Pathogens, Host-Cell Invasion and Disease
Invading pathogens can co-opt even the cells of the immune system. New anti-infective drugs may arise from an understanding of this chemical warfare
Leaving the Infected Cell
However comfortable life in an infected host cell may be, invading pathogens must leave in order to spread to other cells or tissues. Many viruses and bacteria do this in a rather crude way, by destroying the plasma membrane. The host cell simply bursts, releasing the pathogens into the surrounding medium. This process eventually leads to partial destruction of the tissue, leaving in its wake the ruins of dead cells.
Other pathogens, among them many viruses, leave the cell by using a reversal of the initial integration process. New viruses produced by the host cell travel to the plasma membrane, where they are wrapped in a membrane vesicle that buds off into the surrounding tissue.
The sudden release of pathogens is particularly dramatic in the case of Plasmodium. All infected red blood cells rupture synchronously to release into the blood stream a large number of new pathogens, which infect other erythrocytes. This cycle is repeated every two to three days. Plasmodium's proliferation creates toxic metabolic end products, which are released in the blood and cause the regular fever attacks that are typical of malaria.