American Association of Feline Practitioners

Veterinary professionals passionate about the care of cats

Outcomes of Infection


FeLV Clinical Staging

Figure Credit: Julie K. Levy, DVM, PhD, DACVIM, DABVP


Abortive Infection
• Characterized by negative test results for culturable virus, antigen, viral RNA, and proviral DNA

• Only indication of FeLV infection is the presence of antibodies

• Not common after experimental infection, but seems to be more common in the field

• FeLV antibodies in the absence of detectable viral RNA, proviral DNA, or antigen, and without having received FeLV vaccines


Regressive Infection
• Viral shedding does not occur, but the virus does integrate into the cat’s genome

• Can transmit infection if used as blood donors

• Low risk of developing FeLV-associated diseases

• Small risk of reactivation of the virus

• Integration into the DNA can lead to lymphoma or bone marrow suppression


Progressive Infection
• FeLV not contained during the early stage

• Extensive viral replication first in lymphoid tissue, then bone marrow and subsequently in mucosal and glandular epithelial tissues

• Mucosal and glandular infection associated with excretion of infectious virus, mainly in saliva, but also other secretions

• Insufficient FeLV-specific immunity, neutralizing antibodies are not typically detectable

• Shorter survival time and succumb to FeLV-associated diseases within several years



FIV Disease Pathogenesis

  • Acute phase following exposure: often goes unnoticed
  • Immune response: suppression of circulating virus
  • Asymptomatic phase: slow, progressive dysfunction of the immune system
  • FIV-related disease phase: patient developed FIV related clinical symptoms and disease

FIV Acute Phase

  • Transient fever, lymphadenopathy, and lymphopenia

  • Signs can be subtle and transient: +/-fever, +/- general malaise, +/- lymphadenopathy
  • Often goes unnoticed
  • Virus detectable in high concentrations in the blood by culture and PCR
  • CD4+ and CD8+ T cell numbers decline

FIV Immune Response

  • FIV antibodies produced by 60+ days post infection
  • Circulating virus suppressed
  • CD8+ T cells increase above pre-infection levels
  • Inversion of CD4:CD8 ratio
  • Over time both CD4 and CD8 lymphocytes gradually decrease in numbers

FIV Asymptomatic Phase

  • Can last for many years

  • Increased risk of chronic and recurrent infections
  • Neoplasia is 5x more likely
  • Cell-mediated immunity more affected than humoral immunity
  • Hyperglobulinemia may occur
  • Survival time similar to that of non-FIV infected cats

FIV Clinical Phase

  • May never develop FIV-related clinical signs in their lives
  • Clinical signs related to immunodeficiency and/or immunostimulation
  • Related conditions include chronic gingivostomatitis, chronic rhinitis, lymphadenopathy, immune-mediated glomerulonephritis, and weight loss
  • Neoplasia may occur including (but not limited to): B cell lymphosarcomas, myeloproliferative disease, and squamous cell carcinoma
  • Concurrent infections: viral, bacterial, fungal, protozoal, parasitic (e.g. Demodex)


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