Our modern, global village is a crowded, hectic place and that makes us very vulnerable to infectious diseases. In the last few decades, viruses like SARS and AIDS have emerged and spread all over the world. It will take only one highly virulent, highly contagious and lethal virus to eradicate the human race. The H5N1 avian flu is poised to kill hundreds of millions worldwide; what kind of carnage will the next generation of viruses wreak?