Download Training Manual on wildlife diseases and surveillance

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Training Manual on Wildlife Diseases and Surveillance
Since wild animals are the source, or reservoir, for so many important zoonotic
pathogens, one important aspect of pathogen transmission is to consider the different ways in
which wild animals can be the source of zoonotic infections for people. Pathogens can be
transmitted from wild animals to humans by all of the routes of transmission just reviewed.
However, zoonotic pathogen transmission also can be looked at in another way.
– This diagram tries to show the various relationships that can exist among wild
animals, domestic animals and humans through which zoonotic pathogens from wild animals
can be transmitted to humans.
– Pathogens from wild animals may be transmitted directly to people. Examples are
Brucella, Leptospira and plague (Yersinia pestis)
– Pathogens from wild animals may be transmitted to domestic animals, which then
become the source of infection for people. Examples are Nipah virus (from bats to pigs to
people) and bovine tuberculosis (from wild animals to domestic animals to people).
– Pathogens from wild animals may be transmitted to domestic animals, undergo
genetic changes in the domestic animal population, and then the genetically altered pathogen
can be transmitted from domestic animals to people. An example is Highly Pathogenic H5N1
avian influenza virus which entered domestic poultry populations as a low pathogenicity strain
from wild birds, developed into a highly pathogenic strain in domestic poultry and has been
transmitted to people from domestic poultry.
– Pathogens may be transmitted from wild animals directly to humans, but then
undergo genetic modifications within human populations that result in a new human pathogen
which is maintained in human populations, is readily transmitted from person to person and no
longer requires the original wild animal source to persist and continue to cause disease.
Examples are HIV-AIDS, human pathogens derived from viruses in primate populations, and
measles virus, a human pathogen very close to rinderpest virus and which became established in
people through transmission from cattle, probably during the time when cattle were first