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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.