When COVID-19 or flu viruses kill, they often have an accomplice – bacterial infections

Submitted by Michael Frankfort @mfrank_76


When COVID-19 or flu viruses kill, they often have an accomplice – bacterial infections


Research Assistant Professor of Immunology, Tufts University

The 1918 influenza pandemic resulted in the loss of over 3% of the world’s population – at least 50 million people. But it wasn’t the flu virus that caused the majority of these deaths.

An analysis of lung samples collected during that flu pandemic indicated that most of the deaths were likely due to bacterial pneumonia, which ran rampant in the absence of antibiotics. Even in more recent history, like the 1957 H2N2 and 2009 H1N1 flu pandemics, nearly 18% of patients with viral pneumonia had additional bacterial infections that increased their risk of death. And the COVID-19 pandemic is no different.

With yet another flu season fast approaching in the midst of the ongoing COVID-19 pandemic, lessening the harm caused by these viruses is important to prevent deaths and reduce infections. However, many deaths associated with the flu and COVID-19 don’t occur at the hand of the virus alone. Instead, it’s a secondary bacterial infection that is often at the root of the devastating consequences attributed to an initial viral infection.

I am an immunologist who studies why and how cells die during bacterial and viral infections. Understanding the synergy between these microbes is critical not only for effective diagnosis and treatment, but also for managing current pandemics and preventing future ones. My colleagues and I published a study showing how an immune system protein crucial to fighting against viruses also plays an indispensable role in fighting bacteria.

Viruses and bacteria team up

Multiple pathogens can cause multiple infections in different ways. Scientists distinguish each type based on the timing of when each infection occurs. Coinfection refers to two or more different pathogens causing infections at the same time. Secondary or superinfections, on the other hand, refer to sequential infections that occur after an initial infection. They’re often caused by pathogens resistant to antibiotics used to treat the primary infection.

How viral and bacterial infections interact with each other increases the potential harm they can cause. Viral respiratory infections can increase the likelihood of bacterial infections and lead to worse disease. The reason why this happens is often multifaceted.

Within your respiratory tract, the epithelial cells lining your airways and lungs serve as the first line of defense against inhaled pathogens and debris. However, viruses can kill these cells and disrupt this protective barrier, allowing inhaled bacteria to invade. They can also change the surface of epithelial cells to make them easier for bacteria to attach to.

Viruses can also alter the surface of epithelial and immune cells by reducing the number of receptors that help these cells recognize and mount a response against pathogens. This reduction means fewer immune cells report to the viral infection site, giving bacteria an opening to launch another infection.

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