Feline Viral Flashcards
FeLV
o Retrovirus, multiple strains
o Decr prevalence due to testing/vaccination; <5% prevalence (regional variation)
o Transmission:
Vertically (in utero, milk); horizontally – usually oronasal via mutual grooming; also bites
Age dependent, with kittens <4m appearing more susceptible
FeLV Vaccine
non-core; inactivated or recombinant; initial series and boosters
test prior to vaccination
onset of immunity ~2-3wks post vaccination
efficacy incomplete and duration of efficacy unknown
Ab titer does not correlate to immunity - cannot be used to determine need for booster
Current guidelines (AAFP):
Vax all cats <1yr old with initial series and again with one year booster
FeLV vaccine should be given below LEFT stifle
Consider additional boosters in at risk cats: multi-cat households with infected or unknown
status, outdoor exposure, etc.
Clinical Exposure to FeLV
Clinical exposure:
may become infected - usually test Ag positive within 1m of exposure
“transiently infected” = regressive infection = viral infection “contained” during early infection with
effective immune response. No detectable antigen (p27) and aviremic; but FeLV proviral DNA detectable
in blood via PCR integrated into genome. Unlikely to develop FeLV-associated disease. Negative viral
shedding.
Persistently infected = progressive infection = positive antigen (p27), positive viremia, viral shedding
(contagious), proviral DNA in blood
Similarities between FeLV and FIV retroviruses
o both retroviruses labile and easily killed with standard cleaning; can be viable >1wk in biological specimens
o Potential clinical sequelae: anemia, leukopenia, lymphoma, chronic inflammatory conditions, susceptibility to
secondary and opportunistic infections, cutaneous abscesses, stomatitis, ocular lesions, neurologic disease (often
multi-focal), renal disease (FIV)
o Point of care testing – usually combo FeLV/FIV tests, multiple commercial types available, excellent sensitivity/spec
usually in 85-99% range
FIV
o Retrovirus, several clades/subtypes (A-E) based on envelope protein gp120. Subtypes vary geographically and
within subtypes there is genotypic/phenotypic variation and a high mutation rate.
o Stable prevalence, <5% in North America (regional variation)
o Usually horizontal transmission via bite wound (saliva); possible vertical transmission (in utero or milk)
o Most cats mount immune response and infected cats usually low viral load, low antigen levels
o Main viral target cell is CD4+ T cell
o May live similar lifespan as uninfected cats
o Clinical exposure
may become infected - usually test Ab positive within 2m of exposure
Initial transient illness (2-6wks post exposure) may not be recognized by owner ; fever, leukopenia,
enlarged lymph nodes
CD4+/CD8+ cell ratios affected but usually prolonged clinical latency - several months to years,
asymptomatic
Terminal phase – clinical illness; declining CD4/CD8 cells
FIV Vaccine
Controversial, non-core, not usually recommended.
Vaccine to clade A/D only. Efficacy questionable - does not induce broad cross-immunity.
Consider for high-risk animals e.g. outdoor, male, intact cat.
Onset of immunity reported ~3wks with duration of 1yr.
Vaccinated cats will “test positive” for FIV post-vaccination; there is no way to differentiate between Ab
cat produces to vaccine vs. virus infection; vaccine-induced Ab may persist years post-vaccination
When to test for retrovirus
o All cats/kittens when acquired and again at ~2m
o All cats, prior to vaccination with FeLV/FIV
o all sick cats, regardless of past negative testing
o if exposed to infected cat or cat with unknown status, esp if bite wound – immediately and if negative retest at 2m
o annually - uninfected cats living with/not isolated from infected cats
o High risk lifestyles – outdoor, intact male, incr regional prevalence, regular fighting, etc.
o All blood donor cats (retroviruses transmissible via blood)
FeLV testing
o Detects soluble core viral antigen (Ag) p27; usually use peripheral blood
o Generally test positive within 30d (PCR may pick up earlier)
o Testing in kittens –no false + from passive maternal antibodies since Ag test; may test false neg since if not yet
detectable Ag
o Vaccination does not compromise future testing
o If positive, use confirmation testing with different methodology, preferably with higher specificity e.g. IFA, virus
isolation/culture for virus or PCR for proviral DNA/viral RNA. Especially need confirmatory test if
screening/healthy/asymptomatic/low-risk cat
FIV testing
o Detects antibody (Ab) to viral antigen (p24 or other)
o Generally test positive within 60d
o If positive, use confirmatory testing – alternative Ab screen may be ideal, other methods available
o Testing in kittens – can test false + as FIV Ab can be passed via maternal transmission from either infected or
vaccinated queen; most FIV+ young kittens not truly infected and will test negative later; if still positive at 6m,
kitten likely true FIV+
Management of asymptomatic retroviral infected cats
Confine indoors, neuter, do not expose other cats
maintain healthy lifestyle, raw diets should be avoided, adequate control of parasites, infections, etc.
Monitor for: stomatitis, uveitis, lymphoma/other cancer e.g. lymph nodes, mediastinum, etc.
Annually – PE and minimum database with CBC, chem, UA with additional CBC q6m for FeLV-infected.
Regular vaccinations considered for individual – potential concern for modified-live vaccines?
Management of symptomatic retroviral infected cats
Palliative care – protect from secondary infections, etc.
Antiviral eg. Zidovudine (AZT), usually used with stomatitis, neurologic disease. May cause/compound
hematologic issues.
Feline interferon omega – some evidence for improvement (FeLV>FIV), not enough clinical data
Human interferon alpha – some evidence of benefit, not enough clinical data
FIP
o FIP is a viral-related, immune-mediated disease; <5% prevalence (pets)
o Feline coronavirus (FCoV)
FCoV infection is first step in chain of events that culminates in FIP in ~5% of FCoV-infected cats
>90% of FCoV infected cats will NOT develop FIP
generally spread fecal-oral, also aerosol; infects enterocytes
up to ~50% general cat population (~90% catteries) FCoV antibody +; most exposed <4m
fairly stable in the environment , survive longer than retroviruses
FIP etiology
True pathogenesis/etiology remains undetermined
Likely results from complex host-virus interaction, multi-factorial
Hypothesized: Of all cats that get enteric FCoV, some cats have additional chain of events:
o Viral factor(s) - FCoV develops mutation allowing infection of monocytes/macrophages
o Host factor(s) - inappropriate host/immune response, genetic/breed predisposition
FIP clinical disease
infection of monocytes/macrophages
progressive, ~95% fatal
o Result: system organ inflammation predominantly perivascular organ granulomatous disease +/-
vasculitis
General illness (most cats) – inappetant, depressed, weight loss, +/- fever
“Wet” form ~75% - Effusions: ascites, pleural, pericardial; parenchymatous organ inflammatory lesions can
appear mass-like (abdomen, etc.)
“Dry” form ~25% - Ocular and/or CNS lesions predominate; other organs (kidneys, etc.)
FIP vaccination
Vaccination controversial and almost never recommended – lack of efficacy in clinical trials; most cats are
exposed to FCoV prior to even old enough to get vaccine; NO clinical utility if already exposed; will test Ab titer
+ after vaccination, same as would to FCoV infection; concern that vaccine if induces high serum antibody
levels can actually promote antibody dependent enhancement of infectivity (=experimentally can make
disease worse).
