Feline leukemia is a shock for many cat owners. It often comes with no warning signs and can potentially be very dangerous. But learning more about the symptoms of feline leukemia can help you catch it early, potentially saving your cat's life. In this blog post, we'll explore the different signs that can indicate an infection with the Feline Leukemia virus (FeLV), from unexplained weight loss to recurring infections and skin lesions, there are many warning signs that may indicate your kitty is suffering from this serious disease. For both cat owners and veterinarians out there, let's delve into the unmistakable warning signs of feline leukemia!

What is feline leukemia?

Feline leukemia is often due to a viral infection caused by the Feline Leukemia Virus (FeLV). The virus can spread through saliva, nasal secretions, and blood and is also shed in feces, urine, and tears. The exchange of food, water bowls, and litterboxes along with mutual grooming are all common ways for the Feline Leukemia Virus (FeLV) to be spread. Infected queens can transmit the virus directly to their kittens while they are in utero, as well as through nursing after birth.

Kittens born to an infected mother cat, cats with outdoor access, and close contact with other cats who have FeLV are at the highest risk of infection. Additionally, having diseases such as gingivostomatitis, abscesses or respiratory tract issues can make a cat more likely to be infected with FeLV. It isn't entirely clear why these illnesses increase the risk, but it may be because they can weaken their immune system.

FeLV syndromes of the disease

FeLV infection can manifest in a variety of syndromes, each with its own characteristics. To better understand and appreciate the symptoms of feline leukemia, we need to understand the various syndromes of the feline leukemia virus (FeLV).


FeLV has been identified as a cancer-causing oncogene in cats, with the potential to produce different tumors. FeLV genetic material can attach itself to a tumor-producing gene within a cell and cause it to become too active, leading to abnormal cell growth. Lymphoma and leukemia are the most commonly observed neoplasms linked to infections by this virus. The types of tumors most commonly associated with FeLV infection in cats are lymphoma and leukemia.

Secondary infections

FeLV infection affects a cat's immune system, making them more vulnerable to secondary infections. Decreased activity of neutrophils, reduction of immunoglobulins, delayed antibody response, decreased interleukin production, and decreased levels of lymphocytes are all common in FeLV-infected cats.

FeLV is commonly linked with several infection types, including FIP (feline infectious peritonitis), Mycoplasma, and upper respiratory infections.

Blood disorders

FeLV infection is linked to various non-tumor-related, blood-related disorders due to its ability to suppress the bone marrow. These disorders include hemolytic anemia, chronic anemia, persistent or recurrent neutropenia, pancytopenia (low levels of all cell lines), thrombocytopenia (low blood platelet count), and other platelet irregularities.

Immune-mediated disorders

FeLV infection can cause the immune system to malfunction, leading to diseases like glomerulonephritis, uveitis, polyarthritis, and autoimmune hemolytic anemia. These problems occur when infected cells release a protein that disrupts the normal function of T cells (a type of immune cell), or when antibodies form complexes with antigens (e.g. foreign substances).

Neurological disorders

It is widely believed that FeLV exerts neurotoxic effects on cats. As a result, the symptoms of feline leukemia can result in Horner syndrome, anisocoria, mydriasis/spastic pupil syndrome, urinary incontinence, and central blindness have been documented as well.

Symptoms of feline leukemia

The symptoms of feline leukemia can vary greatly between cats and is dependent upon the body system affected.

Generally, the symptoms of feline leukemia are nonspecific such as lack of appetite, weight loss, sluggishness, fever, and gastrointestinal problems like vomiting and diarrhea.

Respiratory issues can cause difficulty breathing, coughing, and regurgitation, while neurological changes can include paralysis, blindness, pupil inequality (anisocoria), Horner Syndrome, sensitivity to touch, muscle weakness, and even urinary incontinence.

Jaundice or icterus (yellowing to the skin and eyes) can sometimes result from either liver problems or anemia. Additionally, lameness may occur due to immune-mediated joint inflammation.

In summary, symptoms of feline leukemia may include the following:

  • Lack of appetite
  • Weight loss
  • Lethargy
  • Fever
  • Poor hair coat quality
  • Gastrointestinal issues (vomiting and/or diarrhea)
  • Difficulty breathing
  • Coughing
  • Blindness and/or unequal pupils
  • Jaundice or icterus
  • Lameness

What is the prognosis for cats infected with the feline leukemia virus (FeLV)?

The prognosis for cats with feline leukemia virus infection depends on the type of condition and its severity. Many cats can live for years with proper care and treatment, while others may succumb to the disease more quickly. Early detection is key in providing the best possible outcome. Owners should stay current with yearly veterinary check-ups to identify any symptoms of feline leukemia virus as soon as they arise. Additionally, asymptomatic cats with FeLV can live a long and healthy life if they receive adequate care.

In conclusion, symptoms of feline leukemia can vary greatly from cat to cat and depend on the body system affected. Common symptoms include lack of appetite, weight loss, lethargy, fever, poor hair coat quality, gastrointestinal issues such as vomiting or diarrhea, difficulty breathing and coughing, blindness or unequal pupils, jaundice or icterus (yellowing skin/eyes), lameness due to joint inflammation. Early detection is key in providing cats with FeLV the best possible outcome; yearly check-ups are recommended for all cats so symptoms can be identified quickly. With proper care and treatment, many cats infected with FeLV can live a long healthy life - regardless if they exhibit symptoms or not. If you have any questions or concerns about feline leukemia symptoms, it is best to speak with your veterinarian.