Influenza A (H5N1)
This page attempts to give an updated and comprehensive picture on the recent outbreak of avian flu in Hong Kong. It links to a variety of web pages on internet touching on H5N1 infection.
How the virus is spread
Water birds such as wild ducks are believed to be the carriers of all avian influenza type A viruses. The viruses are carried inside the birds' intestines and are distributed into the environment via bird faeces. Migratory birds infected with the virus could potentially spread the bird flu to any of the countries they visit.
Wild birds don't usually show symptoms of bird flu. However, the avian influenza virus can kill domesticated birds, such as chickens and turkeys.
Symptoms in birds differ according to the species but can include diarrhoea, breathing difficulties, swollen head and death. A sick bird sheds the virus in its feathers, mucous, saliva and faeces.
Humans who have close contact with sick birds are at risk of infection with bird flu. For example, a person may handle a sick bird, contaminate their hands with chicken faeces, and forget to wash their hands before eating. They will then ingest the infected bird faeces. This is the most common way for a human to catch the bird flu. The virus can also survive in raw poultry meat but is destroyed during normal cooking.
Economic impact of H5N1.
That doesn't sound like much until you look at the numbers: 41 people dead, and 47 million birds slaughtered. Across Asia, the estimates are losses of up to $10 billion—and that doesn't count losses due to the drop in consumption of poultry meat. It will be hard to measure the harm done to whole populations through the loss of protein.
One surprising and encouraging finding: the 1918 virus had been circulating in humans since at least 1900 before it mutated into a lethal form. Unless H5N1 is a lot smarter, we may have several more years to track the virus's changes and to prepare for the jump from birds to humans.
Vietnam: H5N1 losing virulence.
The deadly bird flu virus strain H5N1 that has claimed 42 lives in Vietnam has undergone genetic changes and become less virulent, media reports quoted scientists as saying Wednesday. The reports quoted the National Institute for Hygiene and Epidemiology as saying that, compared with samples taken in early 2004, the percentage of virulence has decreased to 98.2 percent from 99.1 percent.
Another human death in Vietnam.
A man in Vinh Long province who died Monday morning is suspected of contracting bird flu, a disease that has claimed 42 Vietnamese lives since late 2003.
A fifty-four-year-old man in Mang Thit commune was hospitalized Sunday afternoon with high fever, chest pains and labored breathing, with lung X-ray results indicating one-third of his two lungs had sustained damage.
The man's family members said there were dead fowl around the patient's house 10 days ago while he himself had eaten chicken.
Suspected of contracting pneumonia caused by H5N1 strain, the man was rushed to Ho Chi Minh City-based Hospital of Tropical Diseases where he died the next morning.
Boxun News again.
Boxun is reporting that there have been 77 H5N1 deaths in Liaoning Province. Many of the dead were outside workers brought in to help cull the birds. The above list includes the names, ages, and origins of some of the deceased workers. All are listed as dying from H5N1 and being cremated.
If the above numbers are accurate, the level of transmission of H5N1 from birds to humans would be markedly more efficient than reported for outbreaks in other countries such as Vietnam, where reports indicate that no workers involved in culling of H5N1 developed symptoms.
Three more Vietnamese provinces report H5N1.
The Ho Chi Minh City People's Committee recently directed all restaurants, food shops, collective kitchens, and shops selling roasted chicken and ducks to register with relevant agencies the sources of their safe fowl supplies. It noted in a statement that a total of 176 chickens, ducks and geese died
Tuesday in the banner (or county) of Morin Dawa in Inner Mongolia before they
were confirmed by a state avian flu lab as H5N1 subtype highly pathogenic bird
flu cases.
Ominous Thai reaction to fears of H5N1.
It's a worrying preview of how people could react to a real (or feared) outbreak of human H5N1—not just in Thailand, but everywhere. The H5N1 viruses were isolated from two ducks as part of a first-ever
cross-country surveillance program aimed at taking a snapshot of what flu
viruses wild ducks in this country are carrying. After breaking the news just before 5 pm, CBC Radio at 5:30 said it was H5N1.
This appears to have been an error; the claim hasn't been repeated. We'll know
in a day or two just what kind of virus we're dealing with.
H5 in British Columbia?
British radio has just announced (5:00 pm PST) that a duck in Abbotsford, east of Vancouver, has tested positive for H5. It's not known if it's H5N1, but it's not good news at all. Mamtani sees H5N1 as currently limited in its virulence, but warns that it can
still mutate into a much more dangerous form. Since I am in no hurry to see human-to-human H5N1 transmission, I would like to
think the deaths were the result of an undercooked drumstick, not of an
over-mutated virus. Its director, Tang Chi Thuong, said the hospital was making emergency
preparations for a possible pandemic. Since the hospital was always full of
children, he said the flu could spread quickly if H5N1 victims came in waves and
he did not have appropriate measures in place. The deadly H5N1 strain of the virus is believed to have killed 662 birds in
poultry farms at Xiaonan District, Xiaogan City of Hubei Province on November 5,
and 32 chickens in Hotan of the Xinjiang Uygur Autonomous Region on November 10,
the Ministry of Agriculture said in a statement Thursday night. At present, H5N1 cannot pass easily from human to human. It has so far infected
around 125 people in South East Asia, but most of these have had close contact
with infected birds. Hospital in Memphis, said the key could be when H5N1 reaches East Africa, where
HIV/AIDS is rife. Well, we may not need to wait until H5N1 reaches East Africa.
Worst case scenario
The worst case scenario for a H5N1 pandemic is somewhere around 150,000,000 human deaths directly due to H5N1 infection (or two to three percent of the world's human population). No one knows what the chances are for this worst case scenario. In 2004 and 2005, 118 people are known to have been infected with the H5N1 virus and 61 of them died. The mortality rate of this virus is as high as that of the virus H1N1 that caused the Spanish Flu of 1918, which killed over 20 million people world wide. One of the major differences between H1N1 of 1918 and the current H5N1 is the fact that the latter is not (yet) transmissible between humans. Until recently, that prevented the H5N1 virus from becoming a pandemic. Recent research of Taubenberger et al {Taubenberger JK, Reid AH, Lourens RM, Wang R, Jin G, Fanning TG. Characterization of the 1918 influenza virus polymerase genes. Nature. 2005 Oct 6;437(7060):889-893} showed that the 1918 virus like H5N1 was an avian virus. Furthermore, Tumpey and colleagues {Tumpey TM, Basler CF, Aguilar PV, Zeng H, Solorzano A, Swayne DE, Cox NJ, Katz JM, Taubenberger JK, Palese P, Garcia-Sastre A. Characterization of the reconstructed 1918 Spanish influenza pandemic virus. Science. 2005 Oct 7;310(5745):77-80} who reconstructed the H1N1 virus of 1918 come to the conclusion that it is especially the polymerase genes and the HA and NA genes that caused the extreme virulence of this virus. The sequences of the polymerase proteins (PA, PB1, and PB2) of the 1918 virus and subsequent human viruses differ by only 10 amino acids from the avian influenza viruses. Human forms of seven of the ten amino acids have already been identified in currently circulating H5N1. It is not unlikely that also the other mutations eventually will surface and make the H5N1 virus better suited for human-to-human transmission. Another important factor is the change of the HA protein to a binding preference for alpha 2,6 sialic acid (the major form in the human respiratory tract). In avian virus the HA protein preferentially binds to alpha 2,3 sialic acid, which is the major form in the avian enteric tract. It has been shown that only a single amino acid change can result in the change of this binding preference. Altogether it seems that only a few mutations are needed to make the H5N1 bird flu virus a pandemic virus like the one of 1918.
