Sammendrag
In Norway, the Willow Ptarmigan (Lagopus lagopus lagopus) is experiencing population
declines and is nationally Red Listed as Near Threatened. Although disease has not generally been
regarded as an important factor behind population fluctuations for Willow Ptarmigan in Norway,
disease occurrence has been poorly investigated. Both louping-ill virus (LIV) and the closely related
tick-borne encephalitis virus are found along the southern part of the Norwegian coast. We assessed
whether and where Norwegian Willow Ptarmigan populations have been infected with LIV. We
expected to find infected individuals in populations in the southernmost part of the country. We did not
expect to find infected individuals in populations further north and at higher altitudes because of the
absence of the main vector, the sheep tick (Ixodes ricinus). We collected serum samples on Nobuto
filter paper and used a hemagglutination inhibition assay for antibodies against LIV. We collected data
at both local and country-wide levels. For local sampling, we collected and analyzed 87 hunter-collected
samples from one of the southernmost Willow Ptarmigan populations in Norway. Of these birds, only
three positives (3.4%) were found. For the country-wide sampling, we collected serum samples from
163 Willow Ptarmigan carcasses submitted from selected locations all over the country. Of these birds,
32% (53) were seropositive for LIV or a cross-reacting virus. Surprisingly, we found seropositive
individuals from locations across the whole country, including outside the known distribution of the
sheep tick. These results suggest that either LIV or a cross-reacting virus infects ptarmigan in large
parts of Norway, including at high altitudes and latitudes.
Lagopus lagopus, louping-ill virus, ptarmigan, serosurvey, tick-borne viruses.
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