Feline leukaemia. ABCD guidelines on prevention and management

OverviewFeline leukaemia virus (FeLV) is a retrovirus that may induce depression of the immune system, anaemia and/or lymphoma. Over the past 25 years, the prevalence of FeLV infection has decreased considerably, thanks both to reliable tests for the identification of viraemic carriers and to effective vaccines.InfectionTransmission between cats occurs mainly through friendly contacts, but also through biting. In large groups of non-vaccinated cats, around 30–40% will develop persistent viraemia, 30–40% show transient viraemia and 20–30% seroconvert. Young kittens are especially susceptible to FeLV infection.Disease signsThe most common signs of persistent FeLV viraemia are immune suppression, anaemia and lymphoma. Less common signs are immune-mediated disease, chronic enteritis, reproductive disorders and peripheral neuropathies. Most persistently viraemic cats die within 2–3 years.DiagnosisIn low-prevalence areas there may be a risk of false-positive results; a doubtful positive test result in a healthy cat should therefore be confirmed, preferably by PCR for provirus. Asymptomatic FeLV-positive cats should be retested.Disease managementSupportive therapy and good nursing care are required. Secondary infections should be treated promptly. Cats infected with FeLV should remain indoors. Vaccination against common pathogens should be maintained. Inactivated vaccines are recommended. The virus does not survive for long outside the host.Vaccination recommendationsAll cats with an uncertain FeLV status should be tested prior to vaccination. All healthy cats at potential risk of exposure should be vaccinated against FeLV. Kittens should be vaccinated at 8–9 weeks of age, with a second vaccination at 12 weeks, followed by a booster 1 year later. The ABCD suggests that, in cats older than 3–4 years of age, a booster every 2–3 years suffices, in view of the significantly lower susceptibility of older cats.     

Feline leukaemia (lymphosarcoma) symposium. 3. Some comparative aspects of leukaemia in man and animals with particular reference to lymphosarcoma

A review of recent advances made in the study of lymphosarcoma in man and animals has been made. Some aspects of leukaemia are also described.     

The control of lymphosarcoma/leukaemia and feline leukaemia virus

This article discusses a removal programme designed especially for catteries and so–called multiple–cat households in an effort to control lymphosarcoma/leukaemia in cats and transmission of FeLV (feline leukaemia virus).
The removal programme calls for: annual testing of all stud cats; testing of all contacts of a FeLV–positive cat during the previous 2 years; testing of imported cats; and isolation of FeLV–positive cats or, if this is impossible, euthanasia. The FeLV antigen can be demonstrated in cats by the indirect immunofluorescence antibody (IFA) test.
The results of a removal programme carried out over a 4–year period in a large Dutch cat club are discussed. The percentage of FeLV–positive catteries decreased from 11 –5% during the first half of 1974 to 21% during the latter half of 1977; during the same period the percentage of FeLV–positive cats and stud cats decreased from 4–9% and 5–9%, respectively, to 1–2% and 1–0%, respectively.
It is concluded that the recommended removal programme can be carried out without difficulty and produces good results.     

Chronic granulocytic leukaemia/ eosinophilic leukaemia in a dog?

A suspected case of chronic granulocytic leukaemia (chronic myelogenous leukaemia) with eosinophil differentiation and hepatic involvement is described in a 3–5-year-old rottweiler dog. Neoplastic eosinophilic infiltrates were also present in the lungs, kidneys, mesenteric lymph nodes and peribronchial and prester-nal lymph nodes. Both pleural and abdominal effusions contained predominantly eosinophils and their precursors. The bone marrow showed an increase in the myeloid to erythroid ratio and an increase in the marrow granulocyte reserve. The majority of cells identified within the bone marrow were of the eosinophil series. Myelocytes and promyelocytes predominated.     

Hypercalcaemia associated with chronic lymphocytic leukaemia in a Giant Schnauzer.

A 7-year-old male Giant Schnauzer was referred with a history of severe vomiting, lethargy, weight loss, polydipsia and polyuria. Detailed investigations revealed leucocytosis with a marked lymphocytosis, mild non-regenerative anaemia, thrombocytopenia, hypercalcaemia and azotaemia. Circulating lymphocytes were small and well-differentiated, and the same lymphoid population was present in bone marrow. Chronic lymphocyctic leukaemia with associated paraneoplastic hypercalcaemia was diagnosed. Immunohistochemical staining of a bone marrow biopsy revealed a neoplastic B-cell line expressing CD79. The dog responded to therapy with prednisolone and chlorambucil for a period of 8 months.     

Feline leukaemia virus testing

Extract

Sir:- In September 1981 we published the results of leukaemia virus (Felv) testing of cats in New Zealand.⁽²⁾ In addition we detailed recommendations for Felv testing of cats in this country. These recommendations were revised and updated in a second letter to the Journal in 1982.⁽³⁾ Since then a further 465 cats have been tested at Massey University using the leukassay test (ELISA) (Leukassay F, Pitman Moore).