Viruses and Lymphoid System Flashcards
Name a virus cause by Alpharetrovirus (2)
Avian leukosis virus
Rous sarcoma virus
What virus is caused by Betaretrovirus?
Jaagsiekte sheep retrovirus
Name a virus caused by Gammaretrovirus
Feline leukaemia virus
Name a virus caused by Deltaretrovirus
Bovine leukaemia virus
Name a virus caused by Epsionretorvirus
Fish tumour viruses
Name 3 viruses caused by Lentivirus (5)
Human immunodeficiency virus
Feline immunodeficiency virus
Equine infectious anaemia virus
Caprine arthritis-encephalitis virus
Maedi-visna virus
What is the prevalence of FeLV?
- Variable
- Much decreased due to vaccination and test/removal schemes
Strays!
What are the subtypes of FLV?
- FeLV can cause immunosuppression, tumours, anaemia, enteritis.
- Immunosuppression probably due to virus replication in cell progenitors in BM
–cytokine dysregulation? With how they mature and grow
•Different subtypes: A, B, C and T
–B, C and T less common
•Classified according to the viral envelope (gp70)
–Something about this
•FeLV B arises due to homologous recombination between A envelope and endogenous FeLV related DNA
–probably increases rate of tumour formation
•FeLV-C arises, rarely, de novo due to point mutations in the envelope
–causes severe rapid fatal aplastic anaemia
•FeLV-T targets T-lymphocytes
–causes severe immunosuppression
•FeLV-A isolated in all infected animals
How is FelV transmitted?
Virus is labile in the environment so close contact important for spread
Not stable for long in the environment once it dries out
Across placenta – tend to die in utero
Discuss FeLV disease
- transmission by close contact (saliva)
- occasional vertical transmission from infected queens (in utero or after birth via saliva or milk)
- following infection most cats clear virus and recover – some become persistently infected (PI<30%)
- PI cats will typically die within 3 - 4 years
- Clinical signs include leukaemia, lymphoma, anaemia, immunosupression, enteritis
- Young kittens more likely to become PI
- Most cats tend to die 1-2 years
What is the pathogenesis of FeLV?
- Oronasal infection
- Virus infects lymphocytes in oropharynx then spreads to local lymph nodes
- Virus infects local lymph nodes, travels to bone marrow and other lymphoid tissues, then to mucosal tissues
- Incubation period of 3-6 weeks until virus is found in the blood and is excreted in saliva
When should we test for FeLV?
•Signalment
–Younger cat, possible exposure (stray?)
•“Appropriate” clinical signs
–Anaemia
–Neoplasia
•lymphomas, leukaemia
–Immunosuppression
- co-infections e.g. stomatitis, respiratory, chronic illness
- Management of populations
–Multi-cat household, shelters
–Cant always test - ££
How do you diagnose FeLV?
Aim to identify cats that are persistently viraemic
By definition have NO antibody to the virus
- so need to detect VIRUS ANTIGEN (p27)
- or circulating virus
In house screening test kits
What are the pros and con of in house FeLV testing?
–Negative results reliable (NPV >99%)
–Very unlikely it wont have the disease
–If there a clinical signs grumbling on you can then re test
–False positive results are possible (PPV 70-90%)
–Blood haemolysis
–Incorrect test use
–Antigen cross reaction
–Any positive result should be tested by virus isolation or immunofluorescence
–Recent infections should be retested in 12wk
What is the value of qPCR in FeLV?
–Detects provirus in circulating WBCs not viraemia
–Negative predictive value very high
–Does not always correlate with viraemia
–Viral loads need consideration
How can we control and manage FeLV?
Correct diagnosis of PI cats
Test and removal (isolation)
Symptomatic and supportive treatment
Impact on chemotherapy of cancers
Antiviral drugs?
Interferons, Other?
Vaccination of at-risk cats e.g. Eurifel FeLV
What should you do with a PI diagnosis?
–Retest in 12 weeks
–Retest in reputable laboratory
How can retroviruses establish persistent infections?
Lentiviruses typically infect adult hosts
Must evade host immune responses
- (virus accessory genes e.g. decrease MHC expression)
Tend to persist via cycles of cell killing, virus release and re-infection
Cell destruction leads to disease
Infect macrophages/monocytes +/- lymphocytes
KEY POINT: Once infected there is effectively no chance of recovery
What is the relatioship between Lentiviruses and immunodeficiency?
- Infection of monocyte/macrophages and lymphocytes
- Reduction of CD4+ T lymphocyte counts
- Peak in 3 months then IR control
What is the Immunopathogenesis of FIV?
- Infection of CD4 T-helper lymphocytes.
- Decreased CD4 cell count.
- Marked lymphadenopathy.
- Virus also targets CD8 T-cells, B cells, macrophages and glial cells.
- Lymphoid tissues of intestines may also be affected.
- Follicular destruction/dysplasia seen in later stages of disease.
Discuss the stages of FIV
- Acute transient illness several weeks after exposure.
- Long asymptomatic carrier state.
- Chronic disease characterised by secondary infections e.g. respiratory, oronasal, enteric, urinary.
- Severe disease in terminal stages with cachexia, anaemia, diarrhoea, leukopenia, opportunistic infections e.g. Poxvirus, cryptococcus, candidiasis.
What neoplasias are seen with FIV?
B cell lymphoma
Extranodal: gut, liver, spleen
Tumours are rare cf. FeLV
Which cats are at risk of FIV?
Promiscuous (unneutered)
Old
Male
Stray (free-ranging)
Associated with biting
How is FIV transmitted?
Horizontal
rarely transplacental
biting through umbilical cord?
kittens receive maternally derived antibody which persists until 16 weeks of age
How do we diagnose FIV?
- Diagnosis by detection of antiviral Ab
- PPV of SNAP test ~95%, NPV 100%
- Cats may be antibody negative up to 12wk post-infection
- Young kittens born to FIV+ dams will have MDA – wait or test with PCR based test
How do we control FIV?
- Control of feral cat populations
- Prevent transmission from FIV+ cats
- reduce risk of fighting
- no new cats in household
- may occur in the absence of biting?
- Vaccination?
- Not available in UK.
Why is there an obstacle with vaccinatiion for FIV?
Huge genetic variation
What is suppressed with FIV?
CD4 lymphocytes
Equine infectiouc anaemia virus:
A) How is it transmitted?
B) What happens if you find it?
C) How does the virus establish?
D) What is the diease related to?
A) Biting insect
B) Notify
C) Virus establishes persistent infection in face of vigorous host immune response
D) Immune complex formation
What are the clinical signs of Equine Infectious Anaemia Virus in the acute phase?
- Fever, diarrhoea, lethargy, restlessness, colic, rapid breathing, nasal and ocular discharge, emaciation, oedema, paralysis of hindquarters
- Anaemia
- High levels of circulating virus
How do we diagnose equine infectious anaemia virus?
•Confirm horses negative by Coggins test (Agar Gel Immunodiffusion test detects antibody)
Who is affected by Infectious bursal disease virus?
2-6 week old chicks
What is theere tropism for with Infectious bursal disease virus?
Lymphocytes in bursa and thymus
What are the clinical signs of Infectious bursal disease virus?
- watery diarrhoea, cloacal inflammation
- Immunodeficiency: opportunistic infections poor vaccine responses
What is the difference here?
Left - normal bursa
Right - infectious burssal disease
Label
A) Normal
B) Post infection
C) Cysts
How can we control Infectious bursal disease?
- Emergence of very virulent (VV) strains (>50% MR)
- No treatment for disease
- Difficult to eliminate
- Attenuated or recombinant vaccines (variable efficacy)
- Controlled by vaccination of breeding stock
Aleutian disease of mink:
A) Which virus?
B) What happens?
C) What does it lead to?
D)) Whhat does it cause?
E) What happens in ferrets?
A) Parvovirus
B) Viral-Antibody complexes are formed but not eliminated
C) To immune complex disease
D) Chronic disease: Glomerulonephritis, splenomegaly, arteritis etc
E) scending paralysis
What are the clinical findings of Malignant cattarhal fever?
- Single animals
- Depressed, anorexic, milk drop, wt. Loss
- Nasal, ocular discharges
- Corneal oedema
- Marked pyrexia (>41°C), sweating
- Oral, nasal ulceration
- Lymphadenopathy
How do you diagnose Malignant cattarhal fever?
- Clinical signs can be highly suggestive
- Confirmation by antiviral Ab detection or PCR
- No effective treatment
How do you manage Malignant cattarhal fever?
- No vaccine
- Avoid mixing of sheep/cattle around lambing time
- Management systems in zoo collections
What forms with Feline infectious peritonitis?
Immune complexes
What is the effect of Bovine viral diarrhoea on the immune system?
–Immunosupression predisposes to respiratory disease complex in calves (BHV, RSV, Mannheimia etc) or calf diarrhoea
What is the effect of parvovirus on the immune system?
Panleukopenia: decreased white blood cell count, killing of lymphoid and myeloid stem cells
