Several new hepatitis viruses have recently been identified. Hepatitis B has infected two billion people alive today, of whom 350 million are chronically infected and at risk from death from liver disease. The threat of a new global influenza pandemic is increasing. Major shifts in the make-up of influenza viruses occur every 20 years or so, triggering large epidemics and causing thousands of deaths. The next such shift is expected very soon.
Environmental change is a major cause.
Expanding areas of human habitation put millions at risk from pathogens previously rare or unknown as causes of human disease. The effects of climate change may also give some diseases the opportunity to spread to new areas. Antimicrobial drugs have become less effective. Microbes continue to evolve and adapt to their environment, adding antibiotic resistance to their evolutionary pathways. A critical issue that has emerged is how viruses or bacteria 'mutate' to become new varieties.