Roundworms are common parasites in dogs and cats.
As well as making your pet unwell, the worms are a threat to humans, too.
An infected pet can contaminate soil, sand or water with tiny eggs.
Children may ingest the eggs by putting dirty fingers in their mouths.
Infection can also come from unwashed vegetables from the garden or not washing hands thoroughly after gardening in areas where pets are allowed.
In rare cases, toxocariasis from the worms' larvae can cause blindness and other tissue damage.
Ask your vet about regular deworming. Roundworm infection from parks and gardens can also come from fox poo.
It is possible for people to be infected with roundworms and not notice any symptoms before the parasites die off.
Accurate figures are difficult to compile for roundworm infections, but the NHS says there are around 80 cases reported a year in England, Wales and Northern Ireland. Roundworm infections are much more common in tropical and sub-tropical areas of the world and most cases in the UK are contracted abroad, either by travellers or migrants.
If roundworm infection is suspected, a stool (poo) sample may be taken to look for worms or eggs, or a person may notice them after going to the toilet before flushing.
Roundworms can grow up to 30-35cm long.
Medication may be recommended to kill off the parasites in the body.
The key to preventing roundworm infection is good handwashing and hygiene, and avoiding unnecessary contact with animal poo. Take special care with hygiene measures in parts of the world where roundworm is common and local sanitation is poor.
Teach children about leaving animal poo alone, and cover sandpits when they are not in use to stop cats using them as a litter tray.
Food grown in gardens with cats and dogs needs to be washed carefully to remove any parasites.