If you squirm at the word parasite, you’re not alone. The very concept is gruesome: These pesky organisms can infect your intestines, your blood and even your brain.
While some are confined to small corners of the globe, you can come across common parasites in everyday life. In fact, millions of Americans contract parasitic infections each year — sometimes without knowing it.
To help demystify their impact, we asked experts for advice on avoiding parasites, how to identify whether you’ve contracted one and where to find help.
What are parasites?
“Any organism that lives inside us and obtains nutrients while causing harm to us is called a parasite,” says Dr. Vani George, an physician and assistant professor at the Icahn School of Medicine at Mount Sinai in New York City.
Intestinal parasites like tapeworm are an obvious example, but many kinds of parasitic organisms can infect different parts of the body.
The three main classes of parasites that infect humans are:
- Protozoa (single-celled organisms like Giardia)
- Helminths (worms like roundworms and tapeworms)
- Ectoparasites (tiny bugs like scabies mites)
What do parasites do?
Parasites can cause everything from diarrhea and stomach cramps to skin issues like itchy rashes or welts. Some might not even cause symptoms at all.
A few rare parasites can quickly overwhelm the body and lead to death, like the dreaded Naegleria fowleri. You may have seen scary headlines about people succumbing to this brain-eating amoeba after a trip to a swimming hole or water park. It infects people when contaminated water enters the body via the nose — which can happen when you put your head underwater while swimming.
Your chances of contracting one of these deadly parasites is extremely small. It’s much more important to understand common parasites and how to avoid them.
“I don’t really talk about these particularly scary ones with my travel patients,” said Dr. Jessica Fairley, an associate professor of medicine and global health at Emory University in Atlanta whose work can include advising Centers for Disease Control and Prevention employees and others on safe international travel. “But generally, the things I tell people to help prevent common parasites are useful for rarer ones too.”
Most parasites are treatable with medicine, but it’s important to take care of them as soon as possible, no matter the extent of your symptoms. Even common parasites, like tapeworms or toxoplasmosis, can cause serious issues like seizures or pregnancy complications down the line.
Here are some of the most common parasites:
Giardia
Giardia is a waterborne parasite, common in both humans and pets, which you can contract through contact with contaminated food, objects, water or surfaces.
The most common way people get Giardia is through contaminated drinking water. The parasite causes giardiasis, which can cause diarrhea, stomach cramps, vomiting and dehydration, fatigue and, in some cases, fever, itching or swelling of the eyes and joints.
The parasite resides in freshwater lakes and streams worldwide. To avoid Giardia while traveling, Fairley recommends drinking bottled or well-filtered water and avoiding raw fruit and vegetables unless they have a peel you remove before eating. When hiking or camping, only drink from freshwater sources after filtering through a proper water filter.
If you suspect you’ve contracted Giardia, you might want to see a medical provider, who can take a stool sample to check for signs of the parasite. Symptoms can last from two to six weeks, but your provider can prescribe antiparasitic medications to shorten their duration.
Pinworms
Pinworms, also known as threadworms, are small worms about the size of a staple that only live in the colon and rectal area of humans.
They’re most common in young children and can spread quickly via contaminated surfaces in childcare settings. These parasites can cause itching in the perineal area (in and around the anus). Typically, symptoms are mild.
If you suspect you or your child has contracted pinworms, your medical provider will look for signs of the eggs or the actual worms on the body, clothes or bedding. Pinworms are easily treated through prescription or over-the-counter medication.
Because pinworms can survive a long time on clothing and bedding, it’s important to clean thoroughly and keep the infected person’s items away from others in the household. To avoid pinworms, hygiene is paramount, says George: “Practice good hygiene by washing your hands frequently.”
Because pinworms are most common in children, they should receive help washing their hands with soap after using the bathroom. If you’re changing diapers, wash your hands thoroughly before and after.
Scabies
Scabies are small mites that burrow under the skin, causing intense itchiness and a telltale rash. They can spread quickly via close person-to-person contact, especially in close quarters like nursing homes, schools and daycare centers.
Extended scabies infections can cause sores. If left untreated, the sores can become seriously infected. If you have a persistent, itchy rash on your hands, arms, genitals or shoulder blades, schedule a doctor’s visit to get it evaluated.
To avoid scabies, avoid close skin-to-skin contact with a person with a scabies rash and don’t touch or handle bedding or clothes from someone with scabies.
Malaria
Globally, malaria is one of the most common parasitic infections. It’s caused by several different types of Plasmodium, single-celled organisms that are transferred to humans through mosquitos bites.
Malaria symptoms vary widely, depending on the type of parasite involved and the severity of the disease. Some patients experience minor symptoms like fevers, chills, sweating, body aches and headaches. More severe malaria can cause serious anemia, coma, respiratory distress, kidney failure and other symptoms, some of which can lead to death.
If you have traveled to a place where malaria is present and you have any symptoms of malaria, visit a doctor right away. They will administer a blood test to check for malaria and prescribe treatment if you have it. In general, proper treatment should eliminate the malaria parasite from your body.
Anyone traveling to a region with malaria should take preventive measures ahead of time. The CDC maintains an up-to-date list of malaria information by country.
Based on where you’re traveling and your health specifics (age, whether you’re pregnant, etc.), a medical provider can prescribe you the correct antimalarial drug. Avoiding mosquito bites is also important. “Use insect repellent specifically containing DEET,” George says. “Bed nets are also very effective in preventing mosquito bites.”
Cryptosporidium
Cryptosporidium, often called “crypto,” is a waterborne parasite that can cause cryptosporidiosis, which exhibits similar symptoms to giardiasis. These include diarrhea, vomiting, stomach cramps, weight loss and fever.
You can contract crypto through contaminated water, food and surfaces. It can also survive in low levels of chlorine, so outbreaks sometimes occur in public pools.
For most healthy people, crypto resolves without treatment. If you think you have crypto, drink lots of fluids as you eliminate the parasite. Contact your doctor if your symptoms worsen or don’t go away after seven to10 days.
To avoid cryptosporidium while traveling or hiking/backpacking, drink bottled or filtered and treated water. Avoid raw fruit and vegetables without a thick peel, and don’t drink ice made from tap water.
Toxoplasma
Toxoplasma gondii is a single-celled protozoan that causes toxoplasmosis in humans. Researchers estimate about 11 percent of the US population 6 years and older has been infected.
You can contract toxoplasma by eating undercooked meat or shellfish or by eating other contaminated foods. It can also spread through cat feces. Symptoms include mild flu-like symptoms that last for a few weeks, including swollen lymph nodes, muscle aches and fevers.
In rarer cases, toxoplasma can cause an infection in the eye, leading to blurred vision or mild eye pain. If untreated, this can cause permanent eye damage or vision loss.
If you think you’ve got toxoplasmosis, your doctor can confirm with a blood test. If you’re at higher risk from pregnancy or being immunocompromised, medications can treat toxoplasmosis. To avoid it, hygiene is key: Wash hands regularly with soap and hot water, and wash fresh fruits and vegetables thoroughly before eating. Be sure your meat is cooked to the proper temperature. Keep cat litter far away from your cooking and dining area, and if you have a sandbox, keep it covered to prevent cats from pooping in it.
Tapeworms
Tapeworms are worm parasites that live in the small intestine. While not very common, especially in the US, they can be contracted by eating contaminated fish or meat, generally beef or pork. Because the eggs can survive outside the host, unlike the adult worm, you can also contract a tapeworm through contaminated water or surfaces.
Tapeworms may cause no symptoms at all, or they may cause stomach aches or nausea, diarrhea or gas, weight loss, hunger pains or a lack of appetite. In some more advanced cases, the tapeworm larvae can travel to other parts of the body, creating cysts in the organs, spinal cord or brain. These cysts can cause neurological issues or organ disruption, although these cases are rare. Once diagnosed through a stool sample, tapeworms are easily treated with medicine.
To avoid tapeworm, cook meat to proper temperatures. Wash hands frequently with soap and water.
General tips for avoiding parasites while traveling
No matter where you’re going, knowing the risks ahead of time is important. “Talk to your healthcare provider before traveling to determine if any additional precautions, medications or vaccinations are necessary based on your individual health and travel plans,” says George.
During your travels, Fairley says to “be cautious about the same things we would do to avoid food poisoning or traveler’s diarrhea.” That includes drinking bottled or filtered water, avoiding raw fruit and vegetables without a peel and not swimming in very warm freshwater bodies like lakes or ponds, where parasites can spread.
If you do get sick while traveling, don’t panic. Diarrhea and an upset stomach are common while traveling to new places and will generally pass with good hydration. “People can get carried away thinking they have parasites when they don’t,” Fairley said. “It’s just good to be prepared.”