Chronic wasting disease (CWD) in cervids

Abstract

In April and May of 2016, Norway confirmed two cases of chronic wasting disease (CWD) in a wild reindeer and a wild moose, respectively. In the light of this emerging issue, the European Commission requested EFSA to recommend surveillance activities and, if necessary, additional animal health risk-based measures to prevent the introduction of the disease and the spread into/within the EU, specifically Estonia, Finland, Iceland, Latvia, Lithuania, Norway, Poland and Sweden, and considering seven wild, semidomesticated and farmed cervid species (Eurasian tundra reindeer, Finnish (Eurasian) forest reindeer, moose, roe deer, white-tailed deer, red deer and fallow deer). It was also asked to assess any new evidence on possible public health risks related to CWD. A 3-year surveillance system is proposed, differing for farmed and wild or semidomesticated cervids, with a two-stage sampling programme at the farm/geographically based population unit level (random sampling) and individual level (convenience sampling targeting high-risk animals). The current derogations of Commission Implementing Decision (EU) 2016/1918 present a risk of introduction of CWD into the EU. Measures to prevent the spread of CWD within the EU are dependent upon the assumption that the disease is already present; this is currently unknown. The measures listed are intended to contain (limit the geographic extent of a focus) and/or to control (actively stabilise/reduce infection rates in an affected herd or population) the disease where it occurs. With regard to the zoonotic potential, the human species barrier for CWD prions does not appear to be absolute. These prions are present in the skeletal muscle and other edible tissues, so humans may consume infected material in enzootic areas. Epidemiological investigations carried out to date make no association between the occurrence of sporadic Creutzfeldt-Jakob disease in humans and exposure to CWD prions.

Keywords: cervids; chronic; introduction; risk; spread; surveillance; wasting.

Figure 1

Distribution of CWD in North America in as of October 2016. Source: USGS

1. The historical occurrence at the Toronto Zoo (Ontario, Canada) is not shown on the map (https://www.nwhc.usgs.gov/disease_information/chronic_wasting_disease)

Figure 2

Distribution of the 23 populations of wild Eurasian tundra reindeer of Norway. Source: Norwegian Institute for Nature Research

1. The three clinical cases (up 21 November 2016) of CWD have all been detected in Nordfjella (region 11). (http://www.nina.no/english/Home).

Figure 3

Distribution of the Nordfjella wild reindeer population (red), where the three CWD cases had been found, and the borders to the Hardangervidda wild reindeer population (dark green) and the neighbouring herd of semidomesticated reindeer (pink)

1. Map: Bernt Johansen, Norwegian Research Institute (NORUT).

Figure 4

Number of moose shot in Norway per 10 km² hunting area (2016), and geographical distribution. Source: Statistics Norway (https://www.ssb.no/en/jord-skog-jakt-og-fiskeri/statistikker/elgjakt)

Figure 5

The Sápmi region, the part of Fennoscandia traditionally inhabited by the Sami people, and where the majority of the reindeer herding of this region is conducted. Source: (http://www.sim1.se/background/samer/samer_01.html)

Figure 6

Reindeer herding in Norway, Sweden and Finland, indicating the development of reindeer numbers the past century, the stocking density (animals/km²) and the seasonal migration in the spring (arrows) or year‐round pastures (circles)

1. Between Norway and Sweden, cross‐border herding takes place, with many herders having pasture rights on both sides (Source: Pape and Löffler, 2012; © Royal Swedish Academy of Sciences).

Figure 7

Reindeer herding areas of Norway (semidomesticated reindeer; red areas)

1. Map: Bernt Johansen, NORUT. Reindeer herding is conducted in 140 municipalities in Norway, using around 140,000 km² or about 40% of the land area.