Fleas do not live permanently on their host and are less host-specific than other external parasites such as lice. This means that at any one time there are many more fleas in the environment than are on your pet. Humans are susceptible to flea bites and are at risk from diseases such as the plague which is carried by the rat flea.  Fleas easily move by jumping from animal to animal and within the environment so population increase is rapid.
Dogs are mostly commonly affected by the Dog Flea (Clenocephalides canis) although other fleas may also be present.
Results of infestation can include
•    Itchiness and redness of skin
•    Hair loss
•    Severe skin infections
•    Allergic reactions to the saliva of the flea – known as flea allergy dermatitis (FAD) giving rise to ‘hot spots’.
•    Blood loss leading to anaemia
•    Transmission of disease to dog and man
•    Transmission of tapeworm
Fleas are blood feeders, injecting their saliva into the bite wound to increase blood flow and prevent coagulation. It is this saliva which causes the itchiness and irritation common to flea bites. A female flea can consume fifteen times her own weight in blood and if well fed can survive on the dog for 140 days. 24 – 36 hours after a blood meal, she will lay her eggs wherever she is – whether on the animal or in the environment. A single female flea can lay several thousand eggs.  Unlike the tick, the female does not die after laying, but will then find another host to mate, feed and lay again. Within 5 – 12 days the eggs will hatch into larvae which feed on the mother’s faeces, which is mainly blood, before becoming pupae. The pupae are very well protected and difficult to kill. The pupae will remain dormant until conditions are right for emergence and this can be for long periods of time. When stimulated by light, heat or vibration, the pupae will emerge and the young adult immediately jumps onto a host to feed. The life cycle is dependant on conditions such as temperature, humidity and presence of a host and can be from 14 – 140 days.
It is obvious that any flea control program has to include treatment of the environment as well as the dog.
•    Brushing of long haired varieties removes matted hair which is a favoured site for fleas.
•    Flea collars have a limited use.
•    The addition of garlic to the dog’s food is said to deter fleas.
•    Powders and sprays have limited use in toy breeds or breeds with particularly sensitive skin.
•    ‘Spot-ons’ or topical treatments. 
•    Shampoos or approved acaracides
•    Oral treatments break the life cycle by rendering the female flea infertile or interfering with hatching of the eggs. The current population is not killed but will not reproduce.
•    Of vital importance is treatment of the environment, in particular dogs bedding and resting places, with an approved insecticide. In extreme infestations, it may be necessary to fumigate the home as fleas inhabit many places within the home such as wooden floors, in cracks in floors and walls etc.