An ova and parasite (O&P) examination looks for parasites and their eggs in a sample of your stool. Parasites usually infect the lower digestive tract and can live there for years. They often come from unpurified water or food that has been contaminated by the parasite eggs (ova), particularly in countries where there is poor sanitation.
Your sample will be sent to a pathology laboratory where it is smeared onto a slide, stained and investigated under a microscope to identify and count any parasites, ova and cysts that may be present. Other tests can be required to make a diagnosis such as antigen tests which look for specific proteins on the surface of the suspected parasite and genetic molecular tests to look for the DNA of the parasite.
Treatment may include drugs that target a specific parasite. Some infections disappear naturally over time.
There are a wide variety of parasites that can infect humans and cause a range of symptoms including diarrhoea, which can be bloody and prolonged with mucus in the stool, also abdominal pain, nausea, headaches and fever. Symptoms may not occur until many days or weeks after exposure to the parasite.
Most people who are infected by parasites become infected by drinking water or eating food that has been contaminated with the parasite eggs. Parasites and eggs from infected people or animals are released into the stool and can then contaminate any water, food, or surfaces that come into contact with them. This contamination cannot be seen. The food and water will look, smell, and taste completely normal.
In order to diagnose the source of your illness your doctor will ask you questions about your symptoms and your health history as well as any travelling you have done.
Infections from parasites can occur in Australia as well as overseas. The most common parasites in Australia are also found worldwide and these include the single-cell parasites or protozoa such as Giardia,Dientamoeba and Cryptosporidium. They can be present in even the most remote and pristine mountain streams and lakes, and also swimming pools, hot tubs, and occasionally community water supplies.
Parasitic infections are of particular concern for people who can develop serious symptoms and complications from prolonged diarrhoea including infants, the elderly, and people with weakened immune systems such as those with HIV/AIDS.
| Common parasites in Australia and overseas | |||
Name of parasite | Type | Where located | Other features |
Giardia | Single cell parasite | Worldwide - water | May be asymptomatic or cause watery diarrhoea |
Dientamoeba fragalis | Single cell parasite | Worldwide - water | More common in children and causes watery diarrhoea |
Cryptosporidium | Single cell parasite | Worldwide - water | Most common cause of recreational water - related disease in Australia |
Strongyloides stercoralis | Roundworm | Common in rural & remote Australia | Acquired via skin penetration Can cause skin eruptions, gut symptoms, and asthma type symptoms. Requires additional serology testing to be identified. |
Entamoeba histolytica | Single cell parasite | Developing countries | Usually asymptomatic but can cause bloody diarrhoea (dysentery) or liver abscess |
Schistosoma | Roundworm | Developing countries | Bladder, bowel or liver involvement depending on species |
Other tests
Blood antibody tests are sometimes ordered to decide whether someone has been exposed to a specific parasite in the past. Antibodies are made by your immune system as a defence against infection and foreign substances that can harm you. A positive result may indicate a past or a chronic infection but is not used to detect a current infection.
Antigen tests, which detect the presence of specific parasite proteins, have been developed to detect some parasites.
Increasingly, genetic molecular testing is being used to detect the DNA of parasites. This has the advantage of being quicker and more accurate.
A stool sample that has not been contaminated by urine or water should be collected in a clean container. The sample should either be taken to a laboratory within an hour after collection or transferred into special transport vials containing preservative solutions.
To improve the chances of detecting a parasite it may be necessary to collect multiple samples at different times on different days because parasites are shed intermittently and may not be in the stool or other samples at all times.
If Schistosoma haematobium infection is suspected, urine needs to be collected. This should be the end part of urine that you are passing - known as terminal void, not midstream urine - and it is recommended you collect it around midday (10am - 2pm).
Any preparation?
None required
If no ova or parasites are seen in the samples,
If ova and parasites are present in the stool samples,
The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.
You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.
Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:
An O&P test detects only those parasites that live in the digestive tract and whose eggs are passed through the stool. For parasites such as pinworms, or blood parasites that cause malaria, other tests are required.
Re-infection from a parasitic infection is possible if you are exposed again, for example through a family member who has an asymptomatic parasitic infection and continues to shed the organisms and re-infects others.
Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.
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