Flea infestation

Fleas or their faeces are found by combing the coat of an itchy animal. Individual bites form a small red spot with a red halo. Allergic dogs develop redness, hair loss, excoriations, papules and crusts, typically over the lower back, tail base and back of the thighs, often with self-trauma. Allergic cats show miliary dermatitis with nibbling, hair loss and intense itch. Heavy, prolonged infestation can cause iron-deficiency anaemia, especially in young animals.

Flea infestation in pets is mostly caused by the cat flea, Ctenocephalides felis, with the dog flea (C. canis) and human flea (Pulex irritans) also involved. Adult fleas live on the host and feed on blood; heavy or chronic feeding causes iron-deficiency anaemia, most dangerously in puppies and kittens. Saliva injected during feeding contains antigens, and repeated bites can sensitise an animal so that flea allergy dermatitis develops, a hypersensitivity in which a single bite can trigger intense itching. Eggs fall off the host; larvae develop in bedding and carpets, and at cool temperatures fully formed adults can stay in their cocoons for up to 12 months, so most of the population lives off the animal. Fleas are also intermediate hosts of the tapeworm Dipylidium caninum.

The cat flea is the most common ectoparasite of dogs and cats and shows little host specificity, also biting people and wildlife such as opossums, squirrels and feral cats. At room temperature the whole life cycle can finish in about 18 days; females lay 20-50 eggs daily and larvae need warmth and at least 75% humidity. In a large British study, fleas were recorded in 1.17% of cat and 0.25% of dog consultations, peaking July to October, with young animals under 12 months and those from deprived areas at greater risk. Fleas carry zoonotic agents including Bartonella henselae (cat-scratch disease) and Rickettsia felis, and ground squirrel fleas can spread plague.

Canine atopic dermatitis favours the face and underside, whereas flea allergy concentrates on the rump; the two often coexist. Sarcoptic mange shows papules and scaling with a positive ear-foot scratch reflex and mites on scrapings. Cheyletiellosis causes marked scaling along the back; lice leave eggs on hair shafts; food reactions may add vomiting or diarrhoea and respond to an elimination diet. Flea combing and a strict flea-control trial separate flea allergy.

Skin and hair coat (lumbosacral area, tail base, thighs), blood (anaemia), gastrointestinal tract (tapeworm)

Year-round flea prevention in endemic areas using on-animal adulticides (spot-on or oral) plus insect growth regulators; vacuum carpets and furniture, launder pet bedding, treat outdoor areas when needed.

Controllable with integrated treatment of animal and environment, though cocooned adults can survive up to 12 months when cool. Heavy infestation can cause serious iron-deficiency anaemia in puppies and kittens; allergic itch can last days per bite.