First human transmission of bird flu: recent tests show the first probable case of human transmission of bird flu and have prompted calls for urgent investigation to assess whether avian influenza A has acquired the ability to spread more easily among people.

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The Chinese Center for Disease Control and Prevention has investigated the case of a 24-year-old man and his 52-year-old father diagnosed with the avian H5N1 virus within a week of each other in the Jiangsu Province in China in December 2007. The son died and his father survived after antiviral treatment and post-vaccination plasma from a H5N1 trial.

The researchers who have published their work in the international medical journal The Lancet identified the H5N1 isolated in both men as genetically identical except for one small change in the nucleic acid chain making up the virus' genetic structure. "Limited, non-sustained person-to-person transmission of H5N1 virus probably occurred in this family cluster," they concluded.

The son's exposure to H5N1 was attributed to a poultry market visit six days before onset of illness, and the father's, his unprotected exposure to his ill son.

Characteristics of the virus required for human transmission remain unknown. Professor Yu Wang of the Chinese Center for Disease Control and Prevention in Beijing said H5N1 clusters required urgent investigation due to the "possibility that a change in the epidemiology of H5N1 cases could indicate that H5N1 viruses have required the ability to spread more easily among people".

Vietnam's Ho Chi Minh City Hospital for Tropical Diseases Dr Jeremy Farrar said as a precaution all family members of patients diagnosed with probable or confirmed H5N1 should be given chemoprophylaxis and placed under surveillance and personal protection given to health workers looking after patients in hospitals. "Whatever the underlying determinants, if we continue to experience widespread, uncontrolled outbreaks of H5N1 in poultry, the appearance of strains well adapted to human beings might just be a matter of time," he said.

As of 17 April 2008, the World Health Organization (WHO) reported 381 cases of H5N1 infection and 240 deaths from 15 countries since November 2003. Although most cases have been sporadic, some 25% have occurred in clusters of two or more linked people.

WHO has warned avian influenza is "deeply entrenched" in Australia's neighbour Indonesia, the country worst hit by the virus and with the situation described as "grave". Indonesia has had 132 cases of H5N1 and 107 deaths, with 31 out of 33 provinces infected. WHO reports the virus as endemic in Java, Sumatra, Bali and southern Sulawesi.

REFERENCE

Wang, H. Feng, Z. Shu, Y., Yu, H,, Zhou, L., Zu, R., Huai, Y., Dong, J., Bao, C., Wen, L,, Wang, H,, Yang, P., Zhao, W, Dong, L., Zhaou, M., Liao, Q., Yang, H., Wang, M., LU, X., Shi, Z., Wang, W., Gu, L., Zhu, F., Li, Q., Yin, W., Yang, W., Li, D., Uyeki, T. and Wang, Y. 2008. Probable limited person-to-person transmission of highly pathogenic avian influenza A (H5N1) virus in China. The Lancet, 371(9622):1427-34.