Three types of parasites can cause disease in humans. They are protozoa, carried by mosquitos, helminths, such as roundworm, and ectoparasites, for instance lice and bed bugs.

Parasites are organisms that live in or on a living host of another species. They survive by taking nutrients from this host.

In this article, we detail the different types of parasites and parasitic infections that can affect humans.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

Was this helpful?
A type of human parasite viewed under a microscope. -1Share on Pinterest
Ed Reschke/Getty Images

There are three types of parasites that can cause diseases in humans.

  • Protozoa: Protozoa parasites are single-celled organisms. Protozoa can only multiply, or divide, within the host.
  • Helminths: These are worm parasites. They are typically visible to the naked eye at their adult stage. Unlike protozoa, they cannot multiply in humans.
  • Ectoparasites: These live on rather than in their hosts. They include lice, fleas, and mosquitos.

According to the Centers for Disease Control and Prevention (CDC), the following parasitic infections are common in the United States:

Learn more about parasites in humans here.

Many types of parasites can affect humans. Here are some examples of parasites and the diseases they can cause.


Plasmodium is a single-cell parasite that causes malaria. This disease causes fever, headaches, and chills. It can be fatal.

The Anopheles mosquito carries this bloodborne parasite and transmits it through biting humans. There are five types of plasmodium that can cause malaria, and there were an estimated 241 million cases of the disease in 2020.

Chagas disease

This affects the blood, muscles, nerves, heart, esophagus, and colon. It is transmitted through an insect bite. Over 300,000 people in the U.S. have the parasite that can lead to this disease.


This is a parasitic pneumonia that results from an infection with Toxoplasma gondii organism. It affects the liver, heart, eyes, and brain. It occurs worldwide.


This tiny ameba can affect the eyes, skin, and brain. It exists all over the world in water and soil. Individuals can become infected if they clean contact lenses with tap water.


Also known as “trich,” this is a sexually transmitted infection (STI). It is the result of the parasite Trichomonas vaginalis. It affects the female urogenital tract. It can exist in males, but usually without symptoms.

Other protozoa

Other protozoa infections include:

Worms, or helminth organisms, can affect humans and animals. Types of worm parasites include:


Ascariasis, or a roundworm infection, does not usually cause symptoms, but the worm may be visible in feces. It enters the body through food or drink.


These can cause intestinal disease. Hookworms lay eggs in the soil, and the larvae can penetrate the skin of humans. Early symptoms include itching and a rash.

Beef and pork tapeworms

Taeniasis occurs due to the presence of taenia tapeworms in the intestines. People may ingest these tapeworms by eating undercooked beef or pork. Taeniasis also causes cysticercosis, one of the most common parasitic infections in the U.S.


A roundworm transmits this infection from animals to humans. It affects the eyes, brain, and liver. Nearly 5% of people in the U.S. have antibodies, suggesting that millions have been in contact with the infection.


Also known as trichuriasis, whipworms live in the large intestine and lay eggs. The body passes these eggs out in feces. Humans can become infected when ingesting the eggs, for example, on unwashed fruit or vegetables. It is common across the world.

Elephantiasis lymphatic filariasis

This spreads through mosquito bites and affects the lymph system. Infection can lead to lymphedema and elephantiasis, which can cause swelling and enlargement of the arms and legs.

Other helminths

Other types of worm parasites include:

  • Echinococcus tapeworm
  • Diphyllobothrium latum tapeworm
  • anisakiasis
  • raccoon roundworm
  • clonorchiasis
  • dioctophymosis
  • Guinea worm
  • hymenolepiasis
  • Enterobiasis pinworm
  • Fasciolosis liver fluke
  • Fasciolopsiasis intestinal fluke
  • gnathostomiasis
  • Loa loa filariasis
  • mansonellosis
  • river blindness
  • lung fluke
  • schistosomiasis, bilharzia, or snail fever
  • sparganosis
  • strongyloidiasis
  • trichinosis

Ringworm is sometimes mistaken for a worm, but it is not a worm. It is a fungal infection.

Ectoparasites are parasites that live on the outside of the body. Fleas, lice, and bedbugs are common ectoparasites.


Bedbugs are small insects that live on clothing and bedding. Their bites can become itchy and cause skin discoloration and swelling.


Lice are parasitic insects that live off of human blood. The three types of lice that can live on the human body are body lice, head lice, and pubic lice.


Demodex folliculorum are tiny mites that live in and around the hair follicles. Typically they do not cause noticeable adverse symptoms. However, they can cause a range of ocular diseases if they infest the eyelashes or eyebrows.


Scabies is a condition that results from tiny mites, called Sarcoptes scabiei var. hominis, burrowing into the skin. Scabies is highly contagious and can spread through skin-to-skin contact.


Screwworms are the fly larvae that burrow into the skin. They can cause severe infection and disease.

There are three main types of parasites that can affect humans: protozoa, helminths, and ectoparasites. These parasites can live on or in the human body and cause various diseases.

These parasites are often the result of consuming contaminated foods or water, though insects and other animals can also carry parasites.