Parasitism

Parasitism is a non-mutual relationship between organisms, where one organism, the parasite, benefits at the expense of the other, the host. Traditionally, parasites are defined to be smaller than the host organism and to reproduce at a faster rate.

Human head louse, an example of a parasite

Definition and Types

Parasites are organisms that live on or in a host organism and get their food from or at the expense of their host. There are three main classes of parasites that can cause disease in humans: protozoa, helminths, and ectoparasites.

• Protozoa: These are microscopic, one-celled organisms that can be free-living or parasitic in nature. They can multiply in humans, which contributes to their survival and also permits serious infections to develop from just a single organism. Transmission of protozoa that live in a human's intestine to another individual typically occurs through a fecal-oral route.
• Helminths: These are large multicellular organisms and are generally visible to the naked eye when they are adults. They are also known as worms and they are often grouped into the categories of tapeworms, flukes, and roundworms.
• Ectoparasites: These are organisms that live on the skin but not within the body. Fleas, lice, ticks, and mites are among the main types of ectoparasites that cause diseases in humans.

Mechanisms of Parasitism

Parasites use a wide variety of mechanisms to infect their hosts and extract resources. These mechanisms can include penetration of the host's skin or mucous membranes, invasion of host cells, and evasion of the host's immune system. Some parasites form symbiotic relationships with other, smaller parasites, a phenomenon known as hyperparasitism.

Impact on the Host

Parasites may cause disease in humans. Some parasitic diseases are easily treated and some are not. The burden of these diseases often rests on communities in the tropics and subtropics, but parasitic infections also affect people in developed countries.

Parasitic infections can often be prevented through good personal hygiene, regular veterinary visits for pets, and care when traveling to parts of the world where parasitic infections are common.

See Also

• Parasitoid
• Social parasitism
• Parasitic plant
• Antiparasitic

References

• Roberts, L., Janovy, J., & Nadler, S. (2013). Foundations of Parasitology. McGraw Hill Education.
• Despommier, D., Gwadz, R., Hotez, P., & Knirsch, C. (2005). Parasitic Diseases. Springer Publishing.
• Cox, F.E.G. (2001). Concomitant infections, parasites and immune responses. Parasitology, 122(S1), S23-S38.

External Links

• CDC: About Parasites
• WHO: Parasitic Diseases

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