SA Medicine - infectious diseases

what type of virus is feline leukemia virus (FeLV)?

RNA retrovirus (oncornavirus)

how pathogenic is FeLV?

FeLV is the most pathogenic retrovirus of cats

more death and clinical syndromes than any other infectious disease of cats

mortality occurs in what population of FeLV infected cats?

mortality occurs in viremic cats

(50% die within 2 yrs, 80% within 3 yrs)

what is the prevalence of FeLV?

worldwide distribution, seen most in outdoor male cats between 1-6 years old

seroprevalence is 3% in US, higher risk in sick or high-risk cats

how is FeLV transmitted? which mode of transmission is most common?

vertical transmission and horizontal transmission (more common)

what is seen in pregnant viremic cats infected with FeLV?

embryonic death and/or sudden death in kittens due to vertical transmission

are regressive infected FeLV cats able to transmit the virus vertically?

no, regressive infected cats almost never transmit unless the virus is reactivated

regressive infections do not have viremia (if no viremia, no transmission)

how is FeLV transmitted in kittens with viremia?

most likely due to mammary transmission

how does horizontal transmission of FeLV occur?

1. saliva and nasal secretions through prolonged contact:

-grooming

-same water source

- fighting (main way for horizontal transmission)

2. feces and urine

what is an abortive infection (referring to FeLV)?

when a cat is exposed, and the body develops neutralizing antibodies to prevent viremia/virus replication

cat clears infection in 4-6 weeks

what percentage of cats exposed to FeLV will have an abortive infection?

60%

how are cats with abortive infections of FeLV infections diagnosed?

these cats will test negative on all antigen tests

in order to diagnose abortive infections, have to use a serologic test to test for antibodies (there is no good serologic test for these antibodies)

what is a regressive infection (referring to FeLV)?

partially effective antiviral immune response prevents persistent viremia

once the provirus is in the cats genome, causes an initial viremia (can last 1-12 weeks, usually no longer than 6 weeks)

do cats with regressive infections have bone marrow infections?

no, because the viremia is transient due to the body's immune response to clear the virus

what percentage of cats exposed to FeLV will have a regressive infection?

15%

in cats with regressive FeLV infections, where can the virus be found?

virus will be in bone marrow, spleen and liver (provirus in cats genome)

virus is non-replicating (but few viral particles may reactivate during situations such as pregnancy)

how long does it take for regressive infected FeLV cats to eliminate the virus?

majority of regressive-infected cats eliminate virus in 16 months

10% of cats still have infection in 30 months

is it common for regressive infected cats to develop problems/clinical signs?

no, very few develop problems

if they do, these problems include hematological changes, and potential for reactivation

how are progressive FeLV infections distinguished?

bone marrow infection and persistent viremia

what percentage of FeLV cats get progressive infections?

25%

what does FeLV infection involving bone marrow lead to? (as seen in progressive infections)

lack of efficient FeLV-specific immune response

persistent viremia (due to bone marrow/immune suppression)

are FeLV progressive-infected cats with persistent viremia contagious?

yes- if viremia is present, can transmit to other animals

how do most cats with progressive FeLV infections die? what is the life expectancy at this stage?

usually die of FeLV-related diseases, in about 2-3 years

what are the clinical signs of FeLV infections?

clinical signs associated with immune suppression:

-non-specific signs (lethargy, anorexia, weight loss)

-secondary infections

-neoplasia

-vomiting and diarrhea (GI form of FeLV)

-icterus

-rhinitis and pneumonia

-neurologic abnormalities

-glomerulonephritis

-ocular signs

what are the 2 most common neoplasias associated with FeLV?

1. lymphoma (thymic, multicentric, alimentary, or atypical)

2. leukemia

what are 2 possible causes of icterus in FeLV infected cats?

1. IMHA

2. liver failure

what are the most common findings of FeLV infected cats?

non-regenerative anemia

immunosuppression (other infections)

lymphoma (thymic, multicentric, alimentary, or atypical)

what hematologic lab abnormalities are seen with FeLV infections?

1. non-regenerative anemia (most common- will see macrocytosis without reticulocytes)

2. regenerative anemia (immune mediated, haemoplasmosis)

3. immune suppression by invasion of bone marrow: thrombocytopenia, neutropenia, lymphopenia

what other lab abnormalities may be seen in cats infected with FeLV?

myelodysplasia or leukemia

proteinuria

when should cats be tested for FeLV?

1. at least once in the cats life

2. sick cats (know dz's associated with FeLV)

3. known exposures after 30 days (for point of care/ELISA tests)

4. risk exposure (bites)

5. before adoption

6. before vaccination

when will a p27 ELISA test be positive?

can test earlier stages, positive prior to bone marrow infection

positive in:

-regressive infections (transient/1st viremia)

-progressive infection (persistent viremia)

when will a IFA test for FeLV be positive?

positive only after bone marrow infection (progressive infection)

viremia (>90% for life)

patient is contagious bc persistently viremic

how does ELISA testing differ from IFA when detecting FeLV?

ELISA is slightly more sensitive as it can detect 1st (transient) and 2nd (persistent) viremia

IFA is only a predictor of progressive infection bc can only detect 2nd (persistent) viremia

what do PCR tests for FeLV detect?

PCR detects provirus in genome (DNA)

high specificity and sensitivity

does PCR or p27-ELISA become positive first in FeLV infected cats?

PCR is positive before p27-ELISA

ie, PCR is the earliest test to become positive for FeLV

what does RT-PCR detect?

detects RNA-viral particles in blood, plasma, saliva

detects viremia, even in saliva

(first test to become positive, but we dont use it)

what is the positive sequence of tests for detection of FeLV?

1. RT-PCR for viral particles

2. PCR-DNA in provirus

3. ELISA

4. IFA

will the following tests be positive or negative in patients with abortive infections?

a. DNA provirus:

b. ELISA:

c. IFA:

a. DNA provirus: negative

b. ELISA: negative

c. IFA: negative

will be antibody positive with serology- but this is unavailable

will animals with an abortive infection have a normal or reduced lifespan?

normal lifespan- animals will appear normal

will the following tests be positive or negative in patients with regressive infections?

a. DNA provirus:

b. ELISA:

c. IFA:

a. DNA provirus: positive

b. ELISA: positive (from 1st/transient viremia- once this viremia goes away, test will be negative)

c. IFA: negative

will animals with an regressive infection have a normal or reduced lifespan?

if antigen (-) and low PCR (+), +/- normal lifespan

if antigen (+) and PCR (-), +/- normal lifespan

will the following tests be positive or negative in patients with progressive infections?

a. DNA provirus:

b. ELISA:

c. IFA:

a. DNA provirus: positive (1 week)

b. ELISA: positive (6 weeks)

c. IFA: positive (9 weeks)

will animals with an progressive infection have a normal or reduced lifespan?

reduced lifespan if positive ELISA and IFA tests (indicates progressive infection)

if a healthy cat has a negative FeLV ELISA test with no clinical signs, should you trust this negative result?

yes, a healthy cat with negative test and no signs==> no disease

if a healthy cat has a negative FeLV ELISA test with no clinical signs, but a known recent exposure/infection, what should you do?

run ELISA again in 6 weeks (when 1st viremia occurs)

and

run a RT-PCR (for viral particles) in 1 week

what should be the next test if a healthy cat tests positive on ELISA for FeLV?

run a PCR to detect proviral DNA:

-if positive= infected

-if negative= false-positive ELISA

(there are usually few false positives, seen mostly in low prevalence populations)

what does a sick cat with a positive ELISA for FeLV test indicate?

cat either has:

1. progressive FeLV infection

2. clinical signs likely due to FeLV

do PCR/DNA to determine cause of presenting illness

what does a sick cat with a negative ELISA for FeLV indicate?

cat is truly negative or has a regressive infection

test proviral DNA (PCR):

-if positive: regressive infection

-if negative: no FeLV

how can FeLV be prevented?

-house cats indoor

-test and separate seropositive cats (if not possible, vx negative cats)

-avoid sharing of litter boxes and water bowls

-test new cats

-flea control

-at the hospital: individual cages, disinfection, hand washing

-FeLV vaccine

which cats should be vaccinated for FeLV?

FeLV vx is a core vaccine for kittens and cats <1 year of age

cats with sustained risk should receive annual boosters if risk persists

always test before vaccination

which cats are considered high risk cats to contracting FeLV and should therefore receive annual boosters?

outdoor cats

areas with lots of cats

contact with FeLV-positive cats

can FeLV-immune cats get infected when there is a FeLV-positive cat in a cattery?

yes, as neutralizing antibodies do not last for life

cats that were immune may get viremic

infection risk in adults is 10-15%

what does the individual management of a FeLV-positive cat consist of?

strictly indoor, this decreases risk of:

-secondary infections and acquiring other diseases

-infecting other cats

routine vaccination (core vaccines): attenuated FPV

how often should FeLV-positive cats have a physical exam?

should have PE every 6 months, including a CBC to evaluate cell levels

if sick, diagnose

if infection, use aggressive therapy (bc no functioning immune system)

what therapies can increase survival of FeLV-infected cats?

feline ω-interferon- shown to have better survival at 9 months (not after 1 year), but it is hard to get in the US

in FeLV-positive patients with no clinical signs, what therapies should be introduced?

none- there is no therapy in preventing disease from developing

how is gingivostomatits resolved in FeLV-positive cats?

teeth removal

avoid glucocorticoids

what therapies are used for FeLV-positive cats with neurologic signs?

look for other causes first (toxo, lymphoma)

if due to FeLV: zidovudine (AZT) 5mg/kg PO q12

what therapies should be used for recurrent infections?

aggressive therapy: bactericidal antibiotics, longer duration of tx

feline ω-interferon (not available in US)

what therapies can be used in FeLV-positive cats with IMHA-induced regenerative anemia?

immunosuppression is usually effective

what therapies can be used in FeLV-positive cats with haemoplasmosis-induced regenerative anemia?

doxycycline is usually effective

what therapies are available to treat pancytopenia (myelosuppression) causing non-regenerative anemia in FeLV-positive animals?

these usually have a poor response to therapy

what therapies are available to treat pure red cell aplasia (myelosuppression) causing non-regenerative anemia in FeLV-positive animals?

responsive to immunosuppresion

what myeloproliferative diseases are seen with FeLV infections?

erythroleukemia, anemia with macrocytosis

what therapies are available to treat myeloproliferative disease causing non-regenerative anemia in FeLV-positive animals?

poor responses to therapy

how should you treat a FeLV-positive cat with myelophthisis causing non-regenerative anemia?

cytotoxic chemotherapy

(myelophthisis due to lymphoma, CLL, granulocytic leukemia)

how do FeLV-positive cats with leukemia respond to therapies?

poor response to chemotherapy

how should you treat a FeLV-positive cat with neutropenia?

glucocorticoid therapy (bc immune mediated)

how should you treat a FeLV-positive cat with thrombocytopenia?

glucocorticoid therapy (bc immune mediated)

how do FeLV-positive cats with thrombocytosis respond to therapies?

poor response to chemotherapy

what kind of virus is FIV?

RNA retrovirus

genetically diverse virus

what is the seroprevalence of FIV?

1-4% in normal or low risk cats

higher in sick or high-risk cats

how is FIV transmitted?

1. bites

2. milk (FIV-infected queens to kittens)

3. transplacental

which cats are more prone to getting infected with FIV?

older (>6 years), intact male, outdoor cats

what are the initial signs of FIV infections?

low grade fever (due to first viremia), lymphadenopathy

usually these signs go unnoticed

what is the subclinical latent period of FIV infections?

occurs after initial viremia, lasts on average of 7 years (majority of cats never come out of this phase)

what does duration of the subclinical latent period of FIV depend on?

strain and age when infected

can cats in the subclinical latent period of FIV have normal life expenctancies?

yes

what are the clinical syndromes of FIV infections?

1. chronic small bowel diarrhea

2. hematologic changes

3. anterior uveitis

4. glomerulonephritis

5. renal failure

6. CNS signs

7. infections

8. tumors

what hematologic changes can be seen with FIV infections?

non-regenerative anemia

thrombocytopenia

neutropenia (most common)

myeloproliferative diseases

myelodysplasia or leukemia

abnormalities related to clinical syndromes

what tumors are associated with FIV infections?

B lymphoma

myeloproliferative diseases

squamous cell carcinoma

when comparing FIV vs FeLV, which has higher chances of developing tumors?

62 times more likely in FeLV

5 times more likely in FIV

when comparing FIV vs FeLV, which has higher chances of developing neurologic signs?

uncommon in FIV or FeLV

viruses cause viral damage (virus causes cytotoxic effects in the CNS, causing neurologic dz directly)

is bone marrow suppression common in FeLV or FIV?

bone marrow suppression is uncommon in FIV, may see neutropenia

common in FeLV (will see anemia, thrombocytopenia, neutropenia, pancytopenia, progenitor cell infection)

is immune mediated diseases common in FeLV or FIV?

FeLV: uncommon (if it were to happen, IMHA)

FIV: more frequent, glomerulonephritis and uveitis are the top 2 dz's

is immunodeficiency common in FIV or FeLV?

immunodeficiency is common in both FIV and FeLV

is gingivitis common in FeLV or FIV?

common in FeLV

very common in FIV (50% of symptomatic cases)

will FIV infected cats have a normal electrophoresis?

no, will exhibit a polyclonal gammopathy due to increases in multiple immunoglobulins

when a cat becomes infected with FIV, when do antibodies develop?

antibodies develop by the time the first clinical signs develop in the acute phase of the disease

antibodies are present in the acute, asymptomatic, and clinical phases of FIV

when should cats be tested for FIV?

1. cats that never have been tested

2. sick cats

3. before adoption (or newly adopted)

4. recent exposure

5. high risk cats (outdoor, intact males, 2-6 yrs of age)

when does seroconversion for FIV occur?

within 60 days, sometimes up to 6 months

what does a positive serology indicate for FIV?

documents persistent infection

-does not mean clinical signs are due to FIV

can serology for FIV differentiate from vaccine antibodies?

no- all serology tests will pick up the vaccine antibodies

what serology tests are most readily available for FIV?

ELISA and immunochromatographic tests

used for routine screenings

what does a negative POC test in a healthy cat indicate?

the cat is truly negative for FIV and is healthy

what are 2 exceptions for a negative POC result in a healthy cat?

1. if the cat had recent exposure0 retest in 60 days (if the cat is still negative at the 60 days, the cat is actually negative)

2. severe immunosuppression

what does a positive POC test in a healthy cat indicate?

virus is in latent stage, or result is a false positive (if low prevalence)

what tests should be performed to determine if a positive POC test in a healthy cat is a true positive?

PCR or western blot

-if PCR is positive- confirms FIV

-if PCR negative, cat could be either +/- (+ if in latent phase since no viremia, but could also be actually negative)

what does a negative POC test in a sick cat indicate?

FIV is very unlikely

what does a positive POC test in a sick cat indicate?

the cat has FIV