Bird Flu – Page 4 – David Bradley

Human to human bird flu

The World Health Organization has expressed concern that a recent cluster of deaths associated with the H5N1 virus in Indonesia may not have originated with an animal host, suggesting the possibility of human to human transmission of the virus. However, it also cautions that the analytical evidence suggests that the virus has not mutated into a human transmissable form, which means we are not just yet on the verge of a global bird flu pandemic after all.

The news media inevitably picked up on this warning and ran with it, but thankfully the BBC saw the double-edged nature of the WHO announcement points out with some degree of rational response that many people in Indonesia, as in other southeast Asian countries, live in such close proximity to their animals and not necessarily in the most hygienic of circumstances that the likelihood of catching bird flu is much higher in such an environment.

It is the lack of a mutated form of H5N1 among these victims that means we are not yet doomed to see the feathers fly globally.

Youths and Adults First for Flu?

In today’s Science magazine policy forum, Ezekiel Emanuel and Alan Wertheimer of The Clinical Center, at NIH in Bethesda, Maryland, argue that should a [bird] flu pandemic emerge, any time soon, then, they say, priority should go to people between early adolescence and middle age.

Their argument is based on the idea that every one of us should have the opportunity to live through all life stages. They suggest that this offers the best balance of the amount the person has invested in his or her life with their time left to live should this virtual disease prove closely to 100% fatal without vaccination.

Their suggestion contrasts starkly with current recommendations for vaccinating people in the event of a flu pandemic which involves prioritizing vaccination of health workers and the elderly ill at the very top and healthy people aged two through 64 at the very bottom. The pair recommend incorporating another ethical principle that focuses on ensuring safety and the provision of food and fuel. What’s most intriguing about their argument, however, is that their ethical framework is intended to be applied only to the USA and not the whole world. The Science press release pertaining to this suggestion, simply says that this “would then involve more complex issues of global rationing.”

So, what do sciencebase readers think? Who’d care to draw up the list?

Preventing the Spread of Bird Flu

cockerel In the week that the H7 variant of avian influenza has led to the culling of 35000 chickens in England, scientists at Imperial College London have simulated the spread of a “human” bird flu epidemic and say that rapid treatment and isolation of infected individuals not only from the public but their household contacts will be essential to prevent thousands of deaths. They also suggest that vaccine stockpiles should be gathered together in readiness for a pandemic, even if the vaccine is not very potent. However, it is strict border controls and travel restrictions that will be needed to slow an outbreak and prevent a global pandemic.

Neil Ferguson and colleagues used computer modelling to evaluate the influence of a range of anti-pandemic measures, such as treatment and prophylaxis with antiviral drugs, household quarantine, vaccination and restrictions on travel. They found that with a policy of giving antiviral drugs both as treatment to infected cases and prophylactically to the patient’s families coupled with early closure of schools hit by the outbreak, rates of disease could be cut by almost a half.

However, for this policy to be feasible, antiviral stockpiles would need to be sufficient to treat 50% of the population – twice what many countries are planning. Combining such a policy with targeted immunization of children with a stockpiled trial vaccine might reduce illness rates by two-thirds, even if the vaccine was not particularly effective in its protection. Even greater drug coverage would have a correspondingly larger protective impact. Ferguson provides more details in this week’s Nature.

Bird Flu in Britain

The BBC reports this morning that about 35,000 chickens at a poultry farm in Norfolk, England, are to be culled after dead birds tested positive for a strain of bird flu. What makes this interesting is that the newsdesk subbies are now going to have cope with another strain of avian influenza – H7, as opposed to H5N1. H7N7 was, of course, responsible for an outbreak in The Netherlands where 30 million birds had to be slaughtered, but this is the first time it has reached British shores. H7 is not as great a risk to human health as H5N1, although H7N7 infected 80 people in The Netherlands. Bacteriologist Hugh Pennington of Aberdeen University, said that while the H7 strain was “nasty for the birds”, it was “not a public health threat to humans”, the BBC reports. “It’s basically a virus that kills chickens and has been around for many, many years.

So, one might ask, why did the BBC get a quote from a professor of bacteriology, rather than virology?

Bird Flu Poll

H5N1 at last reached British shores this month and now both the Eastern and Western seaboards of the USA are on tenterhooks. In the spirit of serious scientific debate, I’ve posted a poll all about avian influenza on the SciScoop Science Forum.

So, are we all doomed to be tarred and feathered or is it just a load of media fluff and feathers? You decide.Meanwhile, check out SciScoop regular contributor Chad’s excellent ongoing posting on the bird flu story on SciScoop.

Cat Flu Among the Pigeons

Dodgy mixed metaphors in Nature press releases aside, an important paper published this week and leaked by the media ahead of embargo expiration (tut, tut) reports how the first case of a domestic cat dying from the avian influenza H5N1 virus in Thailand in 2004 hit the airwaves.

Since then, numerous cases have emerged globally, including the death and euthanasia of 147 captive tigers fed virus-infected chicken carcasses. As feline fatalities increase scientists are now urging that the role cats might play in spreading avian influenza and the evolution of the virus ought to be reconsidered.

Albert Osterhaus and colleagues at Erasmus University in the Netherlands discuss the latest reports and experimental studies that underline the vulnerability of cats to H5N1 virus infection and the risks that cats pose to agencies fighting its global spread. They emphasise how cats can be infected with the virus through contact with domestic and wild birds, and then excrete the virus from the respiratory and digestive tract, sometimes transmitting infection to other cats. They also note that cats fed virus-infected chickens can be infected directly through the gut. This worryingly novel route for influenza transmission in mammals could be a serious cause for concern.

Despite this evidence, the authors argue that the impact of cats on the epidemiology of the avian influenza virus is still being overlooked by key organizations such as the World Health Organization (WHO).

The authors conclude that they cannot rule out the possibility of the virus mutating into a more dangerous strain in feline and other mammalian hosts, and suggest increased surveillance and precautions to be taken to prevent the virus leaping to humans.

More information in Nature this week.

Bird Flu Vaccine

The BBC reports today that it has been given exclusive “access” to a Belgian trial of a new bird flu vaccine.

400 volunteers signed up to receive either the new vaccine or a placebo in the randomised double-blind trial of the GlaxoSmithkline vaccine. 399 said they were doing it for humanitarian reasons, one admitted it was for the money (300 euros) and the experience. Let’s just hope the “experience” isn’t as interesting as that suffered by volunteers in another recent trial for a drug that also triggers changes in the body’s immune system.

Shikimic Acid Shortage Sorted

Some time ago I wrote about the possibility of a shikimic acid shortage and what science is doing to address the problem. Shikimic acid, you say? The starting material for the influenza drug Tamiflu, of course!

Microbial fermentation seemed to be the way forward, but now chemists have discovered that the seeds of the sweetgum fruit – gumballs – contain significant amounts of shikimic acid. The finding means manufacturers will not have to rely on seasonal supplies of the seeds of the star anise fruit.

Thomas Poon of the W.M. Keck Science Center at The Claremont Colleges in California who heads the team says, “Our work gives the hearty sweetgum tree another purpose, one that may help to alleviate the worldwide shortage of shikimic acid.” The findings, which could help increase the global supply of the drug, Poon told the annual meeting of the American Chemical Society, this week.

Shikimic acid is used to make a generic drug called oseltamivir (Tamiflu) which is used to fight many types of flu viruses. Some health experts believe that this and similar antiviral drugs could help save lives by slowing the spread of the virus in the absence of a bird flu vaccine, which is still in development.

Bird Flu Between People

Why doesn’t H5N1 pass from person to person as easily as it passes from bird to bird? After all, H5N1 can replicate very efficiently in someone’s lungs.

Japanese researchers now think they have an answer to this vexing question. The bird virus, they have found, preferentially binds to cells in different regions of the human airway from those favoured by human influenza viruses.

Flu viruses infecting humans and birds are known to home in on slightly different versions of the same molecule, found on the surface of cells that line the respiratory tract. Yoshihiro Kawaoka and colleagues report in today’s Nature the effect this has on patients. Whereas the version of the molecule preferentially bound by human viruses is more prevalent on cells higher up in the airway, the molecule that is preferentially targeted by avian viruses tends to be found on cells deep within the lungs, in the air sacs, or alveoli, of the lung.

This may explain why human-to-human transmission of H5N1 remains uncommon, explain the authors. The virus may preferentially enter cells deep down inside the lungs, meaning that an infected person is less likely to spread the virus by coughing or sneezing. The researchers add, however, that should the virus ever acquire the ability to infect cells higher up in the airway then it may make the leap to a human to human infectious disease.

Parallel findings are also published today in Science, by Thijs Kuiken and colleagues. They have identified alveoli type II pneumocytes, scavenging cells within the lumen of the alveoli as the cells to which H5N1 predominantly attaches. These findings are in contrast to the received wisdom that avian influenza viruses have little or no affinity for cells of the human respiratory tract.

Double your Money in Bird Flu Lottery

It’s like buying two tickets instead of one for the national lottery, you may shorten the odds ever so slightly, but there’s still very little chance of winning. That should be your first thought on hearing that the strain of avian influenza currently making the media sweat has evolved into two distinct variants. That’s the big news emerging from the International Conference on Emerging Infectious Diseases in Atlanta this week.

Rebecca Garten of the US Centers for Disease Control and Prevention reports that she and her colleagues analysed more than 300 H5N1 samples from infected birds and people between 2003 and summer 2005, and found two distinct sub-types of the virus. The genetically distinct H5N1 strain is thought to have emerged in 2005 and infected people in Indonesia.

The concern is that the existence of this variant points to an increased risk of a human-transmissable form of avian influenza emerging at some stage. Of course, the emergence of distinct strains of a single type of flu virus is nothing remarkable. Flu viruses are notoriously quick to evolve. After all, they wouldn’t be endemic in their host populations if they weren’t, as a second wave of infection would simply be defeated by the already primed immune defences. Evolution provides each successive strain with a new set of proteins to avoid detection by the immune system. Regardless, H5N1 is still a bird virus, it only very rarely infects people. It will take more than a simple single mutation to allow it to leap from a bird host environment to humans and even then, many researchers concede that it is likely to lose virulence when it does so.