Human nose temperature too cold for avian influenz

Avian influenza viruses do not thrive in humans because the temperature inside a person's nose is too low, according to research published today in the journal PLoS Pathogens.

The authors of the study, from Imperial College London and the University of North Carolina, say this may be one of the reasons why bird flu viruses do not cause pandemics in humans easily.

There are 16 subtypes of avian influenza and some can mutate into forms that can infect humans, by swapping proteins on their surface with proteins from human influenza viruses.

Today's study shows that normal avian influenza viruses do not spread extensively in cells at 32 degrees Celsius, the temperature inside the human nose. The researchers say this is probably because the viruses usually infect the guts of birds, which are warmer, at 40 degrees Celsius. This means that avian flu viruses that have not mutated are less likely to infect people, because the first site of infection in humans is usually the nose. If a normal avian flu virus infected a human nose, the virus would not be able to grow and spread between cells, so it would be less likely to damage cells and cause respiratory illness.

The researchers also found that when they created a mutated human influenza virus by adding a protein from the surface of an avian influenza virus, this mutated virus struggled to thrive at 32 degrees Celsius. This suggests that if a new human influenza strain evolved by adopting proteins from an avian influenza virus, this would need to undergo further changes in order to adapt to the conditions in the human body.

The researchers reached their conclusions by growing cells from the human airway and infecting them with different human and avian influenza viruses, including H5N1, to see how well the viruses grew and spread. The human influenza viruses grew equally well in the cells whether they were maintained at 37 degrees Celsius, our core body temperature, or at 32 degrees Celsius, the temperature of the nose. In contrast, the four avian influenza viruses tested grew well at 37 degrees Celsius but grew very slowly at 32 degrees Celsius.

When the researchers added proteins from an avian influenza virus to a human influenza virus, the human influenza virus also grew slowly and struggled to replicate at 32 degrees Celsius.

As viruses kill the cells they infect, the researchers also measured the extent of cell death in the model. This showed that at 32 degrees Celsius, far fewer cells died as a result of infection with avian influenza compared with human influenza, supporting the idea that the avian virus could not thrive at that temperature.

Professor Wendy Barclay, one of the authors of the study from the Division of Investigative Science at Imperial College London, said: "Bird viruses are out there all the time but they can only cause pandemics when they undergo certain changes. Our study gives vital clues about what kinds of changes would be needed in order for them to mutate and infect humans, potentially helping us to identify which viruses could lead to a pandemic.

"It would be impossible to develop vaccines against all 16 subtypes of avian flu, so we need to prioritise. By studying a range of different viruses in systems like this one we can look for warnings that they are already beginning to make the kinds of genetic changes in nature that mean they could be poised to jump into humans; animal viruses that spread well at low temperatures in these cultures could be more likely to cause the next pandemic than those which are restricted," added Professor Barclay.

http://en.wikinews.org/wiki/H5N1_Avian_Flu_virus_has_mutated,_study_says

Thursday, March 13, 2008

Researchers involved in a study at the University of Wisconsin have discovered that the H5N1 Avian Flu virus has mutated into a strain that may make humans more vulnerable to the disease.

Prior to the study, it was known that the virus could only thrive or live in a body which have temperatures of 106°F (41°C). A human's normal body temperature is 98.6°F (37°C). This difference in the temperatures of bodies makes the virus less likely to infect a human, but the recent study suggests the virus has adapted to survive in bodies with temperatures lower than 106°F.

"We have identified a specific change that could make bird flu grow in the upper respiratory tract of humans," said Yoshihiro Kawaoka, the researcher in charge of the study.

Kawaoka also stated that the "viruses that are circulating in Africa and Europe are the ones closest to becoming a human virus," but also stated that the H5N1 virus must undergo several mutations before it can infect a human, who can then spread the virus to other humans.

"Clearly there are more mutations that are needed. We don't know how many mutations are needed for them to become pandemic strains," added Kawaoka.

The World Health Organization (WHO) has stated that despite the study, influenza viruses are constantly mutating from season to season, but that the H5N1 virus is not anymore deadly to humans than before the study.

"Mutations occur in influenza viruses. Separately from that, the (bird flu) virus continues to be deadly. But there is no new jump in deadliness," said Gregory Hartl, a spokesman for the WHO.

comment: This is vague when it comes to noses. We know and have scene improved receptor binding in URI with the Avian mutations. Why organizations suddenly get inspired to release denial of what was previously released as a proven studies puzzles me. I guess only the nose knows. Will look for more nose data as opposed to URT.

Medclincian

It's interesting that this report t6hat bird flu doesn't like nose temperature is being greeted as if it were a new discovery rather than just another study.  The temperature preference has been known for years and here is a link and I'll copy the text too for a discovery a year ago of a bird flu strain that's adapted to human body temps.  Quite a bit of the research that we see is funded by the meat industry and tends to lean towards the message that these virus dangers are all media hype.

http://www.naturalnews.com/022787.html

 (NaturalNews) The avian flu has undergone a critical mutation making it easier for the virus to infect humans, according to a study conducted by researchers at the University of Wisconsin at Madison and published in the journal PLoS Pathogens.

"We have identified a specific change that could make bird flu grow in the upper respiratory tract of humans," lead researcher Yoshihiro Kawaoka said.

The H5N1 strain of influenza, also known as "bird flu," has decimated wild and domestic bird populations across the world since it emerged between 1999 and 2002. This highly virulent variety of the flu has been identified as a public health concern because in the past, varieties of influenza have mutated and crossed the species barrier to humans.

Since 2003, 329 humans have been confirmed infected with H5N1, with 201 fatalities. The vast majority of these worked closely with infected birds, such as in the poultry industry.

One of the primary things that keeps bird flu from infecting humans is that the virus has evolved to reproduce most effectively in the bodies of birds, which have an average body temperature of 106 degrees Fahrenheit. Humans, in contrast, have an average body temperature of 98.6 degrees, with temperatures in the nose and throat even lower (91.4 degrees). This vast temperature difference makes it very difficult for the bird flu virus to survive and grow in the human body.

In the current study, researchers found that a strain of H5N1 has developed a mutation that allows it to thrive in these lower temperatures.

"The viruses that are circulating in Africa and Europe are the ones closest to becoming a human virus," Kawaoka said. But he pointed out that one mutation is not sufficient to turn H5N1 into a major threat to humans.

"Clearly there are more mutations that are needed. We don't know how many mutations are needed for them to become pandemic strains."

"We are rolling the dice with modern poultry farming practices," warned consumer health advocate Mike Adams, author of the book How to Beat the Bird Flu. "By raising chickens in enclosed spaces, treating them with antibiotics, and denying them access to fresh air, clean water and natural sunlight, we are creating optimal conditions for the breeding of highly infectious diseases that can quickly mutate into human pandemics," Adams said. "Given current poultry farming practices, it is only a matter of time before a highly virulent strain crosses the species barrier."

Co-infections of all kinds are a concern during any flu season.

If an ill person in Indonesia runs out into a yard of chickens and falls down...it could possibly happen.

True... just posted info on the fact that there were 5 influenza viruses found in Mexico at the same time.... as perhaps a reason for more deaths there...so it is valid...add to that the 5 pandemics.


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