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Parasites are organisms which live on or in a host and get their food from the host. While there are thousands of known parasites, only about 100 affect humans. The problems caused by parasitic infections range from minor discomfort to serious diseases. The three types of parasites which affect people are protozoa, helminths, and ectoparasites. Some parasitic diseases will eventually disappear on their own, while others can cause disability or death if left untreated.
Protozoa are microscopic, one-celled organisms which are carried to humans primarily through contaminated food or insects bites. An insect which carries a disease through its bite is called a vector. The most common vector is the mosquito, which can transmit yellow fever, filariasis, elephantiasis, heartworms and malaria. Malaria is the most destructive parasitic disease, killing over one million people each year, mainly young children in sub-Saharan Africa. Flies can also be vectors, and various species spread parasitic diseases like sleeping sickness and river blindness.
Helminths, the second category responsible for causing parasitic diseases, are large, multi-cellular organisms that can be seen with the naked eye in their adult form. This group consists of flatworms, suck as flukes and tapeworms, thorny-headed worms, and roundworms. Worms generally do not feed on the host, but they take nutrients from the host. Symptoms of worm infection include itching, vomiting, weight loss, increased appetite, abdominal pain, bowel obstructions, and joint and muscle pain. While parasitic worms may be found world-wide, they are most common in China, the Middle East, South American, Africa and the Caribbean.
Ectoparasites are organisms that attach or burrow into skin for long periods of time, and include ticks, mites, and fleas. Ticks burrow under the skin, releasing toxins that cause a variety of illnesses, including Rocky Mountain spotted fever, Colorado tick fever, and Lymes disease. Mites, such as chiggers and scabies, are common in warm or crowded areas, and cause skin irritations. Fleas can carry typhus and bubonic plague, also known as the Black Death.
Contaminated water and food are frequent sources of parasitic infections. Giardia infection occurs globally, and comes from untreated water. This is more common among people who have been hiking and drinking stream or river water, or who live in areas with inadequate water sanitation. Treating water or using bottled water when traveling in such areas can prevent many of the parasitic diseases. Proper hand washing before preparing or handling food is another significant preventative measure.
Parasitic diseases are rampant in tropical and subtropical climates. The use of pesticides has eliminated insect born maladies, such as malaria, in many parts of the world. Some regions, unfortunately, do not have the resources to enact preventative measures or to treat those who become infected. In addition to those who die of malaria, tropical parasitic diseases such as lymphatic filariasis, onchocerciasis and Guinea worm claim another half million victims annually.
Taking preventative measures such as drinking only treated water, hand washing, and using insect sprays can be very successful in avoiding parasitic diseases. If a person has symptoms of a parasitic infection, he should seek prompt medical attention. Most of these infections can be treated successfully with antibiotics and other medications.