The distribution of diseases of polar bears (Ursus maritimus) has been analysed repeatedly and intensively in Canada, the USA, Norway and Greenland (Follmann et al. 1996, Oksannen et al. 2009). Russian serological studies concerned the Chukchi-Alaska bear population (Follmann et al., 1996), and some studies based in the Kara Sea (Rah et al., 2005). Studies of the Barents Sea bear population have been conducted primarily by Norwegian researchers in Spitsbergen and slightly to the east of it (Tryland et al., 2005).

The aim of our study was to assess polar bear seropositivity for various pathogenic agents in the area around Franz Josef Land. Bears were caught on the islands in 2010-2011 as part of the Russian Arctic polar bear study programme. The animals were sedated from a distance using DAN-Inject JM-25 pneumatic carbines containing a combination of medetomidine (Domitor, Orion Corporation, Finland) with a tiletamine-zolazepam mixture (Zoletil, Virbak, France). Blood samples were taken from the sublingual vein with a syringe, cooled for an hour to an hour and a half, and centrifuged for 20 minutes at 6,000 r/min, after which blood serum subsamples were put into clean Eppendorf tubes and kept frozen at -20°C until analysis. Serological tests for the presence of antibodies for distemper, Aujeszky’s disease, pig flu, toxoplasmosis, Dirofilaria and Trichinella spiralis were conducted on all the samples at the Chernogolovka experimental research base of the Russian Academy of Sciences’ Severtsov Institute of Ecology and Evolution using the enzyme immunodetection method. Commercial kits were used for quantitative assessment of the antibody titre, or by the cut-off method in line with protocols recommended by the manufacturer. Dirofilaria antibodies were detected using immunochromatography based on BVT (France) rapid tests.

Samples were obtained from 26 bears in three age groups: cubs, up to 12 months old: 7; young, 1-2 years: 3; and adult, over 2 years old: 16. The cubs and young bears were subsequently merged into one group of young animals for the purposes of statistical analysis. The percentage of seropositive bears in each age group was used as the comparison criterion.

Among the bears tested, three tested seropositive for distemper (12%, n = 25) – two adults (13.3%, n = 15) and one 12-month-old (10%). So the percentage of seropositive animals was the same in the adult and young age groups, while all seven cubs up to 12 months old tested seronegative for that particular pathogen. The overall percentage of animals testing seropositive for the distemper virus was similar to that registered in Spitzbergen – 8.3% (Tryland et al., 2005), and well below that of the other areas explored, 17-36 % (Follmann et al., 1996, Cattet et al., 2004). To all appearances, polar bears in the Barents-Kara population have the rarest contacts of all with carriers of that pathogen.

Two bears tested seropositive for pig flu (8% n = 25), both adults (12.5% n = 16). No seropositive cubs or 12-month-old bears were found. The chance of pig and bird flu infecting polar bears has not been observed, so the presence of antibodies may reveal only contact with these pathogens.

Two of the 21 bears (9.5%) tested seropositive for Aujeszky’s disease. Both were adults (15.4% n = 13), while all young animals were seronegative. Polar bear deaths from Aujeszky’s disease have been recorded in captivity (Banks et al., 1999) while the incidence of the virus in the wild has not been studied in polar bear habitats. Our results show that bears do have contact with this pathogen in Franz Josef Land.

Two bears tested seropositive for Toxoplasma gondii (7.4%), both adults (12.5% n = 16). The percentage of young and adult seropositive animals was the same. Their occurrence roughly coincided with that in the west of the Barents Sea, in Greenland (Oksanen et al., 2009) and the Chukchi-Alaska population – 6% (Rah et al., 2005). The  percentage of seropositive animals was much higher in Spitsbergen – 25.4% and 28.6% in the east and west, respectively (Oksanen et al., 2009). The  percentage of seropositive animals was much higher in the Kara Sea than in Franz Josef Land – 23.3% (Rah et al., 2005).

One polar bear tested seropositive for Dirofilaria sp. (5.3% n = 19). It was an adult (9.1% n = 11), while all the young bears were found to be seronegative. Though Dirofilaria sp. is a fairly common bear parasite, it has never before been observed in polar bears. We need to conduct thorough tests of the hearts and lymphatic glands of dead bears to study the possibility of Dirofilaria ursi parasitising on polar bears.

Twelve bears tested seropositive for Trichinella spiralis (60% n = 20), 10 of them adults (90.9% n = 11), compared to 2 out of 9 young animals (22.2%), which is significantly less than for adults (p < 0,01). Both cubs, older than 12 months, were from the same litter. Trichinella antibodies were also found in their mother. None of the cubs younger than 12 months tested seropositive for this pathogen. Trichinosis is widespread in Franz Josef Land and elsewhere in the Arctic, as noted as early as the middle of the 20^th century (Connell, 1949). The absence of Trichinella antibodies in bear cubs younger than 12 months was demonstrated in Spitsbergen, to coincide with our data. Seropositivity among adults was 78% in Spitsbergen and 51% in the Barents Sea (Asbakk et al., 2010).

So we can say that polar bears caught in Franz Josef Land encountered all six pathogenic agents being studied (distemper, pig flu, Aujeszky’s disease, toxoplasmosis, Dirofilaria and Trichinella spiralis). Animals in the wild had never before tested seropositive for Aujeszky’s disease, pig flu and Dirofilaria. Young animals, primarily cubs under 12 months of age, tested seronegative for all the pathogens tested, which suggests that bears become infected while devouring their prey after they have been weaned.

Sergei Naidenko (1), Ye. Ivanov (1), Ilya Mordvintsev (), Roman Yershov (2), Vyacheslav Rozhnov (1)

1. The Severtsov Institute of Ecology and Evolution at the Russian Academy of Sciences, Moscow, Russia

2. The State-run Franz Josef Land Nature Reserve, Arkhangelsk, Russia