Parasitic Infections

Types of parasites

Common parasitic infections

Intestinal protozoa

• Giardia: from untreated water (streams, lakes) and person-to-person spread; causes greasy diarrhea, bloating, gas and weight loss, sometimes lasting weeks.
• Cryptosporidium: a common cause of outbreaks linked to swimming pools and water parks; watery diarrhea that can be severe in people with weakened immunity.
• Entamoeba histolytica: dysentery and, rarely, liver abscess after travel.

See traveler's diarrhea.

Worms

• Pinworms: the most common worm infection in the US, mainly in school-age children; causes intense anal itching at night.
• Roundworms, hookworms and whipworms: spread through soil contaminated with feces in tropical regions; can cause anemia and poor growth.
• Tapeworms: from undercooked beef, pork or fish. Pork tapeworm eggs can cause cysticercosis, with cysts in the brain causing seizures. See taeniasis.
• Schistosomiasis: from freshwater in parts of Africa, Asia and South America.

Blood and tissue parasites

• Malaria: spread by mosquitoes in tropical regions; causes fever, chills and can rapidly become severe.
• Toxoplasmosis: from undercooked meat or cat feces; usually mild but dangerous in pregnancy and with weakened immunity.
• Chagas disease and leishmaniasis: in parts of the Americas, Africa and Asia.

Sexually transmitted

• Trichomoniasis: a common, curable sexually transmitted infection.

Skin and hair

• Head lice: common in children; itching and visible nits.
• Scabies: intensely itchy rash, worse at night, spreading among close contacts.
• Bedbugs: itchy bites in lines or clusters.

How parasites spread

• drinking or swimming in contaminated water
• eating contaminated or undercooked food
• poor hand hygiene, especially after using the toilet or changing diapers
• walking barefoot on contaminated soil
• insect bites (mosquitoes, sandflies, triatomine bugs)
• close or sexual contact
• contact with animal feces, including cat litter

Symptoms

• diarrhea, sometimes bloody or greasy
• abdominal pain, bloating and gas
• nausea and weight loss
• itching, especially anal itching or itchy skin
• rash
• fever and chills (malaria and some tissue parasites)
• fatigue and anemia
• coughing in some worm infections as larvae pass through the lungs
• seizures (neurocysticercosis)

Many parasitic infections cause no symptoms.

Diagnosis

• Stool tests: microscopy for eggs and parasites, antigen tests and PCR panels.
• Tape test: sticky tape pressed around the anus in the morning to collect pinworm eggs.
• Blood smears and rapid tests for malaria.
• Blood antibody tests for toxoplasmosis, schistosomiasis, strongyloides and others.
• Skin scrapings for scabies.
• Imaging for cysts in the brain, liver or other organs.
• Travel and exposure history is essential.

Treatment

Treatment depends on the parasite:

• Antiprotozoal medicines for giardia, amoebiasis and trichomoniasis
• Antimalarials, urgently, for malaria
• Antiworm medicines for intestinal worms; pinworm treatment is often given to the whole household and repeated after 2 weeks
• Topical or oral treatments for scabies and lice, with treatment of contacts and washing of bedding
• Fluids for diarrhea, with oral rehydration solution
• Specialist care for complex infections such as neurocysticercosis

Prevention

• Wash hands with soap and water, especially after the toilet and before eating; alcohol gels do not kill some parasites, such as Cryptosporidium.
• Drink safe water; boil or filter water when camping or traveling.
• Cook meat thoroughly and wash produce.
• Wear shoes on soil in endemic areas.
• Use insect repellent, bed nets and antimalarial medicines when traveling to malaria areas.
• Avoid swimming if you have diarrhea, and do not swallow pool water.
• Pregnant women should avoid changing cat litter and eating undercooked meat.
• Practice safer sex.

Frequently asked questions

What are the symptoms of a parasitic infection?

Common symptoms include diarrhea, abdominal pain, bloating, nausea, weight loss, fatigue and itching, especially around the anus or on the skin. Some parasites, such as malaria, cause fever and chills. Many parasitic infections cause no symptoms and are found on testing.

How do you get parasites?

Most parasites are caught from contaminated water or food, undercooked meat, soil, insect bites, contact with animal feces, or close and sexual contact with an infected person. Good hand hygiene and safe food and water greatly reduce the risk.

Can parasitic infections be cured?

Yes. Most parasitic infections are cured with specific antiparasitic medicines, often in a single dose or short course. Some, such as pinworms and scabies, need household contacts treated too, and a repeat dose to prevent reinfection.

Do I need a parasite cleanse?

No. Commercial "parasite cleanses" are not proven to work and may be harmful. If you think you have a parasite, see a doctor for proper testing. Confirmed infections are treated effectively with prescribed medicines.

How are intestinal parasites diagnosed?

Intestinal parasites are usually diagnosed with stool tests, which look for eggs, parasites or their genetic material, sometimes on several samples. Pinworms are diagnosed with a tape test around the anus. Blood tests help for some worms and tissue parasites.