Download Even in Koch`s time, it was recognized that infectious agents could

Even in Koch's time, it was recognized that infectious agents could be
responsible for disease without fulfilling all of the postulates.
LEARNING OBJECTIVE [ edit ]
Recognize the exception to Koch's postulates
KEY POINTS [ edit ]
Koch abandoned the requirement of the first postulatealtogether when he
discovered asymptomatic carriers of cholera.
The second postulate may also be suspended for certainmicroorganisms or entities that cannot (at
the present time) be grown in pure culture, such as prions responsible forCreutzfeldt–Jakob
disease.
The third postulate specifies "should", not "must", because as Koch himself proved in regard to
both tuberculosis and cholera, not all organisms exposed to an infectious agent will acquire
theinfection.
TERM [ edit ]
asymptomatic
not exhibiting any symptoms of disease.
Give us feedback on this content: FULL TEXT [edit ]
Koch's postulateswere developed in the 19thcentury as general guidelines to
identifypathogensthat could be isolated with the techniques of the day. Even in Koch's time,
it was recognized that some infectious agents were clearly responsible for disease, even
though they did not fulfill all of the postulates.
Currently, a number of infectious agents are accepted as the cause of diseases despite their
not fulfilling all of Koch's postulates.
Therefore, while Koch's postulates retain
historical importance and continue to
inform the approach to
microbiologic diagnosis, fulfillment of all
four postulates is not required to
demonstrate causality.
Koch abandoned the requirement of the
first postulate altogether when he
discovered asymptomatic carriers of
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cholera and, later, of typhoid fever.
Asymptomatic or subclinicalinfection carriers are now known to be a common feature of
many infectious diseases, especially viruses such as polio, herpes simplex, HIV, and hepatitis
C. Specifically, all doctors and virologists agree that the poliovirus causes paralysis in just a
few infected subjects, and the success of the polio vaccine in preventing disease supports the
conviction that the poliovirus is the causative agent.
Cholera bacteria
Scanning electron microscope image of Vibrio cholerae bacteria, which infect the digestive system.
The second postulate may also be suspended for certain microorganisms or entities that
cannot (at the present time) be grown in pure culture, such as prions responsible for
Creutzfeldt–Jakob disease.
The third postulate specifies "should", not "must", because as Koch himself proved in regard
to both tuberculosis and cholera, that not all organisms exposed to an infectious agent will
acquire the infection. Noninfection may be due to such factors as general health and
proper immune functioning; acquiredimmunity from previous exposure or vaccination;
or geneticimmunity, as with the resistance to malaria conferred by possessing at least one
sickle cell allele.
In summary, a body of evidence that satisfies Koch's postulates is sufficient but not necessary
to establish causation.