Parasites live in other host organisms and depend on them for survival.

Without a host, a parasite cannot live, grow, and multiply. For this reason, a parasite rarely kills its host, but it can spread diseases, some of which may be fatal.

In this article, we detail the different types of parasitic infections in humans, their symptoms and treatments, and tips to prevent them.

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Parasites vary widely in their characteristics. Many are invisible to the human eye, such as the malarial parasite, but some worm parasites can reach over 35 centimeters in length.

Parasites are not a disease, but they can spread diseases. Different parasites have different effects.

There are three types of human parasites:

  • Protozoa: Protozoa are single-celled organisms that can multiply in humans. These parasites can spread through contaminated food and water, person-to-person contact, and insect bites. Protozoa include Plasmodium malariae, which causes malaria infection, and Cryptosporidium, which is ingestible.
  • Helminths: Helminths are parasitic worms that often root in a person’s digestive tract. These parasites cannot multiply or divide within a human body and eventually pass through a person’s stool. These include Ascaris lumbricoides and hookworm parasites.
  • Ectoparasites: Ectoparasites are small organisms that live on the outside of the body. These include ticks, fleas, and lice.

There are many types of parasites, and symptoms can vary widely. Sometimes, these may resemble the symptoms of other conditions, such as pneumonia or food poisoning.

Possible symptoms include:

However, parasites can pass on a wide variety of conditions, so symptoms are hard to predict.

Often there are no symptoms, or symptoms appear long after infection, but the parasite can still be transmitted to another person, who may develop symptoms.

The tests a doctor may order to diagnose a parasite infection depend on factors such as the person’s symptoms, other medical conditions, and travel history.

The following are some of the tests commonly used to diagnose a parasite infection:

  • Fecal exam: If a person is having diarrhea, gas, or other stomach symptoms, three or more stool samples may be collected on different days and examined for a parasite or parasite eggs.
  • Endoscopy: If stool samples do not contain a parasite, a thin tube called an endoscope may be inserted through the mouth into the intestines to reveal any parasites.
  • Colonoscopy: As an alternative to an endoscopy, a tube may be inserted through the rectum into the intestines to find parasites.
  • Blood tests: A healthcare professional may perform a blood test to detect a specific parasitic infection. A serology is a blood test that indicates antibodies or parasite antigens. Another test is a blood smear, where a drop of blood is examined for parasites under a microscope.
  • Imaging tests: An X-ray can help detect parasite-associated lesions in a person’s organs. For more detailed images of the organs, a doctor may order a magnetic resonance imaging (MRI) scan or computerized axial tomography (CAT).

The treatment for parasite infections depends on the particular type of parasite. Doctors may prescribe medication that kills the parasite and medication that treats any symptoms, such as diarrhea.

The following medications are commonly used to treat various types of parasite infections:

  • Metronidazole (Flagyl): This antibiotic kills parasitic infections in the gastrointestinal tract or reproductive system, including amebiasis, giardiasis, trichomoniasis, and vaginal infections.
  • Ivermectin (Stromectol): This is available as an oral tablet, cream, or lotion and treats parasitic infections in the intestinal tract, eyes, or skin, including scabies and many types of worms.
  • Praziquantel (Biltricide): This medication paralyzes and then dissolves tapeworms, so they detach from the intestinal wall and leave the body through a bowel movement.
  • Pyrimethamine (Daraprim): Doctors may prescribe pyrimethamine and sulfadiazine to treat the flu-like symptoms of toxoplasmosis in healthy people, although treatment is not always necessary.
  • Nifurtimox (Lampit): Nifurtimox and benznidazole treat the symptoms of Chagas disease (American trypanosomiasis). This is a parasitic infection that can eventually cause organ damage.
  • Chloroquine: This is one of the main drugs used to treat malaria.
  • Nitazoxanide (Alinia): This treats diarrhea symptoms caused by parasite infections in the gastrointestinal tract, including cryptosporidiosis and giardiasis.

A person can reduce their risk of parasitic infection by:

  • finding out which parasites are prevalent in their area or in locations they may travel
  • taking precautions, such as using insect repellant in places where mosquitoes are common
  • being careful to eat only well-cooked fish and meat
  • drinking water only from bottles with a sealed top while traveling
  • taking care when bathing in freshwater lakes or rivers
  • using mosquito nets
  • wearing protective clothing
  • eliminating stagnant water
  • following safe sexual practices

Parasites are not a disease, but they may spread diseases that can be fatal. However, many parasitic infections are treatable and preventable.

If a person is experiencing a skin rash, abdominal pain, diarrhea, or other symptoms of a parasitic infection, they should speak with their doctor.

The doctor will order tests, such as blood or fecal tests, that can diagnose the parasite and help them develop a specific treatment plan. Early treatment may help stop the infection from spreading to others.

Taking measures such as using insect repellent, eating properly cooked fish and meat, and drinking water only from sealed bottles when traveling may help prevent a parasite infection.