Altered Receptor Binding in H5N1 Bird Flu in Indo

The 1918–19 influenza pandemic began, in some parts of the world, with mild outbreaks in the spring of 1918. In the fall of that year, a lethal wave swept the globe. Outbreaks occurred in early September in North America, Europe, and Africa and spread rapidly, so that the disease had peaked and declined worldwide by the end of December (1–4). Many areas had an additional wave of the disease in the early months of 1919. In most communities, the fall wave of the pandemic lasted approximately l month, with 25% to 30% of the population experiencing symptomatic disease. Clinically, epidemiologically, and pathologically, the disease was remarkably uniform, suggesting that similar viruses were causing disease worldwide (5). To assess the homogeneity of the 1918 pandemic influenza virus, partial hemagglutinin (HA) gene sequences were determined for strains from five cases, including two newly identified samples from London, United Kingdom. The strains show 98.9% to 99.8% nucleotide sequence identity. One of the few differences between the strains maps to the receptor-binding site of HA, which suggests that two receptor-binding configurations were co-circulating during the pandemic.