Parasite Spillover from Domestic Sheep to Wild Reindeer—The Role of Salt Licks

Abstract

Attraction sites are important for environmental pathogen transmission and spillover. Yet, their role in wildlife disease dynamics is often poorly substantiated. Herein, we study the role of salt licks as potential attraction sites for the spillover of gastrointestinal parasites from domestic sheep to wild reindeer. Eggs from the introduced sheep nematode Nematodirus battus were found in faecal samples of both species, suggestive of spillover. DNA metabarcoding of soil, collected at salt licks, revealed that N. battus, in addition to Teladorsagia circumcincta, were the most frequently occurring parasitic nematodes, with a significantly higher prevalence of nematodal DNA in salt lick soil compared to soil from control sites nearby. The finding of similar DNA haplotypes of N. battus in sheep, reindeer, and salt lick soil supports the hypothesis of spillover to reindeer via salt licks. More detailed investigation of the genetic diversity of N. battus across these hosts is needed to draw firm conclusions. Infection with these sheep nematodes could potentially explain a recently observed decline in the calf recruitment rate of the Knutshø reindeer herd. This study also supports the hypothesized role of artificial salt licks as hot spots for the transmission of environmentally persistent pathogens and illustrates the importance of knowledge about such attraction points in the study of disease in free-roaming animals.

A serological screening for potential viral pathogens among semi-domesticated Eurasian tundra reindeer (Rangifer tarandus tarandus) in Finland

“…This may further affect the level of exposure to viruses and other pathogens in the future. For example, the practice of feeding reindeer, especially if done in corrals and for extended periods of time, may facilitate transmission of infectious agents between animals due to increased nose-to-nose contact, aerosol transmission and poor hygienic conditions at gathering spots [ 44 , 45 ]. Intensive feeding may also represent a closer link between livestock and semi-domesticated reindeer due to e.g., sharing of feed, feed production lines, corrals, animal transport and equipment.…”

Elucidating nematode diversity and prevalence in moose across a wide latitudinal gradient using DNA metabarcoding

“…Therefore, individual foraging and habitat use patterns determine exposure risk and are an important factor affecting infection patterns ( Ezenwa, 2004 ; Ezenwa et al, 2016 ). For example, preferentially spending time in areas rich in resources that attract many individuals may increase the risk of infection to a wider range of nematode species through host aggregation ( Wright and Gompper, 2005 ; Utaaker et al, 2023 ). However, even within species not all hosts are equally susceptible.…”

Cross-transmission of resistant gastrointestinal nematodes between wildlife and transhumant sheep

“…The presence of wild and domestic ungulates in attracting zones such as salt licks, even if not simultaneous, offers good opportunities for parasite transmission, and these areas are therefore considered hotspots for parasite infection (Richomme et al, 2006;Ryser-Degiorgis et al, 2002;Utaaker et al, 2023).…”

“…However, prior to the arrival of livestock, mountain ungulates have been observed using preferentially the same grazing areas as those used by livestock on their arrival (Brivio et al, 2022;Ryser-Degiorgis et al, 2002) and ibex, for example, have been observed to return to the sheep grazing area immediately after the sheep have left (Ryser-Degiorgis et al, 2002). The presence of wild and domestic ungulates in attracting zones such as salt licks, even if not simultaneous, offers good opportunities for parasites transmission, and these areas are therefore considered hotspots for parasites infection (Richomme et al, 2006;Ryser-Degiorgis et al, 2002;Utaaker et al, 2023).…”