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Giardiasis: Microbiology, Pathogenesis, And Management

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Giardiasis also known as beaver fever; is a worldwide diarrheal disease caused by the protozoan Giardia duodenalis (also known as G. intestinalis and G. lamblia). (Esch KJ, 2013) It is found in food-producing animals and in pets .Also , this infection can reduce weight gain and may become a apprehension for zoonotic transmission .(Ortega and Adam, 1997) Giardiasis is one of the infections which is added to the WHO’s “Neglected Disease Initiative” (Savioli et al., 2006) Amazingly, this research investigate more details about giardiasis from its microbiology to the curation methods from it .

Microbiology of Giardia

G.lamblia trophozoites are a pear-shaped cell, 10 to 20 micrometers long. They are motile by way of four pairs of flagella and each G. lamblia cell has two nuclei. (Rodney D,2001)

Trophozoites differentiate into cysts, also contain prominent vesicles termed encystation-specific vesicles and unlike eukaryotes, G. lamblia cells contain no visible mitochondria instead contains a substantially reduced metabolic organelle termed a mitosome. (Faso C, Hehl AB, 2011)Additionally, cells appear to contain no Golgi bodies and instead, the secretory system consists entirely of the endoplasmic reticulum and numerous vesicles spread throughout the cell, termed peripheral vesicles. (Faso C, Hehl AB, 2011)

Giardia lamblia affected humans by ingestion of contaminated water, food, or by the fecal-oral route. Trophozoites are formed in the small intestine by excystation, one cyst of Giardia lamblia can release two trophozoites. (Einarsson E,2016)

Trophozoites reproduce by longitudinal binary fission in the lumen of the proximal small bowel and does not spread to the blood or any other parts of the gastrointestinal tract . Additionally, they can be free or attached to the mucosa epithelium by a ventral adhesive sucking disk .(Rodney D, 2001)

Then, while the parasites pass toward the colon, encystation happens. Both cyst and trophozoites can be found in feces but in different situations. The cyst we found most commonly in non-diarrheal feces they difficulty survived in cold water.On the other hand, trophozoites can be found in diarrheal stools . ( Rodney D, 2001)


The pathophysiological mechanisms that occur during G. Lamblia infection are not perfectly understood.(Buret A.G., Cotton J. 2011)However, one of the research reports find that after a short time of colonisation in the lumen of the small intestinal , Giardia trophozoites which causes severe diarrheal condition lead to decrease on the length of the small intestinal microvilli by several pathophysiological mechanisms including; increasing the rate of enterocyte apoptosis and inhibition of our intestinal barrier function .


Giardiasis is rarely fatal in industrialized countries, but it can cause permanent symptoms and serious complications, especially in infants and children. The most common complications include dehydration; often as a result of severe diarrhea which happens when the body doesn’t have enough water to perform its functions. Also , in children , inappropriate to thrive is another sever complication because of chronic diarrhea from giardia infection can cause malnutrition and impair children’s physical and mental growth. (Donowitz JR and Alam M, 2016) Finally, malabsorption of vitamins (such as vitamin A and vitamin B12) , proteins and fat leading to steatorrhoea which is a stool containing fat.(Cotton JA, 2011)

Besides of these complications , half of those who are infected are asymptomatic carriers that they continue to excrete cysts for long periods .(Einarsson E, 2016)

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Clinical features

However , Giardia infection can cause a variety of intestinal symptoms and clinical features normally develop from nine to two weeks after the exposure .(Barry MA and Weatherhead JE ,2013) The most prominent symptom is chronic diarrhea which is often greasy , watery (non-bloody) and foul-smelling, with a tendency to float. Other symptoms including anorexia, abdominal cramps , nausea and vomiting. Also , minority of patients develop extra gastrointestinal tract symptoms such as itchy skin and swelling of eyes .(Robertson LJ,2010)

Laboratory diagnosis

There are different laboratory diagnostic methods which help physicians to conclude the giardiasis. Firstly, Ova and Parasite (O+P) examination ,which is ineffective method because Giardia cysts can be excreted intermittently, so many cases (>50%) of giardiasis will be missed with a single O+P examination, resulting in under diagnosis. (Minetti C,2016) Secondly, multiple stool collections, or in other word , collection of three stool specimens on separate days . Also, this method is insensitive . Thirdly, microscopical examination of freshly passed stools is used for the confirmation of Giardia trophozoite and cysts .Fourthly, fresh diarrhoeic specimen; by trying to find Giardia lamblia trophozoites.However, is difficult to detect because of trophozoites remain attached to the wall of the intestine. Finally, formed faecal specimen which is done by looking for the Giardia lamblia cyst. (Minetti C,2016)

Fortunately, these methods have an alternative techniques which are more sensitive and specific , called fecal immunoassays . These techniques including :an ELISA test, which helps in detection a Giardia cyst wall antigen in the stool . (Rosenblatt JE, 1993) Additionally ,string test ( Entero-Test); includes swallowing a piece of string until it accomplishs a duodenum so that the trophozoite agglutinates to the string and can be visualized.(Hooshyar H, 2019) Finally , Polymerase Chain Reaction (PCR) which can be used to differentiate the subtypes of Giardia lamblia.


Natural medicine has a large potential to affect the course of Giardia infection.The best way to treat giardiasis naturally may be through a combination approach, by using both phytotherapeutic agents and nutritional interventions. The main goals of using them are to inhibit growth and replication of Giardia trophozoites, decrease the acute symptomatology of giardiasis and enhance host defense mechanisms which can best be achieved by consuming a whole-foods, low-fat, high fiber and low simple-carbohydrate diet. Additionally, the ingestion of probiotics and wheat germ can aid in parasite clearance.

Recently, various drugs can be used to treat Giardia infection such as metronidazole, tinidazole, and nitazoxanide. However, metronidazole is the most commonly prescribed antibiotic for giardiasis. (Escobedo AA, Cimerman S, 2007) Some of these drugs may not be routinely available in the United States.

Several factors may influence the effectiveness of a drug regimen, including medical history, nutritional status, and condition of the immune response. (Upcroft JA, Upcroft P, 1993)However, it was proved that metronidazole as other drugs of the 5-nitro group, has been associated with significant failure rates in clearing parasites from the gut so well as the poor compliance by the patients to the drug. (Upcroft JA, Upcroft P, 1993) Besides, an increasing incidence of nitroimidazole-refractory giardiasis has been reported, particularly in travelers from India and other regions in Asia. Therefore, it is necessary to discuss treatment options with a healthcare provider. (Solaymani-Mohammadi S, Genkinger JM, Loffredo CA, Singer SM,2010)


No vaccine can prevent giardiasis. Also, medicine to prevent infection is not recommended. However, the best way to prevent infection is good traveling habits and good sanitation.Travelers should be careful to avoid food and water that could be contaminated . (Betancourt WQ, 2004)It’s safest to eat food that has been peeled or cooked so that Giardia parasites and cysts killed.

Practicing good hygiene including frequent hands washing is always an important habit that can reduce the risk of Giardia infection. Additionally, you have to wash your hands after using the bathroom and after you care for a sick person or animal.


In conclusion , Giardiasis has significant morbidity rates, known as due to unhygienic criteria in our community and potentially because of contaminated food and water. It is transmitted via fecal-oral route also can be spread by contact with fecal material from infected people. Diagnosis of giardiasis can be done by the detection of cysts or trophozoites in a stool sample.For prevention, it’s important to practice good hygiene, avoid drinking contaminated water and avoid eating food that may be contaminated by using boiled and bottled water and keep away from the consumption of raw fruits and vegetables. However, there are several effective drugs that can be used to treat Giardia infection include metronidazole, tinidazole, and nitazoxanide.


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