What is a parasite?

A parasite is a general term for any living thing that lives in, or on, another living organism. It may feed off its host, or obtain shelter using its host, but contributes nothing to its host’s well-being or welfare. Human parasites include fungi, bacteria, viruses, protozoa and worms.

What is Cryptosporidium?

Cryptosporidium is a parasite that can infect your gut (intestines) and cause ‘cryptosporidiosis’. Cryptosporidiosis is a gastroenteritis infection (an infection of your gut) which can lead to diarrhoea and sometimes vomiting. Cryptosporidium is a protozoan parasite. A protozoan is a microscopic, single-celled organism. Cryptosporidium can infect both humans, cattle and other animals, particularly farm animals. There are two main species of Cryptosporidium that cause infection in humans, Cryptosporidium hominis and Cryptosporidium parvum.

How do you get Cryptosporidium?

The Cryptosporidium parasite passes out in the faeces (stools) of infected humans and animals. It can then be found in soil, water, food, or on surfaces that have been contaminated with the infected faeces.

Human-to-human transmission of infection is possible; for example, by not washing your hands after changing the nappy of an infected child and then putting your hands in your mouth. Outbreaks can occur within a household or, for example, within nurseries. Animal-to-human transmission is also possible. This is commonly through contact with infected animals in farms or zoos or through contact with infected animal dung.

You may also become infected if you drink contaminated water. In fact, the largest outbreaks of cryptosporidiosis have occurred when drinking water becomes contaminated with sewage or manure. Adequate filtration of water is needed to remove the parasite. Swimming in contaminated water (for example in lakes or rivers) can also cause infection. Outbreaks have also occurred through swimming pool contamination as chlorination doesn’t always kill the parasite.

Eating contaminated food is a less common way that you may become infected with Cryptosporidium. For example, food that is washed in contaminated water or fruit or vegetables that are contaminated by infected manure that has been used to encourage them to grow. Unpasteurised milk may also be a source of infection.

If you travel to countries which have poor sanitation, you may be at a greater risk of developing Cryptosporidium infection.

How common is Cryptosporidium and who gets it?

There are between 3,000 and 6,000 confirmed cases of infection with Cryptosporidium each year in the UK. However, the actual number of infected people is likely to be higher as a stool sample may not be tested in the laboratory in all cases.

Anyone can get cryptosporidiosis but it most commonly affects children under the age of 5. Those who look after young children are also more likely to become infected. If your immune system is not working properly for some reason, for example you are undergoing treatment for cancer or you have HIV infection, you are more likely to have serious infection.

What are the symptoms of cryptosporidiosis?

Some people who become infected with Cryptosporidium actually have no symptoms. However, they can still pass on the infection to others. But usually infection with Cryptosporidium causes a gastroenteritis-type illness. It can take between 3 to 12 days after contact with the parasite before you develop symptoms.

The main symptoms are watery diarrhoea with abdominal cramps. Vomiting, fever and loss of appetite are also common. Symptoms usually last around 12 to 14 days but can sometimes last for as long as one month. So, symptoms tend to last for longer than with other common causes of gastroenteritis. Also, in some people, symptoms may seem to improve and then relapse (or get worse again) before the infection clears fully.

How is cryptosporidiosis diagnosed?

Cryptosporidiosis is usually diagnosed when the Cryptosporidium parasite is found in your stool after a stool sample is sent to the laboratory. Occasionally, in people with a weakened immune system and a negative stool sample, the parasite may be detected after a biopsy of the stomach or bowel.

What is the treatment for cryptosporidiosis?

Most people with cryptosporidiosis do not need any specific medication or treatment. Their immune system will usually work to clear the infection. Some studies have shown that drugs such as nitazoxanide may help clear symptoms more quickly in some people but this drug is not routinely used in the UK. More evidence is needed regarding possible drugs to treat Cryptosporidium infection.

However, if you have cryptosporidiosis, there are things that you can do to ease your symptoms and to help avoid complications while your immune system is doing the work. Most importantly, you should make sure that you drink plenty of fluids. The aim is to prevent dehydration, or to treat dehydration if it has developed. Once any dehydration is corrected, you should eat as normally as possible.

Fluids for adults

  • As a rough guide, drink at least 200 mls after each bout of diarrhoea (after each watery stool).
  • This extra fluid is in addition to what you would normally drink. For example, an adult will normally drink about two litres a day, but more in hot countries. The above ‘200 mls after each bout of diarrhoea’ is in addition to this usual amount that you would drink.
  • If you vomit, wait 5-10 minutes and then start drinking again, but more slowly. For example, a sip every 2-3 minutes, but making sure that your total intake is as described above.
  • You will need to drink even more if you are dehydrated. A doctor will advise on how much to drink if you are dehydrated.

For most adults, fluids drunk to keep hydrated should include water, fruit juice and soups. It is best not to have drinks that contain a lot of sugar, such as cola or pop, as they can sometimes make diarrhoea worse.

Rehydration drinks are usually recommended in people who are frail, or over the age of 60, or who have underlying health problems. They are made from sachets that you can buy from pharmacies. (The sachets are also available on prescription.) You add the contents of the sachet to water. Rehydration drinks provide a good balance of water, salts, and sugar. The small amount of sugar and salt helps the water to be absorbed better from the gut into the body. They do not stop or reduce diarrhoea. Do not use home-made salt/sugar drinks, as the quantity of salt and sugar has to be exact.

Note: if you suspect that you are dehydrated, you should contact a doctor. Symptoms of dehydration in adults include tiredness, dizziness or light-headedness, headache, muscular cramps, sunken eyes, passing little urine, a dry mouth and tongue, weakness, and becoming irritable. Symptoms of severe dehydration in adults include profound apathy, weakness, confusion, rapid heart rate, coma, and producing very little urine. This is a medical emergency and immediate medical attention is needed.

Fluids for children to prevent dehydration

You should encourage your child to take plenty of fluids. The aim is to prevent dehydration (low body fluid). The fluid lost in their diarrhoea needs to be replaced. Your child should continue with their normal diet and usual drinks. In addition, they should also be encouraged to drink extra fluids. However, avoid fruit juices or fizzy drinks as these can make diarrhoea worse.

Babies under six months old are at increased risk of dehydration. You should seek medical advice if they develop gastroenteritis. Breast- or bottle-feeds should be encouraged as normal. You may find that your baby’s demand for feeds increases. You may also be advised to give extra fluids (either water or rehydration drinks) in between feeds.

Rehydration drinks may be suggested by a healthcare professional for children at increased risk of dehydration. They are made from sachets available from pharmacies and on prescription. You should be given instructions about how much to give. Rehydration drinks provide a perfect balance of water, salts, and sugar. The small amount of sugar and salt helps the water to be absorbed better from the gut into the body. Do not use home-made salt/sugar drinks, as the quantity of salt and sugar has to be exact.

If your child vomits, wait 5-10 minutes and then start giving drinks again, but more slowly (for example, a spoonful every 2-3 minutes). Use of a syringe can help in younger children who may not be able to take sips.

Note: if you suspect that your child is dehydrated, or is becoming dehydrated, you should seek medical advice. Symptoms of dehydration in children include passing little urine, a dry mouth, a dry tongue and lips, fewer tears when crying, sunken eyes, weakness, being irritable or lethargic. Symptoms of severe dehydration in children include drowsiness, pale or mottled skin, cold hands or feet, very few wet nappies, fast (but often shallow) breathing. This is a medical emergency and immediate medical attention is needed.

Fluids to treat dehydration in children

If your child is mildly dehydrated, this may be treated by giving them rehydration drinks. Your doctor or nurse will advise about how to make up the drinks and about how much to give. This can depend on the age and the weight of your child. If you are breast-feeding, you should continue with this during this time. Otherwise, don’t give your child any other drinks unless the doctor or nurse has said that this is OK. It is important that your child should be rehydrated before they have any solid food.

Sometimes a child may need to be admitted to hospital for treatment if they are dehydrated. Treatment in hospital usually involves giving rehydration solution via a special tube called a ‘nasogastric tube’. This tube passes through your child’s nose, down their throat and directly into their stomach. An alternative treatment is with intravenous fluids (fluids given directly into a vein).

Eat as normally as possible

In children, correcting any dehydration is the first priority when they have cryptosporidiosis. However, if your child is not dehydrated (most cases) or, once any dehydration has been corrected, then encourage your child to have their normal diet. Do not ‘starve’ your child. This used to be advised but is now known to be wrong. So:

  • Breast-fed babies should continue to be breast-fed if they will take it. This will usually be in addition to extra rehydration drinks (described above).
  • Bottle-fed babies should be fed with their normal full-strength feeds if they will take it. Again, this will usually be in addition to extra rehydration drinks (described above).
  • Older children – offer them some food every now and then. However, if he or she does not want to eat, that is fine. Drinks are the most important, and food can wait until their appetite returns.

For adults, it is also advised not to ‘starve’ yourself but to eat small, light meals if you can. Be guided by your appetite. You may not feel like food and most adults can do without food for a few days. Eat as soon as you are able but don’t stop drinking. If you do feel like eating, avoid fatty, spicy or heavy food. Plain foods such as wholemeal bread and rice are good foods to try eating.

Preventing the spread of cryptosporidiosis to others

Cryptosporidiosis is very infectious. This means that you can easily pass on the infection to others. It is therefore essential that you adopt strict personal hygiene measures if you are infected. The following are recommended to prevent the spread of infection to others:

  • Wash your hands thoroughly after going to the toilet. Ideally, use liquid soap in warm running water, but any soap is better than none. Dry properly after washing. If your child wears nappies, be especially careful to wash your hands after changing nappies and before preparing, serving, or eating food.
  • If a potty has to be used, wear gloves when you handle it, dispose of the contents into a toilet, then wash the potty with hot water and detergent and leave it to dry.
  • Don’t share towels and flannels.
  • Don’t prepare or serve food for others.
  • If clothing or bedding is soiled, first remove any faeces into the toilet. Then wash in a separate wash at as high a temperature as possible.
  • Regularly clean with disinfectant the toilets that you use. With hot water and detergent, wipe the flush handle, toilet seat, bathroom taps, surfaces and door handles at least once a day. Keep a cloth just for cleaning the toilet (or use a disposable one each time).
  • You should stay off work, school, college, etc, while you have cryptosporidiosis. You should not return until you have been free of symptoms for 48 hours. Avoid contact with other people as far as possible during this time.
  • Food handlers: if you work with food and develop diarrhoea or vomiting, you must inform your employer and immediately leave the food-handling area. If Cryptosporidium infection is confirmed, you should inform your employer and stay away from work until your doctor advises it is safe to return.
  • You should not swim in a swimming pool for 14 days after your symptoms have cleared. This is because the Cryptosporidium parasite can still be present in your stools during this time.

If you have cryptosporidiosis and you work with vulnerable groups of people such as the elderly, the unwell or the young, you should inform your employer.

Are there any complications of cryptosporidiosis?

As with any gastroenteritis infection, cryptosporidiosis can lead to dehydration and salt (electrolyte) imbalance in your body. This occurs if the water and salts that are lost in your stools are not replaced by your drinking adequate fluids. If you can manage to drink plenty of fluids then dehydration is unlikely to occur, or is only likely to be mild, and will soon recover as you drink. Severe dehydration can lead to a drop in your blood pressure. This can cause reduced blood flow to your vital organs. If dehydration is not treated, kidney failure may also develop. Some people who become severely dehydrated need a ‘drip’ of fluid directly into a vein. This requires admission to hospital.

Also, during any episode of diarrhoea, certain drugs that you may be taking for other conditions or reasons may not be as effective. This is because the diarrhoea means that reduced amounts of the drugs are absorbed (taken up) into your body. Examples of such drugs are drugs for epilepsy, diabetes and contraception. Speak to your doctor or practice nurse if you are unsure of what to do if you are taking other drugs and have diarrhoea.

As mentioned above, symptoms of cryptosporidiosis can be more severe in those with a weakened immune system and can sometimes be life-threatening. The gallbladder and the pancreas gland may also become infected in such people.

One small study has also shown that Cryptosporidium hominis infection may lead to other symptoms in the two months following initial infection in some healthy people. Symptoms can include joint pain, eye pain, headaches and tiredness. It is thought that Cryptosporidium infection may also cause a flare-up of symptoms in those with inflammatory bowel disease such as ulcerative colitis and Crohn’s disease.

Can Cryptosporidium infection be prevented?

In general, good hygiene is essential to prevent the spread of many infections to others (including Cryptosporidium) and to reduce your chance of picking up infections from others. Handwashing is the most important thing that you and your child can do. In particular, always wash your hands and dry them thoroughly, and teach children to wash and dry theirs:

  • After going to the toilet (and after changing nappies or helping an older child to go to the toilet).
  • Before preparing or touching food or drinks.
  • After handling raw food.
  • Before eating.
  • After working, feeding or playing with pets and other animals.

If you smoke, you should also wash your hands before smoking. The simple measure of washing and drying hands regularly and properly is known to make a big difference to the chance of developing many infections.

In addition to this, and particularly when travelling to areas with poor sanitation, you should avoid drinking untreated or unfiltered water. Foods washed or prepared using untreated water should also be avoided. So, avoid:

  • Untreated tap water
  • Ice cream
  • Ice cubes
  • Salads and raw vegetables
  • Fruit that has already been peeled

Also, avoid swallowing the water if you are swimming in lakes, rivers or swimming pools. If you are visiting a farm, make sure that you wash your hands thoroughly after contact with animals and also before eating.

The Chief Medical Officer in the UK advises that anyone who has immunodeficiency that affects a specific type of immune cell known as a ‘T-cell’ should boil all of their drinking water (even in the UK) to reduce their chance of infection. People with T-cell deficiency can include people with cancers affecting their blood, bone marrow or lymph cells and also people with HIV infection with CD4 counts less than 200. Ask your doctor if you think you may have a T-cell deficiency.

References and Disclaimer | Provide feedback


  • Davies AP, Chalmers RM; Cryptosporidiosis. BMJ. 2009 Oct 19;339:b4168. doi: 10.1136/bmj.b4168.
  • Gastroenteritis, Clinical Knowledge Summaries (September 2009)
  • Health Protection Agency; Cryptosporidium
  • Hunter PR, Hughes S, Woodhouse S, et al; Health sequelae of human cryptosporidiosis in immunocompetent patients.; Clin Infect Dis. 2004 Aug 15;39(4):504-10. Epub 2004 Aug 2. [abstract]
  • Hunter PR, Hughes S, Woodhouse S, et al; Sporadic cryptosporidiosis case-control study with genotyping.; Emerg Infect Dis. 2004 Jul;10(7):1241-9. [abstract]
  • Goh S, Reacher M, Casemore DP, et al; Sporadic cryptosporidiosis decline after membrane filtration of public water supplies, England, 1996-2002.; Emerg Infect Dis. 2005 Feb;11(2):251-9. [abstract]
  • Smith HV, Corcoran GD; New drugs and treatment for cryptosporidiosis.; Curr Opin Infect Dis. 2004 Dec;17(6):557-64. [abstract]


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