2009 H1N1 pandemic flu more damaging to lungs, opens opportunities for bacterial infection

September 19, 2011, American Society for Microbiology

Many of the people who died from the new strain of H1N1 influenza that broke out in 2009 were suffering from another infection as well: pneumonia. A new study to be published Tuesday, September 20 in the online journal mBio reveals how the two infections, pandemic influenza and pneumonia, interact to make to make a lethal combination.

Back in 2009, autopsies of 34 of the victims of the H1N1 pandemic revealed that about half showed signs of bacterial co-infection in their lungs. This was a telling sign that the two pathogens are playing off one another, but until now little was known about the between them or why influenza was so lethal when accompanied by pneumonia.

Using mice, Kash et al., from the National Institute of Allergy and Infectious Diseases (NIAID) and the Institute for Systems Biology (ISB), teased the problem apart. They infected some mice with the seasonal flu virus and others with the 2009 pandemic strain and waited 48 hours for the influenza to take hold. Next, they exposed some of the mice to the bacterium , one of the leading causes of pneumonia.

In mice that were only given either of the , influenza had the same effects it has in humans, including weight loss, but all the mice infected with influenza alone survived. The mice infected with seasonal influenza and S. pneumoniae had slightly enhanced damage, but they all survived the dual infections.

In contrast, all the mice co-infected with both the 2009 pandemic flu and S. pneumoniae showed severe weight loss and 100% mortality. The lung tissues of the dead mice revealed that the were severely inflamed and the surfaces of the bronchioles were wiped clean of the protective layer of cells called the epithelium. There was also increased bacterial replication in the lungs of the co-infected mice, a sign that the bacteria were thriving there.

Looking at the mouse genes that were expressed during infection revealed more details about how the virus sets the stage for lethal bacterial infections. Mice infected with the pandemic and S. pneumoniae had a similar inflammatory response as the other mice, but they lack responses that would repair and regenerate their damaged epithelial cells, those protective tissues that would otherwise keep bacteria from penetrating to deeper layers of tissue.

All these factors add up to big problems in the lung: as compared with seasonal flu, infection with the pandemic strain of flu was associated with more extensive damage to the that requires more extensive tissue repair. This opens the body up to attack from bacterial invaders, including Streptococcus pneumoniae.

Keith Klugman, who studies pneumonia and pneumococcal disease at Emory University, edited the paper. He says the study has a number of implications for treatment of pandemic flu.

"One implication is that if you can prevent the bacterial infection, you may be able to prevent a significant fraction of the pneumonia that leads to death. There may be a role for antibiotics in the severe pneumonias that follow influenza," says Klugman.

Klugman points out that a vaccine for S. pneumoniae exists and that it is effective at interrupting transmission of pneumonia in the community. Now that we know causes increased susceptibility to pneumonia, says Klugman, we might head off deadly influenza-S. pneumoniae co-infections with more proactive vaccination programs.

Explore further: Flu helps spread pneumonia

Related Stories

Flu helps spread pneumonia

April 11, 2011
Bacteria that cause pneumonia and meningitis are only able to spread when individuals are infected with flu, says a scientist reporting at the Society for General Microbiology's Spring Conference in Harrogate. The work could ...

Recommended for you

Study reveals how MRSA infection compromises lymphatic function

January 17, 2018
Infections of the skin or other soft tissues with the hard-to-treat MRSA (methicillin-resistant Staphylococcus aureus) bacteria appear to permanently compromise the lymphatic system, which is crucial to immune system function. ...

Newly-discovered TB blood signal provides early warning for at-risk patients

January 17, 2018
Tuberculosis can be detected in people with HIV infection via a unique blood signal before symptoms appear, according to a new study by researchers from the Crick, Imperial College London and the University of Cape Town.

Fresh approach to tuberculosis vaccine offers better protection

January 17, 2018
A unique platform that resulted in a promising HIV vaccine has also led to a new, highly effective vaccine against tuberculosis that is moving toward testing in humans.

New study offers insights on genetic indicators of COPD risk

January 16, 2018
Researchers have discovered that genetic variations in the anatomy of the lungs could serve as indicators to help identify people who have low, but stable, lung function early in life, and those who are particularly at risk ...

Previous influenza virus exposures enhance susceptibility in another influenza pandemic

January 16, 2018
While past exposure to influenza A viruses often builds immunity to similar, and sometimes different, strains of the virus, Canadian researchers are calling for more attention to exceptions to that rule.

Don't hold your nose and close your mouth when you sneeze, doctors warn

January 15, 2018
Pinching your nose while clamping your mouth shut to contain a forceful sneeze isn't a good idea, warn doctors in the journal BMJ Case Reports.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.