Attempting to Understand an Unknown of the Arctic
Evidence of wildlife exposure to Erysipelothrix rhusiopathiae across the Arctic piques the interest of CWHC-Alberta director Dr. Susan Kutz and her team.
CWHC Alberta biologist Collin Letain and University of Calgary veterinarians Owen Slater and Dean Brown work together on a sedated female reindeer.
The Bacteria Erysipelothrix rhusiopathiae
Erysipelothrix rhusiopathiae is a gram-positive opportunistic bacterium that often colonizes its host during periods of stress. Erysipelothrix rhusiopathiae is best known in the swine industry as it causes erysipelas characterized by acute septicemia, subacute cutaneous lesions, or chronic arthritis. Less well known is the bacteria’s ability to infect wild birds, reptiles, fish, arthropods and mammals. People are also susceptible to this bacterium as well, however, infection is rare.
A domestic pig showing subcutaneous lesions characteristic of swine erysipelas.
E. rhusiopathiae in Arctic Wildlife
The bacteria’s relevance to the CWHC and wildlife researchers including Dr. Susan Kutz’s research group at the University of Calgary’s Faculty of Veterinary Medicine began in 2010. Erysipelothrix rhusiopathiae was first reported in wild wood bison in 1973 but landed on the team’s radar following multiple muskox mortality events from Banks Island, NT and Victoria Island, NU between 2009 and 2011. Archived tissues from this cluster of die offs later tested positive for the bacteria and is believed to have played a role in their death. Geographically widespread sero-prevalence across the Canadian North in both woodland and barren-ground caribou has also been demonstrated but source of exposure and the bacteria’s pathogenicity in caribou remains anything but certain.
The lower leg of a barren-ground caribou from Prince Charles Island, NU submitted to the CWHC for diagnostic testing.
A CWHC Case of the E. rhusiopathiae in Barren-Ground Caribou
During spring of 2016, Environment and Climate Change Canada biologists were conducting aerial surveys on Prince Charles Island, NU when they found what was described as an “apocalyptic scene”. Forty-seven barren-ground caribou carcasses were found along the northeast side of the island. Samples were collected by the Government of Nunavut and submitted to CWHC-Alberta. Fat analysis and bacterial culture was performed on bone marrow extracted from 20 of 23 caribou’s metatarsal bones submitted and fecal parasitology was run on the same 23 specimens’ feces submitted for diagnostic testing. Parasitology results came back unremarkable, however, analyzed bone marrow revealed an average fat content of 5.6% while a healthy ruminant’s bone marrow should contain at least 70% fat. This indicated that the 20 caribou tested from the 47 animal die off, likely died due to emaciation and that the fate of the entire herd may have been decided by weather events.
Bacterial culture of the bone marrow samples revealed that 11 of the 20 samples grew what appeared to be E. rhusiopathiae, which was confirmed by identifying the isolated bacteria using PCR. Pathological explanation for this finding is that the animals which tested positive may have been experiencing a subclinical bacteremia as the bacteria was cultured using a highly sensitized technique designed to grow E. rhusiopathiae even if very low concentrations of the bacteria are present. Another theory is that the already emaciated animals were under high environmental stress due to inaccessible food, allowing the opportunistic bacteria to colonize.
Post-doctoral fellow Dr. Kristin Bondo preparing sampling kits for the vaccine trial before and after sample collection.
Wide Spread Exposure Sparks Research into Immune Response
Scientists speculate that exposure to E. rhusiopathiae is widespread but that disease and mortality may be linked to other underlying stressors that increase susceptibility to the bacterial invasion. Erysipelothrix can be maintained by carrier animals and may survive for an unknown period of time in water, soil, meat and animal remains. There is also some evidence that it may be transmitted by invertebrate vectors.
With this bacteria becoming of increasing importance, particularly in sensitive caribou populations, a new vaccine trial has begun on the University of Calgary’s captive reindeer herd. This work is an initiative of the BC Boreal caribou health program, spearheaded by Drs. Helen Schwantje, Government of BC and Bryan Macbeth. The main objective of this trial is to use pre- and post-exposure serum to validate a serological assay for Erysipelothrix exposure in caribou. Patterns and longevity of antibody response in reindeer will also be evaluated and will complement interpretation of ongoing widespread serological surveys for this pathogen in barren-ground and woodland caribou populations in North America.
Owen Slater administers the Erysipelothrix vaccine and takes a blood sample from a sedated female reindeer while Collin Letain keeps the animals head secured.
Contributed by Collin Letain, CWHC Alberta region.