Hong Kong Avian
Influenza Update
The following article was writ
ten largely from an article prepared
by Dr. Charles W. Beard with the
U.S. Poultry & Egg Association
in ml
tion in Hi
The death of a child in Hong
Kong in May 1997 from an avian
influenza virus (HSNI) was the
beginning of what has become a
series of highly publicized an
nouncements and events. Since
that first death, there have been 16
confirmed cases and five suspected
cases of this HSNI avian influ
enza infection in people with at
least four deaths.
At the same time, chickens in
Hong Kong were experiencing
high death losses to a highly
pathogenic avian influenza
(HSNI).
Concern of public health
experts
Public health experts are con
cerned that this H 5 influenza virus
may be the cause of the next
worldwide epidemic (pandemic) of
human influenza. The two previ
ous introductions of new “H” se
rotypes into humans occurred in
that part of the world. The “Asian
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flu” was caused by an H 2 virus
and began in 1957. In 1968, an
H 3 virus began the “Hong Kong
flu’.’ epidemic and variations of
that H 3 virus have been the major
cause of human influenza since
that time. When a different “H”
subtype emerges as the cause of
human influenza, severe disease
and death losses can occur because
no one has residual immunity to
the new “H” (H 5 in this case)
from vaccination or past infec
tions. Additionally, the high death
rate of HSNI has forced concern
over the potential impact of a
pandemic caused by this virus.
Reports have indicated that at
least some of the infected humans
had been in contact with sick
poultry afflicted with avian influ
enza. Both the human and chicken
HSNI viruses have been shown to
cause severe illness and near 100%
mortality in experimentally ex
posed chickens (work done at the
USDA Southeast Poultry Re
search Laboratory in Athens,
Georgia).
Korn
ARMPPA
If the Hong Kong HSNI initi
ates a worldwide pandemic in hu
mans, there is the real possibility
that infected and virus-shedding
poultry caretakers will infect their
poultry flocks. At least one hu
man isolate has experimentally
been shown to be highly lethal for
chickens. Based on the experiences
in Hong Kong with chickens and
laboratory results, the virus would
likely have a more devastating ef
fect on commercial poultry flocks.
Biosecurity measures would be of
very little benefit because infected
caretakers would be a probably
mechanism of HSNI virus intro
duction into the flocks. Biosecu
rity could, however, reduce the
secondary spread from the flocks
initially infected.
If the worse case scenario hap
pens and a human pandemic re
sults, the poultry of the world
(turkeys, layers and broilers) will
be in grave danger. This includes
the genetic stock and breeders. If
the poultry industry were to lose
the majority of its genetic pool it
would have a lasting effect with
probable negative effects on the
world’s food supply.
For the reasons cited above,
since biosecurity cannot be totally
relied upon to protect these valu
able flocks, the only recourse will
be vaccines. If the flocks have
been immunized against fowlpox,
the fowlpox vector vaccines will
likely be of no value. That leaves
inactivated vaccine prepared either
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from vims-laden embryonating
egg fluids or from the recombi
nant baculovirus-insect cell cul
ture system.
It will take many months to
produce and administer the vaccine
needed to protect the genetic
stocks (foundation stock, great
grandparents, grandparents). After
this group is protected, the multi
plier parent flocks for the three
types of poultry should be next,
followed by table egg layers, tur
keys, and lastly broilers. The
fowlpox vectored vaccine can be
utilized for birds not previously
immunized for fowlpox once the
vaccine is demonstrated in the
laboratory to result in adequate
protection against the Hong Kong
HSNI. page 4 of 6
Drug treatment of ponl-
enza
Experiments conducted at the
Southeast Poultry Lab (Beard, et
al.) clearly demonstrated that the
highly pathogenic HSN2 virus
used to experimentally infect
chickens quickly became resistant
to the anti-influenza drug amantad
ine. For that reason, it does not
appear to have any potential for
use in commercial poultry. That
experiment is being repeated with
the HSNI virus at the Southeast
Poultry Research Laboratory to
confirm the earlier finding.
Embryonating eggs for
If the decision is made to pro
vide H 5 vaccine for the world’s
human population, it will utilize
a very large number of fertile eggs
at the 9th or 10th day of incuba
tion. The use of embryonating
eggs to produce the vaccine is the
most likely method in that the
newer methods such as the bacu
lovirus-insect cell culture proba
bly can’t meet the huge demand
for vaccine.
The only source of fertile eggs
beyond the supplies currently util
ized for vaccine production will be
eggs from broiler and layer parent
flocks. I don’t believe that specific
pathogen free (SPF) eggs are re
quired to produce vaccine for hu
mans as they currently are for
poultry vaccines.
The dramatic increase in de
mand for fertile eggs for vaccine
production adds to the significance
of protecting breeder flocks with
vaccines.
Reports indicate that poultry
consumption has declined signifi
cantly in Hong Kong. Consumers
more page 5 of 6_are apparently
afraid of becoming ill with influ
enza from consuming chickens.
Since the live bird market is a ma
jor means of poultry distribution
in Hong Kong, it may be that
some consumers also want to
avoid contact with live poultry.
There is no indication that the
highly pathogenic Hong Kong
HSNI exists in the United States.
Because of the severe disease and
virtual 100% mortality it causes,
it is very doubtful that it could ex
ist in poultry flocks without be-
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ing readily detected by ordinary
observation.
The Hong Kong authorities re
portedly stated that the 1.2 mil
lion poultry in Hong Kong were
destroyed because they believed
they were the source of the human
influenza cases.
Because of the severe signs of
disease and dramatic mortality in
infected poultry, it is difficult to
imagine that a flock infected with
HSNI would be caught and trans
ported for processing in the U. S.
The ante and post mortem inspec
tion of birds at the plant makes
the entry of an infected flock into
the food chain very unlikely. As a
final safeguard, ordinary cooking
readily kills influenza virus. In the
first analysis, it appears highly
unlikely that the consumption of
chicken will have anything to do
with the infection of humans in
the U. S.
There was public outcry over
the killing of poultry in Hong
Kong. Without depopulating a
live bird market, it is impossible
to clean and disinfect it. Authori
ties wanted to remove the live bird
market as a probable source of
HSNI influenza for humans. The
first step in any such program is
to destroy and dispose of the birds
that may be infected with or ex
posed to the virus. Had such steps
not been taken, it is likely that
the birds would have eventually
died of the disease.
Hopefully, they will be able to
remove all virus from the live bird
markets and assure that only
HSNI-negative flocks contribute
birds when the market reopens.
Reports indicate that the Chinese
are screening their flocks so that
they may assure their negative
HSNI status.
Avian Influenza in Penn-
The 1997 virus that initiated
the General Quarantine of poultry
in Lancaster County Pennsylvania
was the H7N2 serotype. While
the quarantine was lifted in No
vember of 1997 recent isolates of
low pathogenic H7N2 in chickens
and waterfowl (December 1997)
will warrant further monitoring.
The initial response to these
recent events is to suspect there is
overreaction. However, the hor
rendous consequences of an H 5
pandemic in people with a virus
that has behaved like the HSNI in
Hong Kong justifies overreaction
rather than underreaction. Many of
the concerns and suggestions con
tained in this document have been
communicated to Dr. Aronoldi,
administrator of veterinary serv
ices, APHIS, USDA. She has
scheduled a meeting for the week
of January 5, 1998, to begin dis
cussions.
Hopefully, the HSNI issue
will pass and no significant prob
lems will develop. It the worst
case-scenario becomes a reality,
thoughtful preparation and deci
sive action will be our only hope.
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imments