Endogenous infections are caused by microorganisms already present in the body, often becoming active due to certain stimuli, while exogenous infections arise from microorganisms in the external environment. For example, E. coli can cause a urinary tract infection if it moves from the gut to the urinary tract, illustrating how both infection types can occur. Notable examples include tuberculosis for endogenous infections, and salmonella enterocolitis and cholera for exogenous infections.

1. What is the difference between endogenous and exogenous infections? What is a protein
allergen?
Solution
Endogenous infections are defined as those infections that are caused by microorganisms that
are already in the body whereas exogenous infections are defined as those which are caused by
microorganisms from the external environment. Usually in endogenous infection, microbes are
already present in the body but in dormant state but are stimulated by some factors, tuberculosis
may be taken as a case. However, in exogenous infection microorganism gain their entry through
respiratory, gastrointestinal, vaginal, urinal or through injury. In case of exogenous infection,
pathogenic bacteria entering the body always cause disease. However, in case of endogenous
infection, some bacteria normally residing in the gut usually don’t cause any infection; however,
if the same bacterium enters the other sterile organ may cause infection there. As an instance, the
residential bacterium E. coli of the GI tract enters the urinary tract. This causes a urinary tract
infection. Sometimes the same type of infection occurs through both the exogenous and
endogenous ways. For example, the exogenous eczema occurs by an external irritant while as
endogenous eczema of which one type is infant eczema occurs by a stimulant already present
within the body. Examples of exogenous infections include Salmonella enterocolitis, Cholera,
Anthrax, Botulism etc. and examples of endogenous infections include tuberculosis etc.