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Influenza Powered By Docstoc
Nomenclature and Classification
1. Influenza family which is subdivided into 3 genera: Influenza
   A, Influenza B, and Influenza C, based on antigenic
   differences in the nucleoprotein (NP) and matrix (M) protein.
2. Influenza viruses are further characterized within type by
   antigenic differences associated with the H and N
   glycoproteins; there are at least 14 subtypes of H and 9
   subtypes of N proteins in influenza A virus.
3. All subtypes have been described in birds and some of them
   have been found in mammals.
4. To facilitate epidemiological studies, individual viruses are
   coded in the following manner:
                                                   Serotype of
 group                                             HA and N
         species               Isolate number

         •A/fowl/Hong Kong/1/98(H5N1)
Virus characteristics
1. Medium sized (80-120 nm diameter), enveloped,
   spherical to slightly pleomorphic in shape.
2. Genome consists of 8 segments of ss RNA which
   code for 10 proteins (5 structural, 3 associated with
   polymerase and 2 non-structural); genetic
   reassortment can occur
3. The envelope contains 2 glycoproteins: H
   (hemagglutinin), and N (neuraminidase)
4\ genetic reassortment occur frequently
5. Can infect humans, birds, swine, equine, seals, mink
   and whales
Influenza virions

nucleocapsid            envelope
(RNA fragments
wrapped in protein)   haemagglutinin and       100 nm
                      neuraminidase “spikes”
                      In envelope
Hemagglutinin and
 sialic acid
 on receptor

             HA     N
                        active site

  site                      variable

Influenza infection:

  Influenzavirus A      horses

                      marine mammals
  Influenzavirus B
  Influenzavirus C
Distribution of HA serotypes in

HA serotype   Birds   Horses   Pigs   Humans
  HA1         yes              yes     yes
  HA2         yes                      yes
  HA3         yes     yes      yes     yes
  HA4         yes
  HA5         yes                      yes
  HA6         yes
  HA7         yes     yes
  HA8-14      yes
Distribution of N serotypes in
           Birds    Horses   Pigs
  N1       yes               yes    yes
  N2       yes               yes    yes
  N3       yes
  N4       yes
  N5       yes
  N6       yes
  N7       yes     yes
  N8       yes     yes
  N9       yes
Evolution and Spread of flu

                 poultry           H1N1
                            humans H2N2
 aquatic birds                     H3N2
                                   (H5N1, H9N2)

                            horses H3N8
 All HA and N                            H7N7
Factors that sustain
   Antigenic drift
   Reassortment and antigenic shift
   Short term immunity
   Cross species transfer
Antigenic Variation
1. Periodic epidemics of influenza Type A are due to
   antigenic shifts in the virus which are believed to occur
   through genetic re-assortment between human and animal
   (or mammalian and avian) viruses. For example, the amino
   acid sequence of H3 protein of human isolates is more
   similar to the amino acid sequence of any Hx of
   mammalian or avian isolates than to the amino acid
   sequence of H2 proteins of human isolates.
         Prior to 1957      H1N1
         1957 (Asian flu)   H2N2
         1968 (Hong Kong)   H3N2
         1977               H1N1
2. Between epidemics, the influenza virus undergoes minor
   changes in the HA and N proteins These differences are
   due to multiple point mutations. These minor changes are
   referred to as antigenic drifts.
Pathogenesis of Influenza Viruses - Respiratory
Day 1
1.   Infection initiated by aerosol route; however, birds can also be infected by
     fecal/oral route b.entrapment of virions in mucus and their removal by the
     mucociliary transport system.
2.   Non-specific neutralization of virus by receptors mimicking glycoprotein
     present in the mucus.
3.   Interferon production.
Day 1 - 3
1.   Infection of individual epithelial cells of trachea
2.   Spread to contiguous cells resulting in loss of ciliary activity
3.   Destruction of goblet cells and mucus glands further compromises the
     mucociliary transport system.
4.   Destruction of cells initiates a local inflammatory response which results in
     increased amount of exudates and transudates.
5.   The surface of the trachea becomes increasingly anaerobic which provides
     optimum conditions for bacterial attachment and colonization.
Pathogenesis of Influenza Viruses - Respiratory
Day 5-9
1.   Infection of the lung resulting in destruction of type I and II pneumocytes
2.   Increasing accumulation of exudates and transudates, loss of surfactant
     produced by type II pneumocytes, blockage of airways and local hypoxia.
3.   Concomitant reduction of macrophage and PMN activity. Secondary
     bacterial infections become established resulting in bronchial pneumonia.
4.   IgA and IgG begin to appear in the upper and lower respiratory tracts,
5.   Secretory IgA appears 8 dpi, reaching a peak in 11 days but declines
6.   Serum antibodies, detectable by HI and VN tests appear 3 to 7 days after
     infection, peaking in 14 days; may persist up to 18 months.
7.   This is followed by recovery or by systemic spread of the virus
8.   Antibody response in young animals is slower and less pronounced
Pathogenesis of Influenza Viruses - Respiratory
1. The best model to illustrate why some influenza
   infections become systemic and others do not is
   illustrated by the avian influenza virus. Essentially
   virulence is determined by the ease by which the HA
   protein can be cleaved.
2. The pathogenesis of avian influenza is quite different
   from that of mammals. The virus replicates in the
   intestinal tract as well as the respiratory tract and is
   readily isolated from the cloaca.
3. Virulent strains (H5 and H7) of AI cause viremia and
   generalized infection which is often complicated by
   secondary bacterial or viral infections.
4. Antibody assays in birds are complicated because the
   adult birds may have experienced infections with many
   different subtypes.
1. In general, orthomyxoviruses are not stable in the
   environment; sensitive to heat (56C, 30 min), acid pH, and
   lipid solvents. Require close contact for transmission.
2. Exceptions are avian influenza viruses. Avian influenza is
   unique in that it can retain its infectivity for several weeks
   outside of its host.
3. Can spread by the aerosol route
4. Epidemiology of AI is poorly understood because of the
   role of wild birds, the great variety of different strains and
   the variable effects in different host species.
5. Wild ducks and geese are refractory to disease but wild
   ducks probably represent the most important reservoir
   for AI viruses. Virus is shed in secretions of respiratory
   tract and in feces. Survives for long time in feces.
    Replication of Influenza Virus

(1) Adsorption: the virus interacts with sialic acid-containing cell receptors via its hemagglutinin and enters via
endocytosis. (2) Fusion and uncoating: the hemagglutinin undergoes a conformational change mediated by the acid
environment of the endosome, which leads to the fusion of viral and cellular membranes. The ribonucleoprotein
complexes are then transported into the nucleus. (3) Transcription and replication: the viral RNA is transcribed and
replicated in the nucleus by the viral RNA polymerase (Two different species of RNA are synthesized from the viral RNA
template: (a) full-length, positive-sense replicative intermediate RNAs, which are used by the polymerase to produce
virion RNA and (b) mRNAs.
Influenza virus replication
              HA cleaved
              proteases              HA binds to

                            virus in
  pH, HA
  fuses          RNA
  membranes      released

                                                   N releases
Cleavage of HA
        receptor                    binds
                      penetrates    receptor

              Clara (mucus),             HA1
              bacterial            HA2
HA cleavage and virulence

May ‘94 ->                    low            low
             PQ--RETR         cleavability   virulence
June ‘94

 Dec ‘94 -> P Q R K R K T R   high           high
 Jan ‘95                      cleavability   virulence

Secondary effects of HA

                               Turns on genes for
                                                     high fever
          oxygen                     TNFa
                     activates                      cell damage
 HA         free                      IL-1
                      NFKB                            cachexia
          radicals                    IL-2
        anti         bacterial
      oxidants       products
  Influenza species specificity
                     Receptor binding             target cell

Avian influenza      a2,3, sialic acid and gal    intestinal epithelial

Human influenza      a2,6 sialic acid-gal         tracheal epithelial

Pigs                 a2,3 and                     tracheal epithelial
                     a2,6 sialic acid-gal

       Pigs are the mixing vessel for Influenza
The big pandemic of 1918
   Major influenza subtypes that have circulated
   in humans and swine since the 1918
   “Spanish Flu” pandemic.

Richard Webby and Robert Webster, “Influenza in Humans: Impact, Evolution and Surveillance.” 2001)
      Relative frequency of influenza subtypes
      isolated from humans in recent years.*

Richard Webby and Robert Webster, “Influenza in Humans: Impact, Evolution and Surveillance.” , 2001)
* The data represent worldwide frequencies that were obtained from: HTTP://OMS2.B3E.JUSSIEU.FR/FLUNET. The WHO influenza
surveillance network homepage.
     Schematic representation of the genetic
     reassortment events that lead to the development
     of the 1957 and 1968 pandemic strains of human
     influenza A viruses.

                                               1918            1957     1968
                                               H1N1            H2N2     H3N2

                                                               H2 HA,   H3 HA,
                                                               N2 NA,    PB1

Christopher Olsen, “The emergence of novel swine influenza
viruses in North America,” Elsevier Science B.V., Article in
Press, 2002.
Human Influenza Viruses

1. Humans are susceptible to Types A, B, and C.
2. Type A causes the classical influenza with which we are
3. Type B causes a mild to severe influenza. Reye's
   syndrome which is characterized by rapidly progressive
   non-inflammatory encephalopathy and fatty infiltration
   of the liver leading to its dysfunction, has been
   associated with type B influenza virus (also with other
   viral-induced respiratory and enteric infections).
4. Type C influenza virus is associated with mild upper
   respiratory disease.
   Clinical Signs and Symptoms of Human
(1) Influenza viruses are spread from person-to-person primarily through the coughing and sneezing of
infected persons.
(2) The incubation period for influenza is 1--4 days, with an average of 2 days.
(3) Persons can be infectious starting the day before symptoms begin through approximately 5 days
after illness onset; children can be infectious for a longer period.
(4) Uncomplicated influenza illness is characterized by the abrupt onset of constitutional and
respiratory signs and symptoms (e.g., fever, myalgia, headache, severe malaise, nonproductive cough,
sore throat, and rhinitis). Reported sensitivity and specificity of clinical definitions for influenza-like
illness that include fever and cough have ranged from 63% to 78% and 55% to 71%, respectively,
compared with viral culture . Sensitivity and predictive value of clinical definitions can vary, depending
on the degree of co-circulation of other respiratory pathogens and the level of influenza activity (28).
(5) Influenza illness typically resolves after several days for most persons, although cough and malaise
can persist for >2 weeks.
(6) In some persons, influenza can exacerbate underlying medical conditions (e.g., pulmonary or
cardiac disease), lead to secondary bacterial pneumonia or primary influenza viral pneumonia, or
occur as part of a co-infection with other viral or bacterial pathogens .
(7) Influenza infection has also been associated with encephalopathy, transverse myelitis, Reye
syndrome, myositis, myocarditis, and pericarditis .
Equine influenza
   A1 H7N7 rare pockets in central Europe??
   A2 H3N8 annual epizootics
   World wide except - Australia, New
    Zealand, Iceland
   Highly contagious, rapid spread
Equine Influenza

 1. Mild to acute upper respiratory disease. 2 subtypes:
    A/equine/1 and A/equine/2
 2. Antigenic drift has been detected periodically:
 3. Virus strain of avian origin was suspected in the
    outbreak in China.
 4. Clinically, the disease is similar to that caused by
    equine herpesvirus type 4 (EHV-4) and equine
    rhinoviruses (Picornaviridae).
 5. Interstitial myocarditis has been reported in horses
    suffering from acute influenza
   resolution in 3 weeks   inhalation
                           (infected animal
                           or fomites)
  no complications
  and rest

                            replication in
                            epithelial cells
                            upper RT
bacterial infections
Clinical signs-EIV
   Sudden onset
   Fever (39-42), biphasic
   Loss of appetite
   Muscle soreness
   Dry cough
   Nasal discharge (serous ->mucopurulent)

    Clinical signs are similar to other respiratory diseases
      such as equine rhinopneumonities and viral arteritis
      Need lab testing
Exercise or Rest
   Gross et al. 1998. Equine Vet. Jn. 30:489
       Exercised group
         More severe disease
         More weight loss

         No difference in recovery time

         Long term effects??
   Clinical signs
   Virus isolation
   Directagen Flu-A
   Serological tests
       HAI
       Single radial haemolysis
EIV Conventional vaccines
   Inactivated, H7N7 and H3N8 isolates
   Adjuvant
   Most -> short lived protection
       Revaccinate at 6 week intervals
EIV Intranasal, attenuated
   Heska Co.
Avian Influenza (AI)

1. Clinical signs/host:
   a. Inapparent to acute systemic disease in chickens
   b. Clinically affected birds may show respiratory, CNS and enteric
      signs of the disease
   c. The more severe form of the disease is sometimes referred to
      as "fowl plague."
   d. Various species of wild birds, mainly waterfowl, constitute an
      important reservoir.
   e. Among domestic birds, chickens and turkeys are most likely to
      develop disease
   f. Pheasants, quail, guinea fowl and partridges are also
Avian Influenza (AI)
2. Virus types:
   a.   All virulent strains that cause disease in chickens are of the H5 and H7
   b.   However, not all subtypes of H5 or H7 cause the same severity of
        disease in chickens
   c.   The amino acid sequence in the hinge region of the HA molecule
        determines virulence. A change in 1 to 4 amino acids in this region
        results in increased virulence.
3. Economic losses:
   a.   Since 1980, infection of turkeys has become an economically important
        disease in many parts of USA.
   b.   Losses arise from condemnation at processing plant due to air saculitis
        caused by secondary bacterial infections (E. coli) and losses in egg
   c.   An outbreak in Pennsylvania and Virginia in 1983-84, caused by an
        H5N2 virus, resulted in the slaughter of > 17 million birds, with
        compensation and other costs in excess of $60 million.
   d.   Again, all 14 known H subtypes and 9 N subtypes in all possible
Avian influenza
   Pennsylvania - 1983 - $61,000,000
   Mexico - 1993-4 - $$?
   Asymptomatic to fatal (sudden death)

    Kristi Askin, Tina Tuason, Elisabeth Ludlage
The emergence of H5N1 influenza in Hong

Robert G. Webster, “Influenza: An Emerging Disease,” Emerging Infectious Diseases,” Vol. 4 No. 3, July-Sept., 1998
(URL: http://www.cdc/gov/ncidod/eid/vol4no3/webster.htm)
Swine Influenza
1. One principal subtype (H1N1) but 2 variants within this subtype in
   United States up until 1998; one is common in Europe and the
   other in the USA.
2. Swine were infected with H3N2 strains – 1998, reassorted virus
   from humans and birds
3. Clinically, upper respiratory disease which generally runs its
   course within a week.
4. Avoiding stress during infection usually results in lower mortality
    (< 1%).
5. Recovered animals either lose weight or their weight gains are
   reduced, attributing to economic loss to producers.
6. Outbreaks in swine occur in late fall and early winter.
7. Swine influenza virus (H1N1) can infect turkeys and humans. In
   turkeys, it causes drop in egg production and increased number of
   abnormal eggs.
SIV in North America
1918 Influenza recognized clinically in pigs    (Koen al 1918)

1930 First swine influenza isolated. classical H1N1(Shope 1931)

1930-1990’s Classical H1N1 in North America (Hinshaw 1976.., )

1976 Swine influenza vaccine in humans

1997-98 Appearance of H3N2 (Zhou et al 1999)
   seropositive to H3 (Olsen 2000)

2000 H1N2 reassortmant of H1N1 and H3N2 (Karasin 2000)
2000 H4N6 avian isolated from pigs (Karasin 2000)
Swine influenza
   H1N1 - two variants
   H3N2
   Ontario (1989-92)
       53% H1N1
       17% H3N2 (similar to human virus)
       4% H1N2 (similar to human virus)
   Genotypes of H3N2
   influenza A viruses
   isolated from pigs in
   North America since 1997.

Christopher Olsen, “The emergence of novel swine influenza
viruses in North America,” Elsevier Science B.V., Article in Press,
 Genotype of the H1N2 influenza A viruses
 isolated from pigs in the United States since

Christopher Olsen, “The emergence of novel swine influenza viruses in North America,” Elsevier Science B.V., Article in Press,
                  Swine Influenza:Zoonosis
• 20 million deaths 1918-19, due to swine influenza
• Continued reports of humans with swine influenza death by
  H1N1 strain of swine influenza

                                  (Kimura et al 1998 Mayo Clin Proc 73:243)

• All 10 islet recipients had antibodies to swine influenza (Butler
  Nature 391:320.1998)
Swine Influenza-zoonosis

Classical swine influenza viruses can also be directly
transmitted to humans as zoonotic infections, sometimes
with fatal consequences. Human infections with swine
influenza viruses have been documented in the U.S. at least
10 times since 1974, including fatal infections, as well as in
Europe and in New Zealand. In addition, data suggest that
zoonotic swine influenza virus infections may actually occur
more routinely among people in regular contact with pigs
than the relatively small number of documented cases would
Swine Influenza Disease
   Respiratory Disease in epizootic
       Fever, lethargy, coughing, nasal/ocular discharge, off
   PRDC porcine respiratory disease complex
       PRRSV, Mycoplasma
Swine Influenza-disease
8. The pathogenesis of swine and equine influenza virus
   infections resembles that in man.

            Influenza Virus-Induced Pneumonia in a Pig
 Body temperature course after intratracheal
 inoculation withH1N1, H3N2 or H1N2 subtypes of

Kristen Van Reeth, “A New Look at Swine Influenza in Europe.” 2001)
          Relationship between H1 antibody titer and protection
          against lung lesions.*

Terri Wasmoen, “Immune Response to Swine Influenza Vaccination.” 2001)
* No data is available for H3N2 at 10 and 20 or H1N1 at 320 and 640 antibody titers (at publication.)
Diagnosis of SIV
 Virus detection

 Virus isolation egg inoculation (EI)
 Virus isolation-cell culture
 Membrane enzyme immunoassay-hu flu (EIA)
 Microwell enzyme immunoassay-hu flu

 Hemagglutination Inhibition
 ELISA to H1 or H3
 MaxiVac®-FLU Pharmaceutical Name
Swine Influenza Vaccine, Killed VirusProduct

Features and Benefits
•Inactivated virus vaccine provides strong, durable immunity against swine flu.
      •Special oil-in-water adjuvant system helps stimulate strong immune response.
      •Protection against clinical disease shown in vaccinates challenged with highly virulent SIV.
      •Significantly reduces circulating virus in lungs after severe challenge which helps prevent costly setbacks due
      to lung tissue damage, consolidation, and opportunistic bacterial infections.
      •Reduced viral shedding helps prevent virulent virus spread.
      •Convenient vaccination schedule fits easily into any herd health program.
Recommendations and Reports April 20, 2001 / 50(RR04);1-46

Prevention and Control of Influenza
Recommendations of the Advisory Committee on Immunization
Practices (ACIP)

Advisory Committee on Immunization Practices Membership List,
February 2001
John F. Modlin, M.D.
Professor of Pediatrics and Medicine
Dartmouth Medical School
Lebanon, New Hampshire
Dixie E. Snider, Jr., M.D., M.P.H.
Associate Director for Science
Centers for Disease Control and Prevention
Atlanta, Georgia
Process for human influenza
   surveillance
   February meeting
       Commonwealth Serum Labs (Australia)
       CDC (USA)
       Natl. Inst. For Medical Research (UK)
       European Inst. For Biological Standardization
       Food and Drug Admin. (USA)
Process for human influenza
   March-April
       Genetic and antigenic characterization of
        approved strains
       Distribution by WHO to manufacturers
       Production of seed stock
       Tests for contaminants (bacteria,
        mycoplasma, viruses)
Process for human influenza
   April-August
       Vaccine production
       License application made
       Clinical trials (to be submitted before
        vaccination season)
Process for human influenza
   August-September
       Distribution begins
     Human Influenza Vaccine Composition (2001-
1.   Influenza vaccine contains three strains (i.e., two type A and one type B.
2.   The vaccine is made from highly purified, egg-grown viruses that have been
     made noninfectious (i.e., inactivated). Subvirion and purified surface-
     antigen preparations are available.
3.   The trivalent influenza vaccine prepared for the 2001--2002 season will
     include A/Moscow/10/99 (H3N2)-like, A/New Caledonia/20/99 (H1N1)-like,
     and B/Sichuan/379/99-like antigens.

4.   To be administered IM
    Flu vaccine recommendations
1. Persons at Increased Risk for Complications
Vaccination is recommended for the following groups of persons who are at increased risk for complications from
•persons aged >65 years;
•residents of nursing homes and other chronic-care facilities that house persons of any age who have chronic medical
•adults and children who have chronic disorders of the pulmonary or cardiovascular systems, including asthma;
•adults and children who have required regular medical follow-up or hospitalization during the preceding year
because of chronic metabolic diseases (including diabetes mellitus), renal dysfunction, hemoglobinopathies, or
immunosuppression (including immunosuppression caused by medications or by human immunodeficiency [HIV]
•children and teenagers (aged 6 months--18 years) who are receiving long-term aspirin therapy and, therefore, might
be at risk for developing Reye syndrome after influenza infection; and
•women who will be in the second or third trimester of pregnancy during the influenza season.
2. Persons Aged 50--64 Years
Vaccination is recommended for persons aged 50--64 years because this group has an increased prevalence of persons
with high-risk conditions.
3. Persons Who Can Transmit Influenza to Those at High Risk
Persons who are clinically or subclinically infected can transmit influenza virus to persons at high risk for
complications from influenza.. The following groups should be vaccinated:
•physicians, nurses, and other personnel in both hospital and outpatient-care settings, including emergency response
•employees of nursing homes and chronic-care facilities who have contact with patients or residents;
•employees of assisted living and other residences for persons in groups at high risk;
•persons who provide home care to persons in groups at high risk; and
   Prevent membrane fusion
       Amantidine (Symmetrel)
       Remantidine (Flumadine)
   Neuraminidase inhibitors
       Zanamivir (Relenza)
       Oseltamivir (Tamiflu)
Human flu vaccine used

 Pasteur Merieux Connaught

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