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Orthopoxvirus DNA in Eurasian Lynx, Sweden | CDC EID

EID Journal Home > Volume 17, Number 4–April 2011

Volume 17, Number 4–April 2011
Orthopoxvirus DNA in Eurasian Lynx, Sweden
Morten Tryland, Malachy Ifeanyi Okeke, Carl Hård af Segerstad, Torsten Mörner, Terje Traavik, and Marie-Pierre Ryser-Degiorgis

Author affiliations: Norwegian School of Veterinary Science, Tromsø, Norway (M. Tryland); University of Tromsø, Tromsø (M.I. Okeke, T. Traavik); National Veterinary Institute, Uppsala, Sweden (C. Hård af Segerstad, T. Mörner, M.-P. Ryser-Degiorgis); Genøk—Centre for Biosafety, Tromsø (M.I. Okeke, T. Traavik); University of Bern, Bern, Switzerland (M.-P. Ryser-Degiorgis)

Suggested citation for this article

Cowpox virus, which has been used to protect humans against smallpox but may cause severe disease in immunocompromised persons, has reemerged in humans, domestic cats, and other animal species in Europe. Orthopoxvirus (OPV) DNA was detected in tissues (lung, kidney, spleen) in 24 (9%) of 263 free-ranging Eurasian lynx (Lynx lynx) from Sweden. Thymidine kinase gene amplicon sequences (339 bp) from 21 lynx were all identical to those from cowpox virus isolated from a person in Norway and phylogenetically closer to monkeypox virus than to vaccinia virus and isolates from 2 persons with cowpox virus in Sweden. Prevalence was higher among animals from regions with dense, rather than rural, human populations. Lynx are probably exposed to OPV through predation on small mammal reservoir species. We conclude that OPV is widely distributed in Sweden and may represent a threat to humans. Further studies are needed to verify whether this lynx OPV is cowpox virus.

Cowpox virus (family Poxviridae, genus Orthopoxvirus [OPV]) was originally considered to infect milking cows and to have zoonotic potential. Because of its relationship to variola virus and immunologic cross-reaction, cowpox virus was used to protect humans against smallpox (1). Later, vaccinia virus, another OPV with unknown origin, was used as a vaccine virus through the global smallpox eradication campaign, and cowpox virus infections became less common in cattle, other animals, and humans. However, during recent decades, cowpox virus infections have reemerged in domestic cats and other animals, including wild animals in captivity (2–4), and have increased in humans subsequent to transmission from cats, rodents, zoo animals, and circus animals (5–9). Cowpox virus seems to be restricted to Eurasia, but spread of poxviruses to new regions through relocation of their natural host species is possible (10).

Cowpox virus was first isolated from felid species—lions (Panthera leo), cheetahs (Acinonyx jubatus), black panthers (Panthera pardus), ocelots (Leopardus pardalis), jaguars (Panthera onca), pumas (Felis concolor), leopard cat (Prionailurus bengalensis), Pallas cat (Otocolobus manul), and domestic cat (Felis catus)—during an outbreak in the Moscow Zoo in 1973–1974 (11) and subsequently from 3 cheetahs in Whipsnade Park, England, in 1977 (12). Since 1978, cowpox virus infections have been diagnosed in domestic cats in several European countries (13–16); the cats were probably infected by contact with rodents, and in some cases infections were transmitted to humans (16–18). Serologic surveys and detection of OPV DNA by PCR have indicated that wild rodents and shrews are likely reservoir hosts of cowpox virus in western Europe (19–23), although infectious virus has never been isolated from these animals.

Anti-OPV antibodies have been demonstrated in carnivores such as European lynx (Lynx lynx), red fox (Vulpes vulpes), and a brown bear (Ursus arctos) (24,25). Anti-OPV seroprevalence was 29% among 17 lynx from the Sarek National Park, northern Sweden, and 1% among 73 lynx from southern Finland (25). Taking into account the human cowpox virus cases reported from Finland, Sweden, and Norway (16,23,26), OPV, presumably cowpox virus, is probably widespread among wildlife in Scandinavia, having small wild rodent populations as a reservoir. Because carnivores are exposed to OPV through predation on rodents, virus-specific DNA or antibodies in carnivores could serve as an indicator for the epizootiologic situation in rodent populations (25).

To our knowledge, no cowpox virus case has been reported in free-ranging wild felids. To evaluate the possibility that cowpox virus may cause disease among Eurasian lynx, we searched for evidence of OPV infection in this large, free-ranging felid in Sweden. We used PCR to detect OPV DNA in tissue samples and compared these data with pathological findings. In addition, to address the possible effects of such viruses in the ecosystems, we searched for phylogenetic relationships between the virus infecting lynx and viruses causing clinical cowpox cases in Scandinavia.

Orthopoxvirus DNA in Eurasian Lynx, Sweden | CDC EID

Suggested Citation for this Article
Tryland M, Okeke MI, Hård af Segerstad C, Mörner T, Traavik T, Ryser-Degiorgis M-P. Orthopoxvirus DNA in Eurasian lynx, Sweden. Emerg Infect Dis [serial on the Internet]. 2011 Apr [date cited].

DOI: 10.3201/eid1704.091899

Comments to the Authors
Please use the form below to submit correspondence to the authors or contact them at the following address:

Morten Tryland, The Norwegian School of Veterinary Science, Section of Arctic Veterinary Medicine, Stakkevollveien 23, N-9010 Tromsø, Norway
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