Giardia in Children: Symptoms, Causes, and Why It’s Often Missed
When we think about gut issues in kids, especially those with autism or ADHD, we often think about constipation, picky eating, or sensitivities. But sometimes, there is something deeper going on—something that can significantly impact how a child feels, behaves, and functions.
One of those often-overlooked contributors is Giardia pathogen.
What Is Giardia?
Giardia is a microscopic parasite that infects the small intestine. It’s one of the most common intestinal parasites in children and is known to interfere with digestion and nutrient absorption.1
Once in the gut, Giardia can:
- damage the intestinal lining
- disrupt enzyme production
- interfere with fat absorption
- trigger inflammation
Where Does Giardia Come From?
Giardia is typically spread through:2
- contaminated water (pools, lakes, untreated water)
- daycare or school exposure
- poor hand hygiene
- contaminated food
- person-to-person contact
Children are especially susceptible because:
- they are more likely to put hands or objects in their mouths
- their immune systems are still developing
- exposure in group settings is common
Common Symptoms of Giardia in Kids
Giardia does not always present the same way in every child, which is why it is often missed. Certainly, Giardia can cause GI symptoms due to its mechanism of action on the GI terrain, but the infection can also drive extraintestinal and even behavioral symptoms.
Gastrointestinal Symptoms
- diarrhea or loose stools
- constipation (yes, both can occur)
- abdominal pain
- bloating and gas
- foul-smelling stools
- greasy or floating stools
Other Symptoms
- fatigue
- irritability
- poor appetite
- nutrient deficiencies
- weight changes
In Children with Autism or ADHD
You may also see:
- behavioral regression
- increased irritability or dysregulation
- sleep disturbances
- worsening focus or attention
- increased sensory sensitivity
Why Giardia Matters
Giardia doesn’t just cause temporary stomach upset, it can have a broader impact on the body, especially when it goes undetected.
It can:
- disrupt the gut microbiome3
- increase inflammation
- impair nutrient absorption
- impact the gut-brain connection
For children already dealing with underlying imbalances, this added stressor can make symptoms significantly worse.
Why It’s Often Missed
One of the biggest challenges with Giardia is that it is not a common aspect of pediatric workup, and not always picked up on standard lab or stool testing.4
- shedding can be intermittent
- symptoms can mimic other conditions
- testing is not always ordered unless there is persistent diarrhea
A Real Example
I recently worked with an 8-year-old child who began experiencing:
- abdominal pain
- changes in stool patterns
- and noticeable regression in behavior and skills
We ran a comprehensive GI‑MAP® stool test, which showed Giardia at 1.15e5. That is a quantitative result of 115,000 microorganisms per gram of stool, a remarkably high level of this intestinal parasite. That’s the beauty of qPCR testing—it gives us so much more insight than just a positive/negative finding.
The family brought this to their medical provider and requested further testing. The provider was initially hesitant but did pursue conventional testing which confirmed positive Giardia.
This was a huge turning point, not only in understanding what was happening, but in validating the clinical picture.
What This Means for Parents and Providers
This is not about assuming every child has a parasite.
It’s about recognizing that:
- persistent GI symptoms deserve investigation
- behavioral changes may have biological contributors
- and the gut plays a critical role in overall health
- the tools you use in clinical practice matter
When Should You Consider Testing?
You may want to look deeper if your child has:
- ongoing GI symptoms (constipation, diarrhea, bloating)
- unexplained regression
- persistent abdominal pain
- poor response to typical interventions
- frequent exposure to high-risk environments (pools, daycare, etc.)
Final Thoughts
Giardia is more common than many realize—and in some children, it can quietly impact how they feel and function.
When we take the time to look deeper and identify what’s going on in the body, we can move from guessing to targeted, meaningful support.
Because sometimes, the missing piece isn’t more therapy or elimination diet.
It’s understanding what’s happening in the gut and having the appropriate clinical toolkit to do so.
Greer McGuinness, MS, RD, CDN, CLT
Greer McGuinness, MS, RD, CDN, CLT, holds a Master of Science in Nutrition and Dietetics and is a Registered Dietitian, Certified Detox Specialist, Certified Master Herbalist, Certified Lyme Specialist, and Certified Mental Health Specialist. Greer is a member of the Clinical Team at Diagnostic Solutions Laboratory and is passionate about teaching practitioners how to use functional medicine testing to optimize outcomes for their patients.
Greer has made significant contributions to the field of pediatric health. Her expertise lies in detoxifying toxins, enhancing gut health, and optimizing nutrient status. As a published researcher, she has focused on autism spectrum disorder (ASD) and alternative medicine, showcasing her commitment to exploring innovative approaches to healthcare.
Greer is the proud owner of Biomedical Healing for Kids, a virtual private practice in New York.
The opinions expressed in this presentation are the author's own. Information is provided for informational purposes only and is not meant to be a substitute for personal advice provided by a doctor or other qualified health care professional. Patients should not use the information contained herein for diagnosing a health or fitness problem or disease. Patients should always consult with a doctor or other health care professional for medical advice or information about diagnosis and treatment.
References
- Gabain IL, Ramsteijn AS, Webster JP. Parasites and childhood stunting - a mechanistic interplay with nutrition, anaemia, gut health, microbiota, and epigenetics. Trends Parasitol. Mar 2023;39(3):167–180. doi:10.1016/j.pt.2022.12.004
- Krumrie S, Capewell P, Smith-Palmer A, Mellor D, Weir W, Alexander CL. A scoping review of risk factors and transmission routes associated with human giardiasis outbreaks in high-income settings. Curr Res Parasitol Vector Borne Dis. 2022;2:100084. doi:10.1016/j.crpvbd.2022.100084
- Fekete E, Allain T, Siddiq A, Sosnowski O, Buret AG. Giardia spp. and the Gut Microbiota: Dangerous Liaisons. Front Microbiol. 2020;11:618106. doi:10.3389/fmicb.2020.618106
- Hooshyar H, Rostamkhani P, Arbabi M, Delavari M. Giardia lamblia infection: review of current diagnostic strategies. Gastroenterol Hepatol Bed Bench. Winter 2019;12(1):3–12.