H5N1 Causes Protein “Storm”
That Overwhelms Immune System
By James Donahue
Nov. 13, 2005
Scientists in Hong Kong said in a medical
report last week that H5N1 is so deadly because it seems to cause a “storm” of immune system chemicals that overwhelms
Writing for the online
medical journal Respiratory Research, the scientists said the H5N1 virus causes proteins called cytokines that rush to the
infected lung tissue. The virus attack is so severe and the cytokine reaction so intense that its impact on the immune system
can be fatal.
The study suggests that
if H5N1 causes a pandemic, the disease could disproportionately strike the young and healthy the hardest. The elderly and
others with compromised immune systems might not be as threatened.
The study also raises
questions about how effective drugs will be in controlling a pandemic like this.
Michael Chan and Malik
Peins of the University of Hong Kong
wrote that the disease appears to be growing more deadly for humans as it mutates among birds.
They said the mortality
rates among humans contacting the virus in Honk Kong in 1997 was 33 percent compared to 55 percent among victims in Thailand and Vietnam
in 2004. “The reasons for this unusual severity of human disease have remained unclear,” they said.
In their study, Chan
and Peins took samples of H5N1 from a patient that died of the infection in a 1997 outbreak and from two patients infected
in Vietnam in 2004. They used the virus
to infect lung tissue samples taken from other non-flu patients.
While the viruses from
both periods brought in a storm of cytokines, the Vietnamese strains caused a bigger cascade.
“This could be
because of continued mutations,” the researchers said.
The study also explains
why patients suffering from the virus complain of severe respiratory distress and difficulty breathing