Arenaviruses

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Arenaviruses

  1. 1. Arenaviruses Dr Preneshni R Naicker
  2. 2. Arenaviruses - outline <ul><li>Introduction </li></ul><ul><li>Virology </li></ul><ul><li>Classification </li></ul><ul><li>Reservoirs </li></ul><ul><li>Transmission </li></ul><ul><li>Viruses and Distribution </li></ul><ul><li>Phylogeny </li></ul><ul><li>Clinical Presentation (Lassa Fever/LCM/S. American VHF) </li></ul><ul><li>Laboratory Diagnosis </li></ul><ul><li>Treatment </li></ul><ul><li>Prevention & Control </li></ul><ul><li>Emergence & Evolution </li></ul><ul><li>New viruses </li></ul>
  3. 3. Introduction <ul><li>Family = Arenaviridae </li></ul><ul><li>Genus = Arenavirus </li></ul><ul><li>Currently 22 recognized species </li></ul><ul><li>2 groups </li></ul><ul><li>- Old World </li></ul><ul><li>- New World </li></ul><ul><li>Rodent – borne pathogens </li></ul><ul><li>Important cause of VHF </li></ul><ul><li>Host cell ribosomes are present in the </li></ul><ul><li>viral particles are responsible for a </li></ul><ul><li>“ sandy” appearance on EM </li></ul><ul><li>Hence the name Arenavirus (Latin: arena=sand) </li></ul>
  4. 4. Virology <ul><li>ssRNA virus “ambisense” </li></ul><ul><li>Genome consists of 2 RNA segments (L) = Large </li></ul><ul><li>(S) = Small </li></ul><ul><li>(L) encodes RNA-polymerase & Zn-binding protein </li></ul><ul><li>(S) encodes NP and GPC </li></ul><ul><li>Virions are spherical to pleomorphic </li></ul><ul><li>Enveloped </li></ul><ul><li>Average diameter = 120nm </li></ul><ul><li>Envelope covered with 8-10nm long projections </li></ul>L
  5. 5. <ul><li>GP1 & GP2 have been shown to bind to α -dystroglycan (cell surface glycoprotein in rodent fibroblasts) </li></ul><ul><li>Inactivated by </li></ul><ul><li>Temp > 56° </li></ul><ul><li>pH < 5.5 </li></ul><ul><li>pH > 8.5 </li></ul><ul><li>UV or gamma radiation </li></ul>
  6. 6. 2 groups Old World Lassa-LCM Serocomplex 5 Species Family: Muridae Subfamily: Murinae Eurasian rodents New World Tacaribe Serocomplex 17 species 3 clades (A,B,C) Family: Muridae Subfamily: Sigmodontinae American rodents * Classification
  7. 7. Rodent - mastomys sp <ul><li>*Fruit-eating bat – Artibeus sp </li></ul>Reservoirs <ul><li>Usually one species, less often 2 closely related species </li></ul><ul><li>Chronic mild infection </li></ul><ul><li>Life long shedding of virus </li></ul><ul><li>Except Tacaribe virus * </li></ul>
  8. 8. Co-evolution <ul><li>Specific rodents are the principal hosts of arenaviruses (Childs & Peters 1993) *except Tacaribe virus – bats of Artibeus sp </li></ul><ul><li>The diversity of arenaviruses due to long-term, shared evolutionary relationship between Arenaviridae and rodents of the Muridae family (termed co-evolution or co-speciation) </li></ul><ul><li>Hypothesis: Ancestral arenavirus type infection of a common rodent ancestor approx 35 million yrs ago </li></ul><ul><li>Each rodent lineage then evolved independently with their own arenavirus resulting in the species-specific association we see today. </li></ul><ul><li>Discrepancies? Spillover from one species or genus to another ?genomic segments exchanged </li></ul>
  9. 9. Transmission <ul><li>Rodent – Rodent </li></ul><ul><li>Vertical </li></ul><ul><li>Horizontal (aerosolized urine, faeces, saliva, bites) </li></ul><ul><li>Rodent – Human </li></ul><ul><li>Aerosolized secreta </li></ul><ul><li>inoculation via cuts, bites </li></ul><ul><li>contaminated fomites, food </li></ul><ul><li>Rodent consumption </li></ul><ul><li>Human – Human </li></ul><ul><li>- contaminated secretions, sexual </li></ul><ul><li>Inoculation </li></ul>
  10. 10. Old and New World Arenaviruses Argentina West Indies Bolivia Brazil Paraguay USA Columbia Bolivia Brazil Venezuela Venezuela Brazil Calomys muscul. Artibeus sp (BAT) Calomys callosu. Oryzomys capito Oryzomys buccin. Sigmodon hispi. Oryzomys albig. Calomys callos. Oryzomys capit. Sigmodon alst. Zygodon brevi. unknown Argentinian VHF LI (laboratory infxn) Bolivian VHF, LI NE NE NE LI NE LI NE Venezuelan VHF, LI Brazilian VHF, LI 1958 1963 1965 1966 1970 1970 1971 1973 1977 1977 1989 1994 NEW WORLD Junin Tacaribe Machupo Ampari Parana Tamiami Picjinde Latino Flexal Pirital Guanarito Sabia Worldwide West Africa C. African Rep S Central Afric C. African Rep Mus musculus Mastomys sp Arvicanthus nilot. Mastomys natale. Praomys sp Meningitis Lassa Fever NE (no evidence) NE NE 1934 1975 1970 1977 1983 OLD WORLD LCMV Lassa Ippy Mopeia Mobala Distribution Rodent Host Human disease Year first isolated
  11. 11. cont. Argentina Argentina USA, Cali USA Peru Brazil Bolomys obs peromysc californ Neotoma alb. Oecomys bicolor Oryzomys capito NE NE NE ? NE NE 1996 1997 1996 1996 2001 2002 Oliveros Pampas(strain) Bear Canyon Whitewater Arroyo Allpahuayo Cupixi Distribution Rodent host Human disease Year first isolated
  12. 12. Copyright © 2006, 1999 by Elsevier Inc. All rights reserved. FIGURE 66-1 Recognized arenaviruses and their geographic distribution. Reservoirs are shown below the viruses in italics .
  13. 13. Phylogeny
  14. 14. Lassa Fever <ul><li>Clinical entity in 1950s </li></ul><ul><li>Up to 300,000 infections and 5000 </li></ul><ul><li>deaths from LF are estimated to </li></ul><ul><li>occur yearly </li></ul><ul><li>Incubation period </li></ul><ul><li>7-18 days </li></ul><ul><li>Estimates of virus exposure </li></ul><ul><li>4% to 6% in Guinea </li></ul><ul><li>15% to 20% in Nigeria </li></ul>
  15. 15. Distribution of Lassa Fever Outbreaks have occurred in the Central African Republic, Guinea, Liberia, Nigeria, and Sierra Leone; serological evidence of human infection has been found in the Democratic Republic of the Congo, Mali, and Senegal
  16. 16. Clinical presentation
  17. 17. Cont.
  18. 18. <ul><li>Poor Prognostic Indicators </li></ul><ul><li>Shock </li></ul><ul><li>Haemorrhage </li></ul><ul><li>Neurological manifestations </li></ul><ul><li>High viraemia </li></ul><ul><li>AST >150 iu/l </li></ul><ul><li>Death occurs 10-14 days after onset of symptoms </li></ul><ul><li>Mortality Rate = 15-25% in hospitalized pts </li></ul><ul><li>Chronic sequelae: ⅓ sensorineural deafness </li></ul><ul><li>Single natural infection provides long-term immunity </li></ul><ul><li>Pregnancy: in 3rdT 20% MR and 87% fetal loss </li></ul><ul><li>Paediatrics: “swollen baby syndrome” </li></ul>
  19. 19. Imported Lassa Fever
  20. 20. Lymphocytic Choriomeningitis <ul><li>Incubation period = 1-2 weeks </li></ul><ul><li>Clinical presentation </li></ul><ul><li>Acute febrile illness </li></ul><ul><li>Headache </li></ul><ul><li>Aseptic meningitis </li></ul><ul><li>Encephalitis (rare) </li></ul><ul><li>Orchitis, myocarditis, arthritis </li></ul><ul><li>Occasionally LAD, maculopapular rash </li></ul><ul><li>Congenital infection: hydrocephalus, chorioretinitis and mental retardation </li></ul><ul><li>Mortality <1% </li></ul>
  21. 21. South American Viral Haemorrhagic Fever <ul><li>Incubation period = 1-2 weeks </li></ul><ul><li>Clinical presentation </li></ul><ul><li>“ flu-like” prodrome </li></ul><ul><li>Fever, headache, nausea, vomiting </li></ul><ul><li>Thrombocytopenia, leukopenia </li></ul><ul><li>Haemorrage: petechiae, bleeding from mucosa, puncture sites </li></ul><ul><li>Neurological: tremors, delirium, convulsions, coma </li></ul><ul><li>Mortality rate = 15-30% </li></ul>
  22. 22. Laboratory Diagnosis ELISA Serum Serology (IgG/IgM) Blood, tissue RT-PCR Liver, spleen, skin, kidney Tissue Immunohistochemistry ELISA/IMF Blood Antigen detection Blood, urine, tissue EM Cell Culture: Vero, Vero B6, BHK Animal: suckling mice, hamsters, guinea pigs Blood, CSF, Tissue Culture Comments Specimen Test
  23. 23. Vero E6 tissue culture cell infected with an arenavirus. Image shows extracellular virus particles budding from the cell surface. Magnification approx. 12,000 times.
  24. 24. Treatment <ul><li>Supportive </li></ul><ul><li>Immunotherapy </li></ul><ul><li>Decreases mortality rate from 16%-1% in Junin VHF </li></ul><ul><li>NB: 10% develop a neurological syndrome 4-6 wks later </li></ul><ul><li>Unsuccessful in Lassa Fever </li></ul><ul><li>Ribavirin </li></ul><ul><li>Must be administered IV and early (within 6 days) </li></ul><ul><li>Decreases mortality from 55% - 5% in Lassa Fever </li></ul><ul><li>30mg/kg LD </li></ul><ul><li>Then 15mg/kg 6hrly for 4 days </li></ul><ul><li>Then 7.5mg/kg 8hrly for 6 days </li></ul><ul><li>Should be considered in any serious arenavirus infection </li></ul>
  25. 25. Prevention & Control <ul><li>Interrupt transmission </li></ul><ul><li>Rodent to human eg. Rodent control in BHF </li></ul><ul><li>- Human to human </li></ul><ul><li>Specimens to Laboratory workers </li></ul><ul><li>Prophylaxis </li></ul><ul><li>Close contacts or possible bioterrorist exposures – should not be given ribavirin, but closely monitored for fever. If fever confirmed, then ribavirin therapy should be begun expectantly </li></ul>
  26. 26. <ul><li>Vaccines </li></ul><ul><li>Junin virus vaccine </li></ul><ul><li>Candid #1 = live attenuated vaccine. </li></ul><ul><li>RCT efficacy >95%. </li></ul><ul><li>Animal studies suggest protection </li></ul><ul><li>against Machupo but not Guanarito or Sabia. </li></ul><ul><li>Live attenuated Mopeia virus – protects monkeys against LASV challenge </li></ul><ul><li>LASV/Vaccinia virus vectors </li></ul><ul><li>Reassortment of Lassa/Mopeia </li></ul>
  27. 28. Emergence of Arenaviruses
  28. 29. Mechanisms of Virus evolution <ul><li>Accumulation of Point mutations </li></ul><ul><li>Appears to be the mechanism most often responsible for virus diversity observed </li></ul><ul><li>The best adapted virions are selected & maintained </li></ul><ul><li>Reassortments </li></ul><ul><li>Not in nature, Experimentally only </li></ul><ul><li>Reassortant virus of Lassa/Mopeia – (L) segment of Mopeia and (S) segment of Lassa </li></ul><ul><li>NB: produced by co-cultivation on Vero cells (bioterrorism) </li></ul><ul><li>Recombination </li></ul><ul><li>Demonstrated for 3 North American arenaviruses (WWA, Tamiami, Bear Canyon) – indicates common derivation from a recombinational event between ancestors in lineage A and B viruses </li></ul>
  29. 30. Newly discovered Arenaviruses <ul><li>Discovery of 7 new arenaviruses in the past 3 years </li></ul><ul><li>2 of these were human pathogens </li></ul>Bolivia Chapare Related to WWA USA Skinner Tank Related to WWA USA Catarina Closely related to Oliveros Brazil Pinhal Australia Dandenong Mastomys sp. Strain of Mopeia Tanzania Morogoro Mus sp. Groups with LCMV Guinea Kodoko Comment Country Virus
  30. 31. April 2008
  31. 32. Assignment to a new species <ul><li>A virus in the genus Arenavirus is assigned to a new species on the basis of a combination of two or more of the following characteristics: </li></ul><ul><li>The host species </li></ul><ul><li>The defined geographic distribution of the virus </li></ul><ul><li>Any associated disease in humans </li></ul><ul><li>Antigenic cross-reactivity with other members of the genus </li></ul><ul><li>Significant divergence from other species in the genus at the amino acid level </li></ul>
  32. 34. <ul><li>Thank you </li></ul>

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