A newly identified respiratory pathogen, also called an emerging or novel respiratory pathogen, that causes acute respiratory infections may be a cause for concern for its potential to impact public health significantly. These infections include those caused by either the emergence of new variants of known respiratory pathogens (e.g. influenza A(H3N2)) or emergence of newly identified or unknown pathogens.
Birds can contract and transmit influenza. They have carried animal influenza viruses, with no apparent harm, for centuries. Wild birds, in particular, are natural carriers of influenza A viruses. Waterfowl (ducks, geese) are known to carry viruses of the H5 and H7 strains or subtypes. These viruses are usually in the low pathogenic form - in other words, they aren't as deadly to birds as highly pathogenic strains.
The avian influenza H7N9 virus was first identified in humans in 2013 in the People's Republic of China. There is no evidence to date that shows this type of influenza is easily transmitted between people.
The avian influenza H5N1 virus continues to cause sporadic human infections in a number of countries. There have been some instances of limited human-to-human transmissions among very close contacts. The World Health Organization (WHO) has monitored cases of H5N1 since 2003 and there has been no sustained human-to-human or community-level transmission identified thus far. In early 2014, a travel-related case of H5N1 was reported in Canada. It was the first and only H5N1 case reported in Canada to date.
Influenza pandemics or worldwide epidemics occur when an influenza A virus to which humans have little or no immunity develops the ability to cause sustained human-to-human transmission leading to outbreaks in the community. This 'novel' virus may arise when human and animal viruses mix together or through genetic mutation. This virus has the potential to spread rapidly around the world, causing a pandemic. History suggests that influenza pandemics occur 3-4 times per century. The last pandemic was declared in 2009, caused by the H1N1 virus. This pandemic had a lower impact than previous pandemics. The virus caused more severe illness in younger individuals compared to older adults. This influenza virus strain continues to circulate and is now included in the seasonal influenza vaccine.