Crayfish plague (Aphanomyces astaci)

The Norwegian Veterinary Institute (NVI) conducts crayfish plague surveillance in control areas, combat zones and risk areas.

The purpose of the program is to monitor the infection pressure and infection development in control areas and combat zones for Aphanomyces astaci, and to substantiate disease freedom and/or provide an early warning of possible infection spread in to risk areas


In 2021, a total of 58, 39, 20 and 36 water samples were collected from selected sites in the Halden-, Mosse-, Glomma watercourse regions and in the Eidskog region, respectively. Sampling locations were strategically selected and focused on both control zones and the risk areas adjacent to crayfish plague control zones. The presence/absence of the three target species was determined simultaneously through screening with species-specific qPCR assays.

  • In the Halden watercourse, eDNA of A. astaci was detected in the south of Lake Rødnessjøen and in River Hølandselva, further upstream than previously detected. No spread of the pathogen was observed in any of the other areas monitored with the eDNA methodology. However, one sample from River Lierelva (risk zone) was positive for signal crayfish eDNA in June. This coincided with the cessation of positive noble crayfish eDNA detections at this site in September. Also two other locations in the risk zone yielded no noble crayfish eDNA, which is a decline in positive noble crayfish detections from previous years.
  • In the Mosse watercourse, no eDNA of A. astaci or signal crayfish was detected, while noble crayfish eDNA was detected upstream of Lake Langen.
  • In the Glomma watercourse, eDNA from noble crayfish was detected at one station - Oppstadåa south. No eDNA was detected from signal crayfish or A. astaci.
  • In Eidskog, all samples were negative for signal crayfish and A. astaci, while several samples were positive for noble crayfish eDNA in the rivers Vrangselva and Finnsrudelva.

In August 2021, the river Mysenelva that is part of the Hæra watercourse was struck by crayfish plague. The Norwegian Veterinary Institute confirmed the detection of A. astaci from dead noble crayfish. This further increases the number of A. astaci infected areas in Norway. The Norwegian Food Safety Authority extended the crayfish plague zone for Glomma to incorporate Mysenelva downstream of Rustadfossen east of Mysen.

In summary, the single positive detection of signal crayfish eDNA in Lierelva is a non-conclusive result and requires close follow-up in 2022 regarding the possible spread of crayfish plague. The observed crayfish plague outbreak in Mysenelva increases the number of infected water systems in Norway, and will be integrated in the crayfish plague surveillance in 2022.

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