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How do parasites cause disease in humans?
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parasitic disease
Trypanosoma brucei in a blood smear (Giemsa-stained light photomicrograph).
Parasites cause disease in humans through various biological mechanisms, often by exploiting host resources or damaging tissues as they grow, reproduce, and migrate within the body.12
Mechanisms of Pathogenesis
- Cellular Destruction: Some parasites, such as the protozoan Plasmodium (the cause of malaria), invade and replicate within host cells. The burden of these organisms eventually causes the cells to rupture, releasing more parasites to infect other cells.1
- Physical Obstruction: Helminths like Wuchereria bancrofti can accumulate in lymph ducts, blocking the flow of lymphatic fluid and causing significant swelling. Similarly, parasites may block bile ducts or cause intestinal perforations.13
- Tissue Damage: Many parasites, including tapeworms, attach to or burrow into tissues such as the intestinal wall, muscle, or the brain, interfering with normal function.1
- Immune Evasion: Some parasites, such as trypanosomes, survive by constantly changing their surface proteins, forcing the immune system to repeatedly produce new antibodies, which exhausts the host's defenses.4
- Intracellular Infection: Others, like Leishmania, infect white blood cells (macrophages) meant to destroy them, eventually overwhelming the host's immune response.14