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Table 1 Five stages leading to endemic human diseases (adapted and summarized from Wolfe et al. [3])

From: Towards integrated surveillance-response systems for the prevention of future pandemics

Stage

Description

I

Pathogens that are present in animals but have not been detected in humans und natural conditions.

II

Pathogens of animals that are transmitted from animals to humans, but are not transmitted between humans.

III

Pathogens of animals that are transmitted from animals to humans. In humans they don’t transmit easily and soon die out.

IV

Pathogens of animals that are transmitted to humans, leading to ongoing human to human transmission without the involvement of the animal host.

V

Pathogens that are exclusive to humans.