Via CIDRAP, Robert Roos writes: Report details brain complications in Canada's H5N1 case. Excerpt from a long, informative post:
The authors say brain infections are uncommon in H5N1 cases, although animal studies show that the virus can invade the central nervous system (CNS). They reference a review of human H5N1 cases published in The Lancet in 2008, which cited one patient who had a coma along with evidence of the virus in CSF, suggesting CNS involvement. That review also said a few autopsies of H5N1 victims suggested that the virus replicated in nonrespiratory tissues, including the brain.
Tim Uyeki, MD, MPH, an influenza expert with the US Centers for Disease Control and Prevention, said neurologic manifestations are seen occasionally in seasonal flu cases and have been reported in a few H5N1 cases.
"There are cases every winter of seasonal influenza–associated encephalopathy or encephalitis, typically in young children," he said in an interview. He noted that influenza virus infection of the respiratory tract can cause cytokine dysregulation, the intense inflammatory response also known as cytokine storm, and this is believed to be the cause of neurologic complications in seasonal flu cases.
"Seasonal influenza viruses are not thought to be infecting the brain," Uyeki said. "But inflammation can produce a fulminant encephalitis."
In the rare H5N1 cases with neurologic complications, however, the picture seems a little different, in that there has been some evidence of actual infection in the brain, he said.
For example, a 2007 report in The Lancet reported on two H5N1 cases, one of which involved a man who had pneumonia and, while hospitalized, experienced irritability and convulsions followed by decreased consciousness. An autopsy revealed evidence of H5N1 virus infection in his brain, Uyeki said, adding, "So that suggests that H5N1 virus can directly infect brain tissue. H5N1 virus can disseminate from the lungs into the blood, and then spread throughout the body, including to the CNS."