Parasites aren’t just a third-world problem
Why they’re underdiagnosed & what to do about it
Quick disclaimer: this is for informational purposed only and not medical advice. I’m not a doctor. As always, do your own research.
There’s been a growing conversation around parasites lately. And honestly, it’s long overdue.
Parasites are far more common than most people think. Especially in places like the U.S., where there’s a widespread (and false) belief that parasites are only a concern in developing countries.
Stool testing is the go-to method for detecting parasites, but here’s the issue: most of the time, these tests come back negative even when an infection is present.
That only reinforces the myth that parasites aren’t a real problem.
But a negative test doesn’t always mean you’re in the clear. Parasites are sneaky. And there are several reasons your test might miss them, including:
Location
Not all parasites stay in the gut. Some migrate to other parts of the body, making them invisible to stool tests.
For example:
Toxoplasma gondii starts in the gut but moves into tissues like the brain, liver and muscles.
Ascaris lumbricoides (roundworm) enters through the mouth, larvae migrate to the lungs then back to the gut where adults live and lay eggs.
In these cases, parasites may not show up in stool even if they’re in the body.
Life cycle phases can hide parasites
Parasites don’t always release eggs, cysts or larvae. When they do, it’s often in cycles, not continuously.
A single stool sample might miss the shedding phase.
Some parasites encyst in tissues and stop releasing anything into the gut. Others move through the body during different stages (like Ascaris, which travels through the lungs before returning to the gut).
If you really want to confirm their presence in the gut, you’d likely need to collect multiple stool samples over different days and test at different times to increase accuracy.
Testing methods have limitations
Not all stool tests are created equal and each has weaknesses:
Microscopy relies on seeing parasites under a microscope. This can miss small or low-level infections.
Antigen testing only finds parasites actively shedding antigens and can’t detect dormant or tissue-based infections.
PCR (DNA testing) only detects parasites if they’re shedding DNA, so dormant forms are often missed.
If stool tests are negative but symptoms persist and you want to look at other methods, consider:
Blood tests: antibody testing, smears, PCR
Urine tests or biopsies
Indirect markers like elevated white blood cells, liver enzymes, ammonia, inflammation
But even if you run multiple different types of testing, the timing has to be right to be able to detect them and get an accurate reading. The chances of false negative are high.