Research Seminar 3.9.2008 3-4 pm, Crayfish plague, a challenge for diagnostics

1.9.2008

<div>Crayfish plaque as induced by the water mould Aphanomyces astaci is the most serious disease appearing in Finland among crayfish. Two crayfish species are found in Finland, as are two types of crayfish plaque. The type of crayfish plaque that originally destroyed the crayfish populations in rivers in Finland still exists in Central, Eastern and Northern Finland. About 40 years ago, the signal crayfish was introduced to patch up the crayfish industry and that brought with it the signal crayfish-type of plaque. In districts in Southern Finland where most populations of signal crayfish occur, populations of river crayfish have diminished while signal crayfish-type plaque epidemics annually are found among remaining populations. Crayfish deaths caused by this type of plaque increasingly is being found also outside the established regions with signal crayfish. </div>

LVM Satu Viljamaa-Dirks, Research Unit for Fish and Wildlife Health, Evira, Kuopio
Evira/Viikki, Auditorium C111 Kalevi
Wednesday on 3 September 3 - 4 pm

For the last ten years, Evira’s branch in Kuopion has compiled an extensive population collection of both types of crayfish plaque. A research project in 2006 and 2007 called ”Rapurutto hallintaan - epidemiologian ja diagnostiikan verkostohanke, i.e., Controlling crayfish plaque – a project for epidemiology and diagnostics” investigated the ability of various populations to instigate disease, and diagnostic methods for establishing infections. Finnish Game and Fisheries Research Institute and Kuopio University as partners in the project investigated on their parts the transfer of crayfish plague from mother crayfish to their young in signal crayfish farming, and genome variations among populations of crayfish plague.

Populations of crayfish plague were found to display significant variations in ability to instigate disease. Populations of the signal-crayfish type were more efficient in causing mortality than river-crayfish type populations, the latter proceeding distinctly slower. Infections slowly causing symptoms among river crayfish explain why crayfish plague has persisted for more than a hundred years in Finland. This is also the most probable reason why the planting of crayfish repeatedly has failed. Finding slightly infected disease-carrying river crayfish in laboratory assessments presents challenges, but is necessary for securing planting activities. Traditional cultivation methods are not applicable to studying carrier crayfish, as they carry minute crayfish-plague mycelia and damaged spots more often than not are contaminated by secondary fungus infections. A Norwegian quantitative PCR method tested by the project proved more efficient than cultivating for actual case samples of disease, but assessing the reliability of establishing disease carriers will require additional research.

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