Protozoan parasites are eukaryotes, or one-celled organisms that have well-developed structures inside membranes. As parasites, they obtain food and protection by dwelling inside other organisms, referred to as hosts. If they get inside a human host, these parasites can cause a wide variety of problems. Some protozoan parasites are responsible for serious and sometimes deadly diseases. Others, such as those that infect the gastrointestinal tract, cause troublesome symptoms but usually do not prove fatal.
These parasites can be found everywhere: in water, food and soil. When they infect their hosts, protozoan parasites are usually in cyst form, a dormant state in which the organism has encased itself in a tough membrane. As a cyst, the parasite can survive harsh conditions and live a long time before finding a host. After the parasite finds a home in a host, it changes its form in order to get nutrition and reproduce itself.
There are many types of parasites. Intestinal parasites are a worldwide problem, especially in places where water and food sources are contaminated. One intestinal protozoan parasite, Entamoeba histolytica, is found in tropical and subtropical areas and is responsible for amoebic dysentery. Another intestinal parasite, Giardia lamblia, is common in temperate areas. It usually affects outdoorsy people like hikers and campers who drink unsafe water in remote regions.
Other protozoan parasites infect the blood. Some of the most dangerous of these parasites are those that cause African sleeping sickness, malaria and leishmaniasis, a disease whose initial symptoms include sores on the skin that spread over time and damages the liver and the spleen. The parasitic protozoa that cause these illnesses need intermediary organisms like insects to infect human hosts. African sleeping sickness requires tsetse flies, malaria requires mosquitoes, and leishmaniasis requires sand flies.
Treating protozoan parasites depends on the type of parasite and which disease it causes. For example, giardiasis and amoebic dysentery are treated with antiprotozoal medication such as metronidazole. Malaria must be treated with antimalarial medication as soon as it is detected. African sleeping sickness responds to medicines that contain arsenic.
Symptoms of protozoan parasites differ, depending on the parasite. Intestinal parasites cause vomiting and diarrhea, while parasites that infect the blood cause symptoms like chills, fever and headache. All parasitic infections are serious conditions. People who have a protozoan infection must see their doctors as soon as possible for prompt treatment. To prevent infection by protozoan parasites, it is recommended that people wash their hands regularly, avoid putting their hands in their mouths, and drink only water that has been treated.