How Rhinovirus Causes Infectious Cough Remains a Mystery

Pharmacists know that a cough can be triggered by many stimuli.

Pharmacists know that a cough can be triggered by many stimuli.

What is not known, however, is the mechanism of infectious cough brought on by rhinovirus. Such knowledge could help lessen the financial burden (around $40 billion in the United States) of the common cold and its accompanying cough.

The common cold itself creates self-limited discomfort, but cough is one of its most annoying symptoms. It often persists after all other symptoms have resolved, and a lingering cough is notoriously difficult to treat.

Now, researchers have published a paper in BMJ Open Respiratory Research that described how the most common cough—which is caused by upper respiratory tract infection with rhinovirus—has no benefit to the host.

Viruses hijacking infected individuals’ natural defense mechanisms is old news. It has long been known that doing so increases viral propagation through the population, but it is not clear how these viruses work.

Researchers have searched for infectious cough’s mechanism for years, given that finding how pathogens create cough could lead to an effective cure. So far, they have been unable to find definitive answers, but they have proposed some theories that may explain rhinovirus’ mechanism.

The current research reports that a few mechanisms seem most likely. They include physical disruption of the epithelial lining, excess mucus production, and an inflammatory response to rhinovirus infection that may be excessive. The most convincing hypothesis is that viruses cause neuronal modulation, which has been closely associated with chronic, lingering cough.

One neuropeptide known as calcitonin gene-related peptide seems to indirectly enhance mucus secretion through vasodilation. Many other substances also seem to disrupt neuronal balance and lead to cough.

The researchers acknowledged that the science surrounding cough is confusing, and many theories overlap.

Currently, studies have identified dozens of potential therapeutic targets, and finding the pathways that influence cough most has proven to be challenging. One concern is that targeting a general mechanism like system immune modulation will generate unwanted adverse effects.

For now, viable approaches include only cough suppressants and possibly modulating the inflammatory response using steroids or nonsteroidal anti-inflammatory drugs.