Fleas (Siphonaptera) are:

  • Wingless, laterally flattened, blood sucking insects that occur on mammals and birds
  • Only the adult stages are found on the host with eggs and immature stages being found in the environment
  • Common parasites of cats, dogs and other small mammals housed in multi-pet households as companion animals
  • Common throughout the UK and Europe, although less common in more northern areas
  • A cause of pruritus, particularly in sensitized individuals, and anaemia in heavily infested animals


Important Considerations

  • Fleas act as vectors for a number of pathogens: for Ctenocephalides felis, the cat flea, these include Rickettsia felis and Bartonella henselae, the causative bacteria of cat scratch disease
  • Both C. felis and C. canis are intermediate hosts for the tapeworm Dipylidium caninum. Fleas can also bite humans and provoke pruritic and cutaneous lesions
  • Fleas not originating from pets will also often bite people, especially in the Autumn or Spring - for example bird fleas from vacated nests or new arrivals respectively


Life Cycle

Tick Life Cycle


Clinical signs

Clinical signs associated with flea infestations on dogs and cats are highly variable depending on the following factors:

  • Numbers of fleas: which can vary from a few to a huge number
  • Grooming behaviour of the individual animal (especially cats) can have a major influence on the number of adult fleas and their longevity
  • Frequency of flea exposure
  • Duration of flea infestation
  • Presence of secondary infections or other concurrent skin disease


Degree of hypersensitivity

  • Non-allergic animals may have few or no clinical signs and only show occasional scratching due to irritation caused by fleas or their bites


Animals that are allergic or develop an immunological reaction to flea saliva, show pruritus, alopecia, broken hairs, papules and erythematous macules with crusts. Moist dermatitis may be seen typically in the dorsal lumbar and tail region. The lesions can extend to the thighs and abdomen. Secondary pyotraumatic dermatitis, pyoderma, and seborrhoea are commonly seen.


In chronic cases, the skin shows thickening of the dermis with acanthosis, hyperkeratosis and lichenification. In addition, especially in young, old or debilitated animals, heavy infestations with a large number of fleas can cause anaemia.


Infection with the tapeworm D. caninum can be a strong indication of a current or recent flea infestation.


Treatment and Control of an Existing Infestation


Elimination of an existing infestation of adult fleas using an approved ectoparasiticide. Individual product leaflets should be consulted for details. Depending on the severity of the infestation and the drug used, treatment may need to be repeated at intervals until the problem is controlled. All other (dogs and especially cats, which maybe overlooked) living in the same household should also be treated

An established adult flea infestation normally accounts for only a very small proportion of the total flea population including immature stages present in the pet's surroundings. Thus control of environmental stages must also be considered, especially in the case of heavy infestations. The regular use of products that eliminate adult fleas on the animal also progressively contribute to the reduction of immature stages in the environment.

Flea eggs, larval and pupal stages may be targeted by using products specific for flea stages present in the environment. Some of these are specially designed for environmental application (sprays etc.), while others are licensed for animal administered application. Environmentally and animal-administered products may contain compounds with adulticidal and/or Insect Growth Regulator (IGR) activity. Environmental treatment should be focussed on areas where the animal spends the most time, such as their basket. It can be difficult to eliminate pupal stages, partly because they tend to be located in hidden locations such as the base of carpets. In cases of severe flea infestation, a combination or concomitant use of environmental and animal administered products is usually necessary and will control the infestation more rapidly. It is important to manage owner expectations: adult fleas may continue to emerge from the environment for a considerable period of time after the initiation of treatment.

Other measures such as vacuuming of carpets and washing of pet's bedding material can help in reducing flea stages in the environment. Combing the animal's hair coat for fleas may be used to monitor the level of infestation. More rarely, flea traps have been used to assess the environmental contamination but this is mainly done for research purposes.

Additional topical or systemic treatments may be necessary to reduce the clinical signs of flea infestation or FAD, until the infestation is brought under control

Prevention and Ongoing Control

In areas where reinfestation with fleas is highly likely, such as warm conditions and multiple animal households, regular prophylaxis using an approved product is recommended. While flea infestations peak in summer and autumn, studies have shown that flea infestation can occur throughout the year, thus year-round flea control might be necessary.

The following questions may help to define an appropriate flea prevention and control strategy:

  • How many dogs, cats and/or other pet animals are present in the house?
  • Does the animal have free access to a place where immature stages may be present?
  • Is the owner prepared to follow a long-term prevention protocol?


Risk Scenarios

Minimal infestation risk (e.g. animals with restricted or no outdoor access):

  • Regular visual inspection should be done preferably using a flea comb and grooming
  • Therapeutic treatment may be required in the event of flea infestation. This can be by the application of any registered insecticide at appropriate treatment intervals to ensure that both adults and developing stages in the environment have been controlled until the problem is eliminated

Regular infestation risk (e.g. animals with regular outdoor access):

  • Regular prevention at appropriate treatment intervals is recommended
  • Daily mechanical cleaning (e.g. vacuuming) of the house and if necessary the car or any other place where the animal has rested, is required. The largest number of eggs and immature stages are found in the places where dogs and cats spend most of their time. Within the home and garden careful observation of the pets habits will reveal the environmental "hot spots" where flea development is concentrated
  • Ensure that treatment is continued until all developing stages in the environment have been controlled

High, continual reinfestation risk (e.g. pet shelters, breeder's premises, mixed-pet households, hunting dogs):

  • Sustained, integrated flea control is recommended
  • Generally monthly application (or application at appropriate intervals) of registered insecticides on the dogs/cats is recommended together with daily vacuuming and mechanical cleaning of cages or beds and bedding
  • Animal administered or environmental treatment for immature stages

Animals with recognised flea allergy dermatitis (FAD):

  • In these animals, exposure to flea salivary antigens needs to be minimised or eliminated to prevent clinical signs. As a consequence, long term flea control is recommended to ensure that the flea population is maintained at very low or virtually non-existent levels
  • This could include frequent, regular application of insecticides to the animals and appropriate environmental control measures
  • If the animal with FAD lives within a multi-pet household with other dogs, cats or other pet animals, these animals should to be considered in any flea control strategy

Flea infestation of the owners:

  • Humans may be infested/bitten where there are large numbers of emerging adult fleas due to heavy environmental infestation
  • Flea control for the owner's pets and environment is then recommended as described in 3) above until the problem is eliminated

Although there is no clear guidance about the risk of selecting for resistance through repeated or continuous treatments, in order to minimise the potential risk, it may be advisable to change to a different class of compounds every year or two.

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Fleas Pet Owner Info Sheet


Fleas Pet Owner Info Sheet - practice letterhead version