Volume 1, Issue 1, March 2006
JSM Peiris & Wilina Lim
Department of Microbiology, The University of Hong Kong & Virology Division, Public Health Laboratory Services Branch, Centre for Health Protection, Department of Health, Hong Kong SAR
Avian influenza A subtype H5N1 is endemic in poultry across south-east Asia and continues to cause zoonotic disease in humans. So far, transmission of virus from avian to humans appears very inefficient and sustained transmission from human-to-human has not occurred. However, with the continued opportunity for human exposure over an ever increasing geographic range, it is possible (though not inevitable) that H5N1 virus may acquire the ability to transmit efficiently from human-to-human, leading to a pandemic.
Human disease caused by H5N1 influenza virus typically presents either as a rapidly progressing viral pneumonia, often with evidence of marked lymphopenia, leucopenia and mild to moderate liver dysfunction. Some patients also have evidence of diarrhea and other gastro-intestinal manifestations. The disease may progress to acute respiratory distress syndrome (ARDS), multiple organ dysfunction and death (1-5). However, in the individual patient, it is not possible to make a reliable diagnosis of avian influenza H5N1 purely on clinical grounds. Furthermore, some patients may manifest a milder course of the disease presenting merely as a self-limited influenza-like illness. Virological diagnosis is therefore essential.