Influenza A Viruses

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Influenza A Viruses
Amman May, 5, 2009

• Mohammad Q Al-Natour, DVM, MPH, Ph.D
• Associate Prof. of Avian Diseases
• mqalnatour_at_yahoo.com alnatour_at_just.edu.jo
• Mobile [phone]
• Avian Diseases Research Lab.
• Department of Pathology Animal Health
• Faculty of Veterinary Medicine
• Jordan University of Science and Technology
• Irbid - Jordan

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Key properties of type A influenza virus

• Multiple serotypes
• Wide spectrum of pathogenicity
• Wide host range
• Global ?
• International trade of economic significance??
• Incubation period (H1N1) 1-3 days in pigs
• Pigs excreting virus within 24 hrs of infection
• Virus shedding for 7-10 days
• Pigs recover within 5-7 days

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Orthomyxoviridae
Humans
Horses
Influenza virus A
Cats
Pigs
Birds
Marine mammals
Influenza virus B
Humans
Influenza virus C
Pigs
Humans
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OrthomyxoviridaeA.I. Virus

• Single stranded RNA ve
• Segmented 8 genes cod for 10 proteins
• Two glycoprotein surface projection
• - Haemagglutinin (HA) H1-H16
• - Neuraminidase (NA) N1-N9
• Enveloped (20 lipid) Sensitive to heat, dryness
  and normal disinfectants
• Antigenic types A, B, C
• Pathogenicity vary

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Haemagglutinin and Neuraminidase
sialic acid on receptor
HA
active site
N
receptor binding site
variable loops
variable loops
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Cleavage of HA
binds receptor
binds receptor
penetrates cell
HA1
Clara (mucus), extracellular, serum, bacterial pro
teases
HA0
HA2
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HA cleavage and virulence
low virulence
low cleavability
May 94 -gt June 94
P Q - - R E T R
respiratory infection
high virulence
Dec 94 -gt Jan 95
P Q R K R K T R
high cleavability
systemic infecton
?
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Influenza virus replication
HA cleaved by proteases
HA binds to receptor
virus buds
virus in phagolysosome
lowered pH, HA fuses membranes
RNA released
N releases virus
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Infection cycle of influenza

1. Binding of virus to cell
2. Cell engulfs virus via endocytosis
3. Membrane of virus fuses with endosome RNA
   released into cell
4. Viral polymerase produces mRNA from viral RNA
5. Protein, new RNA produced
6. Self-assembly produces virions
7. Virions bud off cell membrane

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Infection cycle Binding and endocytosis

• HA contains receptor binding site for virus
• Binds to sialic acid residue on cell surface
  glycoprotein
• Binding triggers receptor-mediated endocytosis
• Virus is taken into endosome
• Low pH of endosome causes fusion of viral and
  endosome membranes

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Type A Influenza Surface Antigens Surface
Antigen Subtype
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Reassortment
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Evolution and Spread of flu viruses
H1N1 H3N2
pigs
poultry
H1N1 H2N2 H3N2 (H5N1, H9N2)
humans
aquatic birds
fecal/oral
H3N8
horses
All HA and N serotypes
H7N7
respiratory
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The avian HK viruses
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Swayne, D.E. Epidemiology of Avian Influenza in
Agricultural and Other Man-Made Systems. In
Avian Influenza. Wylie-Blackwell, in press,
March, 2008.
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Swayne, D.E. Understanding the ecology and
epidemiology of avian influenza viruses
implications for zoonotic potential. In Emerging
Infectious Diseases of Animals. pp. 101-130, ASM
Press, 2000.
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Generation of Pandemic Influenza Strain
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Influenza A(H1N1) - update

• 4 May 2009 -- As of 0600 GMT, 4 May 2009, 20
  countries have officially reported 985 cases of
  influenza A (H1N1) infection.
• Mexico has reported 590 laboratory confirmed
  human cases of infection, including 25 deaths.
  The higher number of cases from Mexico reflects
  ongoing testing of previously collected
  specimens. The United States has reported 226
  laboratory confirmed human cases, including one
  death.
• The following countries have reported laboratory
  confirmed cases with no deaths - Austria (1),
  Canada (85), China, Hong Kong Special
  Administrative Region (1), Costa Rica (1),
  Colombia (1), Denmark (1), El Salvador (2),
  France (2), Germany (8), Ireland (1), Israel (3),
  Italy (1), Netherlands (1), New Zealand (4),
  Republic of Korea (1), Spain (40), Switzerland
  (1) and the United Kingdom (15).

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Influenza A(H1N1) - update

• There is no risk of infection from this virus
  from consumption of well-cooked pork and pork
  products.
• It is considered prudent for people who are ill
  to delay international travel and for people
  developing symptoms following international
  travel to seek medical attention, in line with
  guidance from national authorities. Individuals
  are advised to wash hands thoroughly with soap
  and water on a regular basis and should seek
  medical attention if they develop any symptoms of
  influenza-like illness.
• WHO advises no restriction of regular travel or
  closure of borders.

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The A/H1N1 situation needs to be carefully
monitored.

• Influenza viruses, whether in humans or among
  animals, are constantly evolving genetically,
  along with changes in their ability to cause
  morbidity and mortality in humans or animals.
  Therefore the current A/H1N1 situation should be
  carefully monitored as many of the virus
  characteristics and developments are still
  unknown, Domenech said.

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• Surveillance for porcine respiratory disease
  should be intensified and all cases of porcine
  respiratory syndrome are recommended to be
  immediately reported to veterinary authorities.
  It is also recommended to inform OIE and FAO
  about any occurrence of outbreaks of the new
  A/H1N1 Influenza virus in pigs.
• Strict biosecurity measures including restriction
  of movements of pigs, goods and people should be
  applied on all farms or holdings with swine
  showing signs of clinical respiratory illness
  until diagnosis of the illness has been made.

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• Where A/H1N1 influenza is confirmed, movement
  restrictions should be in force for seven days
  after the last animal has recovered. Governments
  are requested to provide full support in
  improving biosecurity measures particularly to
  small and medium pig farmers.
• Persons who work directly with swine should be
  urged not to go to work if they have any signs of
  respiratory disease, fever or any influenza-like
  illness. Animal handlers and veterinarians should
  wear protective clothing to minimize the risk of
  being infected.
• FAO stressed that there is absolutely no need to
  slaughter animals in view of preventing
  circulation of the A/H1N1 virus.
• The agency emphasized that the A/H1N1 virus
  cannot be transmitted to humans by pork and pork
  products. Pork and pork products, handled in
  accordance with good hygienic practices
  recommended by the FAO/WHO Codex Alimentarius
  Commission and the OIE, will not be a source of
  infection.

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Thank You

• Avian Flu in Arabic Language
• Prof. Abo-Shehada
• Dr. Al-Natour
• 2nd Edition, 2007

M. N. Abo-Shehada M. Q. Al-Natour 2007