The Symptoms and Treatment of Giardiasis

Giardiasis tends to cause issues like diarrhea, fatigue, nausea, and loss of appetite. Since the treatment of giardiasis depends on proper diagnosis, we want to go over the main characteristics in the following article.
The Symptoms and Treatment of Giardiasis
Samuel Antonio Sánchez Amador

Written and verified by the biologist Samuel Antonio Sánchez Amador.

Last update: 27 May, 2022

Do you know what pathogen causes this infection and how it spreads? Are you aware of the symptoms? Knowing the answers to these questions will help you deal with and avoid this infection. Therefore, we want to use the space below to tell you about the most relevant aspects of giardiasis in humans.

About the Giardia genus

Before talking about the symptoms and treatment of giardiasis, it’s important to understand the pathogen. This is a very particular illness since the pathogen isn’t a virus or bacteria. Rather, it’s a protozoan .

Protozoa are unicellular protists that live in moist or aquatic environments. These microorganisms have a complex morphology and are the size of viruses and bacteria.

We’re talking about the species Giardia lamblia, a flagellated protozoan belonging to the Diplomonadida order. This parasite affects several different mammals, including human beings. To be more specific, it lives in the small intestine, where it causes the above-mentioned illness.

The size of this protozoan is small–less than 20 micrometers. What’s more, it’s interesting to know that it lacks certain organules like mitochondria, which are very important to cellular function in living beings.

Giardiasis infects the human intestine.

The complex life cycle of this parasite

Unlike other parasitesGiardia has just one host (in this case, human) over the course of its life cycle. Despite its low complexity as a living creature, it presents two distinct forms over the course of its development

  • Trofozoit: Mobile and flagellated. According to clinical microbiological studies, it has a disk in the form of a suction cup on its ventral surface. This characteristic allows it to adhere to the epithelium of the intestine.
  • Cyst: Immobile and without flagellum. It takes on this structure in order to resist outside of the host and has an infectious capacity.

Discover more: Why Do Cases of Salmonellosis Increase in the Summer?

The symptoms and treatment of giardiasis

Humans contract giardiasis by ingesting cysts in contaminated water or foods. Infected individuals expel these cysts with their feces, and the cysts can remain in the environment for a long time.

Therefore, poor cleansing and purifying of water can put an entire population at risk for this illness.

The symptomatology of giardiasis

The symptoms of giardiasis can vary from one patient to another. However, they tend to include the following :

  • Fatigue
  • Nausea
  • Loss of appetite
  • Diarrhea and oily fecal matter
  • Vomiting
  • Bloating and abdominal pain
  • Weight loss
  • Excessive flatulence
  • Headache

Most of these symptoms are the product of the adhesion of Giardia to the intestinal epithelium. This external pathogen causes a thickening of the microvilli of the intestine. In doing so, it reduces its surface exposure. As a result, it produces various physiological imbalances of varying severity.

The treatment of giardiasis

Some scientific studies indicate that certain strains of Giardia are resistant to the most commonly used medication. However, doctors usually prescribe the following medications to patients with giardiasis:

  • Metronidazole: An antibiotic that patients must take for a week in order to irradicate the infection. Taking this medication is unpleasant, as it can produce nausea and leave a metallic taste in the mouth.
  • Tinidazole: This course of treatment is just as effective as the above, and tends to destroy the pathogen in one dose.
  • Nitazoxanide: This is a good option for children since it treats diarrhea effectively. Also, it’s available in liquid form, and treatment involves only three doses.
  • Paromomycin: Another antibiotic for the treatment of giardiasis in both humans and animals.
A woman with diarrhea.
In cases of giardiasis, a doctor may suggest different types of treatment. Their purpose is to put a stop to severe symptoms like giardiasis.

At-risk groups

As with any other illness, there are certain groups within the population that are at greater risk of contracting giardiasis.

  • Children. Children are more likely to come in contact with fecal matter than adults. That’s because they often play in unhealthy environments or with peers that have been in contact with their own feces. Therefore, giardiasis has an asymmetrical epidemiological pattern according to age.
  • People in low-income countries without access to purified water. As we’ve already mentioned, the cysts can remain in the environment for a long time. Water is a very effective means of transmission and transportation, so untreated water may contain this pathogen.
  • People that practice anal sex: This is quite obvious as this type of sex increases the chances of coming into contact with fecal matter.

Giardiasis: What you need to know

Giardiasis is an illness with a variety of clinical presentations that spreads mostly in environments where hygiene is low. Therefore, it’s important to disinfect food properly and stay hydrated with properly treated water. This is especially important in warm climates, isolated from urban centers.

If you suspect gastrointestinal illness, it’s always best to seek medical attention. That way, your doctor can prescribe medication to make giardiasis go away in a few days.

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

  • Centers for Disease Control and Prevention (CDC). (December 9, 2017). Giardiasis.
    Available in
  • Adam RD. Biology of Giardia lamblia. Clin Microbiol Rev. 2001;14(3):447-475. doi:10.1128/CMR.14.3.447-475.2001
  • Petri WA Jr. Therapy of intestinal protozoa. Trends Parasitol. 2003;19(11):523-526. doi:10.1016/
  • Beer KD, Collier SA, Du F, Gargano JW. Giardiasis Diagnosis and Treatment Practices Among Commercially Insured Persons in the United States. Clin Infect Dis. 2017;64(9):1244-1250. doi:10.1093/cid/cix138
  • Hooshyar H, Rostamkhani P, Arbabi M, Delavari M. Giardia lamblia infection: review of current diagnostic strategies. Gastroenterol Hepatol Bed Bench. 2019;12(1):3-12.
  • Choy SH, Al-Mekhlafi HM, Mahdy MA, et al. Prevalence and associated risk factors of Giardia infection among indigenous communities in rural Malaysia. Sci Rep. 2014;4:6909. Published 2014 Nov 4. doi:10.1038/srep06909

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.