Whirling disease is caused by a single-celled sporozoa (Myxobolus cerebralis), which uses Tubifex (sludge worm/sewage worm) as an intermediate host. This might also be the focus of the infection. It is rare in aquarium fish, but common in pond fish, especially in trout. The spores of the pathogen can survive for decades in a pond and not even be killed off by "liming". The pathogen disturbs bone formation, leads to black colouration of the tail area and causes whirling movement around the body's axis. This is followed by deformation of the skull and spinal curvature. Medical treatment does not produce successful results. Prevention by improved hygiene and disinfection and long rinsing of Tubifex prior to feeding is recommended. Make sure to remove dead fish.