How Dangerous is Bird Flu (H5N1) to Global Public Health? Part 1 (Feb 16, 2011 - Oct 16, 2011)

[Laidback Al]

How Dangerous is Bird Flu (H5N1) to Global Public Health?

The reports of three confirmed human cases of H5N1 in Cambodia (see map below) provides an opportunity for discussing H5N1 as an influenza virus with the potential to start another global pandemic. This thread provides an opportunity to comment and speculate on how such a pandemic might occur, its virulence and mortality rate, treatment, collateral damage, etc.


General map of Cambodia showing the locations of this week's confirmed human H5N1 cases.

[JimO]

I don't know very much about H5N1, but I assume that the mother and child contracted the virus while cleaning and preparing the bird for cooking. It seems that the virus wouldn't survive cooking temps and can it even take hold in the digestive tract?

Does anyone know if there have been reports of other cases associated with the 5-yo in Phenom Pen? If not, then perhaps the title should be changed to ... - 3 deaths, 7 hospitalized.

What jumps out at me is that seven people contracted the virus by cleaning her body for cremation. That sounds like very efficient H2H transmission. Have there been any similar H2H transmissions on that scale before?

Although pH1N1 has been my person focus for the past two years, I still believe the greatest pandemic threat is a variant of H5N1 that adapts to humans.

[Laidback Al]

Many people have contracted H5N1 from just handling infected poultry. There have been some cases of infection from eating infected poultry and even consuming duck blood pudding. At least one individual contracted H5N1 from infected feathers, the individual handmade official shuttlecocks for badminton. Most infections seem to occur as respiratory infections, some of them in the lower tract.

In order to trace contacts of infected individuals and to watch for H2H outbreaks, media reported cases from separate geographic areas are followed in separate threads here at FT.

Seven people infected from body cleansing would suggest H2H transmssion. However, as yet, none of these cases, neither the seven nor the two dead individuals have been confirmed with H5N1.

With a CFR of about .6, an H5N1 pandemic would pose the greatest health threat to the world since the 1918 pandemic. At that CFR, and with easy transmissibility, as many as a billion people could die.

[Giuseppe]

Many people have contracted H5N1 from just handling infected poultry. There have been some cases of infection from eating infected poultry and even consuming duck blood pudding. At least one individual contracted H5N1 from infected feathers, the individual handmade official shuttlecocks for badminton. Most infections seem to occur as respiratory infections, some of them in the lower tract.

In order to trace contacts of infected individuals and to watch for H2H outbreaks, media reported cases from separate geographic areas are followed in separate threads here at FT.

Seven people infected from body cleansing would suggest H2H transmssion. However, as yet, none of these cases, neither the seven nor the two dead individuals have been confirmed with H5N1.

With a CFR of about .6, an H5N1 pandemic would pose the greatest health threat to the world since the 1918 pandemic. At that CFR, and with easy transmissibility, as many as a billion people could die.

The possible outcome of a future influenza pandemic sustained by a transmissible A(H5N1)-derivative virus cannot be predicted.

As every season teaches to us, influenza viruses demonstrate highly variable activity, attack rate and virulence.

The actual epidemiological behaviour of A(H5N1) avian influenza virus is not yet fully understood, and its full clinical spectrum of disease is also poorly known.

Before to start a doomsday prediction about an unknown future, a little bit of caution is well advised.

[alert]

IMO, it is not clear that the H5N1 virus is involved in this incident at all. This could be H1N1, and the exposure to poultry might be coincidental. Alternatively, the two fatalities might be due to H5N1, but the illness in the contacts might not. That fact that all seven seem to be "recovering well" might argue against them all being infected with H5N1.

[sharon sanders]

It is H5N1, not H1N1, referenced here.

The lethality of H5N1 is a threat to global health. Whether it evolves genetically to be more transmissible or it recombines/reassorts with other flu types, it is a concern to be tracked.

[Giuseppe]

It is H5N1, not H1N1, referenced here.

The lethality of H5N1 is a threat to global health. Whether it evolves genetically to be more transmissible or it recombines/reassorts with other flu types, it is a concern to be tracked.

Tracking, yes!

Predictions, not!

[CopitoSP]

Cambodian mother, son die from bird flu


PHNOM PENH - BIRD flu has claimed three lives in Cambodia this month, with a mother and her 11-month-old son becoming the latest victims of the virus, officials said on Wednesday.

The 19-year-old woman died on Feb 12 while her baby died five days later, the Cambodian health ministry and the World Health Organisation said in a joint statement. Tests confirmed both had contracted H5N1 avian influenza.

...

The new victims, from north-western Banteay Meanchey province, were admitted to hospital with high fever and coughing days after 'eating sick poultry' while visiting relatives in southeastern Prey Veng province, the statement said.

...

http://www.straitstimes.com/BreakingNews/SEAsia/Story/STIStory_638114.html

[JJackson]

While I agree with IOH that it is tricky to predict how virulent a human pandemic strain might be based on the animal strain from which it was derived. I think Al is absolutely correct it is wholly reasonable to expect any strain derived from HP H5N1 to be vastly more virulent than one derived from any of the other strains which have caused mild infections in humans. Virulence in the odd zoonotic infection is not a guarantor of the level of virulence we might expect in an eventual pandemic strain but it is the best guide we have and a drop in CFR from over 50% to under 3% - required to be less virulent than H1N1(1918) - is more than a little optimistic.

JimO wondered about the possibility of infection via the alimentary tract. While we do not know if this occurs it should be born in mind that unlike all other known pandemic, or candidate pandemic, strains H5N1 is HP. Two possibly limiting factors to infection are the distribution of host binding sugars and the host proteases needed for HA cleavage, the sugars are not uncommon but for LP strains only a very small subset of proteases can access the cleavage site. The HP cleavage site can be accessed by many proteases and this increased tissue tropism leaves open the possibility of infection in a wide range of host cell types beyond those in the respiratory tract we associate with all the flus we have met before.

[Laidback Al]

The possible outcome of a future influenza pandemic sustained by a transmissible A(H5N1)-derivative virus cannot be predicted.

As every season teaches to us, influenza viruses demonstrate highly variable activity, attack rate and virulence.

The actual epidemiological behaviour of A(H5N1) avian influenza virus is not yet fully understood, and its full clinical spectrum of disease is also poorly known.

Before to start a doomsday prediction about an unknown future, a little bit of caution is well advised.

I hope that none of the readers here take my comments as a "prediction" about a future H5N1 pandemic. As IOH notes there is a lot we don't know, but we do know that an influenza pandemic with a CFR as high as .03 can happen and did happen, in 1918. The consequences of that pandemic were devastating.

From an evolutionary standpoint, H5N1 does not need to decrease its virulence if it spreads through the human population. We often hear that a virus will "burn itself out" or reduce its virulence before spreading widely because of a need to have a long term, continued supply of hosts. That might be true for human influenza viruses which eventually reach an equilibrium in the human population.

The fallacy is that H5N1 is not now a human virus, but a zoonotic virus and its primary hosts are avifauna. It doesn't needs humans to continue its evolutionary survival. It could "accidentally" infect and devastate a large portion of the human population before burning itself out. The H5N1 virus survives by circulating in its avian hosts, it does not need long term survival of human hosts.

Finally, loss of life in a pandemic is not just a result of direct infection. In some scenarios, loss life through collateral damage could greatly exceed deaths from the actual disease. What happens when large portions of the population are sick and debilitated all at one time. People can not make it to work, hospitals are short of staff, infrastructure such as electricity and power start to fail. Trucking of food supplies can not keep up with demand because diesel supplies are short. Oil tankers fail to make it to port on time because of sick crews. Supplies of critical life saving medicine run out. The list can go on.

Such social disruptions could easily produce many more casualties than those that die from infection. So I still think that a pandemic from a novel virus poses the greatest health threat in the future. Right now H5N1 is a candidate for that virus. But that is not to say that some other infectious disease could quickly come on the scene and cause a pandemic as well.

[Giuseppe]

It is emerging a bleak picture from a veterinary point of view, since the start of 2011.

In fact, a number of poultry and wild birds die-off events have been reported in several countries and regions around Eurasia, namely Cambodia, Vietnam, Japan, South Korea, China's Hong Kong, Indonesia, India, Bangladesh.

And these are only the countries who sent official reports to international organizations, FAO or OIE.

The situation is a remind of the almost complete failure in controlling if not eradicating the disease in animals since the A(H5N1) virus appearance in 2003.

Despite an huge amount of papers, meetings, donors' funds pledges - the disease persists and humans serve as 'sentinel' in most cases for detecting poultry outbreaks.

The H5N1 'case' is one of the increasing number of unresolved crisis around the world and despite the potential threat to human health globally, most of the developed nations resist to do enough to help reduce the impact on local population livelihood and contribute to maintain a source of infection.

Since the influenza virus behaviour remains largely unpredictable, any possible effort should be addressed in the field of animal welfare and in novel therapeutical and immunization strategies.

[Laidback Al]

IOH's point is very important. If we are to protect human populations from zoonotic diseases, then there must be an increase in surveillance of the wild and domesticated hosts of these diseases.

[sharon sanders]

Re: How Dangerous is Bird Flu, H5N1 to Global Public Health?

I copied a few posts from this thread:

Cambodia - 2 confirmed H5N1 deaths infected in Prey Veng province - contacts monitored in Banteay Meanchey Province


Thank you everyone!

[sharon sanders]

Re: How Dangerous is Bird Flu, H5N1 to Global Public Health?

IOH's point is very important. If we are to protect human populations from zoonotic diseases, then there must be an increase in surveillance of the wild and domesticated hosts of these diseases.

Hat tip Tetano -

Applied and Environmental Microbiology, August 2010, p. 5496-5499, Vol. 76, No. 16
0099-2240/10/$12.00+0 doi:10.1128/AEM.00563-10
Copyright ? 2010, American Society for Microbiology. All Rights Reserved.
Persistence of Avian Influenza Virus (H5N1) in Feathers Detached from Bodies of Infected Domestic Ducks {triangledown}
Yu Yamamoto,* Kikuyasu Nakamura, Manabu Yamada, and Masaji Mase

National Institute of Animal Health, 3-1-5 Kannondai, Tsukuba, Ibaraki, Japan

Received 3 March 2010/ Accepted 18 June 2010

Asian lineage highly pathogenic avian influenza virus (H5N1) continues to cause mortality in poultry and wild bird populations at a panzootic scale. However, little is known about its persistence in contaminated tissues derived from infected birds. We investigated avian influenza virus (H5N1) persistence in feathers detached from bodies of infected ducks to evaluate their potential risk for environmental contamination. Four-week-old domestic ducks were inoculated with different clades of avian influenza virus (H5N1). Feathers, drinking water, and feces were collected on day 3 postinoculation and stored at 4?C or 20?C. Viral persistence in samples was investigated for 360 days by virus isolation and reverse transcription-PCR. Infectious viruses persisted for the longest period in feathers, compared with drinking water and feces, at both 4?C and 20?C. Viral infectivity persisted in the feathers for 160 days at 4?C and for 15 days at 20?C. Viral titers of 104.3 50% egg infectious doses/ml or greater were detected for 120 days in feathers stored at 4?C. Viral RNA in feathers was more stable than the infectivity. These results indicate that feathers detached from domestic ducks infected with highly pathogenic avian influenza virus (H5N1) can be a source of environmental contamination and may function as fomites with high viral loads in the environment.

http://aem.asm.org/cgi/content/abstract/76/16/5496

[JimO]

Re: How Dangerous is Bird Flu, H5N1 to Global Public Health?

Thanks for the clarification, although some of the technical terms are over my head, I have been reading enough in the past two years to get the gist of it.

It seems that the H5N1 hasn't come into equillibrium with its hosts since there are frequent large die-offs of wild and domestic bird populations. So, it looks like a very unpredictable virus. Although of lesser concern to me personally than a human pandemic, it appears that a slowly evolving avian pandemic is unfolding globally. I fear that it could do great harm to wild populations of birds that are threatened/endangered or those that nest in large communal colonies. An entire population of birds could be wiped out in one nesting season if a virulent form of H5N1 got a foot hold at the right time.

JimO wondered about the possibility of infection via the alimentary tract. While we do not know if this occurs it should be born in mind that unlike all other known pandemic, or candidate pandemic, strains H5N1 is HP. Two possibly limiting factors to infection are the distribution of host binding sugars and the host proteases needed for HA cleavage, the sugars are not uncommon but for LP strains only a very small subset of proteases can access the cleavage site. The HP cleavage site can be accessed by many proteases and this increased tissue tropism leaves open the possibility of infection in a wide range of host cell types beyond those in the respiratory tract we associate with all the flus we have met before.