The first report on Elaphostrongylus rangiferi (reindeer invasive parasite) in Leningrad oblast.
Elaphostrongylus rangiferi is a parasitic nematode specific to reindeer (Rangifer tarandus). In the 20th century, reindeer could not be found in Leningrad oblast. However, several dozen of them were brought from Murmansk oblast and the Yamalo-Nenets Autonomous Okrug by 2020 and introduced in at least seven private menageries. As a result of studying feces of 34 imported reindeers carried out in 2018-2021, nematode larvae were isolated, whose morphological, morphometric, physiological and biological characteristics corresponded to those of E. rangiferi. Species identification was confirmed by subsequent molecular genetic studies. The discovery of larvae in the feces of second generation reindeer (born in 2018-2020) indicated the successful completion of the full life cycle by the helminth, which requires the participation of intermediate hosts such as terrestrial or freshwater gastropods. The following facts, including (1) the occurrence of reindeer infested with E. rangiferi in Leningrad oblast; (2) the presence of wild, agricultural, and zoo-kept ruminants capable of becoming definitive hosts for Elaphostrongylus in Leningrad oblast; (3) the spread of parasite larvae as a result of reindeers roaming freely in the forest, their lease and resale, and commercial sale of non-disinfected manure; (4) the ability of larvae to stay viable in feces and infected mollusks for about 2 years, withstanding freezing and drying; (5) high lethality among infected nonspecific hosts due to parasitic encephalomyelitis, pneumonia, etc.; and (6) the lack of treatment methods, all put ruminants of Leningrad oblast at risk.