Infections
Strongyloides
Antibody test for the threadworm Strongyloides stercoralis; mainly meaningful in people who have lived in or traveled to a tropical area.
Everything about this testWhat it measures
Strongyloides stercoralis is a small worm that occurs mainly in warm, humid areas. The larvae bore in through the skin, usually through bare feet in contaminated soil. The worm can multiply inside the body and can therefore remain present for decades without the person noticing anything. This test measures IgG antibodies against the worm in the blood. Because the worm releases only few larvae into the stool, a stool test is often not enough.
- A long-lasting, often unnoticed infection with Strongyloides stercoralis
- A risk of hyperinfection: an unchecked multiplication of larvae that can develop when the immune system is suppressed
Positive
A positive result fits an infection with Strongyloides, often one that has existed for years without symptoms. This is important to know: if the immune system is later suppressed, for example by a transplant, chemotherapy or a course of corticosteroids, the infection can grow into a hyperinfection that can be fatal. A positive result in someone who has never been in an area where the worm occurs is less likely to be real and can be due to cross-reaction with other worms.
Negative
A negative result makes an infection less likely, but does not fully rule it out, certainly not in people with reduced immunity, who make fewer antibodies. If the suspicion remains, for example because of eosinophilia or typical skin changes, the hospital can do additional stool testing, with culture or PCR. Antibody testing and stool testing therefore complement each other.
If your result is abnormal
With a positive result, treatment with a deworming medicine follows, if needed in consultation with a medical microbiologist or an internist specializing in infectious diseases, and in people who are going to use immunosuppressive medicines this is preferably done before they start. Strongyloidiasis is not notifiable in the Netherlands.
Reliability
According to the Dutch medical specialists' guideline (FMS) on laboratory diagnosis of intestinal parasites, serology is the preferred method for a long-lasting Strongyloides infection, because it is a chronic infection and stool tests then often stay negative. How often the test misses an infection or is wrongly positive has not been well established. The result means the most in someone who has lived in or traveled to an area with this worm, especially before starting medicines that suppress the immune system. In people who have never been in such an area, the chance of an infection is so small that a positive result says little.
Limitations
- Cross-reaction with antibodies against other worms occurs and can give a false-positive result.
- In people with reduced immunity, the test can be negative while there is still an infection.
- Antibodies can remain detectable for a long time after treatment; the test is therefore of limited use as a check.
- For people who have not stayed in an area where the worm occurs, the chance of a real infection is very small, so a positive result is more often wrong than right.
How common is this
Strongyloides does not occur naturally in the Netherlands; it is almost always an infection picked up in a warm, humid area. Because the worm can remain in the body for more than 50 years without symptoms, an infection can still be present long after such a stay. In people who have not stayed in such areas, the infection is very rare.
Who is this useful for
Useful in people who were born in or have lived for a longer time in an area where Strongyloides occurs, and in travelers who have been there, especially before starting medicines that suppress the immune system, such as corticosteroids or chemotherapy. Also with unexplained eosinophilia or typical creeping skin changes. Not useful in people who have never been in such an area and have no symptoms; in them, the chance of a real infection is so small that a positive result says little.
Downsides and risks
- In people who have not stayed in an area where the worm occurs, a positive result is more often wrong than right and can lead to unnecessary treatment.
- A negative result can give false reassurance in someone with reduced immunity, precisely the group at the highest risk.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results