Why does CDC conduct research on bird flu viruses?
Birds are the natural hosts to all known subtypes of influenza A viruses, and while bird flu viruses mainly infect birds, they can—and have—crossed the species barrier to infect humans. Rarely, bird flu viruses may develop the capacity to infect and spread among humans. Those viruses that can spread efficiently among humans may lead to a pandemic. Because bird flu viruses are an important source of potential new human flu viruses, CDC seeks to learn more about these viruses and their properties, and how different bird flu subtypes and strains might affect humans. Highly pathogenic avian influenza A (H5N1) viruses (Asian lineage) or so called “H5N1”, which began spreading in birds throughout Asia in 2003 and continue to spread to other regions, now meet two of the three conditions necessary for a pandemic to occur: • These are new influenza viruses in people to which there is little or no human immunity, and • These viruses have infected humans and caused illness. However, highly pathog
