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Avian Flu
Reproduced
from Reader's Digest Indian edition (October 2005).
(C)Reader's
Digest Association, Inc., Pleasantville,
N.Y., USA.
How Scared Should
You Be?
By Claudia Cornwall
The prospect of a global avian-flu outbreak has created
anxiety among international public health officials. Such pandemics have
occurred in the past, to deadly effect. This time, the fear swirls around a
strain of bird flu—H5N1—that has existed for more than eight years in Asia
and has proven to be incredibly lethal to the few humans who have contracted
it.
How worried should
you be?
Here —in question and answer format—is the latest
information to help you separate fact from fiction.
What is influenza?
It’s a highly contagious respiratory infection that people
give to others by airborne transmission—sneezing or coughing. Flu viruses are
classified as A, B or C. The A viruses, which infect ducks, chickens, pigs
and whales, as well as humans, are the most dangerous. They are divided into
groups based on two proteins—haemagglutinin (HA)
and neuraminidase (NA), which spike out from their surfaces. Scientists have
identified 16 subtypes of HA and nine of NA. This means there are 144
possible combinations of A virus flus.
Flu rolls around every winter, changing gradually through
mutation from one year to the next. Some years the strain is more troublesome
than others, so the number of people affected varies—between five and 15 per
cent of the population. Some people die of the flu, mainly the elderly and
the chronically ill; fatalities range from 250,000 to 500,000 worldwide,
depending on the severity of the strain. But for healthy people, the seasonal
flu is not life-threatening. It is only a slightly different version of what
we’ve had before, so we have some immunity to it.
However, every now and then, a brand new A virus emerges.
This is called an antigenic shift. When that happens, no-one has immunity to
the virus, and it is devastating. An epidemic is a disease outbreak that
affects a lot of people. A pandemic is an epidemic that goes global. There
were three flu pandemics in the 20th century: 1918, 1957 and 1968.
The 1918 pandemic was by far the worst, killing up to 50 million
people worldwide.
What’s happening
with avian flu?
The strain of flu that has health experts worried emerged
as a bird flu that killed thousands of chickens and six people in Hong Kong
in 1997. In response, Hong Kong destroyed all of its chickens—1.5 million of
them. That stopped the outbreak, but the strain— called H5N1—continued.
In February 2003 a man died of avian flu in Hong Kong.
Almost a year later, in January 2004, South Korea, Vietnam, Japan and
Thailand reported large poultry outbreaks. By the end of the month, 28 people
had caught the flu. By early February, 21 had died. Then more countries were
affected: Cambodia, China, Indonesia, and Laos. By March, 120 million birds
had either died or been destroyed. But this massive control effort didn’t
succeed.
In July 2004
another wave of H5N1 hit poultry farms in most of the previously affected
countries as well as in Malaysia. This outbreak, too, was deadly. In villages
in Thailand and Vietnam, eight of nine people infected died. Up to this latest
outbreak, all the human deaths had resulted from bird-to-human transmission.
Peter Cordingley, the Manila-based spokesman for
the World Health Organization (WHO), says, “We have very little information
so far on how people infected actually got the virus—except we know it is
normally transmitted through chicken or duck faeces.
We assume they touched the faeces, then put their
hand to their mouth or nose and inhaled it.”
However, in September 2004, the mother of an 11-year-old
victim in Thailand died of H5NI after catching it from her daughter. “I was
very concerned this might be the beginning of person-to-person transmission,”
says Dr Scott Dowell, former director of the Office of the International
Emerging Infections Programme in Thailand. If the virus mutated to become
easily transmitted through a cough or sneeze, as with other flus, it would spread like wildfire.But
no-one else became ill. “The virus wasn’t capable of efficient transmission,”
says Dowell. So, although highly contagious in birds, H5N1 does not seem to
be highly contagious between birds and humans or from human to human.
So, why the
concern?
Dr Anthony Fauci, director of
the US National Institute of Allergy and Infectious Diseases, explains one
way a new hybrid virus is formed: “Let’s take the scenario that I am infected
with the H3N2 flu, which has been circulating for the last three years. I get
the standard flu; I’m not very sick, just feeling a little poorly. Then I get
simultaneously infected with the H5N1 virus. There could be an exchange of
genes and a resulting hybrid that maintains the virulence of the avian virus
but assumes the transmissibility efficiency of the human virus.”
Widespread viruses in the environment raise the chances of
mutation. “Since 1955 there have been two dozen outbreaks of highly
pathogenic influenza in birds,” says Dr Klaus Stöhr,
coordinator of the Global Influenza Programme at the WHO, in Geneva. “But
we’ve never had one like this, that covered nine
countries with more than 150 million birds dead or culled.” According to Stöhr, H5N1 is becoming more lethal for mammals and is
also infecting ducks. They don’t become ill, but they can pass on the disease
without anyone realizing they’re infected.
On April 30, 2005, an outbreak was detected in migratory
birds at Qinghai Lake in western China. The virus was recorded on a single
islet, but was quick to spread. By May 4, bird mortality was more than 100 a
day; by May 20, the outbreak had spread to other islets, with some 1500 birds
dead. The discovery alarmed scientists for a
couple of reasons. H5N1 is now
not only infecting domestic chickens and ducks, but also several species of
wild fowl. And the birds that spend the summer at Qinghai Lake head to India
and Myanmar for the winter, raising the prospect that they could bring H5N1
to this very densely populated part of the world.
How fast could it
spread if it became easily transmissible?
If H5N1 became transmissible by cough or sneeze, it could
spread rapidly. Dr Danuta Skowronski,
a Canadian physician epidemiologist, says, “Over a billion passengers are travelling by air every year. We saw with SARS how
quickly a virus can be transmitted—within hours—from one part of the globe to
another.”
In the past, both epidemics and pandemics have erupted
unexpectedly. This is unlikely to happen again. In 1952 the WHO established a worldwide
influenza surveillance network. Every year four WHO laboratories work with a
network of 115 national influenza centres in 83
countries, including India, to collect and analyse
between 250,000 and 300,000 samples from flu patients. The same network is
available to deal with H5N1.
What can be done to
stop the spread of avian flu?
“The culling of affected flocks is the most effective way
to extinguish the virus,” says Dr Samuel Jutzi,
director of the animal production and health division of the UN’s Food and
Agriculture Organization (FAO) in Rome. In mid-2004 Thailand deployed a
million volunteers to scour the countryside looking for outbreaks. It killed
3.5 million chickens to stamp out the virus; Thailand has not reported any
human deaths from avian flu since October 2004.
But other countries without the same resources or
commitment have not been able to eradicate the disease. Poultry outbreaks in
Indonesia and Vietnam continue. In Vietnam another man was reported to have
died from the virus in May 2005, bringing the total number of people killed
by avian flu in that country to 38.
Can we make a
vaccine for pandemic flu?
Yes, but not as quickly as we’d like to because it is a
complex procedure involving fertilized hen’s eggs, incu-bation,
virus culture and testing. The global influenza vaccine manufacturing
capacity is currently about 300 million doses per year—enough for about one
in 20 people.
Current doses of vaccine are really three separate
vaccines in one—covering the three flu viruses most likely to cause illness.
In the event of a pandemic, it is expected all of this capa-city
will be dedicated to producing a pandemic vaccine, providing a significant
boost. Research is under way to create a way of growing vaccines in cell
cultures. If this works,
manufacturers can freeze cells in advance, then thaw and grow
them in large volumes if there is a pandemic.
Is it worth making
a vaccine in advance of an outbreak?
It’s a gamble because the virus may be different. But if
it paid off, a nation could have a head start on inoculating some of its
citizens.
The United States is working on a vaccine for H5N1. It’s
currently in clinical trials. Two million doses exist in bulk form and will
be formulated once trials determine the appropriate dose. Ten clinical trials
of avian-flu vaccine are scheduled to begin this year in Australia, Canada,
France, Germany and Japan.
Can we make better
use of the vaccine we do have?
Yes, we can. Two 2004 studies, one in the United States
and one in Belgium, found that vaccines introduced directly between two
layers of the skin, instead of into the muscle, use less antigen (the
substance that stimulates the production of an antibody). This means supplies
would go five times as far.
Do we have any
other lines of defence?
Antiviral drugs are another weapon in our arsenal against
the flu. The WHO has recommended countries stockpile one in particular, oseltamivir (commercial name Tamiflu),
which works by preventing viruses from spreading from one cell to the next.
Unlike a vaccine, “oseltamivir is a broad spectrum
drug,” says Dr Frederick Hayden, an American clinical virologist. Flus can have nine different NA proteins. “Oseltamivir has been shown to be effective against all of
them. It reduces the duration of illness and the risk of complications and
hospitalization,” Hayden says.
“Unfortunately, Tamiflu is
relatively expensive and in short supply,” says Dr Bruce Gellin,
director of the US National Vaccine Programme Office. With 14.6 million
courses, the United Kingdom has enough for nearly 25 per cent of its
population; the United States has 2.3 million courses, enough for less than
one per cent. However, since 2003, Roche, a Swiss company and the world’s
only manufacturer of the drug, has increased production eightfold in the past
two years. As well, Roche is bringing manufacturing to the United States so
there will be another centre of production.
What else can be
done toprevent a pandemic?
Says FAO’s Dr Jutzi, “We can get on top of H5N1 by reducing the amount
of virus circulating within the domestic poultry population.” FAO especially
wants to help poorer countries such as Cambodia, Indonesia, Vietnam and Laos.
So, how worried
should I be?
Concerned but not panicked. H5N1, like all influenza, is a
respiratory virus and is transmitted by air. As of the end of July 2005, it had not become
highly contagious to humans—with 109 cases and 55 deaths reported. Only one
death —the mother in Thailand—is known to have been caused by human-to-human
transmission. If H5N1 doesn’t mutate and become more contagious, it will
remain a health problem to the people of Southeast Asia. If it does mutate,
it’s hard to know what changes it could make – perhaps becoming more virulent
or less virulent. In either case, the spread of a pandemic can be combated
with tools and technologies that did not exist before.
“Our very robust surveillance system, our new virology and
our mass communications systems allow us to see things that are going on both
in birds and in people that were not detectable in the past,” says Gellin. “It can give us an early warning that a new virus
has shown up and is doing things that are worrisome.”
How ready is India?
Infected migratory geese from China began arriving in
India last month, and may have started infecting the local bird population.
The government has banned import of poultry and poultry-related products from
all countries affected by avian flu. The states have been asked to monitor fatalities
among birds, especially poultry, as well as severe respiratory illness in
people who are exposed to birds. A plan to strengthen early warning systems
and laboratory expertise has also been prepared in conjunction with the WHO.
“There are limited stocks of the antiviral Tamiflu
maintained by the WHO in New Delhi, and we can bring in more if needed,” says
Dr Jai P. Narain, director of Communicable Diseases
at the WHO’s Office for South East Asia.
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