Intracellular parasite

Intracellular parasites are parasitic microorganisms that are capable of growing and reproducing inside the cells of a host.

Facultative

Facultative intracellular parasites are capable of living reproducing inside or outside cells.

Bacterial examples include Neisseria meningitidis,^[1] Francisella tularensis and Listeria monocytogenes. Other examples include Brucella, Legionella, Mycobacterium, and Yersinia.

A fungal example is Histoplasma capsulatum.^[2]

Obligate

Obligate intracellular parasites are parasitic microorganisms that cannot reproduce outside their host cell, forcing the host to assist in the parasite's reproduction.

Obligate intracellular parasites of humans include:

• Viruses
• Certain bacteria, including:
  • Chlamydia, and closely related species.^[3]
  • Rickettsia
  • Coxiella
  • Certain species of Mycobacterium such as Mycobacterium leprae
• Certain protozoa, including:
  • Plasmodia species
  • Leishmania spp.
  • Toxoplasma gondii
  • Trypanosoma cruzi

The mitochondria in human cells may also have originally been such parasites, but ended up forming a symbiotic relationship.

Study of obligate pathogens is difficult because they cannot usually be reproduced outside the host. However, in 2009 scientists reported a technique allowing the Q-fever pathogen Coxiella burnetii to grow in an axenic culture and suggested the technique may be useful for study of other pathogens.[1]

References