Cryptosporidium is a tiny parasite

Cryptosporidium is a tiny parasite which affects humans and domestic pets.

It is uncomfortable for most healthy adults but they rarely need to be admitted to hospital for treatment.

However, it can cause severe illness in people with immune problems.

There are between 500 and 1,000 cases in Scotland every year.

Glasgow outbreak

The last serious outbreak was in Glasgow in May 2000 when 90 people were affected by a water-borne infection thought to have come from Loch Katrine.

The North of Scotland Water Authority says its investigations are concentrating on the two treatment works at Mannofield and Invercannie, near Banchory.

Three tiny cracks were found in filter beds at Invercannie. The defects have now been repaired.

However, there is no proof it was the source of the problem.

No special precautions

NHS Grampian said that on the basis of current evidence there is no need for the public to take special precautions apart from practicising standard good hygiene.

Professor Hugh Pennington, of Aberdeen University, said: "It can be very serious if the immune system is damaged.

"In ordinary people it is an unpleasant illness but everyone gets better.

"Clearly kids are at risk because for a kid to get diarrhoea it is more serious than for an adult. They are more likely to spread it to other members of the family too."