Pathogens must enter host cells to cause disease. Explain why or why not.
A pathogen can be defined as the organism which has the potential to cause disease to other organisms Pathogens are widely diverse and comprise viruses and bacteria as well as unicellular and multicellular eukaryotes. Every living organism is affected by pathogens, including bacteria, which are targeted by specialized viruses called bacteriophages.
Pathogens can be divided into two main categories, namely facultative and obligate pathogens.
Facultative pathogens are organisms which does not rely on the host to complete their life-cycle. Facultative pathogens are primarily environmental bacteria and fungi that can occasionally cause infection. They include many of the most problematic hospital-acquired bacteria involved in the antimicrobial resistance pandemic. Typical examples of ‘accidental’ pathogens include Neisseria meningitidis or Escherichia coli.
Obligate pathogens require a host to complete their life cycle. All viruses are obligate pathogens as they are dependent on the cellular machinery of their host for their reproduction. Obligate pathogens are found among bacteria, including the agents of tuberculosis and syphilis, as well as protozoans such as plasmodium and macroparasites.
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