Protozoal Infection

Key facts

• Protozoal infections are caused by single-celled parasitic organisms that enter the body through contaminated food or water, insect bites, or direct contact.
• Depending on the species, they can affect the gut, blood, liver, or skin, and they're a frequent reason people seek medical care in warmer climates.
• Common intestinal forms include giardiasis, amoebiasis, and cryptosporidiosis, which cause persistent loose stools, bloating, cramps, and fatigue.
• Diagnosis usually needs a stool or blood sample, and many intestinal infections respond well to metronidazole.

Common forms and what they look like

The most frequently encountered protozoal infections target the digestive tract: giardiasis, amoebiasis, and cryptosporidiosis. Typical symptoms are persistent loose stools or diarrhoea, bloating, stomach cramps, nausea, and fatigue. Giardia infections often cause notably foul-smelling, greasy stools. Amoebiasis can occasionally spread beyond the gut to the liver, causing pain in the upper right abdomen and fever.

How protozoal infections are treated

Treatment depends on which organism is responsible, so a stool sample or blood test is usually needed to confirm the diagnosis before starting treatment. Many intestinal protozoal infections respond well to metronidazole, an antiprotozoal medicine that disrupts the parasite's ability to survive. Because symptoms overlap with other gut illnesses, treating without a diagnosis risks missing the right medicine entirely.

When to see a doctor

See a doctor if symptoms persist beyond a few days, if there is blood in the stool, or if a high fever develops alongside gut symptoms. Prompt assessment matters because the right antiprotozoal medicine depends on correctly identifying which organism is responsible.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.