Cats living in a multi-cat household with other infected cats, as well as kittens born to mothers infected with FeLV, have a higher chance of developing FeLV. If you suspect your cat has megaloblastic anemia associated with FeLV, take them to the vet immediately.

Megaloblastic anemia in cats is a disorder in which the body produces red blood cells that are larger than normal. These enlarged blood cells are called megaloblasts. This type of anemia is typically associated with the feline leukemia virus (FeLV). Megaloblastic anemia may be a direct result of infection with FeLV, or may be caused by a secondary bacterial, inflammatory, or protozoan infection associated with FeLV.

Cats with megaloblastic anemia will typically show signs of FeLV. Seek immediate veterinary attention as soon as you notice any of the following symptoms:

The primary cause of megaloblastic anemia in cats is infection with FeLV. Feline immunodeficiency virus (FIV) has also been reported as a cause. However, megaloblastic anemia is only rarely caused by FIV. Certain drugs, including methotrexate and phenytoin, may also cause megaloblastic anemia. These drugs are immunosuppressants that treat rheumatoid arthritis and epilepsy, respectively. Other drugs that cause megaloblastic anemia include alkylating agents, plant alkaloids, and antimetabolites.

In some cases, megaloblastic anemia may be caused by a vitamin B12 deficiency. However, this is more common in certain canine breeds.

Your vet will make a definitive diagnosis of megaloblastic anemia by performing blood tests. These may include a complete blood count, blood chemical profile, and blood smear. Your vet will also test for FeLV at this time using the ELISA test. The IFA test may also be conducted in a laboratory if the ELISA test returns a positive result. Both of these methods test for the FeLV protein p27. Bone marrow biopsy may also be used to confirm the presence of megaloblasts.

Unfortunately, there is currently no curative treatment for feline leukemia, and the prognosis for most affected cats is very poor. However, there are drugs that may help manage the symptoms of feline leukemia. Your vet may recommend these drugs based on your cat’s specific situation and your personal and financial preferences.

Bacterial infections associated with FeLV may be treated with an antibiotic regimen. Drugs that stimulate the immune system may also be prescribed for cats with concurrent bacterial or protozoan infection. Vitamin B12 and folic acid supplements may be prescribed for cats whose megaloblastic anemia is caused by a vitamin B12 deficiency. If a drug used to treat another disease has caused megaloblastic anemia, your vet will recommend that you stop administering the medication. Your vet will be able to advise you on a medication to replace it.

Recovery and prognosis may vary depending on the underlying cause. For mild cases caused by drugs or a vitamin deficiency, the prognosis is generally good following treatment. Always follow your vet’s post-treatment instructions carefully. Always administer any medications, particularly antibiotics, exactly as directed for the full duration of the recovery period. Failure to do so may result in recurrence of infection.

If your cat has been diagnosed with feline leukemia, it is imperative that you wear protective clothing and wash your hands thoroughly after handling the infected cat if you live in a multi-cat household. Keep your cat indoors to prevent further spread of infection. Ensure your other cats have been vaccinated against FeLV. FeLV is much easier to prevent than to treat. Routine annual vaccinations for cats generally include the FeLV vaccine. However, it is important to note that the vaccine cannot provide complete protection against FeLV. 

For some cases, follow-up appointments may not be required. For cats diagnosed with FeLV, your vet will schedule weekly follow-up appointments to monitor the condition. Additional bone marrow biopsies may be taken during these appointments.

If you have any questions, or if secondary infection has recurred, contact your vet immediately.