Swine flu infects cells deep in lungs: study
Swine flu infects cells deep in lungs: study
PARIS (AFP) –- Swine flu can infect cells deeper in the lungs than seasonal flu, thus helping to boost the severity of the illness, a study said.
The paper provides the first laboratory corroboration of reports from front-line doctors that some patients with A(H1N1) virus suffer worse symptoms compared to those with run-of-the-mill seasonal flu.
Influenza viruses penetrate cells by attaching themselves to molecules called receptors, located on the outside of the cell wall.
The virus’ docking spike and the receptor are like a key and a lock. Some viruses only open a few cells, while others have something rather closer to a pass key, making it possible to infect a larger cell variety.
Once inside, the virus uses the cell’s machinery to replicate, eventually bursting the cell and going on to attack others.
Seasonal strains attach themselves almost exclusively to cells found in the nose, throat and upper airway, producing a some of influenza’s signature symptoms: runny nose, scratchy throat, a dry cough.
But the new research, published in the journal Nature Biotechnology, shows that the new swine flu — by sticking to a greater range of receptors — can also breach cells deep in the lungs.
Lab-dish experiments were carried out by Ten Feizi of Imperial College London and colleagues in which 86 different receptors were exposed to both seasonal and pandemic flu.
The seasonal strains only locked onto the kind of receptors found in the upper respiratory track.
But the swine flu virus was also able to latch onto receptors found deep inside the lungs, albeit more weakly. The adhesion results in a more severe lung infection.
Feizi spelt out the risk of what could happen if natural selection encourages viral strains that favor this deep-lung penetration.
“If the flu virus mutates in the future, it may attach to the receptors deep inside the lungs more strongly, and this could mean that more people would experience severe symptoms,” said Feizi.
“We think scientists should be on the lookout for these kinds of changes in the virus so we can try to find ways to minimize the impact.”
Using a statistical technique, epidemiologists sifting through data from other countries have found similarly disquieting patterns.
French epidemiologist Antoine Flahault has reported a 100-fold increase, compared to seasonal flu, in the number of swine flu deaths in Mauritius and New Caledonia attributed directly to the virus itself rather than secondary bacterial infections or underlying conditions.
Many of those deaths were caused by acute respiratory disease syndrome (ARDS), which requires intensive-care treatment for an average of three weeks. Only 50 percent of ARDS patients survive.
http://www.tehrantimes.com/index_View.asp?code=203357
Swine Flu: H1N1 Virus More Dangerous Than Suspected, Except To Survivors Of The 1918 Pandemic Flu Virus
ScienceDaily (July 14, 2009) — A new, highly detailed study of the H1N1 flu virus shows that the pathogen is more virulent than previously thought.
In contrast with run-of-the-mill seasonal flu viruses, the H1N1virus exhibits an ability to infect cells deep in the lungs, where it can cause pneumonia and, in severe cases, death. Seasonal viruses typically infect only cells in the upper respiratory system.
“There is a misunderstanding about this virus,” says Kawaoka, a professor of pathobiological sciences at the UW-Madison School of Veterinary Medicine and a leading authority on influenza. “People think this pathogen may be similar to seasonal influenza. This study shows that is not the case. There is clear evidence the virus is different than seasonal influenza.”
The ability to infect the lungs, notes Kawaoka, is a quality frighteningly similar to those of other pandemic viruses, notably the 1918 virus, which killed tens of millions of people at the tail end of World War I. There are likely other similarities to the 1918 virus, says Kawaoka, as the study also showed that people born before 1918 harbor antibodies that protect against the new H1N1 virus.
And it is possible, he adds, that the virus could become even more pathogenic as the current pandemic runs its course and the virus evolves to acquire new features. It is now flu season in the world’s southern hemisphere, and the virus is expected to return in force to the northern hemisphere during the fall and winter flu season.
To assess the pathogenic nature of the H1N1 virus, Kawaoka and his colleagues infected different groups of mice, ferrets and non-human primates — all widely accepted models for studies of influenza — with the pandemic virus and a seasonal flu virus. They found that the H1N1 virus replicates much more efficiently in the respiratory system than seasonal flu and causes severe lesions in the lungs similar to those caused by other more virulent types of pandemic flu.
“When we conducted the experiments in ferrets and monkeys, the seasonal virus did not replicate in the lungs,” Kawaoka explains. “The H1N1 virus replicates significantly better in the lungs.”
The new study was conducted with samples of the virus obtained from patients in California, Wisconsin, the Netherlands and Japan.
The new Nature report also assessed the immune response of different groups to the new virus. The most intriguing finding, according to Kawaoka, is that those people exposed to the 1918 virus, all of whom are now in advanced old age, have antibodies that neutralize the H1N1 virus. “The people who have high antibody titers are the people born before 1918,” he notes.
Kawaoka says that while finding the H1N1 virus to be a more serious pathogen than previously reported is worrisome, the new study also indicates that existing and experimental antiviral drugs can form an effective first line of defense against the virus and slow its spread.
There are currently three approved antiviral compounds, according to Kawaoka, whose team tested the efficacy of two of those compounds and the two experimental antiviral drugs in mice. “The existing and experimental drugs work well in animal models, suggesting they will work in humans,” Kawaoka says.
Antiviral drugs are viewed as a first line of defense, as the development and production of mass quantities of vaccines take months at best.
http://www.sciencedaily.com/releases/2009/07/090713212231.htm