[4] The signs and symptoms of infection with feline leukemia virus are quite varied and include loss of appetite, poor coat condition, anisocoria (uneven pupils), infections of the skin, bladder, and respiratory tract, oral disease, seizures, lymphadenopathy (swollen lymph nodes), skin lesions, fatigue, fever, weight loss, stomatitis, gingivitis, litter box avoidance, pancytopenia, recurring bacterial and viral illnesses, anemia, diarrhea and jaundice.

[6] Once a cat has been infected with FeLV-A, additional mutated forms of the original FeLV-A virus may arise, as may FeLV subgroups B, C and T. In addition to domestic cats, some other members of Felidae are now threatened by FeLV (e.g. lynx and Florida panther).

Therefore, it is recommended that the cat be retested in three to four months after the positive result to determine if the virus has been cleared from the body.

Other than ELISA and IFA testing, routine laboratory blood work may show changes that indicate infection but cannot be used as a definitive diagnosis.

There may be blood cell count changes like leukopenia, decreased Packed Cell Volume (PCV) and Total Protein (TP) levels due to anemia, hemoconcentration and hypoglycemia due to vomiting and diarrhea, electrolyte imbalance caused by dehydration and anorexia, and recurrent urinary tract infections.

[11] Cats diagnosed as persistently infected by ELISA testing may die within a few months or may remain asymptomatic for longer; median survival time after diagnosis is 2.5 years.

In Canada, one feline infected with progressive Feline Leukemia Virus Type C and its Immune-Mediated Hemolytic Anemia complication has been successfully managed so far for over 6 months with the use of high-dose corticosteroids, broad-spectrum antibiotics to treat opportunistic and comorbid infections, antiviral medications, and immunomodulators such as cyclosporine after requiring multiple packed red blood cell transfusions to raise a critically low blood cell count.

The virus comprises 5' and 3' LTRs and three genes: Gag (structural), Pol (enzymes) and Env (envelope and transmembrane); the total genome is about 9,600 base pairs.

[citation needed] In 2006, the United States Department of Agriculture issued a conditional license for a new treatment aid termed Lymphocyte T-Cell Immunomodulator (LTCI).

[20] Lymphocyte T-Cell Immunomodulator is manufactured and distributed exclusively by T-Cyte Therapeutics, Inc.[21] Lymphocyte T-Cell Immunomodulator is intended as an aid in the treatment of cats infected with feline leukemia virus (FeLV) and/or feline immunodeficiency virus (FIV), and the associated symptoms of lymphocytopenia, opportunistic infection, anemia, granulocytopenia, or thrombocytopenia.

The absence of any observed adverse events in several animal species suggests that the product has a very low toxicity profile.

Purification of protein from bovine-derived stromal cell supernatants produces a substantially homogeneous factor, free of extraneous materials.

The bovine protein is homologous with other mammalian species and is a homogeneous 50 kDa glycoprotein with an isoelectric point of 6.5.

Although they are both in the same retroviral subfamily (Orthoretrovirinae), they are classified in different genera (FeLV is a gamma-retrovirus and FIV is a lentivirus like HIV-1).