Lancashire folk are being urged to wash hands, wellingtons and pram and pushchair wheels after visiting farms.
It comes from the Health Protection Unit after several cases of the stomach bug, cryptosporidiosis, were detected following recent educational visits to farms.
Dr Ken Lamden, consultant in health protection, said: "Animals, including farm animals, carry a range of organisms and cryptosporidium is just one, but it is particularly common at this time of the year."
Cryptosporidium causes diarrhoea and abdominal pain, but is not usually serious.
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