Feline leukaemia virus

Question 1

Viruses cats vs dogs

Answer 1

MORE complex in cats than dogs

Question 2

What are the most common retroviruses you will come across?

Answer 2

1. Feline leukaemia virus (FeLV)
2. Feline immunodeficiency virus (FIV)
   - ——– most common above
3. Feline syncytium-forming virus (FeSFV) (less common) but not associated with clinical disease
4. endogenous viruses

Question 3

What is virus classification based on?

Answer 3

1. genome (RNA or DNA)
2. Number and sense of RNA/ DNA strands
3. Morphology
4. Genome sequence similarity
5. Ecology
6. Enveloped (less stable in environment)
7. RNA virus - mutates a lot

Question 4

Retroviridae

Answer 4

1. enveloped = not v stable, important for transmission - not transmitted well in environment
2. RNA virus, mutates a lot
3. characteristic genome structure, 3 same main proteins
4. DIPLOID CELL unique so had 2 copies of RNA
   Once injected, use reverse transcriptase to make DNA of their RNA genome
5. Then move viral DNA into host cell’s nucleus, integrate the DNA copy of their genome into host cell genome = PRO virus
6. every time cell undergoes transcription, makes copy of viral DNA
7. Basically with retrovirus go from RNA - DNA - Pro virus - RNA - translation occurs

Question 5

What is a pro virus

Answer 5

virus genome that is integrated into the DNA of a host cell

Question 6

Feline leukarmia virus, diff types

Answer 6

Three subtypes A, B and C
o distinguished by genome analysis and serology
BUT Only type A is transmissible so in general only type A we are likely to deal with
Also can’t get type B or C without A as need for replication.
Will only ask about A in exam

Question 7

Clinical signs of FeLV (Feline leukaemia Virus)

Answer 7

1. Most common infectious cause of death in young cats
2. RAIN - list of importance
   Neoplasia
   Immunodeficiency
   Anaemia
   Repro failure

Question 8

What are the routes of infection of FeLV

Answer 8

1. excreted in saliva (predominantly) urine, faeces and milk
2. CLOSE contact. FRIENDLY- nursing, multicat household
3. Vertical transplacental transmission = infected queen FeLV pos kittens

Question 9

Difference in route of infection FeLV vs FIV

Answer 9

1. FeLV = friendly, FIV = fights

2. FeLV vertical transmission possible, not in FIV

Question 10

Pathogenesis of FeLV “normal”

Answer 10

1. cats become infected by “friendly” contact
2. Virus replicates locally in oropharynx
3. Primary viraemia
4. In blood
5. replicates in other lymphoid tissues, bone marrow etc
6. secondary viraemia
7. Ineffective immune response
8. Persistently viraemic
9. Clinical disease
10. DEATH

Question 11

What is primary viraemia, what would diff tests show?

Answer 11

1. relatively shortly after infection, before becomes either persistently viraemic or effective immune response
2. tests ran would show positive for pro virus, protein in blood and VIRUS positive (PCR picking up RNA of viral genome)
   BUT antibody negative as shortly after infection

Question 12

Is a cat is persistently viraemic, how would this show up on tests?

Answer 12

1. Provirus positive (hihg)
2. Antigen positive
3. Antibody positive
4. virus positive

Question 13

What is the difference between primary viraemia and
secondary?
FeLV

Answer 13

In secondary Ab POSITIVE but in primary Ab negative

Question 14

BUT how can some cats live with FeLV?

Answer 14

1. At either the primary or secondary viraemia stage they can develop a strong immune response.

Question 15

Talk through infection with FeLV and strong immune response

Answer 15

1. cats become infected by “friendly” contact
2. Virus replicates locally in oropharynx
3. At either primary or secondary viraemia can develop STRONG IMMUNE RESPONSE
4. means suppress virus and appear clinically normal
5. think some cats may eliminate this entirely, not sure though

Question 16

If a cat is has a strong immune response, how would this show up on tests? + why?

Answer 16

o provirus positive but LOW level.
o Antigen NEGATIVE – not sufficient enough virus in blood to make sufficient protein that you detect by measuring antigen
o VIRUS negative – no virus in blood as suppressed to low levels but will have antibody

Question 17

What do we think affects whether a cat becomes persistently infected or overcomes?

Answer 17

1. Dose of virus - hihg more likely persistent
2. Age - susceptibility to persistent infection decreases with age.
   o only 1 in 5 cats >16 weeks old becomes persistently infected – rest die
   o Over 16 weeks age 4/5 cats go to persistent latent infection
3. Immune status
   Maternally derived antibodies for first 4 weeks

Question 18

What secondary disease can FeLV cause? adn why?

Answer 18

TUMOURS

Due to pro virus

Question 19

How does FeLV cause tumours?

Answer 19

1. FeLV provirus is sporadically inserted into host cell’s DNA
2. If this is close to the cellular oncogene gene (most common) or tumour suppressor then can cause tumours
3. e.g. promote replication of the cellular genome = inc division of cell with pro virus in
4. e.g. disrupt tumour suppressor gene

Question 20

The most important clinical disease of FeLV and what it is

Answer 20

RAIN
NEOPLASIA
An abnormal mass of tissue that forms when cells grow and divide more than they should or do not die when they should. Neoplasms may be benign (not cancer) or malignant (cancer)

Question 21

What are the 4 main types of lymphoma associated with FeLV?
and also where can you get them?
How does this affect diagnosis?

Answer 21

o mediastinal (thymic)
o multicentric
o alimentary
o leukaemic
Can also get tumours in lots of other areas e.g. kidney, nose, eye, skin, CNS.
Affects diagnosis as means can have a cat presenting with almost any conditon. e.g. renal failure - tumour in kidney etc
blind, nose bleed due to tumours etc

Question 22

Talk about FeLV and anaemia

Answer 22

1. FeLV probs the most common cause of anaemia in cats

2. FeLV causes Primary and secondary anaemia

Question 23

Primary anaemia

Answer 23

 RBC production switched off
 red cell aplasia (normal WBC, RBC <10%)
 total marrow aplasia (rare; low RBC and WBC)
 non-regenerative; normocytic, normochromic,
• juvenile RBC – bigger and diff colour. RBC production switched off, RBC in peripheral circulation look NORMOCHROMIC (normal colour) and NORMOCYTIC (normal size)

Question 24

Secondary anaemia

Answer 24

 Regenerative – juvenile RBC = bigger and diff colour RBC
 due to space-occupying myeloid tumours in bone marrow
• not as much functional RBC production
 haemolytic anaemia common in FeLV-infected cats - mild and often missed

Question 25

Animal presents witha range of infections that are either worse than they should be or don’t get better after treatment, what are you thinking

Answer 25

FELV and FIV on differential diagnosis list due to immunosuppression of both diseases

Question 26

How to control FeLV?

Answer 26

1. test adn remove: rehome or euthanise
2. Vaccination 8-9 weeks and 3 weeks later!!! still can’t for HIV and FIV:(
3. one food bowl per cat

Question 27

How to test for FeLV

Answer 27

1. test twice to differentiate between negative, primary, secondary or persistent
2. Test all cats in colony
3. Retest all cats 12 weeks later
4. retest all cats every 6-12 months and ALL cats entering colony

Question 28

FeLV treatment:

Answer 28

1. LArgely supporting
2. No specific antivirals
   o Often effective in cell culture but toxic in the cat
3. Interferon may prolong survival
4. Might treat some lymphomas (e.g. thymic) with cytotoxic drugs - but if FeLV +ve, other problems will develop