Gastrointestinal nematode communities detected from soils surrounding salt licks

Attraction sites are frequently mentioned as important for environmental pathogen transmission and spillover, yet their role in wildlife disease dynamics is often unsatisfactorily substantiated. Here we study the role of salt licks as potential attraction sites for spillover of gastrointestinal parasites from domestic sheep to wild reindeer. DNA-metabarcoding of soil collected at salt licks revealed that Nematodirus battus in addition to Teladorsagia circumcincta occurred at significantly higher prevalence in salt lick soil compared with soil from nearby control sites. 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, although more detailed investigation of the genetic diversity of N. battus across these hosts is needed to draw firm conclusions. Increased infection burdens with these sheep nematodes could potentially explain a recently observerd decline in calf recruitment rate in the Knutsho reindeer herd. This study supports the hypothesized role of artificial salt licks as hot spots for transmission of environmentally persistent pathogens and illustrates the importance of knowledge about such attraction points in the study of disease in free-roaming animals.