Avian Influenza

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Avian Influenza

• An Overview

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The History of Avian Influenza

• First described as fowl plague in 1878
• Virus first isolated as cause in 1955

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The Virus

• Single stranded RNA virus
• Belongs to family Orthomyxoviridae
• Family divided into 2 groups
• Influenza A B viruses
• Influenza C viruses
• Avian Influenza is an Influenza type A virus

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The Virus (cont)

• Type A viruses are further divided based on the
  antigenic nature of their surface glycoproteins.
• Haemaglutinin (H) determines virulence
• Neuriminidase (N) responsible for the transport
  of the virus into and out of cells
• 15 different Haemaglutinins identified
• 9 different Neuriminidase identified

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Avian Influenza Overview (cont.)

• AI viruses mutate easily only H5 and H7 viruses
  have the potential to mutate from an LPAI to an
  HPAI form.
• AI viruses vary widely in pathogenicity from
  strain to strain. Therefore not all H5N1 viruses
  are infectious for people or pathogenic to
  poultry.

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The Virus (cont)

• Each subtype is a combination of one particular H
  and one particular N glycoprotein.(e.g. H5N1,H3N2
  etc)
• Each subtype can have various variants.

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The Virus (cont)

• Clinically - two main categories
• Low Pathogenic Avian Influenza (LPAI) e.g. H6N2
• Highly Pathogenic Avian Influenza (HPAI) e.g.H5N1

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The Virus (cont)

• Antigenic Drift gradual changes in an already
  circulating virus
• Influenza viruses constantly undergoing antigenic
  drift
• Eventually virus changes so much that population
  again susceptible to infection.

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The Virus (cont)

• Antigenic shift the sudden emergence of a new,
  different, influenza A subtype.
• Population has no immunity against new subtype
  pandemic possible.
• Occurs only occasionally
• Only Influenza type A viruses change by antigenic
  shift.
• A public health concern as subtypes from
  different species may be able to infect humans.

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Epidemiology of Influenza A viruses

• Natural hosts are migratory water birds,
  especially wild ducks (Not geese!)
• They may not show clinical disease
• Virus spread through the faeces.
• Can introduce the virus to poultry by direct
  contact or feacal contamination of food, drinking
  water, soil etc
• Indirectly via other wild birds

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Epidemiology (cont)

• Within poultry the disease is spread by
• Direct contact
• Contaminated equipment, clothing etc
• Air transmission (short distances)
• Mechanical vectors (rodents)
• etc

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Clinical Signs

• In HPAI, mortality can be up to 100
• Sudden Death
• Depression
• Swollen combs and wattles
• Coughing, sneezing
• Diarrhoea
• Decreased appetite
• Drop in egg production

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Clinical signs (cont)

• Low Pathogenic Avian Influenza
• Mild Respiratory Disease
• Depression
• Decreased egg production

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LP Avian InfluenzaClinical Signs Lesions

• Huddling
• Depression
• Closed eyes
• Sinusitis
• Respiratory signs

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LP Avian InfluenzaClinical Signs Lesions

• Drop in egg production (layers, breeders) first
  sign
• Rough, misshapen eggs
• Hemorrhage in ovary

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LP Avian InfluenzaClinical Signs Lesions

• Yolk peritonitis
• Oviduct edema
• Urates in kidney

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Diagnosis

• Clinical Signs
• Post mortem findings
• Laboratory Diagnosis

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Public Health Considerations

• Avian Influenza viruses normally only infect
  birds and pigs.
• H5N1 and H7N7 subtypes have been recorded in
  humans.
• 180 human deaths have been attributed to H5N1
  infections over the last few years.
• Genetic re-assortment could result in a human
  influenza pandemic

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Public Health Considerations

• There have been 3 human Influenza pandemics in
  the 20th century
• 1918 (H1N1) Spanish flu killed 20-50 million
  people
• 1957 (H2N2) Asian Flu
• 1968 (H3N2) Hong Kong flu

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What has been done

• National Survey ongoing
• Random samples of both commercial and communal
  poultry on monthly basis
• Raising Awareness
• Pamphlets produced and distributed
• Information posters produced
• Training days for rapid response team

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What has been done(2)

• Rapid Response Team
• Voluntary team of Animal Health technicians
• Extra training in disease control
• Essential equipment has been purchased
• Team of 30 trained and equipped technicians can
  be on infected farm within 12 hours
• Practical exercise has been carried out with
  excellent results

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What has been done(3)

• Rapid response Equipment includes
• Fully equipped roadblock trailers
• Protective clothing
• Disinfectants/ Knapsack Sprayers
• Camping equipment
• Lights/generators etc
• Mobile disinfection/shower units
• Other tools and necessary support equipment

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Mapping and Modelling

• All Surveillance data is being mapped on a
  National basis
• KZN Dept Health has prepared a risk map after
  consultation with all role players