The most common parasite, particularly now we're coming into the summer months, is the flea. There are approximately 2000 species of flea worldwide, 60 of which are in the UK.

The most common type, found on both dogs and cats, is the cat flea (Ctenocephalides felis) which will feed several times a day from its host by sucking blood with its specially adapted mouthparts.

The flea injects saliva containing antigens to stop the host's blood clotting. This can sometimes cause an allergic reaction in susceptible individuals, which causes severe itching, and small crusty lesions develop which can be felt on the skin.

Adult fleas are dark-brown in colour and about 2-3mm long. They are very thin which allows them to pass through the animal's coat easily.

The presence of fleas on your pet can often be detected by the flea's droppings. These appear as dark granules, which consist mainly of dried blood, and if rubbed onto a damp piece of white paper will show up red - confirming that fleas are there.

Fleas can cross from one host to another when the animals are in contact at close quarters. This method of infection, however, is not the usual way fleas are picked up. Instead, it is newly-hatched fleas which jump on to a passing host to feed.

The young develop from eggs, which were originally laid by the female flea on the original host. The female flea can produce up to 30 eggs per day and four or five hundred eggs in her lifetime. The eggs are round and shiny and are 'designed' to fall off the animal's coat, congregating in nooks and crannies around the host or in the animal's bedding.

From here they develop into a flea larva, which feeds on organic debris and dust until it becomes a pupa. This pupa can take as little as eight days to become an active flea, or may remain dormant for up to 200 days before its development is stimulated by warmth or vibrations.

If you suspect your pet has fleas it is essential to treat both the animal itself and the surrounding environment where eggs may have been shed. Just killing the fleas on the animal is fine for a short while, but when the eggs become fleas they simply jump back on and re-infest.

Many forms of treatment are available for the animal, such as shampoos, powders, sprays, collars and drops, but always ask for experienced advice before proceeding with any treatment as care is needed to avoid making your pet ill with the wrong choice.

Treatments for carpets, bedding and furnishings can be in the form of aerosol sprays, powders which are sprinkled down and vacuumed up or, for total room treatment, fumigation smoke bombs are available.

Again, make sure you've been given the right advice.

The best household treatment is one which has the longest residual effect that will kill the larva before it has chance to pupate and develop into an adult flea, thus breaking the life cycle and eliminating the source.