Feline leukemia virus (FeLV) is a retrovirus that infects cats. FeLV can be transmitted between infected cats when the transfer of saliva or nasal secretions is involved. If not defeated by the animal’s immune system, the virus can be lethal. The disease caused by this virus is a form of cancer of blood cells called lymphocytes (a leukemia).
Once infected, it causes lifelong infection with most sufferers dying from tumours, progressive anemia or immune compromise within three years of diagnosis. Although after vaccination not all cats will develop immunity against the disease, it is advisable to vaccinate any pet that is at risk. The symptoms are varied and include loss of appetite, poor coat condition, oral disease, seizures, weight loss, fever, fatigue, gingivitis, diarrhea, and some others. The virus is passed by saliva and close contact with one another. Humans cannot get this disease from cats. Approximately 0.5% of pet cats are infected with this disease. Kittens can be born with it, having contracted it from their mother while in the utero.
Stage One: The virus enters the cat, usually through the pharynx where it infects the epithelial cells and infects the tonsorial B-lymphocytes and macrophages. These white blood cells then filter down to the lymph nodes and begin to replicate.
Stage Two: The virus enters the bloodstream and begins to distribute throughout the body.
Stage Three: The lymphoid system (which produces antibodies to attack infected and cancerous cells) becomes infected, with further distribution throughout the body.
Stage Four: The main point in the infection- where the virus can take over the body's immune system and cause viremia. During this stage the hemolymphatic system and intestines become infected. If the cat's immune system does not fight off the virus, then it progresses to:
Stage Five: The bone marrow becomes infected. At this point, the virus will stay with the cat for the rest of its life. In this phase, the virus replicates and is released four to seven days later in infected neutrophils (white blood cells), and sometimes lymphocytes, monocytes (white blood cell formed in the bone marrow), and eosinophils (another white blood cell).
Stage Six: The cat's body is overwhelmed by infection and mucosal and glandular epithelial cells (tissue that forms a thin protective layer on exposed bodily surfaces and forms the lining of internal cavities, ducts, and organs) become infected. The virus replicates in epithelial tissues including salivary glands, oropharynx, stomach, esophagus, intestines, trachea, nasopharynx, renal tubules, bladder, pancreas, alveolar ducts, and sebaceous ducts from the muzzle.