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FeLV
Antigenicity
- Main envelope protein: gp70
- 3 antigenic subgroups:
- Group A
- is transmitted between cats
- is monotypic: one vaccine covers all isolates
- causes lymphosarcoma
- Group B:
- is recombinant with transmissible FeLV-A
- increases the chance of thymic tumors
- Group C:
- is a mutant of A
- isolates are rare, and occur as A+C mixtures
- increases chances of anemia
Pathogenesis
- FeLV is the "disease of friends": transmission usually occurs through mutual grooming
- From the oropharynx, virus spreads to most tissues in the body to replicate, notably:
- Bone marrow
- Thymus
- Salivary glands
- Reproductive tract
- Most kittens but only 30% of adults become viremic for life without producing antibody
- 20% of viremic cats die of tumors
- 30% of viremic cats die of FeLV-associated disease
- 80% die within three years of exposure
- 30% of adults exposed become latently infected and can become viremic when immunosuppressed
- 40% of exposed adults remain healthy and develop Ab and CD8+ Tcells after clearing the virus, without becoming reinfected or silent carriers
Clinical Signs:
- Leukemia
- Multicentric lymphosarcoma: B or T cell tumors, which may be palpable as enlarged lymph nodes (particularly mesenteric)
- Thymic lymphosarcoma: T cell tumors, with only the thymus enlarged
- Results in dyspnoea
- Confirmed by radiography
- Alimentary lymphosarcoma: B cell tumors of the Peyer's patches
FeLV-associated disease:
- Immunodepression causing secondary disease
- Reproductive failure: FeLV crosses the placenta, causing fetal resorption or viremic kittens with thymic aplasia
Epidemiology
- Vertical transmission of FeLV-A from mother to kittens either via placenta, grooming, or milk
- Horizontal transmission occurs via saliva during mutual grooming
- Recovery linked to age and presence of maternal antibody
- Particular concern for intensively bred cats because of crowding, etc.
Diagnosis
- FeLV should be suspect in any cat with recurrent bacterial infections, anemia or weight loss
- ELISA for Antigen (capsid protein p27 or envelope protein gp70)
- Immunochromatography is now trusted as ELISA testing can give false positives
- Virus isolation from heparinised blood can now be performed to confirm a positive diagnosis
Control
- Antigen positive sick cats should be destroyed
- Healthy positive cats should have diagnosis confirmed
- Vaccination:
- Should take place once antigen-negative status has been determined
- Leukogen: Subunit vaccine (using envelope protein gp70) produced in E. coli mixed with Quill-A and alhydrogel
- Others include inactivated virus and canarypox recombinants, but all MUST include FeLV-A