Outbreaks of cryptosporidiosis, which cause prolonged diarrhoea, affect between 3,000-6,000 people a year in the UK, health officials say.
It’s usually waterborne – and those infected either drink water contaminated by the cryptosporidium parasite or swallow dirty water in swimming pools or streams.
It can also be caught from contact with animal manure.
This is usually the most common way people become unwell, with a spike coming in spring when farms hold open days.
Most people recover, but some can become seriously ill such as very young children and those with particularly weak immune systems.
For many, the diarrhoea can last for two weeks or more.
There’s no effective antibiotic for treating it.
The advice is to boil your drinking water and drink plenty of it to prevent becoming dehydrated – and stay away at home until it’s subsided.
If you don’t live in the area affected, you are not in any danger from it spreading.
