This parasite infection can stunt children’s growth

The Australian Centre for Functional Medicine’s Research and Innovation team reports on a new study that uncovers how the parasite Giardia lamblia causes stunt growth in baby mice


Giardiasis is an infection caused by a protozoan parasite of the genus Giardia, which commonly affects the small intestine. Symptoms include diarrhea, bloating, fatty stools, stomach cramps, nausea and vomiting and dehydration. Every year, more than 280 million people are affected by giardiasis worldwide. Learn more about parasites here.

Giardiasis usually affects infants and children but can also occur in adults and pets, like cats and dogs. Infection usually occurs by the ingestion water or food contaminated with Giardia as well as by contact with contaminated faeces or handling of infected animals.

In children, however, giardiasis does not tend to cause acute diarrhea as in adults, but instead, it is associated with impaired growth and reduced weight gain1-3. While this correlation is well-known, the mechanisms explaining how this parasite influences children’s development has remained a mystery.

Now, a new study, published in the journal Science Translational Medicine, proposes how Giardia manages to affect children’s development.


The Parasite – Gut Microbiota – Bile connection


To study the role of Giardia on development, researchers used a mouse model, infected at different ages, with the parasite Giardia lamblia, and performed various analyses, measuring the levels of important metabolites, intestinal and immune function, gene expression, and gut microbiota composition, among other analyses.

Their results provide the first well-supported explanation for how Giardia parasites can cause growth impairment in children. First off, the study found that Giardia increases the production of bile, a yellow-green fluid normally produced in the liver and used to aid with the digestion of fats.

Giardia parasites use these bile fluids to promote their own growth while altering the normal metabolism of mice. The study found that mice infected with Giardia suffered from elevated energy expenditure, altered gut microbiota composition, and dysregulated lipid metabolism, resulting in significant reductions in fat tissue, as well as reduced growth and body weight gain. Learn more about what gut microbiota testing do for your health.

The results of this study provide convincing evidence that indeed Giardia parasites are the cause of the impaired growth and weight gain observed in infected children.


How to prevent Giardiasis


In Western Australia, about 700 infections from Giardia parasites are reported each year. Some of the best ways to avoid infection with this parasite include:

      • Avoiding contact with contaminated water sources, such as polluted water from rivers, ponds, lakes, swimming pools, spas or the sea.


      • Eat only fully cooked food, and be sure to wash fruit and vegetables if eating them raw


      • Wash your hands after handling public toilets, taps, toys, nappy changing tables or any other surfaces may have been used by an infected person


      • Avoid contact with animals or soils that may be contaminated with animal faeces



If you think you or your child may have been exposed to Giardia, please contact the Australian Centre for Functional Medicine for comprehensive parasitic testing.  Our laboratory testing is necessary to confirm the presence of Giardia or any other foreign pathogen.

Once this pathogen has been identified the Australian Centre for Functional Medicine will create a personalised treatment plan based on your personal needs.  This may include antimicrobials and or prescription antibiotics. See the official guidelines on Giardia infections here.




  1. Riba A, Hassani K, et al. 2020. Disturbed gut microbiota and bile homeostasis in Giardia-infected mice contributes to metabolic dysregulation and growth impairment. Science Translational Medicine. Vol. 12, Issue 565, DOI: 10.1126/scitranslmed.aay7019. Read it!
  2. Hollm-Delgado MG, Gilman RH, Bern C, Cabrera L, Sterling CR, Black RE, Checkley W. Lack of an adverse effect of Giardia intestinalis infection on the health of Peruvian children. American journal of epidemiology. 2008 Sep 15;168(6):647-55. Read it!
  3. Centeno-Lima S, Rosado-Marques V, Ferreira F, Rodrigues R, Indeque B, Camará I, de Sousa B, Aguiar P, Nunes B, Ferrinho P. Giardia duodenalis and chronic malnutrition in children under five from a rural area of Guinea-Bissau. Acta Médica Portuguesa. 2013 Dec 20;26(6):721-4. Read it!
  4. Donowitz JR, Alam M, Kabir M, Ma JZ, Nazib F, Platts-Mills JA, Bartelt LA, Haque R, Petri Jr WA. A prospective longitudinal cohort to investigate the effects of early life giardiasis on growth and all cause diarrhea. Clinical Infectious Diseases. 2016 Sep 15;63(6):792-7. Read it!