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Avian flu 2005: first let
us get the facts straight: we are talking about three viruses,
one of which does not yet exist.
- H5N1 Avian flu, which affects birds, and has
infected about 167 poultry handlers so far, of whom more than
60% have died. You have to handle live poultry to catch it.
It is still safe to eat bids from unaffected areas.
- Seasonal Influenza, which will reach the UK/EU
around the end of January, and for which a vaccination exists
- A future H5N1 Influenza virus - the pandemic
virus - which will emerge:
EITHER from mutations in H5N1 avian to enable it to spread from
human to human, ("antigenic drift")
OR from viruses 1 and 2 combining (reassorting) in the bloodstream
of a poultry farmer or other bird worker who manages to contract
both Influenzand avian flu at the same time. ("antigenic
shift")
As H5N1 has such a high mortality rate (i.e. high
virulence) it is devoutly to be hoped that the emergent pandemic
virus will lose some of its virulence if it mutates.
Defending ourselves
The 1918 flu virus killed 20-40 million people
and left thousands crippled with Parkinson's disease. We need
to take this risk seriously, and to put up multi-layered defences.
These are the defences available:
- Prevent the pandemic virus emerging
- Limit or slow the spread of the pandemic virus
if/when it does emerge, using:
2.1 airline cross-infection
management
2.2 transmission
control techniques (isolation and handwashing)
2.3 vaccination
- Treatment
3.1 anti-viral chemotherapy (Tamiflu/Oseltamivir)
3.2 Inhibiting
the cytokine storm
Preventing the emergence of a pandemic virus
Limiting spread of H5N1 Avian
Wild bird migration may play a part in causing
fresh outbreaks, but poultry trading also plays a part. In fact
the outbreak in Suffolk in February 2007 may have been (this is
written during the unfolding outbreak) due to eggs brought in
from Hungary, since the strain of H5N1 is the same as that in
Hungary, and the Suffolk farm has links with that country. The
alternative explanation, that a small infected wild bird flew
into the turkey factory through a vent, is rather improbable.
In May 2006 Dr Kennedy Shortridge, a virologist at the University
of Hong Kong who has researched the H5N1 virus in China since
it first killed humans in 1997, warned against blaming the spread
of the deadly H5N1 virus on migratory birds. He told a conference
in Singapore, organized by the Lancet medical journal, that the
movement of poultry around the world could play a major role.
Dr Shortridge advised researchers not to rush to blame migratory
birds, but to look for the disease also along routes of human
transportation, including by rail, road, and water. Source
The question of poultry workers
The WHO global influenza preparedness plan
The role of WHO and recommendations for national measures before
and during pandemics (WHO/CDS/CSR/GIP/2005.5) states that
countries with cases should:
"... continue promoting vaccination with
seasonal influenza vaccine to limit risk of dual infection in
those most likely to be exposed to the animal virus, and potentially
decrease concurrent circulation of human strains in the outbreak
affected area."
http://whqlibdoc.who.int/hq/2005/WHO_CDS_CSR_GIP_2005.5.pdf
p27
This tactic was used in the successful defeat to the H7N7 outbreak
in 2003:
"People undertaking slaughter of infected chickens, pigs
and turkeys have been vaccinated against human influenza virus
and are also receiving antiviral drug treatment. The aim is not
only to protect them against infection by the bird influenza virus,
but also to avoid a new and more virulent virus being formed from
mixing (reassortment) of human and avian influenza viruses in
someone with co-infection of viruses."
http://www.pighealth.com/influenza3.htm
There is a limitation to this policy is in the
shortage of influenza vaccines. Production of Fluvirin was lost
for 3 months earlier this year. The annual production run is 300,000,000
doses. A full vaccination programme around trouble spots might
need that output to be doubled or trebled. However, as pointed
out above, time, although precious, is still on our side, and
if WHO approved vaccine manufacturers could franchise production
out to smaller companies, it is possible that demand could be
met.
Up to the 25th January 2006 I was pressing for
the WHO to apply this policy in order to prevent reassortment
and emergence of the pandemic strain of H5N1. However, at that
time I became aware of the work of Taubenburger, who showed that
the 1918 strain emerged by antigenic drift, that is by
working out how to spread from human to human without reassorting
with human influenza virus. Moreover, the 1957 and 1968 pandemics,
which were far milder, arose by reassortment "antigenic
shift". We can infer from this that reassortment is the
lesser of two evils, and it would be better to let reassortment
take place, rather than to successfully block reassortment only
for an antigenically drifted H5N1 to occupy the ecological niche
with a more deadly pandemic.
All this is is based on reasoning rather than
"scientific proof" (in fact proof does not happpen in
science, only in mathematics), but the bottom line is that it
would be unwise to try to block the reassortment.
In fact, the WHO policy is being adopted in such
an half hearted manner that it is irrelevant.
Without the vaccination policy, emergence of the
pandemic virus is very probable.
Limiting the spread via air travel
If we fail to immunise workers who have contact
with the virus, and a new H5N1 strain does emerge, we can slow
its global spread by monitoring air travellers.
If an outbreak occurs, air passengers from the
infected area should be monitored. Infra red detectors to pick
out people with raised core temperatures at airports have a place,
but are imperfect since a person who is incubating the virus may
be shedding it, but may not have a raised temperature. On the
other hand, it would be feasible to change airliner cabin air
filters at the end of each leg of the flight. PCR tests could
identify aircraft with cabin air carrying the virus within hours.
Passengers and crew from an infected flight would have to be quarantined
if the virus is found.
A suitable machine to do this work can be found
here.
In addition, hygiene standards in aircraft toilets
should be vastly improved.
These measures are unlikely absolutely to contain
the virus, but they will slow its global transmission, buying
us valuable time to get a vaccine prepared and rolled out.
Please write to your democratic representative
and ask them to put these measures in place.
Dealing with the pandemic
If, despite these barriers, a new strain of pandemic
flu arrives in a country, isolation
of cases will help to limit the percentage of the polulation
is affected.
We need to press hard to get these measures in
place. The professionals and experts have valuable advice to give,
but they work in committees, which are a necessary way of making
plans, but the weakness of committees lies in their tendency to
follow the accepted line, and to be resistant to new ways of thinking.
The proposals laid out in these pages are in addition to, not
in opposition to, official advice.
Treatment
The anti viral drugs Oseltamivir (Tamiflu) and
the amantidine derivatives may help to fight the virus, although
the effectiveness of the older types is being lost due to the
extremely foolish use of the antivirals in giving it to chickens.
This is certain to encourage the virus to learn how to resist
the drugs.
Pandemic influenza will probably kill by cytokine
storm, a positive feedback loop weher defence cells overreact
and swamp the virus infected lungs. There is a cheap, safe, long
established drug which may be able to inhibit this reaction and
offer hope of an affordable treatment. I have had this
letter published in the on-line section of the BMJ.
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