Revealed Why H5N1 Is So Deadly For Humans

The H5N1 bird flu strain has killed over half of the 241 humans it has infected since 2003. A team of scientists from the Oxford University Clinical Research Unit may have found out why H5N1 bird flu infection is so much more deadly than normal human influenza viruses. It is all to do with the patient's viral load and the subsequent inflammatory response.

You can read about this study in Nature Medicine.

Before the study the team had noted that H5N1 causes severe disease in humans, but why it is virulent was unclear. In vitro and animal studies had indicated that high viral load is important for disease pathogenesis. They wanted to asses the relevance of these findings for human patients.

The researchers looked at 27 people at the Hospital for Tropical Diseases, Ho Chi Minh City, Vietnam. 18 of them had been infected with H5N1 while the other 9 had been infected with normal human influenza virus subtypes.

They found that those infected with H5N1 had much higher viral loads - concentrations of H5N1 in their blood and pharynx (throat) - than those with normal human flu. They also found that the H5N1 infected patients who had died had much higher viral loads than the H5N1 infected patients who did not die.

Those with a high H5N1 viral load had the highest levels of cytokines. Cytokines control your body's response to infection. The patients who died also had much lower levels of T-lymphocytes.

Put simply, it means that the higher level of H5N1 a patient has, the greater are his/her chances of dying.

High levels of cytokines, low levels of of lymphocytes, and the resulting intense inflammatory responses, probably contributed to more severe lung damage and a greater chance of death, say Dr. Menno and team. They stressed that preventing this intense cytokine response should be the focus of clinical management. This entails early diagnosis and effective antiviral treatment.

This research points to swift and effective use of antivirals, such as Tamiflu or Relenza, in order to prevent virus levels from rising too fast.

Menno D de Jong, Cameron P Simmons, Tran Tan Thanh, Vo Minh Hien, Gavin J D Smith, Tran Nguyen Bich Chau, Dang Minh Hoang, Nguyen Van Vinh Chau, Truong Huu Khanh, Vo Cong Dong, Phan Tu Qui, Bach Van Cam, Do Quang Ha, Yi Guan, J S Malik Peiris, Nguyen Tran Chinh, Tran Tinh Hien & Jeremy Farrar
Nature MedicinePublished online: doi:10.1038/nm1477
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