Feline Immunodeficiency Virus

Question 1

Virus type

Answer 1

• retrovirus
• genus Lentivirus
• closely related to HIV

Question 2

Are humans susceptible to the cat virus?

Answer 2

• no

Question 3

Subtypes

Answer 3

• A
• B
• C
• D
• E

Question 4

Seroprevalence

Answer 4

• highly variable geographically
• estimates of 1-14% in cats with no CS
• up to 44% in sick cats

Question 5

Which cats are most likely to be infected?

Answer 5

• sick adult cats
• male cats
• entire cats

Question 6

Transmission

Answer 6

• mostly through the inoculation of saliva during fighting
• vertical transmission and transmission between cats in stable households is relatively common
• most natural FIV infections are acquired by biting, presumably through the inoculation of the virus, or virus-infected cells, from the saliva of persistently infected cats
• transmission from queen to kitten may occur but only a proportion of the offspring become persistently infection
  – the proportion of kittens infected depends on the viral load of the queen during pregnancy and birth

Question 7

What are most CS caused by?

Answer 7

• most CS are not caused by the virus
• rather by secondary infections, a consequence of immunodeficiency and/or immune stimulation, which most frequently appears as:
  – chronic gingivostomatitis
  – chronic rhinitis
  – lymphadenopathy
  – immune-mediated glomerulonephritis
  – weight loss

Question 8

Diagnosis

Answer 8

• detecting antibodies using ELISA and immunochromatography
• Western blot is used to confirm questionable results

Question 9

Which subtype is found in the UK?

Answer 9

• only subtype A viruses

Question 10

Pathogenesis

Answer 10

• the major targets for FIV infection are activated CD4+ T-lymphocytes
• latent infection is possible
• in the 1st few days following experimental inoculation, FIV grows in dendritic cells, macrophages and CD4+ T lymphocytes, and may be detected in the plasma within 2 weeks
• the level of virus in the plasma and proviral DNA in the blood monocular cells increase, reaching a peak 8-12w post infection
• during this period, mild to moderate CS such as anorexia, depression and pyrexia may be observed
• these conditions generally subside rapidly
• generalised lymphadenopathy may persist for weeks to months
• the decrease in plasma viral load marks the beginning of the asymptomatic phase that can last for many years, or be lifelong
• during the asymptomatic phase the plasma virus load is stable but there’s progressive decline in CD4+ T lymphocyte numbers which results in a decreased CD4:CD8 T lymphocyte ratio

Question 11

Clinical signs

Answer 11

• FIV is responsible for immunodeficiency or immune stimulation (resulting in IM dz)
• in rare cases, the virus can cause neurological dz
  – altered forebrain or peripheral nerve electrical activity
  – behavioural changes, seizures, disrupted sleep patterns, impaired learning and paresis have been reported
• in the 1st w-m post infection, transient CS lasting a few days to a few weeks may be seen during the primary phase of infection
  – these include mild pyrexia, lethargy and peripheral lymphadenopathy
  – haematology may show a neutropaenia
• infected cats then generally remain free of CS for an extended period of time before problems associated with immunodeficiency develop
  – this asymptomatic period generally lasts for years
• clinical dz is generally seen 4-6y/o or older
• immunodeficiency +/- immunostimulation most frequently appears in the form of chronic gingivostomatitis, chronic rhinitis, lymphadenopathy, immune-mediated glomerulonephritis, and weight loss
• many concurrent viral, bacterial, fungal and protozoal infections have been reported in FIV-infected cats
• unusual clinical presentation e.g. unusual or severe parasitic skin dz (e.g. demodecosis, pediculosis), or tumours
• B cell lymphosarcomas, myeloproliferative dz and SCC have been reported in association with FIV infection
• reproductive failure is described in infected cats and associated with PCR-positive placental and foetal tissues
• renal involvement due to glomerular and tubulointerstitial lesions associated with severe proteinuria is a frequent occurrence in FIV infected cats
• a direct role of FIV in the induction of the renal damage is possible, together with that of renal immune deposits

Question 12

Diagnosis

Answer 12

Virus isolation
- highly reliable
- from heparinised blood
- not used routinely

PCR
- not as good as serology

Serology
- test kits detect antibodies recognising viral structural proteins
- ELISa or immunochromatography
- Western blotting is considered the ‘gold standard’ for FIV serology and is used to confirm questionable results
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