Blastocystis hominis Infection (Blastocystosis)

Blastocystis hominis is a common intestinal parasite that infects people. It’s one of a group of parasites called Blastocystis sp. An infection with Blastocystis sp is called blastocystosis. Most people who have a Blastocystis infection don’t develop symptoms or even realize they’re infected. But for some, it can cause symptoms like stomach pain, nausea or diarrhea. These usually go away with antiparasitic treatment.

What are the symptoms of a Blastocystis infection?

Most of the time, a Blastocystis infection doesn’t cause symptoms. But when it does, symptoms may include:

• Abdominal pain
• Anal itching
• Constipation
• Diarrhea
• Fatigue
• Gas
• Nausea
• Skin rashes
• Weight loss

Some studies show a possible link between Blastocystis infection and irritable bowel syndrome (IBS), but experts haven’t confirmed the connection.

What does a Blastocystis infection do to your body?

Parasites like Blastocystis hominis use your body to feed and multiply. An intestinal parasite takes up residence in your small intestine and feeds off the nutrients there. This gives it the energy to multiply. After multiplying, some parasites may leave your body, but others may remain to repeat the cycle.

If an intestinal parasite stays with you for a long time and continues to grow and multiply, it may start to take too many of your nutrients. Some parasites also release toxins that make you ill. Your immune system may activate to try to remove the parasite. This may cause symptoms like nausea or diarrhea.

How do you get a Blastocystis infection?

Blastocystis parasites most likely spread by the fecal-to-oral route. They live as cysts in the poop of animals they’ve infected — including humans. The poop and cysts may hide in the soil or in bodies of water where people pass through. Traces of it may transfer from people’s hands to their mouths.

Risk factors

You’re more likely to get a Blastocystis infection if you:

• Live or travel to an area with less sanitation
• Work on a farm or with animals
• Work in a daycare with children who wear diapers
• Consume unwashed produce or unfiltered water

Why does blastocystosis cause symptoms in some people but not others?

Experts are still debating this. Some don’t believe Blastocystis directly causes disease. Others think it does — but only under certain conditions, like:

• Lifecycle stages: Blastocystis changes shape as it develops. Some forms may be more likely to cause illness.
• Subtypes: Different Blastocystis subtypes may affect the body in different ways. In the past, researchers assumed all cases were caused by Blastocystis hominis, but now they know that’s not always true.
• Your gut microbiome: Everyone’s gut microbiome is unique. Some people may have microbes that help fight off a Blastocystis infection more effectively than others.

How doctors diagnose blastocystosis

Healthcare providers can diagnose blastocystosis with a stool test. They collect a sample and check it for Blastocystis cysts and other possible causes of your symptoms. If they don’t find another explanation, they may recommend treating Blastocystis.

What is the treatment for Blastocystis hominis?

There’s no specific treatment for a Blastocystis infection. But if you have symptoms, your healthcare provider may prescribe antiparasitic medications. In some cases, they may also prescribe antibiotics to treat bacterial infections.

These treatments often help, but not always. This might happen because:

• Some Blastocystis subtypes don’t respond as well to antiparasitic drugs
• Another infection could be causing your symptoms
• The organism may resist certain medications

You may also see natural treatments, special diets or herbal supplements marketed for blastocystosis. But studies haven’t confirmed their safety or effectiveness. Check with your provider before trying these approaches.

Does it need treatment?

You might not need treatment if you don’t have symptoms. Blastocystosis often goes away on its own. If you want to confirm the infection is gone, you can take another stool test.

What should I expect if I get an infection?

Most people with a Blastocystis hominis infection never develop symptoms. If you do, symptoms usually improve with treatment. If they don’t, your provider may check for other causes.

How can I prevent infection?

To lower your risk of blastocystosis and other infections:

• Wash your hands regularly, especially after using the bathroom or handling animals.
• Practice safe food prep.
• Be cautious with food and water when traveling.
• Take probiotics to support gut health.