Giardiasis is a parasitic disease caused by Giardia duodenalis (also known as G. lamblia and G. intestinalis). About 10% of those infected have no symptoms. Individuals who experience symptoms may have diarrhea, abdominal pain, and weight loss. Less common symptoms include vomiting and blood in the stool. Symptoms usually begin 1 to 3 weeks after exposure and without treatment, may last up to six weeks.Giardia usually spreads when Giardia duodenalis cysts within feces contaminate food or water, which is later consumed orally. The disease can also spread between people and through other animals. Factors that increase possible contamination include travelling in the developing world, changing diapers, consuming raw food, and owning a dog. Cysts may survive for nearly three months in cold water. Giardia is diagnosed via stool tests.

Prevention may be improved through proper hygiene practices. Asymptomatic cases often do not need treatment. When symptoms are present, treatment is typically provided with either tinidazole or metronidazole. Infection may cause one to become lactose intolerant and as a result, it is recommended to temporarily avoid lactose following an infection. Resistance to treatment may occur in some patients.Giardia is one of the most common parasitic human diseases globally. In 2013, there were approximately 280 million people worldwide with symptomatic cases of giardiasis. Infection rates are as high as 7% in the developed world and 30% in the developing world. The World Health Organization classifies Giardia as a neglected disease.

Signs and symptoms

Symptoms vary from none to severe diarrhea with poor absorption of nutrients. The cause of this wide range in severity of symptoms is not fully known but the intestinal flora of the infected host may play a role. Diarrhea is less likely to occur in people from developing countries.

Symptoms typically develop 9–15 days after exposure, but may occur as early as one day. The most common and prominent symptom is chronic diarrhea which can occur for weeks or months if untreated. Diarrhea is often greasy and foul-smelling, with a tendency to float. This characteristic diarrhea is often accompanied by a number of other symptoms, including gas, abdominal cramps, and nausea or vomiting. Some people also experience symptoms outside of the gastrointestinal tract such as itchy skin, hives, and swelling of the eyes and joints, although these are less common. Despite its nickname "beaver fever", fever occurs in only about 15% of people.

Prolonged disease is often characterized by diarrhea, along with malabsorption of nutrients in the intestine. This malabsorption results in fatty stools, substantial weight loss, and fatigue. Additionally, those suffering from giardiasis often have difficulty absorbing lactose, vitamin A, folate, and vitamin B₁₂. In children, prolonged giardiasis can cause failure to thrive and may impair mental development. Symptomatic infections are well recognized as causing lactose intolerance, which, while usually temporary, may become permanent.

Treatment

Treatment is not always necessary as the infection usually resolves on its own. However, if the illness is acute or symptoms persist and medications are needed to treat it, a nitroimidazole medication is used such as metronidazole, tinidazole, secnidazole or ornidazole.

The US CDC lists metronidazole, tinidazole, and nitazoxanide as effective first-line therapies;[  of these three, only nitazoxanide and tinidazole are approved for the treatment of giardiasis by the US FDA. A meta-analysis done by the Cochrane Collaboration found that compared to the standard of metronidazole, albendazole had equivalent efficacy while having fewer side effects, such as gastrointestinal or neurologic issues. Other meta-analyses have reached similar conclusions. Both medications need a five to 10 day long course; albendazole is taken once a day, while metronidazole needs to be taken three times a day. The evidence for comparing metronidazole to other alternatives such as mebendazole, tinidazole or nitazoxanide was felt to be of very low quality. While tinidazole has side effects and efficacy similar to those of metronidazole, it is administered with a single dose.Resistance has been seen clinically to both nitroimidazoles and albendazole, but not nitazoxanide; though nitazoxanide resistance has been induced in research laboratories.The exact mechanism of resistance to all of these medications is not well understood. In the case of nitroimidazole-resistant strains of Giardia, other drugs are available which have showed efficacy in treatment including quinacrine, nitazoxanide, bacitracin zinc, furazolidone and paromomycin. Mepacrine may also be used for refractory cases.Probiotics, when given in combination with the standard treatment, has been shown to assist with clearance of Giardia.

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Journal of Oral Hygiene and Health