Cat fleas can cause allergic reactions in both cats and in other animals such as humans or dogs. The flea injects compounds into the cat's skin when it bites, and the cat's immune system reacts to these compounds. The cat flea allergy causes the cat to itch and scratch and affects the condition of the skin. The allergy is technically known as flea allergy dermatitis (FAD).
Ctenocephalides felis is an example of a cat flea. According the the Merck Veterinary Manual, C. felis is the most common cause of fleas in cats and dogs in North America. The cat flea allergy can also occur in humans. Not every cat, dog, or human will show cat flea allergy after a bite.
When a flea bites a cat, it injects its own spit into the bite. This saliva contains compounds that the immune system targets and reacts to. A bite stimulates production of immunoglobulin E (IgE) and IgD antibodies that are specific to the flea antigens. It also produces a localized inflammatory reaction.
An animal that is constantly bitten by fleas may have a low level of immune response, resulting in an absence of allergic reaction, and this may be the case for cats. An animal that is only bitten by cat fleas occasionally can show a much higher immune system response to each bite. According to the Merck Veterinary Manual, an animal bitten by fleas can show three different types of allergic reaction.
The immune system can react immediately, and an allergic reaction happens after 15 minutes. Alternatively, the reaction can take one or two days to occur, which is known as a delayed reaction. In some cases, both the immediate and the delayed reactions can occur. This may the mechanism of how cat flea allergy works in felines.
Flea allergy dermatitis symptoms depend on the individual cat. The neck, face, and back are the most commonly affected areas. There the skin will be bumpy and may be scabbed over. The cat's hair may also fall out in patches, and an owner may see areas of skin that are scratched by the cat itself.
Treatment of FAD is through insecticides or insect growth regulators. These can be applied directly onto the skin, injected, or given orally. As fleas may be present in many stages of the life cycle, the treatment needs to either remain active for a length of time or be repeatedly applied. The environment may also need to be treated to remove a reservoir of infection.