Feline Leukaemia

Feline leukaemia virus (FeLV) is widespread in Ireland, and can cause severe depression of the immune system in persistently infected cats. Failure to thrive and cancer are some of the many diseases caused by this virus, which are incurable and can ultimately result in death. Vaccination can prevent persistent infection and disease.


Feline leukaemia virus (FeLV) is a virus that is extremely prevalent in Ireland. Any cat may become infected by the virus, but the likelihood of infection varies depending on the cat’s age, lifestyle, general health and environment. The virus does not infect other domestic animals or humans.

FeLV may be transmitted via mutual grooming (and this includes mother to kitten) or a bite wound. The virus is transmitted by body fluids, especially saliva and also urine and faeces. The virus will not survive for long outside of the cat, so close contact is usually essential (i.e. fighting, mating etc.). The virus may also be passed from mother to kitten before birth and also after birth in her infected milk.
Once infected, the virus multiplies in the blood stream. During this initial phase, there is a chance the cat may be able to overcome the infection and rid itself of the virus; without ever showing symptoms. In some cats their defence system cannot overcome the virus and they become persistently infected for the rest of their lives. They will become ill and ultimately die within months to years of the initial infection.


A wide variety of chronic diseases can result from persistent FeLV infection. The most common signs are described here:

  • Fever and lethargy
  • Loss of appetite
  • Progressive weight loss
  • Poor coat condition
  • Enlarged lymph nodes
  • Delayed recovery from other diseases
  • Anaemia is seen leading to pale gums
  • Infections of the skin, or upper respiratory tract
  • Gastrointestinal signs
  • Leukaemia (Cancer of the Bone Marrow)
  • Cancer of one or multiple organs:
  1. Lymph Glands
  2. Thymus Gland
  3. Kidneys
  4. Intestines
  5. Liver
  6. Nose or Eyes


Clinical diagnosis

  • Symptoms are often too vague to be certain of a diagnosis, especially in the early stages.
  • Any cat that is not thriving or is in poor condition can arouse the suspicion of a veterinary surgeon.


Diagnostic tests

  • The presence of the virus in the blood can be confirmed by laboratory tests
  • A simple blood test is commonly carried out by the veterinary surgeon in the practice laboratory
  • Further blood tests may be needed to confirm the diagnosis and complete the clinical picture

There is no medication that will kill the feline leukaemia virus or cure the diseases it causes, and treatment is limited to support. This may, however, maintain a quality of life for a period of time.

General support

  • Prolonged courses of antibiotics are frequently required to overcome any secondary bacterial infections that may be present.
  • Avoidance of all stress, such as cattery stays or change in routine.
  • Avoidance of contact with potential sources of other infectious diseases, e.g. unvaccinated cats, roaming outdoors.
  • Early detection and treatment of even minor health problems.

Confirmed or suspected cases of feline leukaemia virus infected cats should not be bred from and will pose a risk to other cats because they may shed virus. This will be of concern if the cat lives with uninfected cats or goes outside.
Ideally these cats should be isolated to prevent them from infecting others.

Vaccination can prevent persistent infection and therefore disease. The feline leukaemia virus vaccination may be included as part of the general vaccination course, or offered as a supplement to this. Therefore discuss your requirements carefully with your veterinary surgeon.

Your veterinary surgeon will advise you on the most appropriate vaccination schedule for your kitten or cat.
Vaccination will not help an already infected cat. In some cases, it might be important to ascertain the leukaemia virus status of your cat before vaccination. Choosing a kitten whose mother has been confirmed as virus free would be ideal, but in cases of uncertainty, or if adopting an adult, your veterinary surgeon may advise a blood test.

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