Recent study has revealed that novel coronavirus may enter the human brain through the nose. This finding may help explain some of the neurological symptoms observed in COVID-19 patients, and inform diagnosis and measures to prevent infection.
The virus not only affects the respiratory tract, but also impacts the central nervous system (CNS). This eventually results in neurological symptoms such as loss of smell, taste, headache, fatigue and nausea.
Although recent research has described the presence of viral RNA in the brain and cerebrospinal fluid, it remains unclear where the virus enters and how it is distributed within the brain.
The researchers examined the nasopharnyx -- the upper part of the throat that connects to the nasal cavity -- a likely first site of viral infection and replication, and the brains of 33 patients -- 22 males and 11 females -- who died from COVID-19.
The researchers said that they found the presence of SARS-CoV-2 RNA, the genetic material of the coronavirus, and protein in the brain and nasopharynx. Intact virus particles were also detected in the nasopharynx. The highest levels of viral RNA were found in the olfactory mucous membrane.
Moreover, the disease duration was inversely correlated with the amount of detectable virus. This indicated that higher SARS-CoV-2 RNA levels were found in cases with shorter disease duration.
SARS-CoV-2 was also found in other areas of the nervous system, including the medulla oblongata -- the primary respiratory and cardiovascular control centre of the brain.The researchers noted that further COVID-19 autopsy studies that include a broad range of sampling are needed to identify the precise mechanisms that mediate the virus's entry into the brain, and examine other potential ports of entry.