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Fleas are external parasites that live on the skin and survive by feeding on the blood of animals. There are many species of fleas but they are not ‘host-specific’, meaning they can infest more than one species of animal. The main fleas that affect pets are the cat flea and, less commonly, the dog flea. These fleas can also infest other pets such as rabbits, guinea pigs, rats, mice and chickens, as well as wildlife and humans.
Why are fleas a problem?
Flea bites are irritating and painful to animals and cause damage to the skin. Some pets show no response or only respond to flea bites with occasional scratching. Others are more sensitive and will scratch and bite intensely at the area, which causes further trauma to the skin and can lead to secondary infection. Flea bites are the most common cause of skin disease in pets. Dogs and cats can develop a severe allergic reaction (or hypersensitivity) to flea bites which may only involve one flea. This is called flea allergy dermatitis (or ‘summer eczema’), a painful skin condition characterised by hairless itchy ‘hot spots’ usually seen on the back or the base of the tail. A less common problem is anaemia in very young or old pets due to blood loss from heavy flea infestations. Fleas may carry tapeworms which may infect a pet if they eat an infected flea. Tapeworms can be passed from pets onto humans so it is essential to treat pets regularly for worms. Fleas can also spread myxomatosis to rabbits, which is a fatal disease but this risk can be reduced by controlling fleas.
IMAGE: Dog infested with fleas
How do pets get fleas?
In a population of fleas which is infecting your pet, 95% exist as immature forms (eggs, larvae and pupae), which mature into adults (only 5% of the total flea population) under warm and sufficiently humid conditions and when they detect the presence of a host animal. Once they attach to an animal, they lay their eggs on the animal’s hair which then falls into the surrounding environment such as bedding, or under furniture, carpets or in garden soil. This means the main source of infestation is actually the pet’s normal surroundings. Since fleas can leap from host to host, other pets or animals in close contact with an infested pet can also become sources of infection.
IMAGE: Flea dirt in hair from brushed cat
How do I know if my pet has fleas?
Regular grooming allows you to check whether your pet has fleas. Adult fleas are tiny dark brown insects, about 1-2mm long, that appear flattened sideways and may be seen moving quickly through your pet’s fur or on their skin. Fleas do not have wings but can move between host animals and the environment by jumping. If you suspect fleas but cannot find them, check for ‘flea dirt’ (is flea faeces), which appears as dark specks on the skin or can be removed from fur using a fine-toothed comb. It is possible to diagnose the presence of fleas on pets by placing flea dirt on a wet tissue, where it will stain red, indicating dried blood that has been digested by fleas. Physical signs that may indicate the presence of fleas include spots, reddening, loss of hair or thickened skin, such as around the ear edges. Your pet’s behaviour can also be a sign of flea infestation, although this is not a reliable indicator because not all pets will scratch or appear irritated. Some cats will scratch at fleas only when they are not being observed.
IMAGE: Adult fleas in dog hair
How do I prevent and treat flea infestations?
If you have had problems with fleas on your pets where you live, then it is likely that you will need to use a preventative flea product on an ongoing basis throughout the year. Your veterinarian can give you advice about the most suitable product for your pet and how often this should be applied (such as monthly). To be effective, all pets in the household must be treated. Flea preventatives are completely safe if used according to instructions and can be applied at home. The most effective products target all stages of the flea life cycle by preventing fleas from reproducing. These preventatives may take the form of a tablet, oral chew or spot-on applied to the skin. Flea collars or rinses kill the fleas on your pet but will not treat the environment, this is particularly important for animals suffering from ‘flea allergic dermatitis’ as it only takes one flea bite to set off an allergic reaction.
It is important to follow your veterinarian’s advice closely and only use a product that is safe for your pet’s species; products designed for dogs can be fatal if given to cats. It is not advisable to purchase these products from a supermarket without veterinary advice. There is no evidence that alternative treatments, such as tea leaves or citronella, are effective against fleas.
For complete flea control, you must also treat the environment. Fleas can survive for months in the environment without a host animal, so it is important to break the flea life cycle. Treating the environment removes flea eggs, larvae and pupae that are already present and also prevents re-infestation. This involves weekly vacuuming of the sleeping area, floors, furniture and skirting boards and disposal of vacuum cleaner bags. Pet bedding should also be washed weekly at a high temperature, as well as outdoor kennels, runs or enclosures sprayed with an adult flea killer every week until the infestation is cleared. If there is severe infestation, you can also dust skirting boards and other crevices with insecticide powder and use surface sprays. Seek further advice from your veterinarian if you are unsure how to safely remove fleas from your pet’s environment.
Any skin damage on your pet should be treated by a veterinarian without delay. Dogs or cats suffering from flea allergy dermatitis require the area to be clipped and cleaned, and they may be prescribed medications to reduce inflammation. There are tablets available from your veterinarian to instantly kill adult fleas in case of heavy infestations to provide relief to your pet.
If you check your pet weekly to confirm no fleas are present and believe the environment is not contaminated with flea eggs or larvae, then ongoing preventative treatment should not be required. However, if you suspect or see signs of an infestation, immediate treatment should be undertaken.