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[e-drug] Avian influenza should be ruffling our feathers

E-DRUG: Avian influenza should be ruffling our feathers
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[Forget Bin Laden! The *BIG* terrorist is going to be the next influenza 
pandemic. With a vaccine production delayed for 8 months, the world only has 
the neuraminidase inhibitors zanamivir and oseltamivir as potentially effective 
drugs. The existing stockpiles of antivirals are nowhere near adequate to cope 
with a pandemic. 
Are these essential drugs? Anybody planning to write a review about 
anti-influenza drugs for the 2005 WHO Essential Drugs List of these drugs? 
Copied as fair use from the Lancet Infectious Diseases. WB]

http://infection.thelancet.com/journal/vol4/iss10/full/laid.4.10.the_leading_edge.30755.1

Avian influenza refuses to go away. The outbreak of highly pathogenic influenza 
A H5N1 was first reported in poultry in South Korea in December of last year, 
and subsequently spread to another seven Asian countries. After a quiet period 
in the second quarter of this year, the ProMed wires have been buzzing since 
July with news of outbreaks of the virus in poultry in China, Thailand, 
Vietnam, Indonesia, and Malaysia. Fortunately, only Thailand and Vietnam have 
reported human cases (13 cases with nine deaths, and 27 cases with 20 deaths, 
respectively, as of September 10), indicating that the virus transmits poorly 
from birds to people.

Reports from China that H5N1 is widespread in domestic ducks and wild birds 
suggest that the virus is deeply entrenched in the environment and may be 
impossible to eliminate. Experimental infection of cats with H5N1 indicates 
that these animals could serve as a transmission bridge between poultry farms 
or between poultry and people. Perhaps we should not give too much weight to 
disease produced in the laboratory, but cats should be studied in future 
epidemiological investigations of H5N1 transmission.

Of more importance potentially was the announcement, made on August 20 by a 
researcher from China's Harbin Veterinary Research Institute, that H5N1 has 
been isolated from pigs on farms in various parts of China. Pigs can also be 
infected with human influenza A viruses, such as H3N2. The co-circulation of 
influenza viruses of avian, human, and pig origin in pigs might lead to genetic 
reassortment between the viruses, and, in the worse-case scenario, emergence of 
a new pandemic influenza strain.

It has since emerged that H5N1 was isolated once from material collected from 
pigs in Fujian province in 2001, and that of 1936 samples collected from pigs 
in 14 Chinese provinces in 2003 only one was positive for H5N1, also from 
Fujian. A further survey involving 4447 samples from pigs in ten provinces, 
including Fujian, done between April and August this year revealed no cases of 
H5N1 infection. Moreover, testing earlier this year for H5N1 in pigs on 
Vietnamese farms where the disease was rife among poultry, found no evidence of 
infection. And during regular testing in Hong Kong of pigs imported from 
mainland China, no H5 avian influenza subtype has been isolated. So the 
implications for human health of the discovery of H5N1 in pigs in China remain 
unclear.

Nevertheless, there is absolutely no room for complacency in the international 
response to, what now seems to be endemic, highly pathogenic avian influenza. 
The great fear is that avian disease will give rise to a human influenza 
pandemic. Of the three prerequisites for a human pandemic, two have been met: 
emergence of a new influenza virus to which the population has little or no 
immunity and against which there is no effective vaccine; and ability of the 
virus to replicate in human beings and cause disease. As yet, there is no 
evidence of the third prerequisiteefficient human-to-human transmissionbeing 
met.

There has not been an influenza pandemic since 1968 (so called Hong Kong flu). 
However, sources within WHO believe that we are as close to the next pandemic 
as we have been at any time in the past 36 years, with all the necessary 
ingredients currently mixing in Asia. Epidemiological modelling suggests that a 
future influenza pandemic will cause 2774 million deaths worldwide. The severe 
acute respiratory syndrome outbreak of 2003 merely hinted at the likely 
economic consequences of pandemic influenza.

The WHO pandemic preparedness plan was published in 1999 and is in the process 
of being revised. Early detection of unusual outbreaks by the WHO network of 
112 national influenza centres will be key to containment of potentially 
pandemic strains. As Iain Stephenson and colleagues said in this journal in 
August, vaccination is likely to remain the principal means of combating 
pandemic influenza (Lancet Infect Dis 2004; 4: 499509). However, production 
of a vaccine against the H5N1 strain is complicated by numerous technical, 
safety, and regulatory considerations. Indeed, it may be 8 months or more into 
a pandemic before a vaccine is available. Antiviral drugs could be used to 
contain the pandemic and reduce fatalities while vaccine supplies are prepared. 
H5N1 seems to be resistant to the M2 inhibitors (amantadine and rimantadine); 
the neuraminidase inhibitors zanamivir and oseltamivir are effective, although 
oseltamivir-resistant influenza H3N2 in children treated for the disease was 
reported recently. What is certain is that existing stockpiles of antivirals 
are nowhere near adequate to cope with a pandemic.

The threat to human health from pandemic influenza is likely far greater than 
that from bioterrorism. Responsible governments must be prepared to invest in 
global preparedness for the next pandemic.

The Lancet Infectious Diseases



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