Many animals will carry fleas without showing significant discomfort. However control is recommended as fleas may carry tapeworm larvae, fleas can transmit blood borne diseases, fleas can contribute to anaemia, some pets can develop allergies to fleas, and fleas can bite people as well.
Fleas are small, flat insects that live on the pet and produce large numbers of eggs in the environment. Fleas can live for two years and start laying eggs within 48 hours of finding a host. Eggs hatch within 2 days in the environment (bedding, carpets, clothes) and move deep into soft furnishings. Cocoons can survive in the environment without a host for up to 2 years.
It is important to eradicate fleas from the home and vacuuming can help to reduce the burden. All pets in the house should be treated for fleas and an environmental insecticide used as well.
It is recommended to discuss treatment with a vet as there is a wide range of treatments available and some of which work better than others. Many of the over the counter products have poor efficacy. Never use a dog product on a cat as these can be highly toxic. Some "natural" products such as eucalyptus oil or tea tree oil are also toxic to cats so use of natural remedies is not recommended.