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 the patient.

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