Feline leukaemia

FELINE LEUKAEMIA
  • Also known as “Feline lymphoma” and “Feline Lymphosarcoma” the disease is caused by “Feline leukaemia virus (FeLV)”.
  • The virus is associated with a variety of disorders and collectively are the most important cause of deaths in cats.
  • FeLV occurs worldwide, with an incidence of up to 50% in densely populated areas.
  • The virus is transmitted horizontally, primarily through salivary and nasal secretions of the affected cats.
  • Two main results occurs following infection
  • A self-limiting infection (or “regressive infection”). In this the initial virus replication in lymphoid tissue is either totally eliminated by the immune system or may remain as provirus, which is contained (prevented from spreading) through immune mechanisms.
  • About 60% of infected cats fall into this category and do not develop and FeLV-associated disease.
  • Provirus can however, become activated if there is immune dysfunction.
  • In such an event, infected cats may become viraemic and develop FeLV disease.
  • The second outcome is progressive infection with persistent viraemia.
  • The initial viral replication in lymphoid tissues, usually in the oropharynx, is not contained and is followed by viraemia and generalized viral infection of lymphocytes, macrophages, intestines, salivary glands, pancrease and urinary bladder.
  • Theses cats are infectious because virus is excreted through these sites.
  • Persistent infection and viraemia are ultimately followed by several disease processes, which lead to death.
  • This usually requires months or years following infection.
  • However, some infections may cause illness or death within a few weeks.
  • Most viraemic cats die within 3 years of infection.
  • The disorders caused by FeLV are grouped into “Cytoproliferative disease” and “Cytosuppressive disease”.
  • The particular outcome depends on the viral subtype and the age of cat at the time of infection, as well as immune status and genetic make up of the cat.
  • Infection early in life is likely to be followed by viraemia.
  • The main disorders resulting from FeLV infection are:
  • Malignant lymphoma with or without leukaemia is the most common malignancy in cats.
  • It results from viral activation of cellular protoncogenes.
  • On the basis of anatomical distribution, several forms are recognized:
  • Thymic lymphoma occurs mainly in young cats.
  • It is characterized by large tumour masses originating in and replacing the thymus gland and filling the mediastimum
  • Alimentary lymphoma in seen more in older cats.
  • It is characterized by solid tumours which infiltrate the gastrointestinal tract, abdominal lymph nodes, liver, spleen, and kidney.
  • Multicentric lymphoma is seen usually in mature cats.

It is characterized by generalized lymphoma, affecting many oranges and tissues and Unclassified lymphoma.

  • This usually presents as isolated tumour masses in non-lymphoid tissues, such as the eye or central nervous system.
  • Most cases of malignant lymphoma, with the exception of the alimentary form and of T cell origin.
  • Lymphocytic leukaemia : This may occur in connection with malignant lymphoma.
  • Erythroid and myeloid leukaemias (myeloproliferative disorders).
  • These are the most common leukaemias in cats, which may occur together.
  • Myelofibrosis is another outcome.
  • Fibrosarcoma occurs from infection with feline sarcoma virus.
  • This virus is a defective mutant of FeLV.
  • It lacks part of the viral genome and is unable to replicate.
  • However, in the presence of FeLV virus replication occurs.
  • This is because FeLV serve as a helper virus, providing the missing genes.
  • Myelosuppression syndrome:this is characterized by anaemia and / or leukopaenia (lymphopaenia and neutropaenia).
  • It is a frequent out-come of FeLV infection.
  • It results from suppression of erythropoiesis and myelopoiesis.
  • The anaemia may become very severe.
  • Immunosuppression is seen at some stage in most cats infected with FeLV.
  • It is characterized by progressive loss of function, and a decrease in numbers of both T and B lymphocytes as ell as neutrolium.
  • Infertility results from foetal death and resorption due to FeLV infection of the placenta and foetus.
  • Neurological disease has been observed in FeLV infected cats, but has not been studied in detail

Diagnosis

  • The presence of the virus may be demonstrated by electron-microscopic photographs of replicating C-type particles.
  • A fluorescent antibody test is used to detect antigen in leukoytes in blood smears.
  • A third method is to isolate the virus in feline cell cultures from plasma, or oral swabs of cats.
Last modified: Friday, 23 March 2012, 9:45 AM