Chronic Giardiasis: Causes, Symptoms, and Management

March 17, 2025

Chronic giardiasis is a long-term gastrointestinal infection caused by the protozoan parasite Giardia lamblia. This condition is characterized by persistent bloating, watery diarrhea, and malabsorption-related symptoms. While many individuals remain asymptomatic, others may develop severe dehydration, weight loss, and chronic gastrointestinal discomfort. In the United States, giardiasis is commonly seen in international travelers, but it can also occur due to contaminated water sources and poor sanitation.¹

Despite its chronic nature, giardiasis is treatable with antiparasitic medications such as Metronidazole, Tinidazole, or Nitazoxanide. In resistant or recurrent cases, combination therapy with antihelminthics like Albendazole may be beneficial.²

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What is Chronic Giardiasis?

As stated above, giardiasis is a parasitic infection of the digestive tract caused by Giardia lamblia (also known as Giardia duodenalis or Giardia intestinalis). This flagellated protozoan primarily invades the duodenum of the small intestine.³
Chronic giardiasis refers to a persistent, relapsing, or recurrent form of giardiasis. Instead of resolving within a few weeks, symptoms may continue intermittently over an extended period, leading to malabsorption, fatigue, and ongoing digestive issues.⁴

Causes of Chronic Giardiasis

Giardia parasites (Giardia lamblia) reside in the intestines of both humans and animals. Before being excreted in stool, these microscopic organisms form protective cysts, enabling them to survive in the environment for months. When someone ingests these cysts, the parasite undergoes a transformation in the small intestine, releasing trophozoites—pear-shaped, motile forms with two nuclei. These trophozoites attach to the intestinal lining, disrupting normal absorption and leading to infection.⁵

Giardia lamblia Trophozoite

Giardia Infection – Transmission routes

Infection occurs when someone unintentionally ingests the parasite cysts. Following are the Giardia transmission routes:

Drinking Contaminated Water

The primary mode of Giardia infection is ingesting unsafe (contaminated) water. Giardia parasites are present in various contaminated water sources. Household waste, agricultural runoff, or animal feces can contaminate the ground surface water.

Eating Contaminated Food

Contaminated food is another major source of giardiasis. Eating contaminated food, not washing hands before eating, or using unhygienic measures while cooking food can lead to giardiasis.

Person-to-Person Contact

Direct fecal-oral transmission occurs when hands become contaminated with Giardia cysts, particularly in childcare settings, diaper-changing, or through sexual contact (including anal sex).

Animal Contact & Environmental Exposure

Handling infected animals, particularly pets or livestock, can facilitate transmission. Poor sanitation in public restrooms or travel to areas with inadequate water treatment increases infection risk.

Chronic Giardiasis Symptoms

Here are the common symptoms of chronic giardiasis:

Digestive Distress: Giardiasis commonly causes abdominal pain and bloating.
Diarrhea: Persistent diarrhea is a hallmark symptom. Stools may be loose and greasy. Diarrhea may alternate with periods of constipation.
Foul-smelling stools: Stools may have a particularly unpleasant odor due to the giardia parasites in the intestines.
Nausea and vomiting: Some people with giardiasis may feel nauseous and may experience vomiting, contributing to dehydration.
Weight loss: Chronic giardiasis can lead to weight loss due to the ongoing disruption of nutrient absorption in the intestines.
Fatigue: The combination of diarrhea, nutrient malabsorption, and illness can result in fatigue and weakness.
Excessive gas: Increased gas production and flatulence are common symptoms contributing to abdominal discomfort.
Dehydration: Persistent diarrhea and vomiting can lead to dehydration, characterized by symptoms such as thirst, dark urine, and dry mouth.

Diagnostic Aid for Giardiasis

The giardiasis diagnosis is based on the results of a few tests that your doctor may ask. Some common Giardia diagnosis strategies include:

Fecal Microscopic Examination

Microscopic stool examination has historically been a primary diagnostic tool for giardiasis, but it is no longer the most reliable method due to its lower sensitivity. Giardia cysts and trophozoites are identified in stool samples, but because the parasite is shed intermittently, multiple samples on different days may be needed for accurate detection.⁶

Polymerase Chain Reaction (PCR) Testing

PCR is a highly sensitive molecular technique that detects Giardia DNA in stool samples. Although not widely used in routine diagnostics due to cost, it is a powerful tool in research and for diagnosing chronic or asymptomatic infections.

Staining & Culturing for Giardia

Identifying Giardia trophozoite and cyst relies on morphological features. Permanent stains like Giemsa, Iron hematoxylin, and Chlorazol Black are used for detailed examination but are not recommended for all stool samples.⁷
Temporary stains like methylene blue and iodine are preferred for better detection in wet mounts or concentration smears. Trichrome is a quick, permanent stain for fresh fecal specimens and PVA-fixed stool.
Although not routine in clinical labs, culture methods are employed in research settings for various studies.

String Test (Entero-Test)

The string test is an older method used to detect Giardia trophozoites from the upper intestine. A capsule containing a nylon string is swallowed, and after several hours, the string is removed and examined under a microscope. Due to the availability of more sensitive stool antigen tests, the string test is rarely used today.⁸

Immunodiagnostic Tests

Immunodiagnostic tests for Giardia include ELISA, monoclonal antibodies, or direct fluorescent assays for antibody detection and methods of detecting Giardia antigens in human fecal specimens.
Antibody detection involves IgM as an indicator for current infection, IgG for up to 18 months post-infection, and secretory IgA, predominant in duodenal fluid and saliva, as a tool for serodiagnosis.
Studies show elevated IgA and IgG responses in Giardia-infected individuals compared to non-infected.⁹

Antigen Detection Tests

Enzyme-linked immunosorbent assay (ELISA) and direct fluorescent antibody (DFA) tests are now considered the gold standard for diagnosing giardiasis due to their higher sensitivity and specificity compared to traditional microscopy. These tests detect Giardia antigens in stool samples and provide faster and more accurate results.

Chronic Giardiasis -Treatments

Usually, giardiasis symptoms go away spontaneously. But, cases of chronic giardiasis need serious attention and care. The management of giardiasis includes giardiasis medications, hydration, hygiene, and better nutrition.

Giardiasis Medication:

Various giardiasis medications are available. For instance,

Metronidazole (Flagyl®) is administered over five days. It is the most common and effective choice.
Tinidazole (Tindamax®) is another option similar to metronidazole. Although it is used globally for giardiasis infection, it still doesn’t have FDA approval.
Nitazoxanide (Alinia®) is a more suitable option for chronic giardiasis.
Quinacrine hydrochloride, once favored, is no longer available in the US due to adverse effects.
Albendazole is another option. Some studies show albendazole might be just as good as Metronidazole with fewer side effects.¹⁰
Paromomycin is an option available for pregnant women. Although it is less effective, it is not teratogenic.

Hydration:

Since chronic giardiasis involves persistent loose, watery diarrhea, the infected individual is at risk of severe dehydration. So, hydration is an important part of giardiasis treatment. For most patients, just drinking fluids by mouth can help if they have a mild condition. In more serious cases, they might need fluids through a vein.

Maintenance of Proper Hygiene:

Giardiasis is a very common infection in slum areas and places with poor hygiene. Patients should maintain hygiene while receiving treatment for Giardia.

Better Nutrition:

Any infection can be treated with a strong immunity. A healthy diet is the key to strong immunity. Doctors advise giardia patients to eat healthy foods and avoid spicy and fatty foods.

Giardiasis Prevention – How to prevent this infection?

Here are the simple preventive measures to reduce the risk of getting infected with giardiasis:

Wash your hands: Try to wash your hands more frequently. Use soap for washing hands after using the toilet, changing diapers, or before eating anything.
Purify wilderness water: Always drink purified and filtered water. Even if you’re in the wild, do not drink contaminated water.
Wash food: Use filtered water to wash fruits and vegetables. Peel fruits before eating, especially when traveling where water may be unsafe.
Avoid swallowing water in pools: This is a very common occurrence. Avoid swallowing contaminated water in the swimming pools.
Practice Safer Sex: Since anal sex is one of the transmission routes of chronic giardiasis, try practicing safe sex.

Take Away

To sum it up, Giardiasis is a common infection in third-world countries. Chronic giardiasis is a condition with persistent loose, watery diarrhea that won’t go away. The parasite that causes giardiasis is often present in contaminated water and food. Moreover, unprotected anal sex can also lead to giardiasis. Therefore, it is advised by doctors to maintain proper hygiene, boost your immunity with healthy food, and hydrate yourself regularly.

Refrences

1
Hommes, F., Dörre, A., Behnke, S. C., Stark, K., & Faber, M. (2023). Travel-related giardiasis: incidence and time trends for various destination countries. Journal of Travel Medicine, 30(6), taad107. https://doi.org/10.1093/jtm/taad107
2
Periago, M. V., García, R., Astudillo, O. G., Cabrera, M., & Abril, M. C. (2018). Prevalence of intestinal parasites and the absence of soil-transmitted helminths in Añatuya, Santiago del Estero, Argentina. Parasites & Vectors, 11(1), 638. https://doi.org/10.1186/s13071-018-3232-7
3
Horton, B., Bridle, H., Alexander, C. L., & Katzer, F. (2019). Giardia duodenalis in the UK: current knowledge of risk factors and public health implications. Parasitology, 146(4), 413–424. https://doi.org/10.1017/S0031182018001683
4
Lalle, M., & Hanevik, K. (2018). Treatment-refractory giardiasis: challenges and solutions. Infection and drug resistance, 11, 1921–1933. https://doi.org/10.2147/IDR.S141468
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Vivancos, V., González-Alvarez, I., Bermejo, M., & Gonzalez-Alvarez, M. (2018). Giardiasis: Characteristics, Pathogenesis and New Insights About Treatment. Current topics in medicinal chemistry, 18(15), 1287–1303. https://doi.org/10.2174/1568026618666181002095314
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Hooshyar, H., Rostamkhani, P., Arbabi, M., & Delavari, M. (2019). Giardia lamblia infection: a review of current diagnostic strategies. Gastroenterology and hepatology from bed to bench, 12(1), 3–12.
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Mank, T. G., Zaat, J. O., Blotkamp, J., & Polderman, A. M. (1995). Comparison of fresh versus sodium acetate acetic acid formalin preserved stool specimens to diagnose intestinal protozoal infections. European Journal of Clinical Microbiology & Infectious Diseases: Official publication of the European Society of Clinical Microbiology, 14(12), 1076–1081. https://doi.org/10.1007/BF01590942
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Korman, S. H., Hais, E., & Spira, D. T. (1990). Routine in vitro cultivation of Giardia lamblia by using the string test. Journal of Clinical Microbiology, 28(2), 368–369. https://doi.org/10.1128/jcm.28.2.368-369.1990
9
Lass, A., Szostakowska, B., Korzeniewski, K., & Karanis, P. (2017). Detection of Giardia intestinalis in water samples collected from natural water reservoirs and wells in northern and north-eastern Poland using LAMP, real-time PCR, and nested PCR. Journal of water and health, 15(5), 775–787. https://doi.org/10.2166/wh.2017.039
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Alizadeh, A., Ranjbar, M., Kashani, K. M., Taheri, M. M., & Bodaghi, M. (2006). Albendazole versus Metronidazole in treating patients with giardiasis in the Islamic Republic of Iran. Eastern Mediterranean health journal = La revue de sante de la Mediterranee orientale = al-Majallah al-sihhiyah li-sharq al-mutawassit, 12(5), 548–554.

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