These asymptomatic cats can transmit the infective virus through contact with other unprotected cats. Cats from any untested parentage can be infected. Cats from certified FELV-free catteries are usually safe. Any cat off the street can be infected. Cats are most susceptible to infection the first few years of life or if debilitated by other diseases.
Kittens are at highest risk.
Often, lack of energy and appetite with weight loss, fever, or anemia are the only signs. Signs may be subtle or rapid and dramatic. The leukemia virus can invade any organ and depending on the site of damage, cause heart, lung, liver, or kidney disease as well as numerous other problems such as anemia, skin disease, nervous and behavioral changes, respiratory, chronic bladder, or intestinal signs. FELV can mimic respiratory or feline immune deficiency virus. FELV can be even more debilitating.