In Finland, development of S. tundra to the infective stage occurs in mosquitoes, (genera Aedes and Anopheles). Aedes spp. are considered the most important vectors. The prevalence of S. tundra naturally infected mosquitoes in Finland varied from 0.5 to 2.5%. The rate of development in mosquitoes was temperature-dependent. Infective larvae were present approximately 14 days after a blood meal from an infected reindeer in mosquitoes maintained at room temperature (mean 21 C), but did not develop in mosquitoes maintained outside for 22 days at a mean temperature of 14.1 C. The third-stage (infective) larvae were elongated (mean length 1.4 mm), and width 28 um).
Infective larvae were distributed anteriorly in the insect's body, the highest abundance being 70 larvae in one mosquito. Approximately 51% of the infective larvae were located in the mosquito thorax, 31% in the head or proboscis and 18% in the abdomen.
The peak activity of Culicidae (mosquitoes) in the reindeer herding areas of Finland was from the middle of June to the end of July. The warm summer weather was associated with reindeer flocking behaviour on mosquito-rich wetlands (Laaksonen et al., 2009)..
Ecophysiological Parameters:
Molecular detection methods are expanding the knowledgebase of the importance of many species of mosquitoes as vectors of filerial nematodes (Kemenesi et al., 2015).
Kemenesi, G., Kurucz, K., Kepner, A., Dallos, B., Oldal, M., Herczeg, R., Vajdovicz, P., Binjai, K., Jakab, F. 2015. Circulation of Dirofilaria repens, Setaria tundra, and Onchocercidae species in Hungary during the period 2011-2013. Veterinary Parasitology 214: 104-113.
Laaksonen, S., Kuusela, J., Nikander, S., Nylund, M., Oksanen, A., 2007. Outbreak of parasitic peritonitis in reindeer in Finland. Vet. Rec. 160: 835-841.
Laaksonen, S., Solismaa, M., Kortet, R., Kuusela, J., Oksanen, A., 2009. Vectors and transmission dynamics for Setaria tundra (Filarioidea; Onchocercidae), a parasite of reindeer in Finland. Parasit. Vectors 2: 3.
Olos, G., Nowakowska, J., Welc-Faleciak, 2021. Setaria tundra, what do we know, what is still to be discovered?. Annals of Parasitology 67:1-10.