Parasites in the body: what you need to know

Parasite infections are a health issue many people have heard of, but they are often surrounded by questions. They can affect the body in different ways, causing symptoms that range from mild discomfort to more serious illness. Understanding what parasites are, how infections happen, which symptoms to look out for, how to reduce your risk and when to consider testing or treatment can help you make informed decisions about your health.

Table of Contents

• What are parasites and where can they live in the body?

• Recognising symptoms and signs of parasites in the body

• How do you get parasites? Causes, risk factors and prevention

• Testing and treating parasite infections

• Frequently asked questions about parasites in humans

What are parasites and where can they live in the body?

Parasites are organisms that live in or on a host and rely on it to survive. They feed, grow, or multiply at the host’s expense, which can cause illness. While parasites rarely kill their host directly, some can carry serious or even life-threatening diseases.

The three main types of parasites that can affect humans are ectoparasites, helminths, and protozoa.

• Ectoparasites live on the outside of the body. Examples include fleas, lice, mites, and ticks. 

• Helminths are parasitic worms that usually live in the digestive system. Examples include roundworms, tapeworms, and flukes. Some are visible to the naked eye as adults.

• Protozoa are single-celled parasites that can only be seen under a microscope. They may live in the intestines, blood, or tissues, and can spread through contaminated food or water, person-to-person contact, or bites. Examples include Giardia, Cryptosporidium, and Entamoeba histolytica.

Source: Cleveland Clinic, 2023

Recognising symptoms and signs of parasites in the body

A parasite infection does not always cause symptoms straight away. Some people have no noticeable signs at all, while others develop symptoms weeks or even months later. It is also possible to unknowingly pass a parasite to someone else who then becomes unwell.

Common symptoms may include:

• Diarrhoea

• Feeling sick or vomiting

• Stomach pain or cramps

• Unexplained weight loss

• Increased hunger or appetite changes

• Muscle aches

• Fever or chills

• Difficulty sleeping

• Tiredness or fatigue

• General weakness

• Skin irritation or rash

• Neurological symptoms (e.g. seizures, headaches or disorientation)

Always consult a healthcare provider for personalised advice and guidance.

Source: Mayo Clinic, 2024;  Cleveland Clinic, 2023; Cleveland Clinic, 2023 

How do you get parasites? Causes, risk factors and prevention

People can get parasites through contaminated food, water, soil, faeces, or surfaces, as well as through poor hand hygiene, infrequent washing, insect bites, or unprotected sex. Some infections can also pass from a pregnant person to their baby. Risk is higher in areas with poor sanitation, during travel to affected regions, and among young children, caregivers, and people with weakened immune systems.

To reduce your risk:

✓ Wash your hands before eating or cooking, after using the toilet, changing nappies, or touching soil.

✓ Drink bottled or boiled water in high-risk areas when travelling.

✓ Avoid swallowing water in pools, lakes, or rivers, especially in high-risk areas.

✓ Do not swim if you have diarrhoea, and wait at least two weeks after symptoms stop before using a public pool.

✓ Store food safely and cook meat and poultry thoroughly.

✓ Wash or peel fruit and vegetables before eating.

✓ Deworm pets regularly.

✓ Dispose of dog and cat faeces promptly.

✓ Use condoms or dental dams during sex to reduce infection risk.

✓ Protect yourself from insect bites with repellent, protective clothing, and mosquito nets where needed.

✓ Check travel health advice before visiting higher-risk destinations, including whether vaccines or preventive medicines are recommended.

Source: NHS, 2023; Cleveland Clinic, 2023 

Testing and treating parasite infections

Parasite infections are usually diagnosed through a physical examination (skin or other tissue) and a review of symptoms, followed by testing a sample from the affected area, most commonly stool. In some cases, several stool samples may be needed on different days. Depending on symptoms, a healthcare provider may also test blood, phlegm, or fluid around the brain and spinal cord. Other tests may include endoscopy, colonoscopy, X-rays, MRI, or CT scans.

Source: CDC, 2024

Treatment depends on the type of parasite and where it is in the body. A healthcare provider may recommend antiparasitic medicines, antibiotics, antifungals, medicated shampoos, or ointments to clear the infection and relieve symptoms.

Source: Cleveland Clinic, 2023; Cleveland Clinic, 2023 

Frequently asked questions about parasites in humans

Can you have parasites without symptoms?

Yes. Some people can carry parasites without obvious symptoms (Cleveland Clinic, 2023).

When should I go to the ER?

Seek emergency medical help if you have signs of severe illness, such as a fever over 40°C, seizures, confusion, yellowing of the skin or eyes, or dehydration symptoms like extreme thirst, very little urination, weakness, or a fast heartbeat (Cleveland Clinic, 2023).

What else can help get rid of parasites?

Alongside prescribed treatment, a healthy diet and good hydration may support your immune system. Foods and supplements such as fibre, probiotics, garlic, pumpkin seeds, vitamin C, and zinc are sometimes suggested, but evidence varies. Always check with a healthcare provider before using supplements or alternative remedies, as they may interact with medicines or be unsuitable for some people (Cleveland Clinic, 2023).