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Influenza A

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Influenza A

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    1. Influenza A Aimee Mandapat, MD Senior Talk November 28 & 30, 2007

    2. Influenza Transmission electron microscopy of negatively stained Influenza virions

    3. Learning Objectives Impact of Influenza Key surface proteins involved in replication Antigenic Drift vs. Shift Viral Adaptation Diagnosis Historical perspective and current research Influenza vaccines Treatment

    4. Origin of Name 15th-century Italy: cause of the disease was ascribed to “unfavorable astrological influences.” Later known as influenza del freddo, meaning "influence of the cold." 1743: “Influenza" first appears in English. Also known as: epidemic catarrh, grippe (from the French grippe, meaning flu); sweating sickness, and Spanish fever

    5. Influenza A Negative, single-stranded RNA virus, family Orthomyxoviridae Segmented genome of 8 RNA segments which encode 10 genes Polymerase lacks “proofreading” RNA transcriptase makes a single nucleotide insertion error roughly every 10 thousand nucleotides

    6. Influenza A Seasonal influenza kills 250K -500K people worldwide, mostly older adults In the U.S., 36K influenza-related deaths occur annually Annual epidemics often last 5-6 weeks Every 2-3 years, influenza epidemics increase the yearly number of deaths by about 10K-50K Occasionally, flu sweeps the world? pandemic

    7. Influenza Life Cycle Krug, RM, Lamb, RA Orthomyxoviridae: The Viruses and Their Replication 2001 Fields Virology. 4th edition, editors: Knipe DM, Howley PM,. Philadelphia: Lippincott Williams & Wilkins. ISBN: 0-7817-1832-5 Orthomyxoviridae: The Viruses and Their Replication

    8. Influenza A Two key surface proteins: - Hemagglutinin (H): involved in entry into host cells 16 hemagglutinins known to exist - Neuraminidase (N): involved in the process of new virions budding off host cell 9 known neuraminidase proteins

    9. Influenza A Subtypes are defined by expression of the virus’s hemagglutinin and neuraminidase Subtypes are maintained in aquatic birds, which are a continual reservoir of new viruses Of the 15 HA subtypes in birds, only 3 have caused human pandemics

    10. Antigenic Drift vs. Shift Antigenic drift = random accumulation of mutations in viral genes; minor changes, continual process Antigenic shift = the result of two different strains of influenza combining to form a new subtype having a mixture of surface antigens of the originals; major changes. a.k.a reassortment.

    11. Drift vs. Shift Antigenic drift creates influenza viruses with slightly-modified antigens; antigenic shift generates viruses with entirely novel antigens.

    12. Transmission Through talking, coughing or sneezing, which aerosolizes the virus Also present in saliva, nasal secretions, feces, blood Infection can occur through contact with these bodily fluids or contact with contaminated surfaces

    13. Symptoms

    14. Symptoms Abrupt onset Myalgias, arthalgias Coughing and sneezing Fever (100 to 106 F), chills Fatigue, may be prolonged Anorexia Irritated, watering eyes Nasal congestion Nausea and vomiting – children

    15. Viral shedding Viral shedding peaks at 24-48 hours then rapidly declines Little to no virus is detectable after 5-10 days Children and immunocompromised patients can shed virus for longer periods Viral replication only occurs in the respiratory tract

    16. Cold vs. Flu

    17. Cold vs. Flu Monto et al. did a retrospective study on the signs and symptoms (s/s) in 3744 adults and adolescents with flu-like illnesses during the phase 2 and 3 neuraminidase inhibitor trials Best predictor was the combination of fever and cough within 48 hours of the development of symptoms with a PPV of 79% for documented flu.

    18. Cold vs. Flu Call et al. tried to systematically review the precision and accuracy of signs and symptoms of influenza 915 articles from a Medline search; 17 contained data on characteristics of s/s. Of these, 11 were eliminated based on 4 exclusion criteria and availability of primary data

    19. Call et al. Exclusion criteria Study design was a prospective cohort, a randomized controlled trial, or a meta-analysis Inclusion of primary assessment of clinical s/s as predictors of diagnosis Influenza A or B infection proven by culture, antibody titer, PCR or immunofluorescence Study graded A or B on RCE series

    20. Call et al. No specific symptom or constellation of symptoms is diagnostic The data did suggest that fever and cough during influenza season suggests a significant likelihood of influenza among elderly adults Clinicians must pay attention to surveillance data to know when and what influenza viruses are circulating.

    21. Diagnosis Clinical – especially during an influenza outbreak with pt presenting with an acute febrile respiratory illness Rapid tests – employ immunologic or molecular techniques, e.g. immunofluorescence assays, enzyme immunoassays, PCR based tests Viral culture Serologic methods: primarily hemagglutination-inhibition

    22. Complications of the Flu Pneumonia is the major complication Primary influenza pneumonia Most severe, but least common complication Occurs when influenza virus directly infects the lung Suspect when symptoms persist in pt with acute influenza High fever, shortness of breath, cyanosis Predilection for pts with high L atrial pressures, COPD, but also healthy adults

    23. Complications Secondary bacterial pneumonia 25% of all influenza associated deaths Suspect when pts have an exacerbation of fever and respiratory symptoms after an initial improvement Higher fevers, cough, purulent sputum, infiltrates S. pneumonia, Staph aureus (MRSA too) and Haemophilus influenzae

    24. Peltola et al. Peltola et al. demonstrated a mouse model of synergism between influenza virus and S. pneumoniae Neuraminidase activity correlated with increased adherence and invasion of S. pneumoniae May predispose to bacterial infection and increased mortality

    25. Complications cont’d. Myositis Rhabdomyolysis CNS involvement: encephalitis, transverse myelitis, aseptic meningitis, Guillain-Barre syndrome Myocarditis/Pericarditis Toxic Shock Syndrome associated with Staph aureus and influenza B

    26. Pandemics

    27. 1968: Hong Kong Influenza *H3N2 Arose in Southeast Asia Called Hong Kong influenza based on site of emergence to Western attention Characterized as “smoldering” Differed from preceding pandemic by its HA antigen, but retained NA antigen Previous exposure to N2 antigen thought to moderate M&M from this strain 37 years later, H3N2 remains as the major and most troublesome subtype

    28. 1957: Asian Influenza *H2N2 First rapid global spread of influenza available for laboratory investigation With the exception of people >70 years of age, public faced virus with which it had no previous exposure First to show definitively that the virus alone, without bacterial coinfection, was lethal

    29. 1957: Asian Influenza *H2N2 Complement fixation tests quickly identified it as Influenza A HA antigen was unlike any previously seen in humanity, as was the neuraminidase antigen Provided the first opportunity to observe vaccine response in an unprimed population

    30. 1957: Asian Influenza *H2N2 More vaccine was noted to initiate a primary antibody response than with earlier H1 vaccines In 1958-60, as more infections occurred, mean initial antibody levels in populations increased and response to vaccination was better demonstrated Divided doses <4 weeks were more beneficial initially

    31. 1957: Asian Influenza *H2N2 Provided the first opportunity to study how postpandemic disease transitions into endemic disease Decreased incidence of clinically evident cases are either due to an increase in antibody levels in the community or a change in the intrinsic virulence of the virus.

    32. 1957: Asian Influenza *H2N2 In 1960, Kaye et al. showed that hospitalized patients with lab-confirmed infections still had same clinical profiles (uncomplicated to fatal pneumonia), but no “epidemic influenza” in the community H2N2 “disappeared” within 11 years, supplanted by Hong Kong subtype, H3N2

    33. 1918 Pandemic: Spanish Flu Killed more people in one year than the Bubonic Plague of the Middle Ages killed in 100 years Occurred in 3 waves within 9 months W1: Spring-Summer, 1918 Associated with high morbidity, low mortality W2: Summer-Fall, 1918 Extraordinarily high mortality All viral isolates to date are from this wave W3: Winter 1918-1919 High mortality

    34. 2 Clinical-Pathologic Syndromes Acute, aggressive bronchopneumonia featuring epithelial necrosis, microvasculitis/vascular necrosis, hemorrhage, edema; pathogenic bacteria usually cultured at autopsy Severe ARDS-like picture where patients developed “heliotrope cyanosis” and drowned from copious, thin, watery, bloody fluid in the lungs

    35. 1918 Pandemic: H1N1 Taubenberger et al. sequenced the entire 8 segment genome from RNA fragments in victims’ lungs 1918 virus did not arise from gene reassortment like H2N2 and H3N2 Arose from genome adaptation, a previously undocumented mechanism of pandemic flu

    36. Taubenberger et al. H1N1 is ancestrally “avian” BUT, all 8 gene segments are genetically distinct from any of the viruses collected between 1917 and 2006 Viral sequence data suggests the entire 1918 virus was novel to humans shortly before 1918? not a reassortment virus BECAUSE of a greater than expected number of silent nucleotide changes

    37. Deep Genetics 1918 nucleoprotein gene sequence is similar to viruses of wild birds at the AMINO ACID LEVEL But it is highly divergent at the NUCLEOTIDE LEVEL We can determine the evolutionary distance of genes by comparing ratios of synonymous to nonsynonymous nucleotide substitutions

    38. Deep Genetics Synonymous substitution represents a silent change; a nucleotide change in a codon that does not result in an amino acid replacement Nonsynonymous substitution is a nucleotide change in a codon that results in an amino acid replacement

    39. Evolutionary Distance Viral genes subjected to immunologic drift pressure or adapting to a new host exhibits a greater percentage of nonsynonymous mutations Viral genes under little selective pressure accumulates mainly synonymous changes

    40. Evolutionary Distance Since little or no selection pressure is exerted on synonymous changes, these are thought to reflect evolution distance Because the 1918 genome has more synonymous changes than expected, it is UNlikely to have emerged directly from an avian influenza virus sequenced of which we are aware.

    41. Theories One possible explanation is that these novel gene segments were acquired from an influenza reservoir not yet identified; ?swine intermediary To date, the origin of the 1918 virus has not been identified Viral adaptation

    42. Taubenberger et al. Also found 10 amino acid changes in the polymerase proteins consistently differentiate the 1918 and known human influenza virus from avian virus A number of the same changes have been found in recently circulating, highly pathogenic H5N1 viruses ? Are these sequences the key to adaptation of avian influenza viruses to humans

    43. Other 1918 Questions Curve of influenza deaths at age of death are characteristically “U” shaped Nearly half of the flu-related death in 1918 were in young adults aged 20-40, resulting in a “W” shaped curve

    44. The 1918 “W” Curve Taubenberger J, Morens D “1918 Influenza: the Mother of All Pandemics.” Emerging Infectious Diseases 12 (1): 15–22.

    45. Theories 1918 virus had high virulence, tempered in patients born before 1889 because of exposure to a then-circulating virus that offered some protection No trace of such a virus today In 1927, Jordan show that mortality in the >65 years olds decreased from 6% in 1900 to 0.6% in 1918, which is consistent with protective immunity

    46. Tumpey et al. Used reverse genetics to generate an influenza virus with all eight segments of the 1918 pandemic virus to study its virulence High growth in human bronchial epithelial cells Caused death in mice and embryonated chicken eggs at astonishing rate

    47. Tumpey et al. Had the ability to replicate in the absence of trypsin Trypsin cleaves the HA molecule, allowing for multicycle replication 1918 NA had activity that facilitated HA cleavage independent of trypsin Both the 1918 HA and NA sequences lack the obvious sequences that allow for replication in the absence of typsin

    48. Tumpey et al. 1918 HA was essential for severe pulmonary lesions Question re: Lethality to chicken embryos, characteristic of avian H1N1 subtypes Contemporary human H1N1 viruses and 1918 recombinant viruses with 2,5, or 7 genes did not cause mortality of chicken embryos

    49. Tumpey et al. But 1918 HA coupled with the entire 1918 polymerase genes were lethal to chicken embryos Also showed 1918 HA and 1918 polymerase genes are essential for maximal replication in human bronchial epithelial cells

    50. The Next Pandemic Inevitable, but unpredictable Avian influenza H5N1 No pandemic has presented like this, but may be secondary to limited surveillance, lab data Evidence of bird to human transmission proving humans can be infected with wholly avian influenza viruses Intermediate host may not be necessary if reassortment can take place in humans

    51. The Next Pandemic Virulence is polygenic; complementary action among all the gene segments Pandemics have been caused by low, intermediate and highly pathogenic subtypes that effectively adapted to humans Data shows H5N1 is not unique among avian influenza viruses in ability to transmit to humans or to cause human infection

    52. H5N1 Several case clusters reported High case fatality rate Close contact with poultry Ungchusak et al. were first to document possible person-to-person transmission, but usually family members or close contacts Host susceptability vs. shared exposures vs. prolonged contact ? Role of polymerase protein changes described by Taubenberg et al.

    53. Vaccines Trivalent inactivated influenza vaccine (TIV) - any person >/= 6 months - even high risk conditions - used exclusively at UH Live attenuated influenza vaccine (LAIV) - given intranasally - healthy, non-pregnant people 5-49 years old

    54. CDC Recommendations All persons at risk for medical complications from influenza Children 6 mos to 4 years Everyone >/= 50 years old Children & adolescents who are receiving longterm ASA and at risk for Reye syndrome after flu Women pregnant during flu season Immunosuppressed kids and adults

    55. CDC Recommendations All persons at risk for medical complications from flu cont’d. Kids and adults with chronic pulmonary, cardiovascular, renal, hepatic, hematologic, and metabolic disorders Adults and kids with compromised respiratory function, handling of secretions, at risk for aspiration NH, longterm care facility residents

    56. CDC Recommendations All persons who live with or care for persons that are high risk Health care personnel Healthy household contacts (including kids) and caregivers of: children <5 years, adults >/= 50 years, persons with medical conditions that put them at risk for complications from the flu

    57. Influenza Vaccine First developed in the 1940s Consisted of partially purified preps of influenza viruses grown in embryonated eggs Killed vaccines were highly pyrogenic and lacking in efficacy “zonal ultracentrifuge” technique revolutionized the purification process in the 1960s– remains the basis of our current manufacturing process

    58. Influenza vaccine Consists of 3 components H1N1 (hemagglutinin subtype 1; neuraminidase subtype 1 H3N2 influenza A virus Influenza B virus

    59. Influenza Vaccine Changes in the HA of circulating viruses (antigenic drift) requires periodic replacement of the vaccine strains WHO publishes semiannual recommendations on what strains to include for the Northern and Southern Hemispheres

    60. Influenza Vaccine U.S. Food and Drug Administration determines every February which vaccine strains should be included in the following winter’s vaccine Each dose is approximately the amount of purified virus in the allantoic fluid of 1 infected embryonated egg

    61. Influenza Vaccine Manufacturing depends on the availability of embryonated eggs and the vaccine seed strains Still vaccines have the best cost-benefit ratio of any medical treatment

    62. Universal Vaccines Current vaccines are vulnerable to emergence of strains not covered by the vaccine; target highly variable HA and NA regions– effective strategy Goal to make vaccines that are less sensitive to antigenic drift Targeting conserved regions of the Influenza A genome, e.g. transmembrane proteins, HA, NA

    63. Universal Vaccines Current vaccines do not induce antibodies against these conserved regions None of the universal vaccines studied in animal models are as effective as our current vaccines ? Use as adjuvant therapy to current vaccine strategy

    64. Therapies Two classes of antiviral drugs M2 inhibitors *only active against Influenza A Amantadine Rimantadine Neuraminidase inhibitors *active against Influenza A and B Zanamivir *only approved for the treatment, not prevention of the flu Oseltamivir

    65. M2 Inhibitors a.k.a adamantanes Equally effective In 1982, Dolin et al. did a randomized controlled trial of 450 volunteers evaluating prophylactic efficacy of lab documented flu 2 % with amantadine 3% with rimantadine 21% with placebo

    66. M2 Inhibitors Target the M2 protein of Influenza A, which forms a proton channel in the viral membrane needed for viral replication Evidence of drug resistance Can develop 2-3 days into therapy 2004-05, 14.5% showed resistance 2005-06, 92% among H3N2 showed resistance

    67. M2 Inhibitors Generally well tolerated CNS side effects: anxiety, insomnia, impaired thinking, confusion, lightheadedness, hallucinations Side effects more common in elderly Increased rate of seizures in pts with known epilepsy Amantadine has anticholinergic effects so contraindicated in untreated angle closure glaucoma

    68. Neuraminidase Inhibitors Zanamivir approved for treated of influenza in pts >7 years of age Oseltamivir approved for treatment in pts >1 year; prophylaxis for pts >13 years Also active against the strain that caused the 1918 pandemic and avian Influenza A strains

    69. Neuraminidase Inhibitors Mechanism of action Sialic acid analogs that competitively inhibit neuraminidase on the surface of influenza A and B Prevents infection by destroying the receptor that is recognized by the viral hemagglutinin Minimizes release of virus from infected cells Resistence less common

    70. Neuraminidase Inhibitors Generally well tolerated Delivered as an inhaled dry powder Respiratory distress has been reported in pts with COPD January 2000, manufacturer issued a warning for pts with asthma/COPD and recommended using only with readily available bronchodilators Concern for ease of use in elderly Reports of nausea/vomiting

    71. Treatment M2 inhibitors Begin treatment within 48 hours and treat for 2 to 5 days Neuraminidase inhibitors Treat within 48 hours of onset for 5 days

    72. Take Home Points Influenza is a clinical diagnosis; think flu in acute, febrile respiratory illnesses during influenza season Start treatment early Get your flu vaccine every year Encourage your high risk patients to get annual flu vaccines WASH YOUR HANDS!

    73. Employee Health Now known as Corporate Health Now located in the MCCO Bldg Go through Lakeside basement through Rainbow’s basement to the tunnels Follow the signs to the MCCO Bldg Do not have to make an appt As of this morning, still have flu shots

    74. Case #1 45 yo WF 10th grade English teacher visits your office in mid-December 2003 c/o temperature to 101.5. Also c/o dry cough, sore throat, myalgias and malaise that began abruptly about 24 hours prior. Many kids 2 teachers at her school have been absent with similar symptoms. What else do you want to know?

    75. Case #1 PE 38.6, 95, 18, 120/60, 98% on RA Mild pharyngeal erythema, no exudates No LAD RRR, no m/g/r CTAB No rashes

    76. Case #1 What is your pre-test probability? CDC website Tests? Therapy?

    77. References Belshe, RB. The Origins of Pandemic Influenza– Lesosns from the 1918 Virus. NEJM 353; 21, 2209-2211. Call SA, Vollenweider MA, Hornung CA, Simel DL, McKinney WP. Does this Patient Have Influenza?. JAMA 2005: 293(8) 987-997 Dolin R, Reichman RC, Madore HP et al. A controlled trial of amantadine and rimantadine in the prophylaxis of influenza A infection. NEJM 1982: 307:580. Gerhard W, Mozdzanowska K, Zharikova D. Prospects for Universal Influenza Virus Vaccine. Emerging Infectious Diseases 2006: 12(4) 569-574. Jordan E. Epidemic influenza: a survey. Chicago: AMA, 1927 Kilbourne ED. Influenza Pandemics of the 20th Century. Emerging Infectious Diseases. 12(1): 9-14. Monto AS, Gravenstein S, Elliott M et al. Clinical signs and symptoms predicting influenza infection. Arch of Intern Med 2000; 160: 3243. Morens DM, Fauci AS. The 1918 Influenza Pandemic: Insights for the 21st Century. JIV 2007: 195, 1018-1028.

    78. References Palese P, Making Better Influenza Virus Vaccines? Emerging Infectious Diseases. 12 (1): 61-65. Peltola VT, Murti KG, McCullers JA. Influenza virus neuraminidase contributes to secondary bacterial pneumonia. J Infectious Diseases 2005: 19:249. Reid AH, Janczewski TA, Lourens RM, Elliot AJ, Daniels RS, Berry CL, Oxford JS, Taubenberger JK. 1918 Influenza Pandemic Caused by Highly Conserved Viruses with Two Receptor-Binding Variants. Emerging Infectious Diseases. 9 (10): 1249-1253. Reid AH, Fanning TG, Hultin JV, Taubenberger JK. Origin and evolution of the 1918 “Spanish” influenza virus hemagglutinin gene. Proc Natl Acad Sci 1999; 96 1651-1656. Reid AH, Fanning TG, Janczewski TA, Lourens RM, Taubenberger JK. Novel Origin of the 1918 Pandemic Influenza Virus Nucleoprotein Gene. J of Virology 2004: 78(22) 12462-12470. Treanor JJ, Hall CB. Influenza and infections of the trachea,bronchi, and bronchioles. In Betts RF, Chapman SW, Penn RL, eds. Reese and Betts’ A Practical Approach to Infectious Diseases, 5th ed. Philadelphia: Lippincott, Williams and Wilkins, 2003; 278-287.

    79. References Taubenberger JK, Morens DM. 1918 Influenza: the Mother of all Pandemics. Emerging Infectious Diseases 2006: 12(1) 15-22. Taubenberger JK, Reid AH, Lourens RM, Wang R, Jin G, Fanning TG. Characterization of the 1918 influenza virus polymerase genes. Nature. 2005 Oct 6;437(7060):889-93. Tumpey TM, Basler CF, Aguilar PV, Zeng H, Solorzano A, Swayne DE, Cox NJ, Katz JM, Taubenberger JK, Palese P, Garcia-Sastre A. Characterization of the Reconstructed 1918 Spanish Influenza Pandemic Virus. Science 2005(310) 77-79. Ungchusak et al. Probable Person-to-Person Transmission of Avian Influenza A (H5N1); NEJM 352;4 333-340. Wikipedia “Influenza” Zachary KC, Hirsch MS. UptoDate. Pharmacy of antiviral drugs for influenza.

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