Lecture 3: FeLV and FIV

What is the etiology

Retrovirus - which has a protein core of single stranded RNA and is protected by viral envelope

what are endogenous retroviruses

inherited (nonpathogenic)

what are exogenous retroviruses

foreign (pathogenic)

can be transmitted horizontally

FeLV/FIV/FeSFV

FeLV Infections are transmitted through which route

oronasal

FeLV replicates in what areas

salivary glands and respiratory epithelium

FeLV may spread to the

bone marrow

In the bone marrow, FeLV infects _______ precursor cells, which is then transcribed by RT into DNA _________.

hematopoietic; provirus

what happens when FeLV creates the DNA provirus?

DNA copies of the viral RNA are transcribed and integrated into daughter cells

FeLV is typically _______ - either recomnination with endogenous genes or mutation form variations

exogenous

Which FeLV subgroup is associated with neoplasia

subgroup B

how many FeLV + cats are positive for subgroup B FeLV

50%

What is FeLV subgroup B

recombinant between transmissible FeLV-A and endogenous B envelope genes

How many cats are positive for subgroup C FeLV

1%

What is Felv Subgroup C

mutant variant (2nd pathway of infectious form)

which subgroup of FeLV is associated with non-regenerative anemia (bone marrow lesion)

subgroup C

Why has there been a massive decrease in FeLV prevalence from 30 years ago

due to the emergence of a vaccine and feline breeders taking appropriate preemptive measures

which cats have an increased risk for FeLV

• unvaccinated, outdoor cats

• adults (young are more likely to be sick)

• males

• communal housing

• concurrent illness

• behavior - social grooming or biting

what is the estimated FeLV prevalence today

1-2% in most healthy populations

what are ways for FeLV to be transmitted

• saliva

• milk

• blood

• urine

• other body secretions

• close prolonged contact

  • mutual grooming

  • sharing bowls

  • sharing litter boxes

Why are young cats more susceptible to FeLV?

adults cats have higher antibody titres (can fight against it) and there is a higher rate of persistent viraemia in kittens

in younger kittens, the felv receptors decrease the

macrophage response. over time response changes, which is why it’s rare for cats over 3 to get FeLV

regressive cats can either get better over time or they can move into _______ ______ if they are stressed

progressive stage - high viremia and high risk of FeLV

If FeLV goes into the oronasal route and causes replication in local lymphoid tissues, what is able to block the disease from progressing

cell-mediated immunity

what characterizes aborter cats that have cell-mediated immunity to block FeLV

• no viraemia

• negative antigen tests

• high level of neutralising antibody

• good immunity

What does it mean to be viraemic

circulation of FeLV P27 in serum

what are the two pathways that occur once Felv replicates in local lymphoid tissue

eliminate virus after 3-6 weeks (transiently viremic)

bone marrow infection

what are the two pathways from bone marrow infection?

regressive (latent) infection

persistent infection

what describes regressive infection

• viral genome integrated into host DNA

• no viral proteins produced

what describes persistent infection

low levels of neutralising Abs

replicating virus in lymphoid organs

How many cats develop fatal FeLV-associated disease within 3 years?

80%

how increased is lymphoma in FeLV positive cats

60x increased

lymphoma does or does not predispose FeLV

dot not, not the same vice versa

What are some characteristics of bone marrow suppression in FeLV infected cats

• anemia

• thrombocytopenia

• granulocytopenia

• some cytopenias → terminal myelodysplastic syndrome or leukaemia

secondary infections associated with FeLV:

-Respiratory viruses

•Haemoplasmas

•Dermatophytosis

•Generalised toxoplasmosis 

•FIP

other clinical findings for persistently infected FeLV

• Reproductive failure

•Glomerulonephritis 

•Generalised lymphadenopathy

•Panleukopenia-like syndrome

•Neurologic signs•Urinary incontinence

•Pupillary spasm

What is panleukopenia-like syndrome

harsh diarrhea, also referred to as cat AIDS due to symptoms

what are usual presenting complaints for FeLV (non-specific)

• weight loss

• fever

• dehydration

• rhinitis

• diarrhea

• conjunctivits

• oral infection

• lymphadenopathy

  • abscesses

what is the in-ptractice test for FeLV

• ELISA to detect p27 antigen

• free in plasma

  • positive early in disease

what is the specificty of ELISA Felv

98%

A single positive ELISA result in a healthy cat is evidence of viremia?

it is not, we have to confirm the result

Fluorescent anitbody

• detects p27 Ag within blood cells

• Blood or bone marrow

• only be positive after infection of BM

• no longer commonly used

Virus isolation detect viable whole virus in _____ or _____ _____.

blood or bone marrow

what is virus inoculation

inoculation of plasma onto specific cell culture. this is not a commonly used diagnostic, and takes 7 days or longer to get results. it is also dependent on the presence of a viable virus

PCR

detects general material of virus using blood or bone marrow. It detects miniscule amounts of DNA and amplifies them.

What are the advantages of PCR

• does not depend on viable virus

• can detect high and low levels

• rapid results

• usually very sensitive and specific

qPCR

• quantifies genetic material present in sample

• more sensitive than conventional PCR

• less cross contamination than the conventional PCR

what do you do in the case of a positive ELISA, but negative direct FA/PCR

• repeat or assess PCR in 6-8 weeks

• may have transient viremia or false positive

What do you do in the case of positive PCR, but negative ELISA/direct FA

• Suspect regressive infection. May not demonstrate cx, not infectious

• should not be used as a blood donor

what should you do for negative tests in kittens thought to be exposed?

re-test in 4-6 weeks

Positive ELISA: may have transient viraemia, therefore

retest in 6-8 weeks and if remains positive after a further 10 weeks

positive ELISA and Direct FA:

very low likelihood of transient viraemia (3-9%), most likely persistently infected

What is the outcome for FeLV-positive healthy cats