Rabies in the Arctic Fox Population, Svalbard, Norway

Abstract

ABSTRACT:Arctic foxes, 620 that were trapped and 22 found dead on Svalbard, Norway (1996Norway ( -2004, as well as 10 foxes trapped in Nenets, North-West Russia (1999), were tested for rabies virus antigen in brain tissue by standard direct fluorescent antibody test. Rabies antigen was found in two foxes from Svalbard and in three from Russia. Blood samples from 515 of the fox carcasses were screened for rabies antibodies with negative result. Our results, together with a previous screening (1980-1989, n5817) indicate that the prevalence of rabies in Svalbard has remained low or that the virus has not been enzootic in the arctic fox population since the first reported outbreak in 1980. Brain tissues from four arctic foxes (one from Svalbard, three from Russia) in which rabies virus antigen was detected were further analyzed by reverse-transcriptase polymerase chain reaction direct amplicon sequencing and phylogenetic analysis. Sequences were compared to corresponding sequences from rabies virus isolates from other arctic regions. The Svalbard isolate and two of the Russian isolates were identical (310 nucleotides), whereas the third Russian isolate differed in six nucleotide positions. However, when translated into amino acid sequences, none of these substitutions produced changes in the amino acid sequence. These findings suggest that the spread of rabies virus to Svalbard was likely due to migration of arctic foxes over sea ice from Russia to Svalbard. Furthermore, when compared to other Arctic rabies virus isolates, a high degree of homology was found, suggesting a high contact rate between arctic fox populations from different arctic regions. The high degree of homology also indicates that other, and more variable, regions of the genome than this part of the nucleoprotein gene should be used to distinguish Arctic rabies virus isolates for epidemiologic purposes.

Dynamics and persistence of rabies in the Arctic

“…In these low-density Arctic fox populations, immigration caused sporadic outbreaks of rabies, which is reflected by a strong correlation between the immigration rate of infectious Arctic foxes and cumulative density of rabies cases in sensitivity analysis. This result is consistent with empirical data from Svalbard, Norway, where episodic rabies cases in a relatively low-density Arctic fox population appear to be caused by the infrequent introduction of the virus by a small number of long-distant migrants coming from Russia (Mørk et al 2011). This important potential role of immigration and long-distance movement in rabies dynamics and persistence in the Arctic suggests that metapopulation modelling or spatially explicit simulation approaches may be key avenues for future research.…”

“…When rabies virus is no longer circulating locally in the Arctic fox population, new rabies outbreaks could be triggered by the reintroduction of the virus following immigration of infected Arctic foxes from other areas (Mørk & Prestrud 2004). The role of migrants in reintroducing rabies to regions where it has died out is also supported by genetic studies of the Arctic rabies virus variant that suggest disease spread by Arctic foxes travelling across the sea ice from Russia to Svalbard (Mørk et al 2011) and from North America to Greenland (Mansfield et al 2006).…”

Spatiotemporal distribution of rabies in Arctic foxes in Greenland

“…The link between the cyclic occurrence of rabies outbreaks in Arctic fox populations reported here and in related studies is often reported as being correlated to fox population density, relying in part on cyclic variations in prey abundance, e.g., rodents (Ballard et al 2001;Dalén et al 2005;Norén et al 2011b). When Arctic fox populations peak in numbers, the likelihood of encounters between individuals increases once the foxes disperse (Tabel et al 1974;Mørk and Prestrud 2004;Mørk et al 2011). Studies on dispersal distances in Canada (Tarroux et al 2010) and Russia (Goltsman et al 2005) indicate that movement distances of more than a thousand kilometers are not uncommon in Arctic foxes.…”

Unique genetic features of canine adenovirus type 1 (CAdV-1) infecting red foxes (Vulpes vulpes) in northern Norway and arctic foxes (Vulpes lagopus) in Svalbard

“…Red foxes from the Norwegian mainland do not get in direct contact with arctic foxes in Svalbard, but the red fox population may have contact with other European wildlife populations (Norén et al, 2015). One explanation for the arrival of the virus to Svalbard can be through migration of arctic foxes from other Arctic regions, as suggested for other pathogens arrived in Svalbard from Russia (Henttonen et al, 2001, Mørk et al, 2011. It is known that arctic foxes in Svalbard get in contact with other high-Arctic wildlife populations by using the sea ice as platform for migration (Geffen et al, 2007).…”