Transcript Retroviridae - University of Saskatchewan

Retroviruses
October 5,6,7 2010
Retroviruses
Viral RNA
Viral DNA
(integrated into host genome)
Viral mRNA,
genome
Reverse (retro) transfer of genetic information
Usually, well adapted to their hosts
Endogenous retroviruses
Retroviridae
Feline leukemiavirus
Oncovirinae
Lentivirinae
Avian leukosis viruses
Feline, bovine, human
immunodeficiency viruses
Equine infectious anemia virus
Spumavirinae
“Foamy” agents
A retrovirus virion
envelope
(ENV)
p15e
gp70
RNA dep. DNA pol
(POL)
nucleocapsid
p27 (GAG)
genome (2 copies)
The viral genome
Long terminal (oncornaviruses)
repeat
LTR
RNA dependant DNA
polymerase
GAG
Group specific antigens
(nucleocapsid)
POL
ENV
LTR
Envelope proteins
(type-specific antigens)
All three genes - GAG, POL, ENV - required for replication
Replicative cycle
receptor
uncoating
RNA
viral dsDNA integrated
into host genome
blocked
receptors
ds DNA
mRNA
proteins
pro-virus
genomic RNA
assembly
Interference
receptor for
FeLV-A
FeLV-A
FeLV-A infected
cell
FeLV-B
receptor for
FeLV-C
receptor for
FeLV-B
blocked
receptors for
FeLV-A
FeLV-C
Pseudotypes
FeLV-A
P
FeLV-B
P
How do oncoviruses cause
cancer?
Peyton Rouse and the cancer
causing chicken virus
Rockefeller University 1912
The Rouse sarcoma virus genome
LTR
GAG
POL
ENV
LTR
GAG
POL
ENV
SRC
LTR
LTR
D. Stehelin, H.E. Varmus and J.M. Bishop
1976
DNA related to the transforming gene of avian sarcoma
virus is present in normal avian DNA
Nature 260:170-173
Retroviruses and cancer
Transduction of oncogenes
GAG
POL
LTR
LTR
src
Activation of oncogenes
GAG
POL
ENV
LTR
myc
LTR
Inactivation of
tumour-suppressors
GAG
Rb
LTR
POL
ENV
LTR
Rb
Other transduced oncogenes
1. Sis - platelet derived growth
factor (PDGF) cDNA by wooly
monkey or cat in simian sarcoma
and feline sarcoma viruses
Sis
protein
proliferation
PDGF receptor
Cell transformed by SSV
Other transduced oncogenes
2. Erb. Epidermal growth factor receptor transduced by avian
erythroblastosis and fibrosarcoma causing viruses
ligand binding site
kinase domain
inhib. phos. site
P
P
stim. phosp.
site
EGRF receptor
P
vErb
Feline leukemia viruses
• Most common infectious cause of death in
cats
• Cytoproliferative and cytosuppressive
diseases
• High mortality in persistently infected cats
(>80% in 3 yrs)
Endogenous and Type A, B, C
viruses
GAG
LTR
• Endogenous sequences
GAG
• Group
Type AA
LTR
• ubiquitous, in all infectious samples,
non-virulent
• Group
Type BB
GAG
POL
ENV
LTR
POL
ENV
LTR
POL
ENV
LTR
LTR
• in 40% of infectious samples,
endogenous X FeLV-A, virulent
• Group
LTR
Type CC
• in 1% of infectious samples.
Derived by mutation from A
GAG
POL
ENV
LTR
feline sarcoma and acute
leukemia viruses
• defective viruses that transduce cellular
oncogenes
GAG
LTR
POL
oncogene
LTR
Pathogenesis
infection by oral route
infection by bite
replication in tonsils
replication in draining lymph
node
bone marrow
thymus
protective immune response
recovery
latency
Peyer’s patches
inadequate immune response
viremia
Consequences of viremia
cytoproliferative
fibrosarcomas
cytosuppressive
anemia
pancytopenia
lymphosarcomas
leukemias
thymic
multicentric
alimentary
immunosuppression
secondary infections
chronic stomatitis
gingivitis
non-healing skin lesions
respiratory infections
Haemobartonella felis
Diagnostic tests
•
•
•
•
Antigen capture ELISA “FeLuke test” (p27)
Fluorescent antibody test
Virus neutralization
PCR
Disease progression and
diagnostic tests
infection by oral route
infection by bite
replication in tonsils
ELISA sometimes +
replication in draining lymph
node
bone marrow
thymus
protective immune response
recovery
latency
PCR on bone marrow
Peyer’s patches
inadequate immune response
viremia
epitheial cells
(shedding)
ELISA +
FAT +
Prevention of FeLV infection
• Management
• Vaccines
Management
• Multi cat households or breeders
– Can spread rapidly
– to solve problem
• test
• isolate + cats
• retest
– + -> + PI
– + -> - consider – - -> + retest 12 weeks later
– to maintain
• test and quarantine before new introductions
• single cat +
– retest
– inform owner of consequences
Vaccination
• Inactivated virus or subunits
– FeLV-A
– FeLV-A, FeLV-B, FeLV-C
– FOCMA
•
•
•
•
Adjuvants
Vectored
In practical terms only FeLV-A needed
Most vaccines have comparable efficacy
Evaluation of vaccine efficacy
• challenge systems
• “preventable fraction”
• factors to consider
–
–
–
–
number in study
criteria for persistent infection
method of challenge
number of controls with persistent infection
http://www.inspection.gc.ca/english/anima/vetbio/prod/felchae.shtml
A,B
A,B,C
A,B
A,B,C
A,B
A,B,C
A,B,C
Considerations for vaccination
• risk?
• test before vaccination
• vaccine site sarcomas
Treatment
• Antivirals (experimental)
• Immunostimulants (may not be effective)
Feline immunodeficiency virus
(lentivirus)
• 1 to 5% of domestic cats infected (older male cats
more likely)
• 5 sub-types with considerable antigenic variation
• May lead to AIDS like disease
• High rate of infection in some felids (lions,
cheetahs) with no obvious sickness
Pathogenesis
bite
(virus shed in saliva)
inapparent in
most cats
virus infects B-cells,
T-cells and macrophages
B-cell proliferation
(swollen lymph nodes)
variable
time
reversed CD4:CD8 ratios
immunodeficiency
(opportunistic infections, B-cell lymphomas)
Diagnostic test
• ELISA (antibody capture)
– antibodies (most infected cats have low levels of
circulating antigen)
– maternal antibodies - false +ves
FIV vaccine
Cat retroviruses and endangered felids
Iberian Lynx
http://www.lynxexsitu.es
PLoS One. 2009;4(3):e4744. Epub 2009 Mar 9.
Equine infectious anemia virus
swamp fever
(equine lentivirus)
• Per-acute (rare)
• Acute/chronic
• Inapparent - Asymptomatic carriers
CFIA - EIA page (fact sheet and stats)
Transmission
• Blood (>million viruses/ml)
– Tack, instruments
– Biting insects
•
Virus in all secretions
– venereal
– Milk, colostrum
– In utero
horse fly
deer fly
Venereal transmission
http://www.inspection.gc.ca/english/anima/heasan/disemala/equianem/equianemfse.shtml
Tashjian, 1984, JAVMA, 184:282
Transmission by injection of semen from EIA+ and during natural breeding
Transmission by injection of colostrum and natural feeding of foals
(Insect transmission can not be ruled out)
Transmission by insects
feeding is interrupted
fly feeds uninterrupted
virus is inactivated before next blood meal
fly bites horse nearby
(< 100m)
Pathogenesis (chronic infection)
anemia
virus multiplies in immune
leukocytes
complexes
thrombocytopenia
antigenic change
Fever and
viremia
infectious phases
Secondary effects of
thrombocytopenia
petechial haemorrhages
edema
Slides: Hugh Townsend
Asymptomatic carriers
infectious
phase
viremia
stress
or
steroids
Diagnostic Tests
• Agar gel immunodiffusion (AGID or Coggin’s
test)
• ELISA kit (replaced AGID, August 2008)
• Horse inoculation
• Immuno-blot
• cELISA
Coggin’s test
test samples
reference
positive
sera
antigen
False reactions on Coggin’s test
• False positive
– Foal with passive antibody (6 months)
• False negative
– Recently infected horse
Excerpts from CFIA Disease Control
Manual of Procedures, 1998 (section 7)
• Blood (no anticoagulants) collected by accredited
vet and tested by accredited laboratory
• If accredited vet suspects exposure must inform
District vet
• If sample positive, the animal, other in-contact
susceptible animals and epidemiologically linked
animals(30 days) re-bled and sent to The
Retrovirology Centre of Expertise, PEI
Follow up after lab conformation of
a Reactor
•
•
•
•
Owner notified
Premises declared infected, cold brand reactor (R)
Clinical examination of all reactors and exposed animals
Destruction order for animals showing clinical signs and
asymptomatic reactors not isolated
• Compensation (up to $2,750)
• In contacts or animals pastured in contiguous pastures
tested (30 days prior to testing)
• Owner’s responsibility and movement restrictions
Animal movement restrictions removed
when:
• Reactor removed
• Remaining animals negative on tests 40 days apart
– (first test after removal of reactor)
Conditions of isolation
•
•
•
•
•
•
•
•
Must be asymptomatic
Must not be used for breeding purposes
Premises inspected at least 4times/yr unannounced
Separated from other susceptible animals
Completely fly proof, vestibuled doors
Isolation notice posted on door
Exercise only in enclosed fly proof arena attached to stable
Exercise outside
– in enclosed area
– if daily high <0oC.
– No non-reactors within 200 yards
• All bandages, syringes etc. incinerated
Pregnant mares and their foals
• Remove foal from infected area (under license) not later
than 6 months
• Moved to place where there are no other susceptible
animals
• Tested after 40 days in isolation
• If positive(maternal antibodies) retested in 4 months
• If positive treat as a reactor.
CFIA - EIA control program
CFIA - EIA page (fact sheet and stats)