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Training Manual on Wildlife Diseases and Surveillance
VI. Reservoirs of infectious pathogens
In the above diagram of transmission of zoonotic pathogens, wild animals are shown as
the source of zoonotic pathogens, which they very often are. In such situations, we often say that
wild animals are the reservoir for these pathogens. Generally, what we mean by this is that the
wild animals in question not only are the source of a zoonotic pathogen for infection in people or
domestic animals, but also that these wild animals are the natural habitat for the pathogen. The
pathogen is maintained and persists over time within these wild animal populations.
The majority of human and animal infectious pathogens are able to infect more than one
species:
– 62% of all human pathogens are classified as zoonoses
– 77% of livestock pathogens infect multiple species
– 91% of domestic carnivore pathogens infect multiple hosts
– Nearly all pathogens that threaten endangered species around the world, like Chytrid
fungi threatening tropical amphibians, infect multiple species.
Thus, many infectious pathogens may have reservoirs in other species from which they
can be transmitted to the species of concern.
There are several different definitions of pathogen ‘reservoirs’ in the scientific literature.
A paper published in 2002, Daniel Haydon and his co-authors offered a unified way of defining
and understanding pathogen reservoirs that is very useful.
A pathogen reservoir is ‘one or more epidemiologically connected populations or
environments in which the pathogen can be permanently maintained and from which infection
is transmitted to the defined target population’
We can look at this concept of a reservoir in diagrammatic form:
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