Feline Leukemia - Leukemia in Cats

Feline Leukemia - Symptoms of Feline Leukemia

Feline leukemia virus
(FeLV) is a single-strand RNA virus in the family Retroviridae, subfamily Oncovirinae. The principal route of infection by feline leukemia virus is prolonged contact with infected cat saliva and nasal secretions; grooming or sharing of common water or food sources effectively results in infection. Because the organism does not survive in the environment, feces, or urine, fomite and aerosol transmissions are unlikely. Transplacental, lactational, and veneral transmission are less important than casual contact. Feline leukemia virus has worldwide distribution; the seroprevalence of infection varies geographically and by the population of cats tested. Infection is most common in outdoor male cats between 1 and 6 years of age.

The feline leukemia virus replicates first in the oropharynx, followed by dissemination through the body to the bone marrow. If persistent bone marrow infection occurs, infected white blood cells and platelets leave the bone marrow with ultimate infection of epithelial structures, including salivary and lacrimal glands. Approximately 30% of exposed cats become persistently viremic; self-limiting infections occur in the remaining cats. Cats with persistent feline leukemia usually die of a FeLV-related illness within 2 to 3 years. Approximately 30% of exposed cats are transiently viremic, develop neutralizing antibodies, and clear the infection within 4 to 6 weeks. Latent and sequestered infections can be activated by the administration of glucocorticoids or other immuno-suppressive drugs.

Owners generally present cats infected with feline leukemia virus for evaluation of non specific signs such as anorexia, weight loss, and depression or for evaluation of abnormalities associated with specific organ systems. Of the feline leukemia virus infected cats evaluated at necropsy, 23% had evidence of neoplasia (96% lymphoma/leukemia) and the remainder died due to numerous other nonneoplastic diseases. Clinical syndrome can result from specific effects of the virus or from opportunistic infections secondary to immunosuppression.

Bacterial or calicivirus-induced stomatitis occurs in some FeLV-infected cats due to immunosuppression. Feline leukemia virus infection can result in vomiting or diarrhea from a form of enteritis clinically resembling panleukopenia, from alimentary lymphoma, or from secondary infections due to immunosuppression. Clinical signs of rhinitis or pneumonia occur in some FeLV-infected cats from secondary infections. Dyspnea from mediastinal lymphoma occurs in some cats. These cats are generally less than 3 years of age and may have decreased cranial chest compliance on palpation, as well as muffled heart and lung sounds if pleural effusion is present.

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