Intracellular parasite

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

Contents 1 Facultative 2 Obligate 3 Susceptibility 4 References

Facultative

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

Bacterial examples include

• Francisella tularensis
• Listeria monocytogenes
• Salmonella^[1]
• Brucella
• Legionella
• Mycobacterium
• Nocardia
• Rhodococcus equi^[2]
• Yersinia
• Neisseria meningitidis^[3]

Fungal examples include:

• Histoplasma capsulatum.^[4]
• Cryptococcus neoformans^[5]

Obligate

Obligate intracellular parasites cannot reproduce outside their host cell, meaning that the parasite's reproduction is entirely reliant on intracellular resources.

Obligate intracellular parasites of humans include:

• All viruses
• Certain bacteria, including:
  • Chlamydia, and closely related species.^[6]
  • Rickettsia
  • Coxiella
  • Certain species of Mycobacterium such as Mycobacterium leprae
• Certain protozoa, including:
  • Apicomplexans (Plasmodium spp., Toxoplasma gondii and Cryptosporidium parvum^[7])
  • Trypanosomatids (Leishmania spp. and Trypanosoma cruzi)
• Certain fungi
  • Pneumocystis jirovecii^[8]

The mitochondria in eukaryotic cells may also have originally been such parasites, but ended up forming a mutualistic relationship (endosymbiotic theory).

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.^[9]

Susceptibility

People with T cell deficiencies are particularly susceptible to intracellular pathogens.^[10]

References