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Shifting from "if" to a "best case scenario" of a global 7.4 million dead

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By late September 2005, estimates by WHO and others placed the death toll of an H5N1 avian flu pandemic at 150 to 200 million. Within two days, citing that WHO "can't be dragged into further scare-mongering," the organization reduced the death toll  towards the "best case scenario" of 7.4 million dead.

Not if but how many millions. How great the change from my November 2004 note, The flu season not yet underway and uncomfortable signs that 'when, not if' is shifting to 'soon, not when'.

I find it remarkable that Bush43 has publicly mooted the halting of air transport, the imposition of a regional quarantine and the use of US military assets to enforce that quarantine. That is refreshing given that broad surprise from the lay community greeted the outgoing US Secretary of Health and Human Services, Tommy Thompson, in December 2004 when he described avian flu was a "really huge bomb" that frightened him above all other threats. Only in September 2004 did the US begin ordering a promising vaccine from France's Sanofi-Aventis, but the two million doses is only a pittance of that needed and one wonders under what "emergency conditions" will decide who gets what when if it comes to that.

The virulence of H5N1 is remarkable, even as it is not well understood. The invasion of Influenza viruses typically proceed from the throat to the windpipe and then the lungs where the outcome can be either viral or bacterial pneumonia. Some H5N1 strains greatly exceed that usual worst case condition by:

  • Replication triggering in organs other than the lungs, e.g., liver, intestines and brain, creating a "whole-body infection"
  • Excessive human immune system response generating high volumes of cytokines which at normal levels aid the immune response but at high levels cause damage to the victim's own tissue

H5N1 virulence as a percentage of deaths from infection is stunning, some 51% of those known infected die. (As of 5 August, 57 of 112 known infections in four nations died: Cambodia (4 cases), Indonesia (one case), Thailand (17 cases) and Vietnam (90 cases)). During the same period H5N1 has killed "more than 150 million birds in 11 nations."

It helps to put that virulence beside previous flu pandemics. The 1918-1919 Spanish Flu (H1N1) pandemic only killed 2.6% of those infected to reach its 40 to 50 million global fatalities (500,000 in the US) - and that in an era of relatively low personal mobility. Scaling that death rate to today's global population points to a possible 200 million dead. The 1957-58 "Asian Flu" (H2N2) killed an estimated 2 million while the 1968-1969 "Hong Kong Flu" (H3N3) killed some 750,000 people. While the origin of the 1918 virus is unclear, the 1957 and 1968 viruses are thought to have resulted human and avian influenza viruses. These three pandemics "tend to infect 25 percent to 35 percent of the population" unlike the usual seasonal flu viruses that infect "between 5 percent and 20 percent" with a death rate of under 1% for an annual toll of 250,000 to 500,000 dead.

Influenza A is a simple virus constantly undergoing genetic reassortment. H5N1 is rapidly mutating:

The highly lethal H5N1 viruses isolated from last year's human cases of avian flu were genetically 99 percent identical to each other. The slightly less lethal -- but perhaps more transmissible -- virus taken from patients in northern Vietnam early this year is only 98 percent identical to last year's; more important, it isn't completely inhibited by antibodies to last year's strain. It may be on its way to becoming a new, human-adapted strain.

Such flexibility makes an H5N1 pandemic merely a "matter of probability and opportunity," especially as ducks may become a "permanent reservoir of H5N1 virus" even as it is fatal to chickens, and one of the duck virus variants was fatal to ferrets thereby jumping the bird-mammal boundary.

It now appears that a potential human to human (instead of wildfowl to human) transmission clustering is occuring in the Soreang District of South Sulawesi. Indonesian H5N1 avian flu cases are now spreading throughout the country and are appearing as clusters. In Jakarta there are now clusters of clusters. (See maps here, here and here).

These larger growing clusters define phase 5 of a pandemic and as the reports accumulate daily, it seems that Indonesia is very close to the final phase 6, which is defined by sustained transmission in humans. Some of the members of the familial clusters may have become infected by a common source, but the vast majority have a 5-10 day gap between the onset of symptoms in the index case and family members. This time gap is characteristic of human-to-human transmission.

How many, not if. I again suggest readers review Using SARS to predict H5N1 Avian Flu impacts on regional & global supply chains along with its part 2.

Part 2 of this note

Bush Weighs Strategies to Counter Possible Outbreak of Bird Flu
By BRIAN KNOWLTON
International Herald Tribune
October 4, 2005

World Health Agency Tones Down Alarm on Possible Flu Pandemic
By THE ASSOCIATED PRESS
Published: October 1, 2005

Bird flu pandemic 'could kill 150m'
James Sturcke
Guardian (UK)
September 30, 2005

H5N1 Cluster in South Sulawesi Increases Pandemic Concerns
Recombinomics Commentary
September 29, 2005

H5N1 Cluster in Samerang Raises Phase 5 Concerns
Recombinomics Commentary
September 29, 2005

Avian Influenza in Asia: September 2005 Update
Overseas Security Advisory Council (OSAC)
28 Sep 2005
PDF

Richer Nations Seek Protection From Bird Flu
By ELISABETH ROSENTHAL
International Herald Tribune
Published: September 19, 2005

EU Concerned About Spread of Bird Flu
By THE ASSOCIATED PRESS
Published: August 25, 2005
Filed at 1:09 p.m. ET

Scientists Race To Head Off Lethal Potential Of Avian Flu
By David Brown
Washington Post
August 23, 2005

U.S. and other nations brace for bird flu
By Steve Mitchell
UPI Medical Correspondent
Published July 14, 2005

Agonist.org Bulletin Board
Spotlight => Disease outbreaks => Message started by: christian on July 31, 2005, 03:32:53 pm

Gordon Housworth



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