Zoonoses 4
th
year 19-02-2017 Dr.Osama muwafg
1
Zoonoses:
(“zoonosis” is singular) are diseases the agents of which are
transmitted between vertebrate animals and people. It is the
interaction of agent, host (degree of susceptibility), and the
environment they share that determines whether or not
transmission of the agent will be successful, leading to infection
and, ultimately, occurrence of disease.
Initial Recognition of the Agents
1. Vertebrate animals (including people) are the reservoirs of
zoonotic infections and the agents are transmitted directly or
indirectly between them.
2. Individual identification of the agents of the zoonoses began
after the invention of the microscope, starting with the larger
parasites in the 1700s.
Microscopic examination of the unstained agents remained
virtually the only means of characterizing them until the
introduction of cultural techniques and staining with aniline dyes
in the latter half of the 1800s.
3. Except for a few diseases such as rabies, characterization of the
host relationships of the zoonoses, particularly the modes of
transmission, awaited the 20th century. This is true for all
vectorborne zoonoses because it was not until the 1890s that this
mode of spread was first recognized.
4. Some diseases caused by infection with zoonotic agents have
been recognized clinically since early history whereas others are
only now being recognized for the first time.
Zoonoses 4
th
year 19-02-2017 Dr.Osama muwafg
2
In some instances, it is evident that the clinical syndrome and
associated agent are truly newly emerging entities. For most,
however, recognition has evolved over the past century as a result
of careful clinico-epidemiologic observations and innovative
applications of diagnostic laboratory techniques.
5. Except for vaccination against smallpox, there were few tools to
protect people and their livestock from specific diseases until the
past century. Cooking meat (or not eating it), boiling milk, and
avoiding exposure by quarantining immigrant people and their
cattle were nonspecific protective measures used by some early
societies. With recognition of the agents has come an ever-growing
search for drugs to cure the diseases they cause and for vaccines to
prevent them.
6. Since its introduction in the 1920s, commercial milk
pasteurization has become the most effective tool in preventing
brucellosis and tuberculosis (M. bovis) in people. Seaports where
programs have been implemented to control rats and the oriental
rat fleas they harbor have remained free of urban plague
epidemics. Since programs to eliminate the Aedes aegypti
mosquito have been undertaken in seaports and other susceptible
areas, there have been no outbreaks of urban yellow fever. With
the introduction of DDT and other chemical insecticides in the
1940s came the first highly effective means of halting outbreaks of
vectorborne disease. Beginning in the 1950s, programs to
immunize dogs have been effective in eliminating canine rabies.