A large-scale survey of helminths in reindeer (Rangifer tarandus) in Russia was initiated by the author in 2018. A previous similar study was conducted in 1930-60 by K. I. Skrjabin, V. Yu. Mizkewich, and other Soviet scientists. Climate change, human expansion in the Arctic region, and animal introductions and translocations might have intensified the presence of helminth fauna in reindeer.
More than 500 fecal samples of wild and semi-wild reindeer were collected throughout Russia from Murmansk Oblast in the West to Chukotka in the East and from Franz Josef Land in the North to Buryatia and Altai in the South. This research covered nature reserves, agricultural units, and all the zoos in Russia. When possible, autopsy was also performed. In total, about 200 reindeer were examined post mortem. Fecal samples were processed via larvoscopic and ovoscopic (flotation and sedimentation) techniques, along with fecal examination (in order to find macrohelminths). DNA analyses were made of adult worms and larvae primarily by targeting the internal transcribed spacer region.
The diversity of helminths found via fecal examination is represented by Fasciola hepatica; Paramphistomum spp.; Dicrocoelium spp.; Moniezia expansa; Moniezia spp.; small strongylids, including Ostertagia gruehneri (major morph) and O. arctica (minor morph), O. leptospicularis, and O. ostertagi; Nematodirus spp.; Nematodirella longissimespiculata; Dictyocaulus spp.; Elaphostrongylus rangiferi; Orthostrongylus spp.; Varestrongylus eleguneniensis; Trichuris spp.; Capillaria spp.; Ascaris mosgovoyi; and Skrjabinema tarandi. The helminths recovered via autopsy were Paramphistomum spp.; Dicrocoelium chinensis; Oesophagostomum; Dictyocaulus spp.; E. rangiferi; Trichuris discolor; Setaria spp.; Onchocerca flexuosa; Onchocerca spp.; Echinococcus spp.; and Taenia spp.
The following helminths were reported for reindeer in Russia for the first time: Orthostrongylus spp., Varestrongylus eleguneniensis, Oesophagostomum spp., and T. discolor. The Orthostrongylus spp. and T. discolor nematodes were reported for the first time for reindeer at the world scale.
Thank you! You are asking essential questions. I wish I had a simple answer for the whole, but it doesn't work like this. So, let me try to explain point by point.
Orthostrongylus: it was initially described in the Nearctic region (not for reindeer). First we inclined to think that it was introduced into Russia with muskoxen in 1970s. However, it was not found in any muskoxen (nor it was ever reported for them). Lately we have also found very similar larvae in wild reindeer. Thus, now we guess, it was always here, but only in the East of Russia, and only in wild reindeer. Soviet scientists focused mainly (or completely) on the domestic ones.
Varestrongylus eleguneniensis: it was initially described both for R. tarandus and O. moschatus (muskoxen), yet only in the Nearctic region. We did found it in the wild reideer in Russia, as well as DSL in introduces muskoxen. That is why we considered muskoxen as the vectors for both V. eleguneniensis and Orthostrongylus. However, previously domestic reindeer from Russia were delivered to Akaska. It made our American colleagues consider Russian reindeer as the source of V. eleguneniensis. Why it was not found by Soviet scientists? Probably, due to similarity of the larvae (Varestrongylus and Elaphostrongylus) and lack of DNA analyses technology back in those days. Still, it may be newly introduced worm.
Oesophagostomum: it was predicted to be found in reindeer back in 60s, and later it was indeed found in the North America. Our findind in Russia is related to the Zoo conditions, so it is not much surprising. Reindeer might be considered more as an incidental host.
Trichusis discolor: this finding might be new, I guess, due to the change in systematics of Trichuris. T. ovis was reported in reindeer long ago, and T. ovis is closely related (and sometimes mistaken) to T. discolor. Without genetic it was really hard to tell them apart (I might be terribly wrong here) back in those days. Not to mention that among different Truchures there is no strong correlation between DNA and morphology.
So, returning to your question, my guess is that it is a complex phenomenon: 1) insufficient sampling (preferring domestic and missing wild forms); 2) expansion of parasites to other host (due to increasing sympatry of reindeer and muskoxen + increasing number of zoo reindeer that encounter other ungulates in direct proximity); and 3) environmental factors (global warming, as we found F. hepatica (not reported in this paper but already published) on the Severny island of the Novaya Zemlya archipelago.
Of course, further research is needed.
Good luck with your research and and publications!
