To replicate, the coronavirus makes people sneeze. The coronavirus protein PLpro stimulates the trigeminal and vagus nerve pain receptors that innervate the respiratory tract, causing sneezing. During sneezing, up to 40,000 virus droplets are formed, and the coronavirus can spread between people.
The PLpro protein is necessary for the replication of the coronavirus and for suppressing the body’s immune response. Two days after infection, cells in the respiratory tract produce PLpro. The PLpro protein acts on neighboring cells and endings of sensitive neurons in the respiratory tract.
Sensitive neurons transmit pain, itching, temperature, and touch sensations. Pain receptors (nociceptors) of the trigeminal nerve are responsible for sneezing, nasal discharge, facial pain, and mouth cavities, common symptoms of viral infection.
Scientists from the University of California studied which viral symptoms PLpro causes. Scientists experimented on mice: PLpro or a control mixture was introduced into the mice’s noses. Within 14 seconds, PLpro caused the mice to sneeze intensively. In contrast, mice receiving the control mixture sneezed less and only after 30 seconds. Additionally, PLpro induced pain behavior in mice – the mice rubbed their noses with their front paws, unlike itching, which is responded to by scratching with the hind paw.
PLpro is expressed by all coronaviruses, including SARS and MERS. SARS also activates respiratory tract nociceptors. Cold viruses also produce the PLpro protein, which contributes to sneezing.
The SARS-CoV-2 coronavirus changes the gene expression in sensitive neurons, enhancing pain perception. Direct ganglia infection can lead to changes in gene expression, promoting pain hypersensitivity and inflammation.
Conclusion
Symptoms of viral infection such as sneezing, coughing, and headaches result from abnormal activation of sensitive neurons and branches of the vagus nerve, which under healthy conditions regulate breathing, contribute to protective respiratory reflexes, and are responsible for pain sensations. The coronavirus activates sensitive neurons through the PLpro protein, promoting sneezing and pain hypersensitivity. Medicinal compounds that block PLpro can alleviate coronavirus symptoms and reduce its replication and spread.
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Reference
SARS-CoV-2 papain-like protease activates nociceptors to drive sneeze and pain
