The idea of having a parasite might make your skin crawl, but parasitic infections are more common than you might think. Some spread through contaminated food or water, while others are passed through close contact or insect bites.
Fortunately, many parasitic infections are treatable. Knowing how they spread and what symptoms to watch for can help you protect yourself and recognize when it’s time to see a doctor.
Common parasites in humans include Giardia, pinworms, scabies mites, malaria-causing parasites, Cryptosporidium, Toxoplasma, and tapeworms. Some cause digestive problems, while others affect the skin, blood, or other organs. Symptoms and treatment depend on the parasite involved.
What are parasites, and how do humans get them?
Parasites are organisms that live on or inside another organism, called a host, and obtain nutrients at the host’s expense.
According to the Centers for Disease Control and Prevention (CDC), parasites that cause human disease fall into three main categories:
- Protozoa: Microscopic, single-celled organisms, including Giardia and Cryptosporidium.
- Helminths: Parasitic worms, including pinworms and tapeworms.
- Ectoparasites: Organisms that live on or burrow into the skin, such as scabies mites.
People can become infected through contaminated food or water, insect bites, close physical contact, or exposure to contaminated surfaces.
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What are 7 common parasites in humans?
These seven examples illustrate different types of parasitic infections. They are not a ranking of the most prevalent infections worldwide. Some are relatively common in the United States, while others are more frequently associated with international travel.
Common parasites at a glance
| Parasite | How it spreads | Common symptoms |
| Giardia | Contaminated water, food, or surfaces | Diarrhea, gas, stomach cramps |
| Pinworms | Swallowing eggs from contaminated hands or objects | Itching around the anus, especially at night |
| Scabies mites | Prolonged skin-to-skin contact | Intense itching and rash |
| Malaria parasites | Bites from infected mosquitoes | Fever, chills, headache, body aches |
| Cryptosporidium | Contaminated water, food, or surfaces | Watery diarrhea, stomach cramps |
| Toxoplasma | Undercooked meat or exposure to contaminated soil or cat feces | Often none; sometimes flu-like symptoms |
| Tapeworms | Eating certain raw or undercooked meats | Often none; sometimes abdominal discomfort |
1. Giardia
Giardia is a microscopic parasite that causes an intestinal infection called giardiasis.
It’s found worldwide, including in the United States. People commonly become infected by swallowing contaminated water while drinking, swimming, or participating in outdoor activities.
Symptoms may include diarrhea, gas, nausea, fatigue, and greasy, foul-smelling stools.
Giardia can sometimes cause prolonged digestive symptoms. A healthcare provider may recommend stool testing and prescribe medication when appropriate.
2. Pinworms
Pinworms are small, white intestinal worms that commonly affect young children.
They spread when someone accidentally swallows microscopic eggs transferred from contaminated hands, clothing, bedding, or other surfaces.
The most recognizable symptom is itching around the anus, particularly at night.
Treatment typically involves antiparasitic medication and careful hygiene. Healthcare providers may recommend treating household members simultaneously to prevent reinfection.
3. Scabies mites
Scabies is a skin infestation caused by microscopic mites that burrow into the skin.
Unlike intestinal parasites, scabies mites primarily spread through prolonged skin-to-skin contact.
Symptoms include intense itching, often worse at night, and a rash that may appear between the fingers, around the wrists, or in other skin folds.
Scabies requires treatment with prescription medication. Close contacts may also need treatment to prevent the infestation from spreading.
4. Malaria parasites
Malaria is caused by Plasmodium parasites transmitted through bites from infected Anopheles mosquitoes.
It’s most common in certain tropical and subtropical regions.
Symptoms can include fever, chills, headache, fatigue, and muscle aches. Severe malaria can cause life-threatening complications.
If you develop a fever during or after travel to an area where malaria occurs, seek medical evaluation immediately. Malaria can progress rapidly and requires prompt diagnosis and treatment.
5. Cryptosporidium
Cryptosporidium, often called “crypto,” is a microscopic parasite that causes cryptosporidiosis.
It spreads through contaminated water, food, and surfaces. Outbreaks can occur in swimming pools because the parasite can survive normal chlorine levels.
The most common symptom is watery diarrhea, sometimes accompanied by nausea, cramps, or dehydration.
Many otherwise healthy people recover without specific medication. However, severe illness, dehydration, or infection in someone with a weakened immune system requires medical attention.
6. Toxoplasma
Toxoplasma gondii causes an infection called toxoplasmosis.
People may become infected by eating undercooked meat, consuming contaminated food, or accidentally swallowing the parasite after contact with contaminated soil or cat feces.
Most healthy people experience no symptoms. Others develop mild flu-like symptoms.
Toxoplasmosis is particularly concerning during pregnancy and for people with weakened immune systems because complications can be serious.
If you’re pregnant and suspect exposure, contact your healthcare provider.
7. Tapeworms
Tapeworms are parasitic worms that can live in the intestines.
Certain species infect humans through raw or undercooked beef, pork, or fish.
Many infections cause few symptoms, although some people experience abdominal discomfort, nausea, or changes in appetite.
One important distinction: Intestinal pork tapeworm infection results from eating infected pork, while swallowing pork tapeworm eggs can cause cysticercosis, a separate infection that may affect the brain or other tissues.
Healthcare providers can diagnose intestinal tapeworm infections through stool testing and prescribe appropriate medication.
What are the signs of a parasitic infection?
Symptoms depend on the type of parasite and where it lives in the body.
Possible warning signs include:
- Persistent diarrhea
- Stomach cramps or bloating
- Unexplained digestive discomfort
- Nausea
- Itchy skin or rashes
- Anal itching, especially at night
- Fever or chills
- Unexplained fatigue
These symptoms can also have many other causes. Having one or more doesn’t necessarily mean you have a parasite.
How can you prevent parasitic infections?
Many infections can be prevented through everyday hygiene and food safety practices.
A few precautions make a meaningful difference:
- Wash your hands with soap and water after using the bathroom and before preparing food.
- Cook meat and fish to recommended safe temperatures.
- Drink treated water, especially while traveling or camping.
- Avoid swallowing water in pools, lakes, and rivers.
- Wash fruits and vegetables thoroughly.
- Use insect repellent and protective clothing in areas with mosquito-borne diseases.
- Avoid close contact with someone who has untreated scabies.
- Follow your healthcare provider’s travel-related prevention recommendations.
The CDC provides additional guidance on how parasites spread through food, water, and other exposures.
When should you see a doctor for a possible parasite?
Consider scheduling an appointment if you experience persistent diarrhea, unexplained digestive symptoms, recurring itching, or other symptoms that could indicate a parasitic infection.
Your provider may recommend stool tests, blood tests, or a skin examination depending on your symptoms and exposure history.
Seek prompt care for bloody diarrhea, significant dehydration, severe abdominal pain, or symptoms that are worsening. Fever after travel to a malaria-risk area requires urgent evaluation, even if you’ve returned home.
If you’re experiencing symptoms while traveling, our guide on what to do if you get sick on vacation offers additional guidance.
The bottom line
Common parasites in humans can affect the intestines, skin, blood, and other parts of the body. Although some infections cause significant illness, many are treatable with appropriate medical care.
Practicing good hygiene, preparing food safely, and taking precautions while traveling can reduce your risk.
If you’re concerned about a possible parasitic infection, you can use Zocdoc to find a primary care provider or book an urgent care appointment.
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Frequently asked questions
What is the most common parasite in humans?
It depends on the region and type of infection. Giardia is a leading cause of intestinal parasitic illness in the United States, while pinworms are the most common intestinal worm infection in the country.
How do you know if you have parasites?
Symptoms may include diarrhea, abdominal discomfort, itching, or fatigue, but some infections cause no symptoms. A healthcare provider can recommend testing based on your symptoms and possible exposures.
Can parasites go away without treatment?
Some parasitic infections resolve without medication, while others require prescription treatment. The appropriate approach depends on the parasite, symptoms, and your overall health.
How are parasitic infections treated?
Treatment varies. Healthcare providers may prescribe antiparasitic medication, recommend supportive care, or perform additional testing to determine the most appropriate treatment.
The information in this article is provided for general informational purposes only and should not be relied on as medical advice. It is not intended as, and Zocdoc does not provide, medical advice, diagnosis or treatment. Zocdoc does not recommend any specific provider. Find one you’ll love on Zocdoc today.