The flu and bacteria, a deadly combination

 

 As temperatures drop, the flu epidemic is spreading in France, prompting calls for vaccination against the virus for people at risk. In 2013, a study pointed to the co-responsibility of bacterial infections, which would be the main cause of death due to influenza. The virus would decrease the action of the immune system and facilitate the development of pathogens.

 When winter arrives, seasonal flu threatens. Annual influenza epidemics affect between two and eight million people, and are responsible for around 1,000 deaths per year in France. The flu is a viral a

nd contagious infection that can affect birds and various mammals, including pigs and humans.

 The virus mainly attacks the upper respiratory tract, nose, throat and bronchi, and more rarely the lungs. A recent study published in the journal Science shows that the main killer of influenza is not the virus itself, but additional bacterial infection. This work was carried out by a team from the University of Medicine in Vienna, Austria.

 When a person is sick, their immune system is overrun and they become more susceptible to an infectious attack. The flu is no exception to the rule, and Legionella knows it well. This bacterium, which has the scientific name Legionella pneumophila, is responsible for legionellosis. This disease can lead to the development of pneumonia, an acute infection of the lungs that can be fatal if left untreated.

 Co-infection with influenza and fatal legionella in mice

 During their work, the scientists used the mouse as an animal model. They showed that rodents infected with both influenza and legionella developed fatal pneumonia. "In our model, co-infection with the influenza virus and Legionella is fatal," explains Amanda Jamieson, study director. She adds that "what is surprising is that the development of Legionella is the same in mice with influenza and non-influenza".

 Why are mice with the flu more susceptible to legionella? To answer this question, the authors analyzed lung tissue from diseased mice. They find that the lungs are not properly repaired in animals with influenza. Thus, during an additional infection with Legionella, the bacteria could more easily enter the lungs, and thus cause fatal infections.

 Scientists then tested drugs that help the immune system repair damaged tissue. The results are encouraging, as fewer co-infected mice would die. This study paves the way for the production of new means of treating bacterial infections in people with influenza.