Stage 1 to 2 Pre-emergence ● Change in ability of the pathogen to infect human ● Host range increases ● vectors into closer contact with humans ○ Agriculture ○ Environment/Climate ○ Urbanization ○ Cultural practices ex) As climate increases, flea carriers such as deer move northwards. This makes Canada to increase in lyme disease rate Change in land use may also introduces new transmission between species Stage 2 to 3: Going Global ● Opportunity ○ Global travel and trades ○ Role of Superspreaders ● Virus population dynamics ○ Virus shed in sufficient quantities ○ Transmitted efficiently enough to sustain chain of transmission ○ No- pre-existing immunity ■ Cannot avoid with immune system ex) Nipah virus, transmission from bats to pigs. Transmission from animals to humans, but later is only limited to human-human transmission. Rare. But has potential to go widespread. ex)H5N1 Avian influenza, Bird flu. Reservoir as wild birds or poultry. Mainly transmission from birds to humans. Human- human transmission is rare. Have not been into pandemic level but is in watch list Virus Reservoir Stage Human-to-Human Transmission H5N1 Birds (poultry) 2-3 Rare, limited (not sustained) H1N1 Initially pigs 5-6 Sustained, efficient human-to-human spread H1N1 has reached pandemic level in 2009. This is because unlike H5N1, H1N1 has human-human transmission possible.