Intracellular Parasite - Obligate

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:

• viruses
• Certain bacteria, including:
  • Chlamydia, and closely related species.
  • Rickettsia
  • Coxiella

• • Certain species of Mycobacterium such as Mycobacterium leprae
• Certain protozoa, including:
  • Apicomplexans (Plasmodium spp., Toxoplasma gondii and Cryptosporidium parvum)
  • Trypanosomatids (Leishmania spp. and Trypanosoma cruzi)
• Certain fungi
  • Pneumocystis jirovecii

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.