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Symptoms and Signs of Giardiasis

Doctor's Notes on Giardiasis

Giardiasis is the most common cause of parasitic gastrointestinal disease. It is caused by an infection of the small intestine with the parasite Giardia duodenalis, also known as Giardia lamblia and Giardia intestinalis. The parasite is typically acquired in situations where there is inadequate sanitation or treatment of drinking water. Giardiasis is a cause of so-called “travelers’ diarrhea”. It can also be spread in any situation where fecal-oral contamination is likely, such as day-0care centers.

The most common symptoms of giardiasis are diarrhea and abdominal pain. The stools may be foul-smelling and may float. Other possible associated symptoms and signs can include bloating, fatigue, malaise, nausea, weight loss, and vomiting. These symptoms can vary in intensity from mild to severe.

Medical Author:
Medically Reviewed on 3/11/2019

Giardiasis Symptoms

Giardiasis can show itself in different ways. Some people can be carriers of the parasite and have no symptoms of the disease, but they pass cysts in their stool and pass the disease to others. Others may develop acute or chronic diarrheal illnesses in which the symptoms occur 1-2 weeks after swallowing the cysts.

Acute diarrheal illness may have the following symptoms

  • Diarrhea: Most people with giardiasis complain of diarrhea. Stool is usually described as profuse and watery early in the disease. Later in the disease, stools become greasy, foul smelling, and often floats. Blood, pus, and mucus are usually not present. Symptoms may last for one to several weeks.
  • Weight loss, loss of appetite
  • Bloating, abdominal cramping, passing excessive gas, sulfur-tasting burps
  • Occasional nausea, vomiting, fever, rash, or constipation

Chronic diarrheal illness may have the following symptoms

  • Diarrhea: Stools are often greasy, foul-smelling, yellowish, and may alternate between diarrhea and constipation.
  • Abdominal pain worsens with eating
  • Occasional headaches
  • Weight loss

Giardiasis Causes

Giardia lamblia cysts are transmitted to humans in various ways.

  • Contaminated water supplies: Giardia lamblia is one of the most common causes of water-borne diarrhea outbreaks. Sources of contaminated water include public facilities that improperly filter and treat water, water in developing countries, or rivers and lakes used by hikers. Overseas travelers and hikers are at a high risk for infection.
  • Contaminated food: Food that may have been washed in contaminated water, exposed to manure, or prepared by an infected person can transmit the disease.
  • Person-to-person contact: Infection may be caused by poor hygiene and most commonly occurs in daycare centers, nursing homes, and during oral-anal sexual contact. Family members, daycare workers, and others in contact with infected stool may then themselves become infected.

What's Inside Your Drinking Water? Slideshow

What's Inside Your Drinking Water? Slideshow

Let’s start with the basics. Water needs three simple atoms to exist: two hydrogens and one oxygen, which bond to make the molecule H2O. Those two common chemicals give water some rather uncommon properties. For instance, when most liquids freeze and become solid, they sink rather than float. If it sank instead, ice would kill the fish that live beneath freezing ponds and lakes, and also any plants living below, wiping out whole ecosystems.

It takes plenty of warming energy to heat water, too. This is due to something called specific heat capacity. Because water’s specific heat capacity is so high, it maintains its temperature fairly easily. Think about how a pool or an ocean can still feel cold on a hot day. Now consider that the cells of our bodies are full of water content, which comprises as much as 75% of our bodies depending on our age and other factors. Since water maintains its temperature easily, so do we. That means we don’t have to work as hard as we might to stay within a comfortable temperature range.

Since we depend on drinking water, it is important to know what’s actually in there. In this article, learn about potential drinking water health hazards, environmental protections put in place to protect your water, and safe treatments that can assure you are getting the best quality of healthy water.


Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.