The parasite is transmitted from person to person through contact with infected faeces, either directly (such as between children) or indirectly via contaminated food, water and inanimate objects.
People become infected when they swallow the cysts which have been shed in an infected person's or animal's faeces. Common causes include:
- Eating food prepared by infected people
- Drinking from a poor quality water supply e.g. roof or stream water
- Swimming in water that has been contaminated with faecal matter
- Contact with pets, especially puppies and kittens with diarrhoea
- Contact with manure from farm animals
- Contact with infected people, including children and babies
Another source of infection is consumption of unpasteurised/raw milk.