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ARBOROVIRUSES

ARBOROVIRUSES

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ARBOROVIRUSES

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  1. ARBOROVIRUSES Mohammed El-Khateeb 2ndApril 2015

  2. Overview • Etiology • Epidemiology and history • Pathogenesis and Pathology • Clinical Manifestation • Diagnosis • Treatment • Prevention and Control

  3. Arthropod-Borne Viruses Arthropod-borne viruses (arboviruses) are More Than 600 Differentviruses that can be transmitted to man by arthropod vectors. The WHO definition is as follows: “Viruses maintained in nature principally, or to an important extent, through biological  transmission between susceptible vertebrate hosts by hematophagus arthropods or through transovarial and possibly venereal transmission in arthropods.”

  4. Arthropod-Borne Viruses Arboviruses belong to three families 1. Togaviruses e.g. EEE, WEE, and VEE 2. Bunyaviruses e.g. Sand fly Fever, Rift Valley Fever, Crimean- Congo Hemorrhagic Fever 3. Flaviviruses e.g. Yellow Fever, dengue, Japanese Encephalitis

  5. Arthropod-Borne Viruses • Togaviridae a) Sindbis b) Semliki Forest c) Venezuelan equine encephalitis d) Eastern equine encephalitis e) Western equine encephalitis f) Chikungunya • Flaviviridae a) Dengue b) Yellow fever c) Japanese encephalitis d) West Nile encephalitis e) St. Louis encephalitis f) Russian spring-summer encephalitis g) Powassan encephalitis

  6. Negatively Stained Virions of Semliki Forest Virus Togaviridae, genus Alphavirus

  7. Arthropod-Borne Viruses FAMILY ENVELOPE Yes. Heat, detergent labile Yes, Heat, detergent labile no SYMMETRY Icosahedral 40-75 nm 40-45 nm Helical Icosahedral GENOME ssRNA (+ve) ssRNA (-ve) segmented dsRNA, segmented

  8. VIRAL STRUCTURE It has three proteins • Envelope protein • Core protein • Membrane protein

  9. General Antigenic Properties of Flaviviral Proteins - 1 • E-glycoprotein • Most important flaviviral antigen • Very immunogenic • Most serological assays detect reactivity with this protein • Capsid • Elicits primarily group-reactive antibody • M-protein • Very small (75 a.a.) • Embedded in the virion envelope membrane and not highly immunogenic

  10. Replication

  11. Arthropod Vectors Mosquitoes Japanese encephalitis, dengue, yellow fever, St. Louis encephalitis, EEE, WEE, VEE etc. Ticks Crimean-Congo haemorrhagic fever, various tick-borne encephalitides etc. Sandflies Sicilian sandfly fever, Rift valley fever.

  12. Examples of Arthropod Vectors Aedes Aegyti Assorted Ticks Culex Mosquito Phlebotmine Sandfly

  13. Animal Reservoirs In many cases, the actual reservoir is not known. The following animals are implicated as reservoirs Birds Japanese encephalitis, St Louis encephalitis, EEE, WEE Pigs Japanese encephalitis Monkeys Yellow Fever Rodents VEE, Russian Spring-Summer encephalitis

  14. Transmission • The most common route of infection is bite of infectious mosquito • Other transmission modes where revealed in 2002 such as • Blood Transfusion • Organ Transplantation • Intrauterine • Percutaneous exposure (occ. exposure) • Breastmilk (probable)

  15. Transmission Cycles • Man - arthropod -man • e.g. dengue, urban yellow fever. • Reservoir may be in either man or arthropod vector. • In the latter transovarial transmission may take place. • Animal - arthropod vector - man • e.g. Japanese encephalitis, EEE, WEE, jungle yellow fever. • The reservoir is in an animal. • The virus is maintained in nature in a transmission cycle involving the arthropod vector and animal. Man becomes infected incidentally. • Both cycles may be seen with some arboviruses such as yellow fever.

  16. Man-Arthropod-Man Cycle Man - arthropod -man e.g. dengue, urban yellow fever. Reservoir may be in either man or arthropod vector. In the latter transovarial transmission may take place.

  17. Animal-Arthropod-Man Cycle Animal - arthropod vector - man e.g. Japanese encephalitis, EEE, WEE, jungle yellow fever. The reservoir is in an animal. The virus is maintained in nature in a transmission cycle involving the arthropod vector and animal. Man becomes infected incidentally.

  18. Epidemiologic Feature • The major outbreaks coincided with the heavy rainfall or floods. • Seasonal: more common in summer, July to October • Infection provides life long immunity. • Worldwide distribution • More than 530 species, 150 pathogen to man

  19. Pathogenesis The nature of flavivirus disease is determined primarily by • The specific tropisms of the individual virus type • The concentration of infecting virus • Individual host response to the infection

  20. Disease Syndromes of the Alphaviruses and Flaviviruses

  21. Pathogenesis Virus Mononuclear Phagocyte Blood Circulation Viremia Adequate Weak Immunological Immunological Response Response Subclinical or mild Invades the CNS Systemic disease induce mortality

  22. Four stages • A Prodromal Stage • An Acute encephalitic Stage • The Convalescence Stage • A Sequela Stage

  23. Diseases Caused • Fever and rash - this is usually a non-specific illness resembling a number of other viral illnesses such as influenza, rubella, and enterovirus infections. The patients may go on to develop encephalitis or haemorrhagic fever. • Encephalitis - e.g. EEE, WEE, St Louis encephalitis, Japanese encephalitis. • Haemorrhagic fever - e.g. yellow fever, dengue, Crimean-Congo haemorrhagic fever.

  24. Pathogenesis and immunity • Besides viral receptor, virus may attach to Fc receptor (macrophages and monocytes) via Ab to result in an increase of virus infection. • Antibody is produced to block infection. However, non-neutralizing Ab may have antibody dependent enhancement (ADE) effect to enhance virus replication by hundred folds.

  25. Arthropod-Borne Viruses a) Dengue b) Yellow fever c) Chikungunya

  26. Fever/Rash/Arthritis 1. Triad of fever/rash/arthritis is characteristic of Chikungunya, o’nyong-nyong, Ross River, Mayaro, and Sindbis viruses 2. Symptoms generally appear after 2-3 days incubation a) fever, chills, myalgia b) polyarthralgia mainly affecting small joints c) maculopapular rash 3. Arthritis generally resolves in a few weeks, but may persist for months, or years in some cases.

  27. Arthropod-Borne Viruses Encephalitis • West Nile encephalitis • Japanese encephalitis • St. Louis encephalitis • Russian spring-summer encephalitis • Powassan encephalitis • Venezuelan equine encephalitis • Eastern equine encephalitis • Western equine encephalitis

  28. Humanscan be infectedvia mosquito bites. Transmission of six encephalitis arboviruses Small mammalsare hosts for VEE andCalifornia viruses only. Encephalitis arbovirusescan overwinter insidemosquito eggs. Mosquitoesare vectors. Wild birds Horses,and rarely other domestic mammalsare hosts for equine viruses. Domestic fowls Birds are hosts forall six encephalitisarboviruses.

  29. West Nile Virus • Flavivirus • Primary host – wild birds • Principal arthropod vector – mosquitoes • Geographic distribution: • Africa, • Middle East, • Western Asia, • Europe, • Australia, • North America, • Central America

  30. Encephalitis • Small proportion of individuals infected (a few days after the onset of fever) may develop drowsiness, neck rigidity, progressing to confusion, paralysis, convulsions and coma. • Case-fatality rates average 10 – 20 % (higher in elderly). 3. Survivors may be left with permanent neurologic sequelae such as mental retardation, epilepsy, paralysis, deafness, and blindness.

  31. Diagnosis • Materials of epidemiology • Clinical • Laboratory Tests • Tentative diagnosis • Antibody titer: HI, IF, CF, ELISA • JE-specific IgM in serum or CSF • Definitive diagnosis • Virus isolation: Blood, CSF sample, brain

  32. Diagnosis • Serology - usually used to make a diagnosis of arbovirus infections.Antibody titer: HI, IF, CF, ELISA • Culture - a number of cell lines may be used, including mosquito cell lines. However, it is rarely carried out since many of the pathogens are group 3 or 4 pathogens. (Blood, CSF sample, brain) • Direct detection tests - e.g detection of antigen and nucleic acids are available but again there are safety issues.

  33. Prevention • Surveillance- of disease and vector populations • Control of vector - pesticides, elimination of breeding grounds • Personal protection - screening of houses, bed nets, insect repellants • Vaccination - available for a number of arboviral infections e.g. Yellow fever, Japanese encephalitis, Russian tick-borne encephalitis

  34. Treatment/Vaccines/Control measures • A. Encephalitis • 1. Vaccines exist for a number of these viruses, but are used mainly for horses, at risk lab workers, and some fowl known to be intermediate hosts • 2. Control of mosquitoes is major countermeasure. • B. Yellow Fever • 1. Live attenuated virus vaccine. Used when going to endemic areas

  35. Epidemiological Triangle The Host Interaction The Virus The Vector

  36. Prevention • Vector (Mosquito) control • Eliminate mosquito breeding areas: Chemical larvicides, Biolarvicides, Environmental management • Adult and larval control: Anti-larval treatment • Vaccination • Personal protective measures • Avoid prime mosquito hours: from dusk to dawn • Indoor spray and fogging: Use of Insecticide

  37. Repellent Guidance • Skin • DEET still “gold standard” • Both new additions good for shorter term protection • Picaridin • Roughly equivalent to DEET at same concentration • Only a 7% product currently sold in US • Oil of lemon eucalyptus • Plant based • 30% product similar to low concentration DEET • Not for kids <3 years old • Clothing • Permethrin

  38. Arboviruses • Structure • Positive sense ssRNA genome, icosahedralnucleocapsid, enveloped • Pathogenesis • Transmitted by bite of insect from host species; sylvan and urban cycles • Replication in cytoplasm; budding • Viremia to target tissue • Influenza-like initial symptoms; different viruses cause encephalitis, hemorrhagic fever, hepatitis, rash, arthritis • Diagnosis • Serology and nucleic acid • Treatment/prevention • No human vaccines except for Yellow Fever live attenuated vaccine, control of insect population

  39. Disease Vector Host Distribution Disease Alphaviruses Sindbis* Aedes and other mosquitoes Birds Africa, Australia, India Subclinical Semliki Forest* Aedes and other mosquitoes Birds East and West Africa Subclinical Venezuelan equine encephalitis Aedes, Culex Rodents, horses North, South, and Central America Mild systemic; severe encephalitis Eastern equine encephalitis Aedes, Culiseta Birds North and South America, Caribbean Mild systemic; encephalitis Western equine encephalitis Culex, Culiseta Birds North and South America Mild systemic; encephalitis Chikungunya Aedes Humans, monkeys Africa, Asia Fever, arthralgia, arthritis Flaviviruses Dengue* Aedes Humans, monkeys Worldwide, especially tropics Mild systemic; break-bone fever, dengue hemorrhagic fever, and dengue shock syndrome Yellow fever* Aedes Humans, monkeys Africa, South America Hepatitis, hemorrhagic fever Japanese encephalitis Culex Pigs, birds Asia Encephalitis West Nile encephalitis Culex Birds Africa, Europe, central Asia, North America Fever, encephalitis, hepatitis T2 St. Louis encephalitis Culex Birds North America Encephalitis Russian spring-summer encephalitis lxodes and Dermacentor ticks Birds Russia Encephalitis Powassan encephalitis lxodes ticks Small mammals North America Encephalitis The nomenclature of arboviruses are mostly based on endemic areas and symptoms induced by viruses, including fever, encephalitis and hemorrhagic fever

  40. RETROVIRUSES

  41. RetroViruses • RNA Viruses • DNA From RNA by Reverse Transcriptase • Insertion of new DNA into cellular DNA • Hijacks the cell machinery to make VIRUS • The virus only grows on T4 cells that are proliferating • in response to an immune stimulus • Difficult to grow in culture • Robert Gallo : HTLV-3 • Luc Montagnier: LAV • Human Immunodeficiency Virus (HIV)

  42. Introduction to Retroviruses I. Overview of retroviruses A. History B. Shared characteristics C. Classification II. Function of different regions of the retroviral genome A. Cis acting elements B. Gag proteins C. Pol proteins D. Env proteins III. Details of life cycle: A. Early stage B. Late stage

  43. General Introduction to Retroviruses Retroviruses • Ubiquitous; found in all vertebrates • Large, diverse family • Includes HIV, FIV and FeLV Definition and classification of retroviruses • Common features- structure, composition and replication • Distinctive life cycle: RNA-DNA-RNA • Nucleic acid is RNA in virus, and DNA in infected cell Transmission may be either: • Horizontal - by infectious virus (exogenous virus) or vertical- by proviruses integrated in germ cells (endogenous virus) • Can transmit either as free viral particle or (for some retroviruses) through cell-cell contact

  44. A Little Retrovirus History 1960s:Howard Temin: suggested DNA “provirus” was part ofreplication cycle: RNADNA RNA Protein Won Nobel prize (with Baltimore) in 1970 after they independently discovered RT activity in infected cells 1980: Human T-cell leukemia virus discovered, the first pathogenic human retrovirus. 1982: Human immunodeficiency virus discovered. 1990: First gene therapy trial involving the use of retroviral-based vectors in patient with a deficiency in adenosine deaminase (ADA). 2006: Xenotropicmurine leukemia-related virus discovered.

  45. Retroviruses • Strange Viruses ? At time-“central dogma of molecular biology”:DNARNAProtein So.. RNA couldn’t be template for DNA • Unique replication cycle based on reverse transcription. Flow of information from RNA to DNA. (1971 Nobel Prize Temin / Baltimore) • Retroviruses have been isolated from numerous species including chickens (RSV), mice (MLV), monkeys (SIV), and humans (HIV, HTLV) • “Simple Retroviruses” encode only the genes gag, pol, and env (RSV) • “Complex Retroviruses” encode in addition regulatory genes (HIV) • Retroviruses are single-stranded RNA viruses that replicate through a double-stranded DNA intermediate.

  46. They are association with the development of tumors in their host organisms. • Study of these viruses eventually led to the discovery and development of the oncogene theory of tumorgenesis • Some of the viruses actually contained oncogenes within their genomes, while others interacted with oncogenes in either a direct or indirect way to contribute to tumor formation.

  47. Historically, because of their pattern of pathogenicity, these viruses were grouped into three subfamilies: • The acutely oncogenic retroviruses, or oncoretroviruses (such as those described above) • The lentiviruses (associated with “slow” diseases or those with long latent periods) • The spumaviruses (“foamy” viruses, named because of the pathogenic changes observed in infected cells).

  48. THE OLD NOMENCLATURE Members: • Oncogenic viruses (Oncoviruses) (endogenous) • Avian oncoviruses: RSV, AMV, AEV, RAVs [ RAV- 0; RAV-1 ]. • Murineoncoviruses: e.g.,MoMLV, A-MuLV. • Mammalian oncoviruses: e.g., FeLV, HaMSV, SSV . • Mouse Mammary Tumor Virus (MMTV); [ the only B- type particle ]. • Mason-Pfizer Monkey Virus (MPMV); [ one of the few D-type particles ]. • Human T-Cell Lymphotropic Virus ( HTLV-1 & 2 ). • Lentiviruses- HIV-1, HIV-2, SIV, FIV, EIAV, CAEV. • Spumaviruses– HFVs, SFV. 2 and 3 non endogenous

  49. Retrovirus Classification Example Genus Genome Avian leukemia virus Alpharetrovirus Simple Betaretrovirus Mouse mammary tumor virus Simple Murine leukemia virus Feline leukemia virus Xenotropic murine leukemia-related virus Gammaretrovirus Simple Human T-cell leukemia virus Deltaretrovirus Complex Wall-eyed sarcoma virus Epsilonretrovirus Complex HIV, SIV, FIV Lentivirus Complex Human foamy virus Spumavirus Complex Yeast TY-3 Metavirus Drosophila melanogaster Gypsy Errantvirus