Texas scientist warns of new SARS-CoV-2 neuroinvasion pathway involving the trigeminal nerve

Medical News: An Overlooked Pathway for Virus Entry into the Brain
While SARS-CoV-2, the virus responsible for COVID-19, has largely been understood as a respiratory pathogen, its ability to invade the nervous system is becoming an area of growing concern. A leading researcher from Texas, Dr. Jason C. Hsu of the University of Texas Medical Branch, Galveston, and his team have uncovered alarming new evidence suggesting that the virus can exploit the trigeminal nerve as a pathway to the brain. This research has significant implications for how we understand the neurological symptoms associated with COVID-19, such as headaches, loss of smell, and even more severe outcomes like strokes and seizures.


Texas scientist warns of new SARS-CoV-2 neuroinvasion pathway involving the trigeminal nerve

This Medical News report delves into the study that explored this overlooked route of viral invasion and the broader implications it could have for COVID-19 treatment and management. Until recently, scientists believed the olfactory nerve, which controls the sense of smell, was the primary route the virus used to access the brain. However, the discovery of viral activity in the trigeminal nerve shifts the focus to new territory in the fight against the disease.
 
Understanding the Trigeminal Nerve
The trigeminal nerve is the largest cranial nerve and is responsible for transmitting sensations from the face to the brain, including pain, touch, and temperature. Its location and proximity to nasal tissues make it a potentially easy target for viral invasion. The nerve ends near the nasal cavity, a region exposed to respiratory viruses, making it a viable candidate for infection.
 
Dr. Hsu’s team was initially focused on the olfactory nerve when they observed unexpected viral activity in the trigeminal nerve. They used AC70 human ACE2 transgenic mice, a model that mimics human viral infections, to study the neuroinvasive potential of SARS-CoV-2. What they found was alarming: the virus quickly spread from the trigeminal ganglion - a cluster of nerve cells connected to the trigeminal nerve - into the brain. Within days of infection, SARS-CoV-2 had invaded multiple regions of the brain, including areas critical to motor and sensory functions.
 
Key Findings of the Study
The study, conducted at the Galveston National Laboratory, one of the leading research institutions in the United States, revealed several critical findings about how the virus behaves once it infiltrates the trigeminal nerve. Unlike previous assumptions that the virus only attacked respiratory cells, this research shows that neurons, particularly those linked to the trigeminal nerve, are also susceptible.
 
Major takeaways from the study:
-Viral Replication in the Trigeminal Ganglion: The researchers found that the trigeminal ganglion was an early site of viral replication. SARS-CoV-2 was present in significant quantities within the ganglion even before visible symptoms like w eight loss appeared in the mice. This suggests that the virus may be able to infiltrate the brain through the trigeminal nerve before it is detectable elsewhere in the body.
 
-Spread Throughout the Brain: Once inside the brain, the virus quickly spread to various regions. The study identified several areas where viral replication occurred, including the olfactory bulb, hypothalamus, hippocampus, and brainstem. Notably, the virus appeared to have a preference for neurons, which are essential for transmitting signals in the brain.
 
-Lack of Inflammation: Despite the widespread viral presence, the researchers were surprised to find minimal signs of inflammation in the brain. While inflammatory cytokines (proteins that signal the immune system to fight infection) were present, there was little evidence of the kind of immune response typically associated with brain infections. This lack of inflammation could explain why many COVID-19 patients suffer from long-term neurological symptoms without experiencing the classic signs of brain infection, such as fever or swelling.
 
-Alteration of Gene Expression: Another critical finding was the virus’s ability to alter the expression of genes involved in neural function. The study showed that several key genes related to neurotransmitter pathways, such as those involving dopamine, were significantly affected. This alteration could explain the cognitive symptoms seen in many COVID-19 patients, such as memory loss, brain fog, and attention deficits.
 
Implications for COVID-19 Treatment
The discovery that the trigeminal nerve serves as a route for SARS-CoV-2 to invade the brain could have profound implications for how COVID-19 is treated. Current treatments focus largely on managing respiratory symptoms, but this new research suggests that protecting the nervous system from viral invasion is equally important.
 
Dr. Hsu and his team emphasize the need for further research to determine how widespread this trigeminal nerve involvement is in human patients. If confirmed, it could lead to new therapeutic approaches aimed at blocking the virus’s access to the brain. For example, antiviral treatments or vaccines could be developed specifically to target the trigeminal nerve, preventing the virus from reaching the brain in the first place.
 
The Long-Term Impact on COVID-19 Survivors
One of the most concerning aspects of this discovery is the potential for long-term neurological damage in COVID-19 survivors. Many patients who recover from the initial infection report lingering symptoms, a condition now referred to as "long COVID." These symptoms often include cognitive difficulties, headaches, and even more severe conditions like strokes and seizures.
 
This research suggests that some of these symptoms could be the result of the virus’s invasion of the trigeminal nerve and subsequent spread to the brain. By understanding this pathway, scientists hope to develop treatments that can prevent or mitigate these long-term effects.
 
Conclusion: A New Understanding of SARS-CoV-2 Neuroinvasion
In conclusion, this groundbreaking research from the University of Texas Medical Branch sheds new light on how SARS-CoV-2 invades the nervous system. The discovery that the virus uses the trigeminal nerve as a pathway to the brain adds a new dimension to our understanding of COVID-19’s effects on the body. While much work remains to be done, these findings could lead to new treatments and preventative measures that protect the brain from viral invasion.
 
The study findings were published in the peer-reviewed journal: Frontiers in Microbiology.
https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1455462/full
 
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