Giardiasis "Major Diarrheal Disease"

Giardiasis is a major diarrheal disease found throughout the world. 

Giardiasis is caused by the tiny, flagellated anaerobic Giardia parasite, which is commonly found in contaminated water sources. The Giardia parasite is a very common intestinal parasite. The parasite attaches itself to the lining of the small intestines in humans, where it causes diarrhea and blocks the body's absorption of fats and carbohydrates from digested foods.

Many people, as many as one out of every 10, can carry Giardia without ever knowing they are a carrier. Everyone seems to develop at least some immunity after a case of giardiasis.

Seasonality

Giardia infections tend to increase during the summer months for several reasons.

People are more likely to engage in recreational water activities such as swimming in lakes, rivers, and pools during the summer. Giardia parasites can survive in contaminated water, and individuals can become infected by swallowing even small amounts of water from these sources. Increased outdoor activities can lead to increased exposure to contaminated water sources.

Summer is a popular time for travel, including to areas where giardiasis is more common. This can increase the risk of exposure to Giardia through contaminated food and water.

Warmer temperatures can promote the survival and spread of Giardia cysts in the environment, including in water and on surfaces.

Summer activities often involve more interaction with animals, which can be carriers of Giardia. This can increase the risk of zoonotic transmission (transmission from animals to humans).

Risk Groups

Giardia infection is far more common in children than it is in adults. Children, travelers to endemic areas, individuals with compromised immune systems, and those engaging in outdoor recreational activities are at higher risk. Children are more likely to come in contact with feces, especially if they wear diapers, are toilet training or spend time in a childcare center. People who live or work with small children also are at higher risk of developing Giardia infection.

People without access to safe drinking water are also at higher risk of developing Giardia infection. The risk is greatest in rural or wilderness areas.

Causes

Giardia parasites live in the intestines of people and animals. Before the microscopic parasites are passed in stool, they become encased within hard shells called cysts, which allows them to survive outside the intestines for months. Once inside a host, the cysts dissolve and the parasites are released.

Giardia can spread from one person to another. It can also spread through contaminated water, food, surfaces, or objects. Infection occurs by accidentally swallowing the parasite cysts. This can occur by swallowing unsafe water, by eating infected food or through person-to-person contact.

The most common way to become infected with Giardia is after swallowing unsafe (contaminated) water. Giardia parasites are found in lakes, ponds, rivers and streams worldwide, as well as in public water supplies, wells, swimming pools, water parks and spas. Ground and surface water can become infected with Giardia from agricultural runoff, wastewater discharge or animal feces. Children in diapers and people with diarrhea may accidentally contaminate pools and spas.

Giardia parasites can be spread through food — either because food handlers with Giardia infection don't wash their hands thoroughly or because raw produce is irrigated or washed with unsafe (contaminated) water. Food is a less common source of infection than water, because cooking food kills Giardia.

Potential Complications

Giardia can cause serious complications, especially in infants and children. Giardiasis can cause dehydration and malabsorption which can result in weight loss and deficiencies in essential vitamins and minerals.

Giardiasis can cause growth delays and developmental issues due to poor nutrient absorption, and damage to the intestinal lining which can lead to temporary or permanent lactose intolerance.

Some individuals may develop irritable bowel syndrome after a giardiasis infection, experiencing symptoms like abdominal pain, bloating, and altered bowel habits. In rare cases, giardiasis can trigger reactive arthritis, causing joint pain and inflammation.

Chronic infection may cause a disturbed intestinal balance with changes in the microbiota, villus blunting, leaky gut, nutrient malabsorption, and stunted growth.

Symptoms

Giardiasis symptoms can be mild to severe, and some people never have symptoms. The infection typically clears by itself after a few weeks, but people with weaker immune systems may have a harder time clearing it.

Early symptoms often begin by having diarrhea 2 to 5 times per day and feeling more and more tired.

Common short-term symptoms include profuse diarrhea, gas, smelly, greasy poop that can float, stomach cramps or pain, upset stomach or nausea, and dehydration (loss of fluids).

Less common short-term symptoms include fever, itchy skin, hives (skin rash with red, itchy bumps), swollen eyes, and swollen joints.

Symptoms usually start 1 to 2 weeks after swallowing Giardia germs. They typically last for 2 to 6 weeks. Without treatment, Giardia can become chronic, but this is rare. It can last for years, with repeated bouts of diarrhea, vitamin deficiencies, and tiredness.

Immunodeficiency is a risk factor for the onset of severe Giardia infection. With immunodeficiency symptoms may last longer than 6 weeks. In some cases, symptoms may seem to be gone but will return after several days or weeks.

Pathogenesis

Thus, there is no single mechanism to explain the diarrhea and malabsorption caused by Giardia, which currently should be regarded as a multifactorial process.

Giardia produces a wide range of clinical presentations, including chronic diarrhea with weight loss, post-infectious complications of irritable bowel and chronic fatigue, growth stunting, and asymptomatic infections. These varied manifestations may result from host, parasite, or microbiota differences and make it particularly difficult to elucidate the mechanisms resulting in this range of illness.

Giardia infection causes enterocytes (absorptive cells in the lining of the intestinal mucosa) damage and loss of brush border of the epithelial cells of the intestine that leads to shortening of microvilli and altered epithelial barrier function. This pathology results in aqueous diarrhea, steatorrhea, nausea, abdominal pain, vomiting and weight loss.

Climate Change Impact

Giardiasis cases increase with rising temperatures and more extreme events. The parasitic Giardia load is often amplified in animals such as rats or beavers. Intensified and more frequent heavy rainfall events, associated with climate change, have the potential to increase Giardia concentrations in water bodies, hence the infection risk. Floods can lead to contamination of natural water sources when Giardia cysts originating from manure wash out from fields.

The same can happen when the capacity of sewage systems is exceeded. Droughts on the other hand may increase pathogen concentrations to harmful levels or cause low flows causing the Giardia parasite to settle in the mud or the sand.

Prevention

Avoid drinking untreated water from lakes, rivers, and streams. Boil water or use water filters/purification tablets.

Always wash hands after contact with farm animals, pets, animal feces, and animal environments.

Wash hands after using the bathroom and changing diapers, and before handling or eating any food. Make sure that persons with diarrhea, especially children, wash their hands carefully and frequently with soap to reduce the risk of spreading the infection. This is particularly important in daycare/preschool settings, where many outbreaks have occurred due to person-to-person spread.

Wash fruits and vegetables thoroughly and avoid eating undercooked or raw foods in areas where Giardia is common. Avoid swallowing recreational water.