Michael Shiloh, a physician who specializes in infectious disease research at UT Southwestern Medical Center in Dallas, says he regularly sees coughing patients who have been sick for weeks. “We see that there are no longer any viral particles left, and yet they continue to cough,” he says.
How can recovering people sometimes continue to suffer from a persistent cough? Research into how infections affect the nerves in our airways offers a solution.
Why do we cough?
Coughing is an important reflex that protects the airways from threats such as harmful emissions, water and suffocation, says pulmonologist and researcher Lorcan McGarvey of Queen's University Belfast.
This reflex is triggered by nerves that extend to the bronchi. These nerves are covered in receptors: proteins that respond to changes in the environment, such as cold air or capsaicin, the substance that makes peppers hot. If the receptors come into contact with an irritant, the nerves send a signal to the brain, causing the person to feel the coughing stimulus. From there, the brain sends a command to the windpipe to cough, or to suppress the feeling. Therefore, people sometimes have conscious control over certain types of cough.
While it's obvious that we cough to clear mucus from our throat, it's also possible that the virus makes us cough to spread itself further. For example, many infections are accompanied by a dry cough without mucus. So there are still a lot of unanswered questions.
Cough after a viral infection
What we do know is that viral infections lead to inflammation. When we're sick, this inflammation makes the nerves in the bronchial tubes more sensitive, stimulating the cough response more quickly. Research has shown. Hence, one hypothesis is that persistent coughing after infection is caused by hypersensitive nerves.
Researchers had already noticed it in 1990 Influenza infection in guinea pigs led to increased sensitivity of airway nerves, resulting in a human-like cough. Sick guinea pigs were more likely to cough when exposed to irritants than healthy individuals – something that has also been shown in humans.
In 2016, scientists did just that Another discovery. They saw that infection with an influenza-like virus caused certain nerves in the bronchial tubes to make extra copies of a receptor called TRPV1, which responds to capsaicin and other stimuli. Therefore, researchers suspect that hypersensitivity of airway nerves is related to these and other receptors.
When do you go to the doctor?
The cough usually stops about two to three weeks after infection. If your cough persists for more than eight weeks, Shiloh and McGarvey recommend seeing a doctor. If the cough is accompanied by pain or other symptoms, such as fever, shortness of breath, bloody mucus, or weight loss, researchers advise consulting a doctor sooner.
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