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Flashcards

Retroviridae

Rachael Jones Animal Disease 2 English 102 cards

Cards in this deck (102)

  1. 1What is the structure of retrovirus?+ve sense RNA virus (diploid genome), coding for gag, pol and env proteins
  2. 2HRNA converted to DNA by reverse transcriptase; DNA incorporated into host
    cell genome; new virus produced from DNA in genome
  3. 3What occurs is some retroviruses have oncogenes?Cellular oncogenes genes are involved in host cell growth; dysregulation can lead to tumours. Retroviruses can incorporate oncogenes and promote tumour development; they do this in a variety of different ways
  4. 4Give 2 examples of disease caused that have oncogenes in their genome.Jaagseikte
    FeLV
  5. 5How else can other retroviruses cause disease?Immunodeficiency or other chronic disease syndromes
    e.g. lentiviruses such as FIV
  6. 6Give 4 important retroviruses.o Jaagsiekte causes pulmonary adenomatosis in sheep
    o FeLV is an important cause of neoplasia and other chronic conditions in cats
    o FIV causes feline immunodeficiency syndrome
    o Maedi/visna and Equine Infectious Anaemia cause chronic inflammatory conditions in sheep/horses respectively
  7. 7In general what is the retroviridae family?Large family containing several genera each of which has members that cause diseases of veterinary importance. Most are chronic in nature and may involve the development of tumours and leukaemia.
  8. 8How can the structure of the retroviruses be described?Three ring structure:
    Outer membrane
    Area of stuff
    Blob in the middle
  9. 9What is found on the outer structure of the retrovirus?Lipid envelope, with transmembrane proteins, matrix proteins, receptor binding proteins
  10. 10What is found further into the centre of the virus structure?Enzymes (protease, integrase, reverse transcriptase)
    2 copies of +ve sense RNA
  11. 11What does diploid mean?Each particle has two complete genome copies
  12. 12What are the three regions that code for the virus genome?- gag (which stands for group specific antigen) encoding the capsid proteins,
    - pol encoding the virus polymerase and
    associated enzymes
    - env which encodes the envelope-associated receptor binding and transmembrane proteins.
    - Stretches of untranslated RNA sequences at either end of the genome
  13. 13What are the initial steps of virus replication?Virus peplomer membrane proteins bind to receptors on the host cell surface and the virus enters the cell either by fusion to the cell membrane or by fusion with the endosome membrane following endocytosis
  14. 14What can the initial steps of replication limit?Type of host cell infected and the host species range
  15. 15Give an example of how the virus binds and this limiting the host species.Feline immunodeficiency virus:
    - binds with high affinity to the CD134 molecule on activated CD4+ T-helper lymphocytes of cats
    - Change in the shape of receptor which becomes able to bind to a co-receptor molecule (the chemokine receptor CXCR4).
    - Enables a further change in the receptor molecule complex that causes fusion of the cell membrane and virus envelope releasing the capsid into
    the cytoplasm.
  16. 16What occurs once the virus is in the cytoplasm?- Virus remains within its capsid and synthesis of nucleic acid begins.
    - Uses an RNA dependant DNA polymerase enzyme (reverse
    transcriptase) to make a double stranded DNA copy of its RNA genome.
  17. 17What triggers the process of reverse transcriptase making DNA?Entry of Ca++ and Mg++, which diffuse into the virus once the envelope is removed: these metal cations are essential co-factors for the virus polymerase enzyme
  18. 18How many molecules of reverse transcriptase is it estimated that each virus carries?30
  19. 19What is the structure of reverse transcriptase and how does it work?- Hand holding onto a rope (double strand of nucleic acid) passing across the palm.
    - In the palm are two catalytic sites associated with divalent metal cations.
    - The enzyme binds to the double strand of nucleic acid and moves along the template strand of RNA from 3’ to 5’.
    - As it does so the complementary DNA is synthesised by adding bases to the 3’ end of the growing chain.
    - When the template strand of RNA passes by the second active site it is periodically cut by the RNAse H enzymatic function
  20. 20What is involved to help insert the viral DNA into the hosts?Viral enzyme integrase
  21. 21What strands of host DNA will retroviruses insert into?Any - said to be random
    Most readily become inserted into regions of the genome which are unwound and actively being transcribed, thus in any given cell there are parts of the genome into which integration is more likely to occur
  22. 22What are features of the early stages of reverse transcriptase?- All take place within the virus particle and do not require any protein synthesis.
    - This whole process of cell infection by retrovirus does not require viral protein synthesis, does not induce interferon and is refractory to treatment of the cells by interferon
  23. 23What is caused by reverse transcriptase having high error and no ability to proof read or correct mistakes?Within a single strain retrovirus progeny are highly variable
  24. 24What does the virus have to be able to do once inside the host cell genome?Able to recruit host cell RNA polymerase enzyme complexes in order to express
    its own messenger RNA and to produce new copies of its genome
  25. 25What are promotors?- DNA sequences
    - The production of RNA is tightly controlled within eukaryotic cells in part by sequences of DNA that are situated upstream from genes and form sites at which the RNA polymerase complex can bind and assemble
  26. 26What influences gene expression?Binding the polymerase complex, the rate at which the complex goes on to initiate RNA synthesis
  27. 27What are transcription factors and what do they do?- In eukaryotic cells, number of proteins that bind DNA
  28. 28What are the DNA sequences that bind to transcription factors called?Enhancers
  29. 29Where are promotors and enhancers found in retroviruses?Strong promoter and enhancer sequences which are present within the repeated sequences at either terminus of the virus.
  30. 30What can the virus promotors and enhancers act upon?Not limited to the virus genes but can act on host cell genes may kilo-bases downstream from the virus insertion site
  31. 31What is cis-activation?The powerful effect of these
    promoters and enhancers in not limited to the virus genes but can act on host cell
    genes may kilo-bases downstream from the virus insertion site. This type of gene
    activation influencing genes on the same chromosome is called cis-activation.
  32. 32How are new viruses formed?- Synthesis of mRNA takes place within the nucleus
    - Carried out by host cell enzymes which transcribe the DNA provirus into RNA
    message (make a 5’ cap and 3’ polyA tail)
    - Messages move to the cytoplasm and there make new virus proteins
    - Host cell enzymes are used to make full genomes
    - New virus at cell surface by budding
  33. 33What are oncogenes?Many retroviruses are associated with neoplastic disease, the pathogenesis of which is due to the effects that retrovirus promoters can have on genes that influence host cell division and replication
  34. 34How were oncogenes originally named?Names according to the type of tumour with which they were associated
    eg v-myc, v-mos, v-fos, v-src (>60)
  35. 35What is now known about oncogenes?Normal functions involved in the regulation of cell growth
  36. 36What is c-myc?Transcription factor that binds to DNA and enhances the expression of other genes
    involved in cell growth
  37. 37Will any oncogene cause cancer on its own?No but inappropriate high levels of expression driven by viral
    promoter/enhances elements often leads to increases in cell proliferation that can
    eventually lead to disease progression.
  38. 38Do host cell oncogenes have to be directly incorporated into the virus genome to be activated?Do not have to be incorporated directly into the virus genome; they can also be activated by the promoter sequences associated with nearby insertion
    of a retrovirus this is termed cis –activatio
  39. 39What are trans-activators?Some oncogenes are themselves
    transcription factors that can enhance the expression of cellular oncogenes on a
    different region of the host cell genome
  40. 40What are V-oncogenes?Encode a range of proteins that affect growth promoting cell signalling pathways (cell growth = virus growth)
  41. 41What are the issues with v-onc?Differ from host genes:
    They do not have introns
    are expressed out of their normal cellular context.
    under the control of strong viral promotors.
    have a high frequency of mutations.
    (generated during reverse transcription)
  42. 42What is a provirus?Once a retrovirus is incorporated into host cell DNA
  43. 43What are features of proviruses?- Genome is flanked by short host cell DNA repeats,
    - Contains all components needed to make new virus
    - Replication competent
    - Powerful promoter/enhancer sequences may lead to the cis-activation of host cell oncogenes.
    - Slow transforming as they only rarely give rise to tumours.
  44. 44What creates a Replication-defective rapidly transforming virus?Oncogenes can become incorporated into the virus genome due to mistakes in the recombination events that occur during virus replication
  45. 45What is the problem for replication-defective rapidly transforming viruses?They are unable to replicate itself as essential parts of the genome are missing or interrupted
  46. 46What does the oncogene being under the direct control of the virus promoter mean for replication-defective rapidly transforming viruses?Expressed at high level and transformation of cells may take place
  47. 47How can replication defective viruses make new copies of themselves?- If a non-defective provirus is in the
    same cell and able to make whichever viral proteins the first one lacks.
    - Diploid so a helper virus is usually present
    - New virus particles that contain one defective and one normal copy of the genome can also be made and lead to spread of this rapidly transforming virus to other cells where its expression
    of a v-onc can lead to tumour formation
  48. 48What is a Replication-competent rapidly transforming virus?Insertion of an oncogene does not disrupt the genome of the retrovirus
  49. 49Give an example of a Replication-competent rapidly transforming virus.Rous sacroma virus of chickens the v-src gene is inserted in such a way that it does not disrupt the virus genome and the virus is both able to replicate itself and expresses an oncogene so it is rapidly transforming.
  50. 50What are Trans-acting retroviruses?An oncogene gene which does not directly affect cell growth pathways, but acts as a transcription factor which can enhance the expression of other genes.
    - genes need not to be close (other chromosome = transactivation)
  51. 51What are general features of trans acting retroviruses?Slow at causing tumour development and the process may take several years
  52. 52Give an example of a transacting retrovirus.Bovine leukemia virus (not UK atm)
  53. 53What are endogenous retroviruses?- Proviruses which originally became incorporated into the germline DNA of either an egg or a spermatozoon.
    - Lost their own promoters but are otherwise intact.
    - Present in every cell of the infected
    individual
    - Found in most species
    - Transmitted via the germline from mother to offspring
  54. 54What are features of endogenous retroviruses?- Not transcriptionally active
    - Do not usually contain an oncogene
    - Not replication incompetent
    - Can become activated by host cell promoters under certain circumstances or by chance insertion of another retrovirus upstream of their DNA.
    - Under these circumstances they can also act as helper virus for replication defective viruses that contain an oncogene.
  55. 55What do all chickens contain?Endogenous Retro viruses
  56. 56Give an example and features of alpha retrovirus in birds.Avian leukosis virus:
    - exogenous viruses,
    - replication competent
    - (no v-onc, cis acting slow transforming)
    - they cause disease sporadically in birds >13 weeks
  57. 57What can Feline leukaemia virus (FeLv) lead to?Neoplasia such as lymphoma and is associated with a number of other conditions in cats
  58. 58What do carry cats of FeLV do?Shed the virus in nasal and salivary secretions and infection spreads by respiratory routes, grooming or through bites
  59. 59Where does FeLV have a higher prevalence?High- density of cat population
  60. 60How does FeLV infect cats?Virus infects mononuclear leukocytes and spreads to other lymphoid organs and the bone marrow; dividing cells like these contain the host cell DNA synthesis and repair enzymes that are important in viral replication
  61. 61Why are adult cats more resistant to infection of FeLV than kittens?Most adults will mount an immune response and clear the virus soon after
    infection
  62. 62When do kittens become most infected with FeLV?- 6-14 weeks - maternal antibodies are protective
    - 50% of these young cats become immunetolerant so develop a persistent infection and viraemi
  63. 63Where can virus be produced from when a kitten is infected and carries on being persistently infected?Glandular and mucosal epithelial cells leading to shedding of virus in saliva and other secretions, they act as the source of infection for other cats
  64. 64How do you diagnose FeLV?- Cats that develop disease are the immuno-tolerant, persistently
    infected cats that do not produce any antibodies.
    - Diagnosis depends on the detection of virus antigen (P27 virus antigen) in blood or serum of persistently infected cats.
    - Antigen-capture ELISA and rapid detection by immunodiffusion tests
  65. 65What vaccines are available for FeLV?- Cell culture derived gp70, FOCMA antigen
    (Leucocell 2/quantum cat FeLV)
    Vaccines
    - E. coli expressed Subunit vaccine (Leucogen)
    - Recombinant canary pox virus
    - Non core vaccine
  66. 66What is expressed by cells that are infected with FeLV?Feline Oncovirus Cell Membrane Antigen
    (env gene product of ERV FeLVC)
  67. 67What occurs in immune competent cats with FeLV?Self limiting infection associated with antibodies to viral antigens and FOCMA, remain non viraemic
  68. 68What occurs with immune tolerant cats with FeLV?Persistent infection with viraemia, no antibodies to virus antigens or FOCMA.
    Infectious to other cats and develop disease.
  69. 69What is FeLV and what diseases can it cause?- FeLVA is a slow transforming (cis-acting) virus
    - Wide range of diseases can be caused by this virus. Depending on cell type/ oncogene involved
    - Lymphosarcomas 30% of feline tumours; thymic, muticentric (T-cell), alimentary (B-cell)
    - Myeloproliferative:
    erythromyelosis (red cell precursor),
    granulocytic leukemia (neutrophil precursor),
    myelofibrosis(fibroblasts)
    lymphocytic leukaemia
  70. 70What is Jaagsiekte?Jaagseikte or ovine pulmonary adenomatosis is caused by an exogenous beta retrovirus
  71. 71What is found in both sheep and goats genome?Several (27) related endogenous retroviruses (JSRV)
  72. 72What does Jaagsiekte do?- Env protein of Jaagsiekte virus binds to hyaluronidase_2 found on many cells
    particularly type II alveolar cells and bronchial epithelium.
    - Infects and transforms type II alveolar cells and non-ciliated bronchial epithelium, giving rise to multiple tumours which replace the normal lung tissue
    - Can metastasise to the local lymph nodes.
    - In these cases the virus does not itself contain an incorporated voncogene
    and the pathogenesis of the tumours has not been explained fully
  73. 73What is the issue with PCRing sheep?Carry closely related endogenous retroviruses, PCR tests to detect virus DNA that codes for proteins would all be positive in tissue samples
  74. 74How do you diagnose Jaagsiekte?- Amplifies virus DNA within the promotor regions (long terminal repeats) of incorporated exogenous Jaagsiekte retrovirus is used to distinguish infection with wild type replication-competent retrovirus from endogenous retrovirus
    - Peripheral blood monocytes
  75. 75What happens to sheep that become infected with Jaagsiekte?Not all sheep that become infected with the virus will develop overt disease in their lifetime; the disease incidence in infected flocks is usually below 5%. A much higher number of sheep (about 60%) will have detectable virus in their lymphocytes
  76. 76What is immune tolerance of Jaagsiekte caused by?Expression of protein by a closely related endogenous retrovirus in the developing
    foetus leading to immuno-tolerance to the virus. This endogenous retrovirus protein has to be expressed in the developing placenta to enable implantation and pregnancy to progress so we now appear to have a situation where an endogenous virus has
    evolved to become an essential part of the sheep genome
  77. 77How is Jaagsiekte transmitted?Spread by the respiratory route, disease incidence can be as high as 20%
    following introduction of virus.
    - But more commonly 1-5% of sheep in endemic flocks become affected
  78. 78What are the clinical signs of Jaagsiekte?Breathlessness, lung sounds, large amount of pulmonary fluid only seen in some cases
  79. 79What is the JSRV genome?- JSRV env protein has transforming
    properties when transfected into a wide range of cells through binding to Phosphatidylinositol 3-kinases.
    (a cell signalling pathway).
    - enJSRV env protein does not bind PI3_Kinase and lacks transforming properties.
    But enJSRV Env is expressed in the placenta and foetus where it has an important function in the development of the multinucleated trophoblast cells essential for implantation.
  80. 80What happens with infection of JSRV?- Initial infection of a cells by JSRV is much more efficient in dividing cells.
    - Type 2 pneumocytes are actively dividing in lambs in which JSRV is more likely to establish lung infection leading to the development of lung lesions.
    - In Older sheep intercurrent disease with lung damage leads to pneumocyte division as part of the healing process
    which increases the risk of tumour development
    - Co-expression of mutant GAG proteins from some endogenous retroviruses disrupts assembly and exit of mature wild type virus; hence act to limit JSRV spread within the lung and prevent development of tumours.
  81. 81How do you diagnose JSRV?- PCR test for pro-viral DNA
    - Amplification of LTR region
    (avoids endogenous retrovirus false positive results)
    - PCR able to detect 1 copy of viral DNA,
    but this requires an infected lymphocyte to be in the initial sample:- so false –ve results do occur
  82. 82Give examples of lentiviruses.FIV,
    Maedi/Visna,
    Equine Infectious Anaemia
  83. 83What are general features of Lentiviruses?- Slow and reflects the rate of onset of the disease which these viruses cause.
    - This common feature is in part due to the ability of these viruses to remain hidden from the immune system as provirus integrated into the genome of
    host cells (usually cells of the immune system itself).
    - Their rapid rates of mutation enable them to avoid immune responses by mutating epitopes to which the immune
    response is directed; this also contributes to their ability to persist.
  84. 84What is FIV?Feline Immunodeficiency Virus
  85. 85What is FIV?- A widespread and common virus of cats
    which was first identified in 1987.
    - 3-6% of healthy cats positive for antibodies 30% of sick cats
    - Related to HIV and similar in pathogenesis
  86. 86How is FIV spread and what happens when infected?- Lifelong infection: virus is present in blood and saliva
    - Cats become infected usually by fighting, biting and grooming but can be trans-placental or at parturition (viraemic mother)
  87. 87How does FIV infect cells?Env binds to receptors CD134 and CXCR4
    Virus infects activated feline CD4+ T-cells
  88. 88What is phase 1 of FIV?- Infects CD4+ T-cells
    - Virus replicates in these cells and once
    released will spread to other cells
    - Rapidly disseminated to all lymphoid
    organs - enlarged lymph nodes, pyrexia and neutropenia
    - Peak about 8 weeks after infection - antibodies
    - Cytotoxic CD8 T-cells which kill virus infected cells
    - Provirus can remain undetected within the genome of CD4+ T-cells so the virus
    cannot be completely eliminated
  89. 89What is phase 2 of FIV?- Begins with an apparent clinical recovery
    - May last for several years
    - Continued infection of CD4+ cells with a gradual loss of their numbers
    - Cells can be killed by cytotoxic T-cells or may undergo apoptosis
    - Mutations of the virus allow it to escape from CD8+ T-cell control
    - Loss of CD4 T-cells further weakens the immune system
  90. 90What is the problem with the central role of CD4+ T-helper cells being reduced?Drop in CD4+ T-cell numbers, leads to impaired immune functions.
    reduced IL2 production
    reduced antibody production,
    reduced blastogenesis
    reduced Cell Mediated Immunity
  91. 91What is phase 3 in FIV?- Onset of symptoms due to immunosupression associated with opportunistic infections
    - High frequency of fevers, gingivitis and mouth ulcers
    - Also an increased risk of tumour development, particularly B-cell lymphomas in cases where there is concurrent FeLV infection. Nevertheless in spite of all these risks not all infected cats go on to develop disease.
  92. 92How is FIV diagnosed?- Depends of the detection of antibodies to virus
    - Give false –ve results in some cases where antibody levels are low. Detection of proviral DNA in blood samples using PCR is also possible but complicated by the inherent variation in virus sequences.
  93. 93How is FIV treated?- Azidothymidine which inhibits reverse transcriptase is partially effective.
    - Several experimental vaccines but none effective virus persists in the presence of antibody and cytotoxic response.
  94. 94What is Maedi?- Sheep
    - Infection of Monocytes and monocyte precursors, new virus is produced when monocytes become activated
    - Spread by the respiratory route
    - Lifelong infection with late onset of disease symptoms, chronic inflammation/fibrosis induced by infected monocytes
  95. 95What are the symptoms of Maedi?Symptoms of breathlessness, consolidation of lungs and enlarged bronchial lymph nodes, fibrosis and hyperpalsia of alveolar septae with monocyte infiltration
  96. 96What is Visna?A chronic demyelinating encephalitis with monocyte infiltration caused by a distinct subtype of virus. (Rare)
    SHEEP
  97. 97What is the issue with Maedi and Visna?- Virus persists in the presence of
    antibody and cellular immune response
    possibly due to constant mutation
    and generation of escape variants.
    - Transmission from mother to lambs in colostrum milk.
    - Transmission of virus by aerosol from symptomatic sheep or from blood by biting insects.
  98. 98How can Maedi and Visna be controlled by eradication?Removal of symptomatic sheep
    Removal of seropositive sheep
    Removal of PCR +ve sheep
  99. 99What is Caprine arthritis encephalitis?Similar virus to maedi/visna but lesions occur as a proliferative synovitis
    with lymphocyte plasma cell and monocyte infiltration.
    Spread in colostrum and milk.
    (kids develop neurological symptoms)
    Joints and arthritis!!!!
  100. 100What is Equine infectious anaemia?Retrovirus infects horses, donkeys and mules in many countries. Like all lentiviruses it causes a lifelong infection
  101. 101What does Equine infectious anaemia infect?Macrophages, monocytes and kuppfer cells, causing a cell associated viraemia.
    - This viraemia enables the virus to be spread by biting flies such as horse flies and stable flies. The spread is mechanical due to blood being transferred on the insect mouthparts
  102. 102What are features of equine infectious anaemia?Frequently asymptomatic (avirulent strains)
    Virulent strains (acute viraemia, throbocytopaenia and anaemia)
    Cyclical pathology (immune escape mutations)
    Partial recovery with time
    Notifiable in UK
    Antibodies in blood (Coggins test)
    Chinese attenuated vaccine

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Animal Disease 2 (Specific Viruses - DW) Flashcards on Retroviridae, created by Rachael Jones on 16/11/2017.
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