ReinBRAIN – Parasites in the brain – a climate problem for reindeer


Infection with the parasitic nematode Elaphostrongylus rangiferi is of increasing concern for reindeer (Rangifer tarandus tarandus) in Norway because of a warming climate. The parasite has an indirect lifecycle with a highly temperature-dependent development in gastropods (slugs and snails) as intermediate hosts, from L1 stage larvae to infective L3 stage larvae. This means that in a normal summer in a subarctic climate, Elaphostrongylus larvae shed that year only become infective to reindeer in the following year, in a two-year cycle. However, with increasing average temperatures, a shortening of the developmental time to a one-year cycle is predicted, entailing a much higher infection risk for reindeer. Exposure occurs by the accidental ingestion of L3-bearing slugs and snails during grazing. The period with the highest L3 parasite loads in gastropods is in July to August, although infection can occur before and after the peak period. Disease severity is related to the number of infective L3 larvae that have been ingested. After uptake, the larvae migrate through the body to the central nervous system (CNS), where they develop further into sexually mature adults. The adult parasites move then to the skeletal muscle, producing eggs that develop into L1 larvae, which in turn migrate to the lungs, are sneezed, swallowed again and finally excreted with the faeces. Adult nematodes are estimated to survive up to three years in the host.

Norway has semi-domesticated reindeer that are almost exclusively herded by the indigenous Sami people, in addition to wild reindeer. Both types are free-ranging throughout the year. The semi-domesticated herds are only rounded up a few times a year; the timing of which varies considerably between geographic regions. Calves are marked in late spring/summer (June-August), and in late autumn/early winter (October-January), the flocks are separated for slaughtering. Traditionally, there are no round-ups during the grazing season in late summer/early autumn. This limits the opportunities for carrying out prophylactic treatments against brainworm to the period of calf-marking. Any treatment given during this time would need to have a sufficiently long effect to provide protection for the remaining weeks/months of summer and autumn, when the risk for brainworm infections is predicted to be at its highest.

Aims of the Project

The feasibility of using the sustained release formulation LongRange® to reach sufficient plasma concentrations of the anthelmintic eprinomectin, a macrocyclic lactone drug used in other ruminant species, was investigated in reindeer for long-term protection against nematode infections. By determining the pharmacokinetic characteristics after a single s.c. application, we wanted to evaluate if this drug preparation could maintain sufficiently high eprinomectin levels over time to protect against brainworm and thus solve one of the problems in treating free-living semi-domesticated reindeer. At the same time, we analysed eprinomectin concentrations in faeces to estimate the ecotoxicological impact of the treatment.

FFL/JA funded project, 2021.

Project leader, R. Davidson, Norwegian Veterinary Institute, Tromsø, Norway


After a single subcutaneous injection at 1mg/kg bodyweight in adult reindeer and calve, plasma and faeces concentrations were determined using ultra-high performance liquid chromatography high resolution mass spectrometry (UHPLC-HRMS). Plasma concentrations remained above the presumed effect level of 2 ng/mL for 80 days, demonstrating the drug’s potential. Pharmacokinetic parameters were compared to other species using allometric scaling. Calves and adults had slightly different profiles. No viable faecal nematode eggs were detected during treatment, demonstrating the effectivity of the treatment. Eprinomectin was measurable in the reindeer faeces for up to 100 days, which is of environmental concern.

Publications and presentations

  • Davidson RK, Fæste CK, Uhlig S, Tukun F-L, Lian H, Solvang HA, Thorvaldsen R, Folkow L, Sánchez Romano J, Kilvær MV, Holmgren KE, Nymo IH. Pharmacokinetics of a long-acting subcutaneous eprinomectin injection in semi-domesticated reindeer (Rangifer tarandus tarandus) – a pilot study. Environ Toxicol Pharmacol 2022 97:104041.
  • Davidson RK, Mørk T, Holmgren KE, Oksanen A. Infection with brainworm (Elaphostrongylus rangiferi) in reindeer (Rangifer tarandus ssp.) in Fennoscandia. Acta Vet Scand 2020, 62:1-15.
  • Davidson R, Ciezarek A, Closset N, Evans A, Fæste CK, Folkow L, Miller A, Mørk T, Nymo I, Rauseth G, Stuut M, Tukun F-L, Tveraa T, Uhlig S, Vineer HR. Mitigation measures for climate sensitive infections – challenges with Elaphostrongylus rangiferi. 15th International Congress of Parasitology – ICOPA 2022, 21.-26.8.2022, Copenhagen, Danmark.