Felis ISSN 2398-2950

Feline leukemia virus disease

Synonym(s): FeLV

Contributor(s): Stephen Barr, Severine Tasker

Introduction

  • Cause: feline leukemia virus (FeLV) Feline leukemia virus.
  • Signs: relate to specific malignancies, eg:
    • Weight loss.
    • Diarrhea.
    • Vomiting.
  • Immunosuppression, eg:
    • Chronic or repeated infections.
    • Anemia.
    • Reproductive disorders and glomerulonephritis.
  • Diagnosis: ELISA, RIM, immunofluorescence, PCR or virus isolation.
  • Treatment: cannot stop viral excretion; specific treatments for lymphomas and infections; supportive, eg transfusion.
  • Prognosis: good if transient viremia, poor if persistently viremic.
    Print off the Owner factsheet on FeLV Feline Leukaemia Virus (FeLV) to give to your client.

Pathogenesis

Etiology

Predisposing factors

General

  • Age (resistance develops with age).

Specific

  • Multi-cat households.
  • Outdoor access (contact with infected cats).
  • High local prevalence of infection.
  • Sick cats.

Pathophysiology

  • FeLV oronasal infection   →   replication in local lymphoid tissue   →    FeLV spreads via mononuclear cells = transient viremia and production of free p27 antigen   →    after ~3 weeks infection of bone marrow occurs   →    infected granulocytes and platelets occur which are positive for cell-associated p27 antigen   →    the longer the bone marrow is infected, the more likely persistent viremia is to occur.
  • The cat can mount an immune response to FeLV at different times following infection:
    • Abortive recovery occurs if the effective immune response occurs before a transient viremia develops.
    • Recovery is still possible after transient viremia, either before or shortly after bone marrow infection has occurred. Transient viremias typically last about 3 weeks but can be a maximum of 16 weeks.
    • If bone marrow infection occurs before recovery, cats can become latently infected after resolution of the transient viremia.
    • Not all, but the majority of cats that undergo bone marrow infection will become persistently viremic.
  • Latent infections can theoretically be reactivated by stress or corticosteroids (immunosuppression)   →   persistent viremia but this is believed to be rare.
  • Focal (localized) infections can result in a small percentage of infected cats. Here FeLV is sequestered in certain tissues (eg gastrointestinal tract, lymph nodes, spleen, bone marrow) where viral replication occurs.
  • Persistent viremia   →   various pathogenic variants of FeLV, eg immunosuppressive, anemogenic or tumorogenic.
  • There are three subgroups of FeLV:
    • FeLV-A - inter-host transmission; all infected cats.
    • FeLV-B - may be associated with increased risk of neoplastic disease; 50% infected cats.
    • FeLV-C - associated with the development of non-regenerative anemia via direct effect on erythroid precursors in bone marrow; <2% infected cats.
  • FeLV-B and FeLV-C are variants that are derived from FeLV-A which have differing vitro cell tropisms from the parent wild type (FeLV-A).

Timecourse

  • 85% persistently infected cats die within 3 years (cf 20% non-viremic controls).

Epidemiology

  • Free range, single cats: 50% exposed to FeLV, 1% develop active infection   →   low risk of disease.
  • Multi-cat household: 100% exposed to FeLV, 40% develop active infection   →   high risk of disease.
  • Latent/localized infection - virus can sometimes be transmitted in milk.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

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