Corynebacterium freneyi Bacterial Septicemia Secondary to Contagious Ecthyma in a Wild Muskox (Ovibos moschatus) Open Access

In February 2018, an Inuit hunter discovered a moribund male muskox calf (Ovibos moschatus) near Cambridge Bay, Victoria Island, Nunavut, Canada (68°54′47″N, 104°59′0.9″W). The animal was euthanatized, collected by wildlife conservation officers, and submitted to the Canadian Wildlife Health Cooperative Alberta Region, Faculty of Veterinary Medicine, University of Calgary, for diagnostic investigation by an anatomic veterinary pathologist (J.L.R.) certified by the American College of Veterinary Pathologists.

The calf was dehydrated and in poor nutritional condition with minimal fat stores. Ulcerative and proliferative dermatitis was present on the haired skin, lips, and mucocutaneous junction of the muzzle, consistent with contagious ecthyma (CE) associated with orf virus infection (Fig. 1A). There was associated suppurative cellulitis of head and neck with suppurative lymphadenitis of the mandibular and cervical lymph nodes (Fig. 1B).

Total DNA was extracted from minced tissue from the muzzle lesion using a E.Z.N.A.® Tissue DNA Kit (Omega Bio-Tek Inc., Norcross, Georgia, USA) according to the manufacturer's protocol. A negative control (water) was used for all reactions. The PCRs were performed in duplicate using the TaKaRa Ex Taq® DNA Polymerase (Takara Bio USA Inc., Mountain View, California, USA) with an annealing temperature of 55 C. For virus DNA detection, parapoxvirus-specific primers targeting the major viral envelope protein B2L gene (Inoshima et al. 2000) and the DNA polymerase gene (Bracht et al. 2006) were positive, confirming the presence of orf virus.

Routine bacterial culture yielded Corynebacterium freneyi (very heavy growth), Trueperella pyogenes (moderate growth), and Staphylococcus aureus (moderate growth) in the muzzle lesion. Both C. freneyi and T. pyogenes were isolated from the brain, liver, kidney, spleen, and purulent lymph nodes; higher yield of C. freneyi was present in most tissues. Multiple tissues were negative for Erysipelothrix rhusiopathiae when tested (Forde et al. 2016).

We fixed samples of lesions, hooves, and major organs in 10% neutral buffered formalin for 48 h. Tissues were processed by routine methods, and 4-µm-thick sections of paraffin-embedded tissues were stained with H&E prior to examination with light microscopy.

Histologically, there was necrotizing and proliferative suppurative dermatitis with folliculitis and abscesses in skin lesions from the muzzle (Fig. 2A–C). We did not identify intracytoplasmic inclusion bodies in the sections examined. Additional lesions included suppurative lymphadenitis, necrotizing laminitis (Fig. 2D), suppurative meningoencephalitis (Fig. 2E), and necrosuppurative hepatitis indicative of bacterial septicemia.

Contagious ecthyma is a viral disease caused by orf virus (genus Parapoxvirus, family Poxviridae) of wild and domestic ruminants, cervids, and other animal species that is spread through direct contact and environmental sources in which it can persist for several years (Spyrou and Valiakos 2015). Zoonotic disease most often occurs in people with frequent contact with infected animals (farmers, veterinarians, and hunters) and is particularly relevant in Arctic communities where subsistence hunting makes up an important dietary component (Spyrou and Valiakos 2015; Cuyler et al. 2020). However, there currently are no data on the occurrence of human orf virus infection in the region where this muskox originated.

Dermatitis due to orf virus infection compromised the skin, providing an entry point for opportunistic bacterial pathogens to breach the dermal barrier. This likely led to localized cellulitis of the head, then suppurative lymphadenitis, culminating in septicemia that included hepatitis, encephalitis, and laminitis. This animal had terminal septicemia when it was euthanatized. Secondary bacterial infections with Staphylococcus sp., Streptococcus sp., and Corynebacterium sp. have been reported following CE in domestic animals, although secondary infections are not always described in CE outbreaks with high mortality (Spyrou and Valiakos 2015). Investigation of an outbreak of CE in wild muskox identified Trueperella pyogenes, Staphylococcus sp., and Streptococcus sp. as secondary infections in CE skin lesions and lymph nodes (Vikøren et al. 2008). The animals in that study were euthanatized, possibly earlier in their clinical course than in our case and did not appear to have bacterial septicemia (Vikøren et al. 2008). Our case shows a probable link between orf virus infection and terminal septicemia. This result highlights the importance of investigating mortality events with prompt field responses to obtain high-quality samples that minimize post-mortem changes and determining proximate causes of death by use of histopathology and ancillary tests.

In our case, C. freneyi appeared to be the main bacterial pathogen of the septicemia because higher yields were obtained in most tissues cultured for bacteria. Corynebacterium spp. are common opportunistic pathogens in animals and people (Bernard 2012). Although C. freneyi has not been described in the literature as a veterinary pathogen, in human patients it has been associated with opportunistic infections that include a wound, an abscess, and bacteremia (Bernard 2012). Trueperella pyogenes was also present in several tissues and is a common pus-forming bacterium of ruminants.

Contagious ecthyma is one of many diseases implicated in the decline of Alaskan muskoxen (Afema et al. 2017). Outbreaks in captive herds have reached 100% mortality in affected calves (Dieterich et al. 1981; Kummeneje and Krogsrud 1987). Macroscopic and microscopic lesions in this muskox were similar to those described in these previous outbreaks, with typical CE lesions of ulcerative and proliferative crusting dermatitis affecting the lips and muzzle. In some individuals in previous outbreaks, lesions were also present on the skin of the eyelids, perineal, neck, and thorax (Dieterich et al. 1981; Kummeneje and Krogsrud 1987). On Victoria Island (in the same area and population as this muskox), Tomaselli et al. (2016) described CE in a hunter-harvested muskox with Brucella sp. osteomyelitis and verminous pneumonia.

Muskoxen are an important species in the Arctic and are highly valued by local human communities for food, income, and cultural importance (Cuyler et al. 2020). The Victoria Island muskox population has experienced a severe decline over the last decade (Cuyler et al. 2020), which may be associated with Erysipelothrix rhusiopathiae (Kutz et al. 2015; Tomaselli et al. 2018; Cuyler et al. 2020). Additionally, cumulative stressors such as rapid climate change, low genetic diversity, and an increase or emergence of other pathogens, including orf virus, Brucella suis biovar 4, and lungworm infections, are likely contributing factors (Kutz et al. 2015; Tomaselli et al. 2019; Cuyler et al. 2020).

Local knowledge from Cambridge Bay reports signs consistent with CE infection in this muskox population in the mid-2000s (Tomaselli et al. 2018). The virus was first isolated and confirmed in 2014 (Tomaselli et al. 2016) and has been isolated from several muskoxen since (Dalton 2019). Reasons for the apparent increase in CE are unknown, but, in combination with other cumulative stressors, CE may contribute to muskox population declines (Cuyler et al. 2020), potentially through fatal secondary bacterial infections as was highlighted by this case. The confirmation of terminal septicemia associated with orf virus is important because it provides additional mechanistic information about the pathogenesis of fatal orf virus infections in this dwindling population.

We are grateful to Brandon Langan for finding and reporting the muskox to the conservation officers of Cambridge Bay and to Candice Pederson, who coordinated logistics for carcass collection and submission. Many thanks to Susan Calder-Lodge, Jennifer Larios, Melencio Nicolas, Chris Bergeron, Jim Carlsen, and Paul Gajda for technical support. Krista La Perle provided invaluable histopathology support. Funding and logistical support for this case was provided by the University of Calgary Faculty of Veterinary Medicine, the Government of Nunavut, a Polar Knowledge Canada grant to S.J.K. and the Polar Knowledge Canada's Canadian High Arctic Research Station. J.D.F. is supported by a Morris Animal Foundation Fellowship Grant.