White-clawed Crayfish and Porcelain Disease

 

White-clawed Crayfish with Porcelain Disease

Porcelain disease is a disease caused by the microsporidian parasite Thelohania contejeani which is moderately common in White-clawed Crayfish Austropotamobius pallipes populations throughout Europe although is considered relatively uncommon within the UK. In the UK this disease occurs in less than 5% of individuals in healthy populations. White-clawed Crayfish populations in Britain are in serious trouble at the moment and my personal view is they may well go extinct in this country in the not so distant future. Porcelain disease is usually not a particularly significant issue and compared with other issues like crayfish plague is not the biggest threat to the species. 

However there has been a recent worrying increase in the disease, in UK populations. Signal Crayfish Pacifastacus leniusculus have many issues affecting White-clawed Crayfish and it appears the spread of Porcelain disease may be another. Signal Crayfish carry several microsporidian parasites including Thelohania, whilst showing no symptoms and in some USA populations this may develop into Porcelain disease, although it is rarely recorded from the UK. 

Porcelain disease gets its name from the opaque like colouration of the underside of the crayfish (see picture), as oppose to the more translucent muscle usually seen on the underside. This disease is a lethal disease although most individuals survive 1-2 years after initially showing the first signs of the disease. The exact infection method of the disease remains unknown. 

The prevalence of the disease within the population is usually less than 5%, several Rivers in West Yorkshire now show extremely high rates between 20-50% of the population being infected. It is suggested that the disease becomes more prevalent when the population is under stress from other factors including low pH, urban/road run-off, agro-chemical run-off or random pollution incidents. Additionally changes in physical river structure like straightening or reduction of shelter can increase stress rates which then leads to increased rates of the disease. The occurrence of the disease may also of course be liked to the populations genetics. It is also highly likely that increased stress to White-clawed Crayfish populations from Signal Crayfish, induces higher rates of Porcelain disease in the population.