AVIAN INFLUENZA
Prof. Dr. SALAH M. HASSAN College Vet. Medicine Mosul UniversityCLASSIFICATION Family: Orthomyxoviridae
Influenzavirus Ahumans
horses
pigs
birds
marine mammals
Influenzavirus B
humans
Influenzavirus C
humans
swine
Avian influenza (AI)
asymptomatic infection to respiratory disease and drops in egg production to severe, systemic disease with near 100% mortalityEtiology
Orthomyxoviridae, genus Influenzavirus A single-stranded RNA surface is covered by two types glycoprotein projections (HA), (NA).
Type A Influenza
OrthomyxovirusNegative sense
RNA Single stranded Segmented Enveloped 16 H 9 N
Influenza Subtypes
16 Hemagglutinin subtypes 9 Neuraminidase subtypes 144 possible antigenic subtypesOnly viruses of H5 and H7 subtypes have been shown to cause HPAI in susceptible species
Avian InfluenzaHPAI emerges from LPAI
Avian InfluenzaNot all H5 and H7 viruses are HPAI
Avian InfluenzaSusceptibility to Chemical and Physical Agents
Unstable in the environment. Physical factors such as heat extremes of pH drynessReassortment (antigenic shift)
AI VirionRNA Segments
Major Antigen
‘Classical’ Model for Cross Species Spread of Flu Reassortment in swine
Virus with new host specificity?
?
?
In Waterfowl, Influenza Viruses Replicate preferentially in the Intestinal tract. Virus transmission Among aquatic birds is via Contaminated water-oral Route.
Transmission and Carriers
All 16 HA and 9 NA Subtypes Of Influenza A Virus are Maintained in aquatic Bird populations (Ducks, Shorebirds and gulls)Major Outbreaks of Avian Influenza in Domestic Poultry
Comments
Impact
Location
Subtype
Year
A serologically identical but apparently mild virus had been circulating in poultry in the area for 6 mo (see References: Beard 1998). No human cases were identified.
Caused severe clinical disease and high mortality rates in chickens, turkeys, and guinea fowl. 17 million birds were culled.
Pennsylvania
H5
1983
An LPAI virus mutated to an HPAI virus and caused an outbreak in 1994-1995. The H5N2 strain has continued to circulate in Mexico since that time. No human cases have been identified.
Nearly a billion birds have been affected.
Mexico
H5N2
1994-2003
A vaccination campaign apparently ended the outbreak. No human cases were identified.
About 3.2 million birds died from avian influenza during initial outbreak in 1995.
Pakistan
H7N3
1995-2003
18 human cases with 6 deaths were recognized. Prior to this outbreak, H5N1 was not known to infect humans.
Virus was isolated from chickens; avian mortality rates were high. 1.5 million birds were culled in 3 days.
Hong Kong
H5N1
1997
Over 80 human cases were reported, and one veterinarian died (see References: Fouchier 2004, Stegeman 2004). Most of the human cases involved conjunctivitis.
30 million birds out of 100 million birds in country were killed; 255 flocks were infected. Disease spread to Belgium but was quite rapidly contained.
The Netherlands
H7N7
2003
More than 410 human cases have been recognized, with more than half of them fatal, in Azerbaijan, Bangladesh, Cambodia, China, Djibouti, Egypt, Indonesia, Iraq, Lao People's Democratic Republic, Myanmar, Nigeria, Pakistan, Thailand, Turkey, and Vietnam.
Panzootic avian influenza, with outbreaks occurring in many countries around the globe. By August 2006, an estimated 220 million birds had died or been culled (see References: FAO 2006: Caucasus, Balkans at high risk for deadly H5N1 virus).
Asia, Europe, Africa
H5N1
2003-2009 (ongoing)
Two human cases were recognized; both patients had conjunctivitis.
Over 19 million birds were culled.
British Columbia
H7N3
2004
No human cases were identified.
About 200,000 birds were culled.
North Korea
H7
2005
aAdditional outbreaks of HPAI have been identified in a variety of countries. Adapted from Capua 2004 (see References).
Countries Affected by H5N1 in Poultry and Wild Birds as of March 2009
Africa
Siberia, Central Asia, Middle East
Europe
East Asia, Southeast Asia
Benin Burkina Faso Cameroon Djibouti Egypt Ghana Ivory Coast Niger Nigeria Sudan Togo
Afghanistan Azerbaijan Bangladesh Cyprus Georgia India Iran Iraq Israel Jordan Kazakhstan Kuwait Nepal Pakistan Turkey Ukraine Russia (Siberia) Saudi Arabia West Bank and Gaza Strip
Albania Austria Bosnia-Herzegovina Bulgaria Croatia Czech Republic Denmark England France Germany Greece Hungary Italy Poland Romania Russia (European Russia) Scotland Serbia Slovakia Slovenia Spain Sweden Switzerland
Cambodia China Hong Kong Indonesia Japan Lao PDR Malaysia Myanmar Mongolia South Korea Thailand Vietnam
2005
20062007
20082009
How is the disease transmitted and spread?Several factors can contribute to the spread of AI viruses including globalization and international trade (legally and illegally), marketing practices (live bird markets), farming practices and the presence of the viruses in wild birds.
Mechanism for pathogenicity in poultry
Sequences in HP viruses can be cleaved in many tissue types resulting in systemic infection (arginin + lysine) cleavage by protease.HP
Mechanism for pathogenicity in poultry
Some sequences can only be cleaved by enzymes in the respiratory tract or intestinal tract arginin.( trypsin like enzymes)LP
LP
Incubation Period
3 up to 14 days dose of virus route of exposure species exposed ability to detect clinical signsMorbidity and Mortality
LP AI less than 5% unless HP AI 50—89% and can reach 100%
Properties of virulent and avirulent AI
PropertyAvirulent strains
Virulent strains
HA subtype
H1-H16
H5, H7
Replication
Respiratory and/or intestinal tracts
Most organs.
Disease
Inapparent or mild Respiratory signs)
systemic or "fowl plague" symptoms
Mortality
Low
High (up to 100%)
Plaque formation in cell culture without exogenous protease
No
Yes
HA cleavage by intracellular proteases
No
Yes
HA cleavage site sequence
Single
Multiple basic amino acids
Sinusitis
Sinusitis