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United Kingdom

Feline Leukaemia Virus

unimpressed cat in vets arms



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

Cancer develops in some cats and may be of the following types;

  • Bone marrow (leukaemia)

  • Cancer (lymphosarcoma) in one or more of these organs:

Lymph glands

Thymus gland




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.


Feline leukaemia virus (FeLV) is a virus that is found worldwide. Any cat may become infected by the virus, but the likelihood of infection varies greatly 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 contained in body fluids, especially saliva and also urine and faeces. The virus will not survive for long away from the cat, so close contact is usually essential. 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, the cat may be able to overcome the infection and rid itself of the virus for good; 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.

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. 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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