Two unrelated captive-born arctic foxes (Alopex lagopus) developed a similar unusual progressive neurological disease while at the same institution. A 2½-year-old female developed episodes of abnormal mentation, somnolence, temporary collapse, difficulty to rouse, lack of fear, and aggression. The clinical condition deteriorated over 3 months with loss of body condition and development of generalized seizures, ataxia and circling. Cytology of cerebrospinal fluid demonstrated increased proteins and lymphocytic inflammation. Euthanasia was elected. Postmortem examination revealed a severe necrotizing meningoencephalitis with extensive malacia, mononuclear perivascular cuffing, gliosis and Wallerian degeneration of the most rostral forebrain. The histopathological features suggested a viral etiology. Tests for the most common infectious agents associated with encephalitis in carnivores were negative.
Six months later, a 5-year-old male cagemate developed a similar milder syndrome. Magnetic resonance imaging of the brain revealed pronounced bilaterally symmetrical intra-axial lesions in the frontal cortices and olfactory bulbs that were consistent with the lesions seen in the female. Given the poor prognosis and the suspicion of viral encephalitis, an empirical antiviral treatment (famciclovir 10 mg/kg q 12 h PO) was administered for 6 months. The clinical condition of this individual has been stable now for over 8 months.
The clinical and pathological findings in these animals are very similar to several cases of necrotizing encephalitis that may be associated with a novel herpesvirus recently described in arctic foxes in Sweden.1,3 This condition, which has not been reported in North America, also bears similarity to the necrotizing meningoencephalitis described in small-breed dogs.2
The authors would like to thank Drs. Colleen Mitchell and Jonathan Huska from the Toronto Veterinary Emergency Hospital for their help in the interpretation of the MRI and for guidance regarding medical treatment in this case. The authors also acknowledge Dr. Frederik Widén from the Swedish University of Agricultural Sciences, Dr. Liljana Petrovska from the Animal Health and Veterinary Laboratories Agency (Weybridge, UK) and the Wildtech project (EU 7th Framework Program for Research and Technological Development, grant agreement no. 222633) for assisting with and supporting the virology and molecular work. We finally would like to thank the Animal Care staff of the Toronto Zoo.
1. Berg AL, Gavier-Widén D, Nilsson K, Widén F, Berg M, Gregorius S, Agren E, Erlandsson M, Mörner T. Necrotizing encephalitis of unknown cause in Fennoscandian Arctic foxes (Alopex lagopus). J Vet Diagn Invest. 2007;19:113–117.
2. Cooper JJ, Schatzberg SJ, Vernau KM, Summers BA, Porter BF, Siso S, Young BD, Levine JM. Necrotizing meningoencephalitis in atypical dog breeds: a case series and literature review. J Vet Intern Med. 2014;28:198–203.
3. Widén F, Sundström E, Gavier-Widén D, Berg AL, Dillner B, Berg M. Detection of herpesvirus DNA in Arctic foxes (Alopex lagopus) with fatal encephalitis. Res Vet Sci. 2012;92:509–511.