Intracellular parasite

Intracellular parasites are microparasites that are capable of growing and reproducing inside the cells of a host.^[1] They are also called intracellular pathogens.^[2]^[3]

and closely related species.^[14]

Chlamydia

Rickettsia

Coxiella

Certain species of such as Mycobacterium leprae, that survive in phagocytes

Mycobacterium

^[b]^[15]

Anaplasma phagocytophilum

Viruses use a number of host receptors to gain entry to the cell, usually by causing .^[7] See viral entry for more on this well-studied topic.

endocytosis

Bacteria are also generally small enough to be engulfed by endocytosis, which they trigger with adhesins. Unlike viruses, they can and often do manipulate the cell's behavior beforehand, by injecting effector proteins into the cytosol.

[7]

[22]

When an intracellular parasite goes to enter a host cell, it is particular about the type of host cell. This is because most intracellular parasites are able to infect only a few different cell types.^[21]

Other intracellular parasites have developed different ways to enter a host cell that do not require a specific component or action from within the host cell. An example is intracellular parasites using a method called gliding motility. This is the use of an actin-myosin motor that is connected to the intracellular parasites' cytoskeleton.

Nutrition[edit]

The majority of intracellular parasites must keep host cells alive as long as possible while they are reproducing and growing. In order to grow, they need nutrients that might be scarce in their free form in the cell. To study the mechanism that intracellular parasites use to obtain nutrients, Legionella pneumophila, a bacterial facultative intracellular parasite, has been used as a model. It is known that Legionella pneumophila obtains nutrients by promoting host proteasomal degradation. Self-degradation of host proteins into amino acids provides the parasite with its primary carbon and energy source.^[23]

Susceptibility[edit]

People with T cell deficiencies are particularly susceptible to intracellular pathogens.^[24]