Scientists are now beginning to unravel the biological mechanisms, which have been something of a mystery: The neurons that detect odors lack the receptors that the coronavirus uses to enter cells, prompting a long debate about whether they can be infected at all.
Insights gleaned from new research could shed new light on how the coronavirus might affect other types of brain cells, leading to conditions like "brain fog," and possibly help explain the biological mechanisms behind long COVID — symptoms that linger for weeks or months after the initial infection.
The new work, along with earlier studies, settles the debate over whether the coronavirus infects the nerve cells that detect odors: It does not. But the virus does attack other supporting cells that line the nasal cavity, the researchers found.
The infected cells shed virus and die, while immune cells flood the region to fight the virus. The subsequent inflammation wreaks havoc on smell receptors, proteins on the surface of the nerve cells in the nose that detect and transmit information about odors.
The process alters the sophisticated organization of genes in those neurons, essentially short-circuiting them, the researchers reported.
Their paper significantly advances the understanding of how cells critical to the sense of smell are affected by the virus, despite the fact that they are not directly infected, said Dr. Sandeep Robert Datta, an associate professor of neurobiology at Harvard Medical School, who was not involved in the study.
"It's clear that indirectly, if you affect the support cells in the nose, lots of bad things happen," Datta said. "The inflammation in the adjacent cells triggers changes in the sensory neurons that prevent them from working properly."
In Europe, Doors Shut to Mideast Migrants Are Flung Open for Ukrainians 歐洲廣開善門收難民 限烏克蘭人
Russia's invasion of Ukraine has pushed tens of thousands of people out of their homes and fleeing across borders to escape violence. But unlike the refugees who have flooded Europe in crises over the past decade, they are being welcomed.
Countries that have for years resisted taking in refugees from wars in Syria, Iraq and Afghanistan are now opening their doors to Ukrainians as Russian forces carry out a nationwide military assault. More than 2.4 million refugees have left Ukraine, according to United Nations estimates, and at least half of them have crowded onto trains, jammed highways or walked to get across their country's borders in what officials warn could become the world's next refugee crisis.
U.N. and U.S. officials described their concerted diplomatic push for Ukraine's neighbors and other European nations to respond to the outpouring of need. President Joe Biden "is certainly prepared" to accept refugees from Ukraine, Jen Psaki, the White House press secretary, said Thursday, but she noted that the majority of them would probably choose to remain in Europe so they could more easily return home once the fighting ended.
In Poland, government officials assisted by American soldiers and diplomats have set up processing centers for Ukrainians. The Polish government is spending hundreds of millions of dollars on a border wall, a project it began after refugees and migrants from the Middle East tried to reach the country last year but ended up marooned in neighboring Belarus.
The military in Hungary is allowing in Ukrainians through sections of the border that had been closed. Hungary's hard-line prime minister, Viktor Orban, has previously called refugees a threat to his country, and his government has been accused of caging and starving them.