Transcript Avian Influenza

Avian Influenza
Saad Gharaibeh DVM, PhD, Dip ACPV
Dept. of Pathology and Animal Health
Faculty of Veterinary Medicine
Jordan University of Science and Technology
Irbid 22110, Jordan
[email protected]
02/720-1000 ext 22059
Avian Influenza
History
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1878 Fowl plaque was described (Italy)
1901 Fowl plaque is caused by a virus
1955 It is type A influenza virus
1970 AGP test introduced
1972 Waterfowl is a reservoir
1979 Virulence and hemagglutinin
cleavability was established
1997 Direct transmission of H5 AIV from
birds to humans
Avian Influenza Virus
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Orthomyxoviridae
Pleomorphic RNA viruses, single stranded,
negative sense genome.
Has glycoprotein projections HA, NA
Three antigenic types A, B, C (Avian
influenzas are all type A)
8 gene segments code for 10 proteins
Vary in pathogenicity
NI test
HI test
AGP test
ELISA test
Jong et al., 2000, Journal of Infection
HI test
ELISA test
NI test
AGP test
Nomenclature
A/chicken/Hong Kong/220/97 (H5N1)
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A: Type of virus A, B, C
Chicken: Host of origin
Hong Kong: Geographic origin
220: Strain Number (Case number)
97: Year of isolation
(H5N1): H & N subtype
Infectious Virus
1. Needs HA0 cleaved into HA1 & HA2
2. Intracytoplasmic:
a) Furin-like enzyme (ubiquitous proteases): HP
b) Trypsine-like enzyme: All AIV
Cell Types for Replication
1. All AIV (trypsine-like enzymes):
a) Respiratory epithelium
b) GI epithelium
2. HP AIV (Furin-like enzymes):
Variety of cells resulting in a systemic
infection.
Approaches Used to Characterize
AIV Pathogenicity
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In vivo methods:
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In vitro methods (evaluation of HA cleavability):
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Laboratory Inoculation of chickens
Chicken embryo lethality
Plaques or CPE assays (CEF does not have trypsin)
Direct detection of cleaved HA
Nucleotide sequence of HA cleavage site
Direct measure of pathogenicity potential:
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b)
Identify pathogenicity increases during virus passage in
chickens under controlled conditions
Virulence in mice and ability to infect other mammals
Criteria for HP
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AIV lethal for 6,7, or 8 / 8 four-to-six-weekold susceptible chickens within 10 days
following IV inoculation with 0.2 ml of 1:10
dilution of a bacteria free, infectious
allantoic fluid.
H5 or H7 has amino acid sequence at the
hemagglutinin cleavage site compatible
with HPAIV
Non-H5 or H7 that kills 1-5 chickens and
grows in cell culture w/o added trypsin
Signalment & Clinical Signs
(Low pathogenic AI disease)
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Respiratory signs
Diarrhea
Drop in egg production 7-10 days 5-30%
Mild increase in Mortality (2o bacterial
infection will increase mortality)
Gross Lesions
(Low pathogenic AI disease)
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Catarrhal rhinitis / tracheitis
Ocular discharge
Airsaculitis
Ovarian involution and hemorrhage
Yolk peritonitis
Swollen kidney and urates
Signalment & Clinical Signs
(Highly pathogenic AI disease)
a) Sudden onset of high mortality (up to 100%)
b) Depression
c) +/- nervous signs
Gross Lesions
(Highly pathogenic AI disease)
a) Edematous to necrotic comb and wattles
b) Edema, necrosis, and hemorrhages in
different organs
High Path Avian Influenza Diagnosis
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Clinical features in commercial poultry give
a tentative diagnostic
Sudden death and high mortality rate
RT-PCR and sequencing
Virus isolation and identification is the gold
standard but very few laboratories in the
world can handle such a virus capable of
infecting humans.
Commercial antigen capture ELISA (lack
sensitivity and will cross react with other
endemic subtypes)
Serology: AGP, ELISA, HI, NI
RT-PCR
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Testing can be performed in one day for
multiple agents.
Sensitivity is very high and comparable to
virus isolation.
Can be applied on samples from any
species.
Decrease the chance of contamination with
live virus.
RT-PCR Diagnostics in JUST
Safety Considerations
RT-PCR Diagnostics in JUST
Chicken Respiratory Disease viruses
MWM
AI
IB
ND
APV
Serologic Testing and Surveillance
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AGPT: Type specific (available at JUST)
ELISA: Type specific (available at JUST)
HI: Subtype specific (available at JUST)
NI: Subtype specific
Antigen capture ELISA (available at JUST)
RT-PCR: Surveillance and diagnosis
(available at JUST)
Agar Gel Precipitation
ELISA Readings
Negative Flock
Positive Flock
Hemagglutination Inhibition
Control & Prevention
1. Biosecurity
2. Stamping out infected flocks
3. Vaccination of flocks at high risk :
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Killed vaccines
Viral vector vaccines
Live attenuated vaccines are not licensed for
poultry
Drastic measures in some Asian countries
www.animalactivism.org/ documents
AI crossed Species Barrier into Humans
A/chicken/Hong Kong/220/97 (H5N1)
What conditions favor AI spread?
Densely populated countries
Very popular Live-bird
markets
Free Range Poultry
Is H5N1 AI bad for economies?
Disease
‘mad cow’
Cholera
Plague
H5N1 flu
Country
UK
Peru
India
Hong Kong
Year
1990-98
1991
1995
1997
Impact
Beef export
Seafood export
Tourism, trade
Loss of poultry
Cost ($US)
9 billion
770 million
2 billion
22 million
Cholera
Nipah
Tanzania
Malaysia
1998
1999
Seafood export
Loss of swine
36 million
540 million
West Nile
SARS
H5N1 flu
US
Worldwide
SE Asia
1999
2003
Tourism, trade
2003-05 Loss of poultry
(1.5 million birds)
(0.9 million pigs)
(~140 million birds so far)
400 million
80 billion
~10 billion?
(and growing)
Sources: WHO, Institute of Medicine, FAO, OIE, Asian Development Bank, World Bank
High Risk Areas in Jordan
Should we start vaccinating poultry
against H5N1?
Killed Vaccines
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Will result in only humoral antibody
response against all viral proteins
except NS1.
Will significantly reduce shedding of the
challenge virus.
Will interfere with AGP, ELISA, HI, and
NI if (homologous).
If sequence of the HA gene is identical
to the challenge virus it may eliminate
shedding completely.
Swayne et al., 2000, Veterinary Microbiology
Advantages of Vaccines
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Reduces the number of chickens from which AI
challenge virus could be reisolated.
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Decreased the titers of virus detected in the cloaca
and oropharynx (up to 99.99%)
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Reduced environmental contamination and prevented
subsequent bird to bird transmission.
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The use of killed H5N2 vaccine in the face of HPAI
H5N1 virus challenge was able to protect chickens
from disease and interrupt virus transmission.
DIVA
Differentiating Infected from Vaccinated Individuals
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The use of killed vaccine and unvaccinated sentinels:
leaving 0.5-1% of the flock unvaccinated and marked
(wing band) and these individuals will be subjected to
serological monitoring.
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Heterogonous killed vaccine: Screen for field infection
using NI.
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Measuring serological response to NS1 by ELISA or
western blot.
Vaccine / Industry / Politics
1. The use of vaccine to aid in the control of AI is
a political issue and different people have a
different say on this.
2. In some countries financial constrains
preclude stamping out policy.
3. In some countries, export markets are not an
issue to prevent vaccination.
4. In some countries, stamping out attempt may
be unsuccessful.
5. “With the ubiquitous nature of AI in wild birds
it may be vaccination the most feasible tool to
soften the sting of AI” Beard 1981
Vaccine / Industry / Politics
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“Field results have not shown vaccine to increase the
risk of undetected infection; in fact, field experience
has shown that vaccination greatly enhances a
control program.” Halvorson, 2002, Avian Pathology
There is no way a vaccinated flock can be a greater
threat to disease control than a non-vaccinated flock
that breaks with AI. Halvorson, 2002, Avian Pathology
Epidemiological observations have shown that
serologically positive birds are not associated with AI
transmission. (Kradel, 1992)
Should the government set the rules when no
indemnity (compensation) is paid?