Ashworthius sidemi Schulz, 1933 is an alien and ecologically invasive parasite species of ruminants, which has been spreading in Europe since the second half of the twentieth century. Its occurrence has gradually increased over recent years, especially in cervids, but also among free roaming wild bovids. While for Cervidae it is a typical parasite and occurs in infections usually not exceeding several hundred specimens, for non-specific and new Bovidae hosts, its intensity of infection may reach tens of thousands of specimens, and cause pathogenesis even leading to mortality [1, 2]. Moreover, in cervids, a typical infection site for A. sidemi is the abomasum, in other highly affected ruminant hosts, the nematode also parasitises the small and large intestines . The pathological ashworthiosis-related changes include oedema, hyperaemia and effusion in the gastrointestinal mucosa, leading to chronic diarrhoea, deterioration and cachexia, or the animal’s death .
The first description of this trichostrongylid worm was by Schulz  in sika deer (Cervus nippon Temmink, 1838) living in farm conditions in the Russian Far East. A. sidemi was also discovered in introduced sika deer in the former Czechoslovakia  and registered in maral (Cervus elaphus sibiricus Severtzov, 1873) introduced from Asia into the European part of Russia . Therefore, its presence among wild ruminants in several European countries can be explained by parasite translocation with sika deer from Asia . In France, A. sidemi was found in sika deer, fallow deer (Dama dama Linnaeus, 1758), roe deer (Capreolus capreolus Linnaeus, 1758) and red deer (Cervus elaphus Linnaeus, 1758) . In Sweden, it was registered in fallow deer of Hungarian origin . In the European part of Russia, apart from sika deer and maral, the worm species was registered in native elks (Alces alces Linnaeus, 1758) and roe deer [6, 10]. In Belarus, it was found in European bison (Bison bonasus Linnaeus, 1758)  and in the Ukraine, it was detected in roe deer . In Czechoslovakia, apart from sika deer, red deer and mouflon (Ovis aries musimon (Pallas, 1811)) have also harboured this parasite .
In Poland, the introduction of A. sidemi has been documented from 1997 . The parasite was observed for the first time in the country in a few European bison in the Bieszczady Mountains (Eastern Carpathians, south-east of Poland). Following confirmation of ashworthiosis in red deer and roe deer living in this region, Dróżdż et al.  concluded that the origin of A. sidemi was local red deer, which brought the parasite from the neighbouring Ukraine and Slovakia along the Carpathian ecological corridor. Next, in 2001, the nematode was observed in lowland European bison in Białowieża National Park . Another documented focus of ashworthiosis was Dulowa Primeval Forest, south of Poland, where fallow deer introduced from Hungary turned out to be infected . Recently, further and rapid expansion of the nematode has been observed among all Cervidae species living in the country, including elk , and the parasite has also been identified for the first time in domestic cattle (Bos taurus Linnaeus, 1758), by means of a polymerase chain reaction .
The Tatra chamois (Rupicapra rupicapra tatrica (Blahout, 1971/1972)) is a representative of the Bovidae family and is the northernmost subspecies of the northern (Alpine) chamois (Rupicapra rupicapra (Linnaeus, 1758)), which is native to the mountainous parts of central and southern Europe and Asia Minor. In the Alps, where the bulk of the northern chamois population is found, the species is relatively secure and consequently, it is assessed as least concern (LC) in the International Union for Conservation of Nature’s Red List of Threatened Species . However, several chamois subspecies, including the Tatra chamois which are listed as critically endangered (CR), qualify as globally threatened and require urgent conservation action.
The Tatra chamois occur in the Tatra mountains of Poland and Slovakia, and live in areas protected by the national parks of both countries, i.e. in the High, Belianske and Western Tatras. The population has been declining steadily in number since the 1960s and had dropped below 200 individuals by 2002 . Since then, by strict regulation of tourism and suppression of poaching, the population started to recover, reaching the highest ever population of 1,431 individuals recorded in 2018 .
In Slovakia, Tatra chamois have also been artificially introduced (30 individuals) to the Low Tatras, to create a reserve population there . However, in Slovakia, the Alpine chamois were introduced for hunting purposes before the Tatra chamois were officially classified as a separate subspecies, and the Low Tatra population of R. r. tatrica crossbred with Alpine chamois migrating from the Fatra mountains and the Slovak Paradise National Park. Therefore, as a no longer pure population, it cannot act as a reserve population for the Tatra chamois. On the contrary, according to Shackleton et al. , the R. r. rupicapra introduced into Slovakia should be removed as they pose a threat to the wild population of R. r. tatrica living in the High Tatras, from which they are separated only by a single valley – a distance of about 30 km.
The present study aimed to determine the threat to both populations of chamois living in the Tatras from an alien Ashworthius sidemi nematode. Due to the greater opportunity of contact with cervids of the crossbred population living in the Low Tatras, particular attention was paid to the emergence of infection with this parasite there. If confirmed, then a much higher risk of A. sidemi appearance in the second, pure R. r. tatrica population living in the High, Belianske and Western Tatras, could be indicated.