Feline leukemia virus is a retrovirus that infects cats. FeLV can be transmitted from infected cats when the transfer of saliva or nasal secretions is involved.
Flea Allergy Dermatitis in Cats VCA Animal Hospitals.
ABCD cats & vets: GUIDELINE for Feline Leukaemia Virus Infection.

Flea allergy dermatitis in an adult cat. Self-induced alopecia is evident along the lateral thorax, lateral abdomen, and tailhead. Eosinophilic plaques are present on the lateral thorax.
Flea-allergic dermatitis (FAD) is an allergy to flea saliva. Cats with FAD experience intense itching and a rash each time they are bitten by a flea.

Although cats with asthma can be allergic, most cats with allergies lick or chew their fur and scratch their skin. Major Allergy Types in Cats. Flea Allergy Flea allergic dermatitis is the most common skin disease in cats.
Flea allergy dermatitis is a common cause of itching and scratching in dogs and cats. Flea allergic dogs are often itchy at the back and rump and base of the tail, and may have hot spots that can become bloody and infected.

Furthermore, visual representations like the one above help us fully grasp the concept of Flea Allergy Leukemia Disease In Cats.
FLEA ALLERGY DERMATITIS (FAD) It is the leading cause of allergies in dogs. It mostly affects cats and dogs which already have an underlying skin problem or those with sensitive skin. Best prevention is over the counter medications for fleas.
For cats with flea allergy, implement flea control twice monthly (sometimes weekly, depending on product and bathing protocol) for 4 to 8 weeks or until clinical signs resolve.