Giardia duodenalis (Giardia lamblia or Giardia intestinalis)

Giardia duodenalis is a microscopic parasite that infects the small intestine of humans and many other animals. It is also known as Giardia lamblia or Giardia intestinalis. It causes a diarrheal illness called giardiasis, which can affect people of all ages and backgrounds. Giardiasis is one of the most common causes of waterborne and foodborne diseases in the world.

Giardia duodenalis has two forms: a motile trophozoite that attaches to the intestinal lining and feeds on nutrients, and a dormant cyst that is shed in the feces and can survive for weeks or months in the environment. The cysts are resistant to chlorine and other disinfectants, making them difficult to eliminate from water sources. The infection occurs when a person ingests cysts from contaminated water, food, or hands. The cysts then hatch into trophozoites in the small intestine and multiply by binary fission. Some trophozoites may encyst and be excreted, while others may remain attached and cause symptoms.

The symptoms of giardiasis vary from person to person, depending on the number of parasites ingested, the immune status of the host, and other factors. Some people may have no symptoms at all, while others may experience abdominal cramps, bloating, gas, nausea, vomiting, diarrhea, weight loss, and malabsorption. The symptoms usually appear within one to three weeks after exposure and may last for several weeks or months if untreated. In some cases, giardiasis may lead to chronic complications such as growth retardation, failure to thrive, lactose intolerance, irritable bowel syndrome, and allergic reactions.

The diagnosis of giardiasis is based on the detection of cysts or trophozoites in stool samples using microscopy, antigen tests, or molecular methods. The treatment of giardiasis involves the use of antiparasitic drugs such as metronidazole, tinidazole, nitazoxanide, or paromomycin. The prevention of giardiasis relies on the provision of safe drinking water, proper sanitation and hygiene practices, and health education.

Giardia duodenalis is a fascinating parasite that has a complex evolutionary history and a remarkable ability to adapt to different hosts and environments. It is also a major public health problem that affects millions of people worldwide, especially in developing countries where access to clean water and sanitation is limited. Understanding the biology, epidemiology, pathogenesis, diagnosis, treatment, and prevention of giardiasis is essential for reducing its burden and improving the quality of life of those affected by it.

Giardia duodenalis is a protozoan flagellate that belongs to the phylum Metamonada and the order Diplomonadida. It is one of the five species of Giardia that infect animals and humans.

Giardia duodenalis can further be differentiated into seven genotypes or assemblages, from A to G, based on molecular markers such as ribosomal RNA genes. Each genotype has a distinct host range and geographic distribution.

Genotypes A and B are the most common and widespread genotypes that infect humans and other mammals, such as dogs, cats, cattle, sheep, goats, pigs, horses, rodents, and primates. Genotypes C and D are mainly found in dogs and occasionally in other animals or humans. Genotypes E, F, and G are mostly associated with livestock (cattle, sheep, pigs) and rarely infect humans.

The classification of Giardia duodenalis is still a matter of debate, as different molecular methods may yield different results and the genetic diversity within each genotype is not well understood. Moreover, some studies have suggested that there may be hybridization or recombination events between different genotypes, especially A and B, which may complicate the taxonomy and epidemiology of this parasite.

Therefore, it is important to use standardized and reliable methods for the identification and characterization of Giardia duodenalis isolates from different hosts and regions, in order to better understand its biology, evolution, transmission, pathogenicity, and control.

History and Distribution of Giardia duodenalis

Giardia duodenalis is one of the earliest protozoan parasites to have been recorded. It was first observed by Dutch scientist Antonie van Leeuwenhoek in 1681 in his own diarrheal stools. He described the parasite as "animalcules" that had a "very strong and swift motion" and a "very odd shape".

The parasite was later named after two scientists who independently discovered it in human patients in the 19th century: Alfred Mathieu Giard of Paris and Vilem Lambl of Prague. Giard reported the parasite in 1888 and named it Giardia intestinalis, while Lambl reported it in 1859 and named it Cercomonas intestinalis. The name Giardia lamblia was proposed by Stiles in 1915 to honor both researchers. However, many consider the name Giardia duodenalis to be the correct taxonomic name for this protozoan, as it reflects its location in the duodenum of the host.

Giardia duodenalis has been recognized as a pathogen since the mid-1900s, when outbreaks of giardiasis were linked to contaminated water sources. The parasite is now the most common protozoan pathogen causing both endemic and epidemic intestinal disease and diarrhea worldwide. Its prevalence is high in people with low socio-economic status and poor living conditions, as well as people in over-crowded areas with poor environmental sanitation, improper garbage disposal, unsafe water supply, and unhygienic personal habits. It is also common among travelers, hikers, campers, children in day-care centers, male homosexuals, and immunocompromised individuals.

Giardia duodenalis can infect humans and other mammals, such as dogs, cats, cattle, sheep, goats, pigs, horses, rodents, and primates. The parasite can be differentiated into seven genotypes (or assemblages) from A to G based on molecular markers. Genotypes A and B are the most prevalent and can infect both humans and animals (zoonotic), while genotypes C to G are mostly host-specific. The distribution of genotypes varies geographically and epidemiologically. For example, genotype B is more common than genotype A in Europe and North America, while genotype A is more common than genotype B in Asia and Africa. Genotype E is mainly found in livestock animals, while genotype F is mainly found in cats.

Giardia duodenalis can survive for weeks to months outside the host body in moist environments. The parasite forms a protective cyst that is resistant to environmental stressors and somewhat tolerant to chlorine disinfection. The cyst is the transmission stage and can contaminate food, water, soil, surfaces, and objects. When ingested by a susceptible host, the cyst releases two trophozoites that attach to the intestinal epithelium and multiply by binary fission. The trophozoites can cause damage to the intestinal mucosa and malabsorption of nutrients. Some trophozoites transform back into cysts in the colon and are excreted in the feces. The cysts are immediately infectious when passed or shortly afterward.

Giardia duodenalis lives in the duodenum and upper jejunum of the small intestine of humans and other mammals . It is the only protozoan parasite found in the lumen of the human small intestine. It attaches to the intestinal wall using its ventral sucking disk, which helps it to avoid being swept away by peristalsis .

Giardia duodenalis can also survive outside the host in water, especially in freshwater sources such as lakes, rivers, and streams . It is protected by an outer shell called a cyst, which allows it to withstand harsh environmental conditions and makes it somewhat tolerant to chlorine disinfection. The cysts can remain viable for several weeks or months in cold water or soil . The cysts are the infective stage of the parasite and can cause giardiasis when ingested by a new host .

Giardia duodenalis can spread through contaminated water, food, hands, surfaces, or objects that have come into contact with feces from infected people or animals . It can also spread through person-to-person contact, especially among children, male homosexuals, and mentally ill persons. It can also spread through unprotected anal sex or swallowing contaminated water while swimming .

Giardia duodenalis is a cosmopolitan parasite that can infect people of any age, race, or socioeconomic status. However, it is more prevalent in people with low hygiene standards, poor living conditions, unsafe water supply, improper garbage disposal, and unhygienic personal habits. It is also more common in travelers to endemic areas, immunocompromised individuals, and people with blood group A.

Giardia duodenalis exists in two forms: trophozoite and cyst.

Trophozoite

The trophozoite is the active and motile form of the parasite that lives in the small intestine of the host.

• It has a pear-shaped or heart-shaped body, with a convex dorsal surface and a concave ventral surface.
• It measures about 12-15 µm in length and 4 µm in thickness.
• It has two nuclei, each with a central karyosome and four peripheral chromatin granules. The nuclei are located at the anterior end of the cell, near the base of the flagella.
• It has eight flagella, arranged in four pairs: two lateral, one ventral, and one caudal. The flagella arise from basal bodies (blepharoplasts) that are located near the nuclei. The flagella help in locomotion and attachment to the intestinal mucosa.
• It has a ventral adhesive disc (sucking disc), which is a concave structure composed of microtubules and microribbons. The disc covers about two-thirds of the ventral surface and helps in anchoring the parasite to the epithelial cells.
• It has two axostyles, which are rod-like structures that run along the longitudinal axis of the cell. The axostyles are composed of microtubules and help in maintaining the shape and rigidity of the cell. They also serve as attachment sites for the median bodies.
• It has two median bodies (parabasal bodies), which are sausage-shaped organelles that lie transversely behind the adhesive disc. The median bodies are composed of dense granular material and may be involved in carbohydrate metabolism. They also contain enzymes such as pyruvate:ferredoxin oxidoreductase (PFOR) and hydrogenase, which are involved in anaerobic energy production.
• It has a simple cytoplasm, which contains ribosomes, endoplasmic reticulum, Golgi apparatus, mitochondria-like organelles (mitosomes), and vacuoles. The cytoplasm also contains glycogen granules and lipid droplets as energy reserves.

The trophozoite exhibits a characteristic "falling leaf" motility, which involves alternating periods of gliding and tumbling movements. The trophozoite can also change its shape by contracting or expanding its cytoplasm. The trophozoite reproduces by binary fission, forming either more trophozoites or cysts.

Cyst

The cyst is the dormant and resistant form of the parasite that is excreted in the feces of the host.

• It has an oval or ellipsoidal shape, with smooth and thick walls. The walls are composed of proteins and carbohydrates that protect the cyst from environmental stressors such as desiccation, temperature changes, and chemical agents.
• It measures about 11-14 µm in length and 7-10 µm in width.
• It contains two or four nuclei, depending on the stage of maturation. The nuclei are similar to those of the trophozoite, but smaller and more condensed. The nuclei are located at opposite poles of the cyst or along its long axis.
• It contains remnants of flagella, basal bodies, axostyles, and median bodies, which are arranged diagonally across the cyst wall. These structures are visible as refractile bodies under light microscopy or as fibrillar structures under electron microscopy. They may help in excystation or reactivation of the parasite in a new host. [^4

Giardia duodenalis has a simple life cycle that alternates between two forms: the trophozoite and the cyst. The trophozoite is the active, feeding, and multiplying stage that lives in the small intestine of the host. The cyst is the dormant, resistant, and infective stage that is excreted in the feces and can survive in the environment for weeks or months .

The transmission of giardiasis occurs when a person ingests Giardia cysts from contaminated sources, such as water, food, hands, surfaces, or objects . The cysts can also be transmitted by direct person-to-person contact, especially among children, male homosexuals, and mentally ill persons. In addition, swallowing contaminated water while swimming in pools, lakes, or other water bodies can also result in infection. The infective dose is estimated to be as low as 10–25 cysts.

Once inside the host`s small intestine, the cysts undergo excystation and release two trophozoites each . The trophozoites attach to the epithelial cells of the upper intestine by a ventral sucking disk and feed on nutrients from the host . They multiply by longitudinal binary fission and can be free or attached to the mucosa. As they move toward the colon, they undergo encystation and form cysts that are passed in the stool . The encystation process is influenced by factors such as bile salts, alkaline pH, and cholesterol starvation. The cysts are immediately infectious when passed in the stool or shortly afterward .

The life cycle of Giardia duodenalis can be summarized as follows:

• Ingestion of cysts from contaminated sources
• Excystation of cysts in the small intestine
• Attachment and multiplication of trophozoites in the upper intestine
• Encystation of trophozoites in the lower intestine
• Excretion of cysts in the stool
• Transmission of cysts to new hosts

• Giardia duodenalis is a non-invasive parasite that attaches to the intestinal epithelium by means of a ventral sucking disk .
• The attachment causes disruption of the intestinal epithelial brush border, leading to increased permeability and malabsorption .
• The malabsorption affects various nutrients, such as fats, carbohydrates, proteins, vitamins, and minerals .
• The parasite also produces variant-specific surface proteins (VSSPs) that help it evade the host immune system and cause persistent infection .
• The pathogenicity of Giardia duodenalis depends on several factors, such as the parasite genotype, the host susceptibility, the inoculum size, and the environmental conditions .
• As few as 10–25 cysts can initiate the infection .
• The infection can cause acute or chronic giardiasis, with symptoms ranging from asymptomatic carriage to severe diarrhea and malabsorption .
• The most common symptoms include watery diarrhea, abdominal pain, bloating, nausea, vomiting, loss of appetite, weight loss, and flatulence .
• Some patients may develop lactose intolerance, vitamin deficiencies, protein-losing enteropathy, or growth retardation .
• Extraintestinal manifestations are rare but may include urticaria, anterior uveitis, retinal changes, and arthritis .
  
  
  

  Clinical manifestation of Giardia duodenalis

Giardia duodenalis infection can cause a wide range of clinical manifestations, from asymptomatic carriage to acute or chronic diarrheal disease. The symptoms and severity of giardiasis depend on several factors, such as the parasite genotype, the host immune status, the nutritional status, and the presence of co-infections .

The incubation period of giardiasis is variable, usually ranging from one to three weeks (average 12-20 days) . In the majority of cases, infection remains asymptomatic or causes mild gastrointestinal disturbances. Symptomatic infection is more common in children than adults because of their lower immunity and higher exposure to the parasite .

The most common clinical presentation of giardiasis is acute diarrheal illness, characterized by watery diarrhea, abdominal pain, bloating, belching, flatus, nausea, vomiting, loss of appetite, and weight loss. The diarrhea is often foul-smelling and greasy due to fat malabsorption. Fever is uncommon and blood or mucus in the stool is rare . The acute stage usually lasts for one to two weeks but may resolve spontaneously or persist for months if untreated .

Chronic giardiasis may develop after an acute episode or without a previous symptomatic infection. It is characterized by intermittent and recurring symptoms of diarrhea, abdominal pain, bloating, flatulence, malabsorption, weight loss, and growth retardation in children. Chronic giardiasis may also cause lactose intolerance, vitamin B12 and folic acid deficiency, protein-losing enteropathy, and steatorrhea . Chronic giardiasis may last for several weeks to years and may be associated with impaired quality of life and cognitive function .

Extraintestinal manifestations of giardiasis are rare but have been reported in some cases. These include urticaria, anterior uveitis, retinal changes, arthritis, reactive arthritis, eosinophilic enteritis, cholecystitis, pancreatitis, and malabsorption syndrome . The pathogenesis of these complications is not fully understood but may involve immune-mediated mechanisms or direct invasion of the parasite into other organs .

Laboratory diagnosis of Giardia duodenalis

The laboratory diagnosis of Giardia duodenalis infection is based on the identification of the parasite in stool samples or duodenal contents. There are various methods available for this purpose, such as microscopy, antigen detection, antibody detection, and molecular methods.

• Microscopy: This is the most widely used and inexpensive method for diagnosing giardiasis. It involves direct wet mount preparations of the stool samples to detect the motile trophozoites, or iodine wet preparations to detect the cysts. However, microscopy has low sensitivity and specificity, and requires multiple stool samples and experienced personnel. Concentration techniques, such as formalin-ether or zinc sulfate flotation, can improve the detection rate of cysts. Alternatively, duodenal contents can be obtained by invasive methods, such as enteroscopy or string test (entero-test), and examined for trophozoites .
• Antigen detection: This is a more sensitive and specific method than microscopy, and can detect Giardia antigens in stool samples using enzyme-linked immunosorbent assay (ELISA), immunochromatographic strip tests, or indirect immunofluorescence (IIF) tests. These tests use monoclonal antibodies that recognize Giardia-specific antigens, such as antigen 65 (GAS 65). Antigen detection can also be used for quantification of cysts and monitoring of treatment response .
• Antibody detection: This is a serological method that can detect antibodies against Giardia in serum samples using IIF or ELISA. This method is useful for epidemiological and pathophysiological studies, but not for clinical diagnosis, as it cannot differentiate between recent and past infections, and lacks sensitivity and specificity. Moreover, antibody levels may not correlate with parasite burden or clinical symptoms .

• Molecular methods: These are the most sensitive and specific methods for diagnosing giardiasis, and can detect Giardia DNA or RNA in stool samples using polymerase chain reaction (PCR) or reverse transcription PCR (RT-PCR). These methods can also be used for genotyping and subtyping of Giardia isolates, which can provide information on the source, transmission, and pathogenicity of the infection .

  Treatment of giardiasis caused by Giardia duodenalis

Giardiasis is a gastrointestinal infection caused by Giardia duodenalis, a protozoan parasite that colonizes the small intestine. Giardiasis can cause symptoms such as diarrhea, abdominal pain, bloating, gas, nausea, vomiting, weight loss and malabsorption. Some people may have no symptoms or mild symptoms that resolve on their own. However, in some cases, giardiasis can lead to complications such as dehydration, electrolyte imbalance, lactose intolerance and growth retardation in children.

The treatment of giardiasis depends on the severity of the symptoms, the medical history and the immune status of the patient. The main goal of treatment is to eliminate the parasite from the intestine and to prevent transmission to others. The following are some of the options for treating giardiasis:

• Antibiotics: Several antibiotics can be used to treat giardiasis, such as metronidazole , tinidazole , nitazoxanide , paromomycin, quinacrine and furazolidone. These drugs work by interfering with the metabolism or DNA synthesis of the parasite. The choice of antibiotic depends on factors such as availability, cost, efficacy, side effects and resistance. Some of these drugs may not be readily available in the United States. The dosage and duration of treatment vary depending on the drug and the patient`s condition. For example, metronidazole is usually given at a dose of 250 mg three times a day for 5 to 7 days , while tinidazole is given as a single dose of 2 g . The cure rate with metronidazole is more than 90%. However, metronidazole use has been associated with significant failure rates in clearing parasites from the gut and with poor patient compliance. Tinidazole has similar efficacy as metronidazole but with fewer side effects and better compliance. Nitazoxanide is a newer drug that has been shown to be effective against Giardia and other intestinal parasites. It is given at a dose of 500 mg twice a day for 3 days. Paromomycin is an oral aminoglycoside that can be used as an alternative to metronidazole or tinidazole in pregnant women or patients who cannot tolerate these drugs. It is given at a dose of 25 to 35 mg/kg per day in three divided doses for 5 to 10 days. Quinacrine is an antimalarial drug that can also be used to treat giardiasis, but it is not widely available and has more side effects than other drugs. It is given at a dose of 100 mg three times a day for 5 to 7 days. Furazolidone is another option for treating giardiasis, especially in children, as it has fewer adverse effects than other drugs. It is given at a dose of 100 mg four times a day for 7 to 10 days.
• Fluids and electrolytes: Patients with giardiasis may lose fluids and electrolytes due to diarrhea and vomiting. Therefore, it is important to drink plenty of fluids while sick to avoid dehydration (loss of fluids). Infants and pregnant women may be more likely to become dehydrated from diarrhea caused by Giardia infection. Dehydration can be life-threatening for infants, so it is especially important to talk to a doctor about treatment options if your infant is sick. Oral rehydration solutions (ORS) are recommended for replacing fluids and electrolytes lost due to diarrhea. ORS are available over-the-counter or can be made at home by mixing one liter of boiled or treated water with six level teaspoons of sugar and half a teaspoon of salt. ORS should be given frequently and in small amounts until diarrhea stops. In severe cases of dehydration, intravenous fluids may be needed.
• Nutrition: Patients with giardiasis may have difficulty absorbing nutrients from food due to damage to the intestinal lining caused by the parasite. This can lead to malnutrition and weight loss. Therefore, it is important to eat a balanced diet that provides adequate calories, protein, vitamins and minerals. Foods that are easy to digest and do not aggravate diarrhea, such as rice, bananas, toast, applesauce and yogurt, are recommended. Foods that are high in fat, fiber, lactose or spices should be avoided, as they may worsen diarrhea or cause gas and bloating. Some patients may develop lactose intolerance due to reduced lactase activity in the intestine. Lactose intolerance is the inability to digest lactose, a sugar found in milk and dairy products. Symptoms of lactose intolerance include abdominal pain, gas, bloating and diarrhea after consuming lactose-containing foods. Patients with lactose intolerance should avoid or limit dairy products or use lactase supplements or lactose-free products. Vitamin B12 and folic acid supplements may also be needed in some cases of malabsorption.

• Prevention: Giardiasis can be prevented by avoiding exposure to contaminated water and food and practicing good hygiene. The following are some of the measures to prevent giardiasis:

  • Proper disposal of wastewater and feces.
  • The practice of personal hygiene like hand-washing before eating and proper disposal of diapers.
  • Prevention of food and water contamination.
  • Community chlorination of water is ineffective for inactivating cysts.
  • Boiling or filtering of potentially contaminated water.
  • Avoiding drinking untreated water from lakes, rivers, streams or wells.
  • Avoiding eating raw or undercooked food that may be contaminated with feces.
  • Avoiding contact with animals that may carry Giardia, such as dogs, cats, beavers and sheep.
  • Avoiding sharing personal items such as towels, cups or utensils with someone who has giardiasis.

Prophylaxis of Giardia duodenalis

Giardia duodenalis infection can be prevented by avoiding exposure to contaminated water, food, and fecal matter. The following measures can help reduce the risk of acquiring or transmitting giardiasis :

• Boil or filter water before drinking or using it for cooking, especially if the source is uncertain or potentially contaminated by animals or humans.
• Wash hands thoroughly with soap and water after using the toilet, changing diapers, handling pets, or before preparing or eating food.
• Wash fruits and vegetables with clean water before eating them raw, and peel them if possible.
• Avoid eating raw or undercooked meat, fish, or shellfish that may be contaminated by animal feces.
• Avoid swallowing water when swimming in pools, lakes, rivers, or other recreational water sources that may be contaminated by human or animal feces.
• Use condoms during sexual contact that involves oral-anal contact or exposure to fecal matter.
• If traveling to areas where giardiasis is endemic or where sanitation is poor, follow the above precautions and consider taking prophylactic medication such as metronidazole or nitazoxanide.
• If infected with Giardia duodenalis, seek medical attention and complete the prescribed course of treatment to avoid relapse and transmission to others. Do not return to work, school, daycare, or swimming until at least 24 hours after the last episode of diarrhea.
• In addition to the above measures, some studies have suggested that probiotics may have a beneficial role in the prevention and treatment of giardiasis by modulating the intestinal microbiota and enhancing the immune response. However, more research is needed to confirm the efficacy and safety of probiotics for giardiasis.

The laboratory diagnosis of Giardia duodenalis infection is based on the identification of the parasite in stool samples or duodenal contents. There are various methods available for this purpose, such as microscopy, antigen detection, antibody detection, and molecular methods.

• Microscopy: This is the most widely used and inexpensive method for diagnosing giardiasis. It involves direct wet mount preparations of the stool samples to detect the motile trophozoites, or iodine wet preparations to detect the cysts. However, microscopy has low sensitivity and specificity, and requires multiple stool samples and experienced personnel. Concentration techniques, such as formalin-ether or zinc sulfate flotation, can improve the detection rate of cysts. Alternatively, duodenal contents can be obtained by invasive methods, such as enteroscopy or string test (entero-test), and examined for trophozoites .
• Antigen detection: This is a more sensitive and specific method than microscopy, and can detect Giardia antigens in stool samples using enzyme-linked immunosorbent assay (ELISA), immunochromatographic strip tests, or indirect immunofluorescence (IIF) tests. These tests use monoclonal antibodies that recognize Giardia-specific antigens, such as antigen 65 (GAS 65). Antigen detection can also be used for quantification of cysts and monitoring of treatment response .
• Antibody detection: This is a serological method that can detect antibodies against Giardia in serum samples using IIF or ELISA. This method is useful for epidemiological and pathophysiological studies, but not for clinical diagnosis, as it cannot differentiate between recent and past infections, and lacks sensitivity and specificity. Moreover, antibody levels may not correlate with parasite burden or clinical symptoms .

• Molecular methods: These are the most sensitive and specific methods for diagnosing giardiasis, and can detect Giardia DNA or RNA in stool samples using polymerase chain reaction (PCR) or reverse transcription PCR (RT-PCR). These methods can also be used for genotyping and subtyping of Giardia isolates, which can provide information on the source, transmission, and pathogenicity of the infection .

  Treatment of giardiasis caused by Giardia duodenalis

Giardiasis is a gastrointestinal infection caused by Giardia duodenalis, a protozoan parasite that colonizes the small intestine. Giardiasis can cause symptoms such as diarrhea, abdominal pain, bloating, gas, nausea, vomiting, weight loss and malabsorption. Some people may have no symptoms or mild symptoms that resolve on their own. However, in some cases, giardiasis can lead to complications such as dehydration, electrolyte imbalance, lactose intolerance and growth retardation in children.

The treatment of giardiasis depends on the severity of the symptoms, the medical history and the immune status of the patient. The main goal of treatment is to eliminate the parasite from the intestine and to prevent transmission to others. The following are some of the options for treating giardiasis:

• Antibiotics: Several antibiotics can be used to treat giardiasis, such as metronidazole , tinidazole , nitazoxanide , paromomycin, quinacrine and furazolidone. These drugs work by interfering with the metabolism or DNA synthesis of the parasite. The choice of antibiotic depends on factors such as availability, cost, efficacy, side effects and resistance. Some of these drugs may not be readily available in the United States. The dosage and duration of treatment vary depending on the drug and the patient`s condition. For example, metronidazole is usually given at a dose of 250 mg three times a day for 5 to 7 days , while tinidazole is given as a single dose of 2 g . The cure rate with metronidazole is more than 90%. However, metronidazole use has been associated with significant failure rates in clearing parasites from the gut and with poor patient compliance. Tinidazole has similar efficacy as metronidazole but with fewer side effects and better compliance. Nitazoxanide is a newer drug that has been shown to be effective against Giardia and other intestinal parasites. It is given at a dose of 500 mg twice a day for 3 days. Paromomycin is an oral aminoglycoside that can be used as an alternative to metronidazole or tinidazole in pregnant women or patients who cannot tolerate these drugs. It is given at a dose of 25 to 35 mg/kg per day in three divided doses for 5 to 10 days. Quinacrine is an antimalarial drug that can also be used to treat giardiasis, but it is not widely available and has more side effects than other drugs. It is given at a dose of 100 mg three times a day for 5 to 7 days. Furazolidone is another option for treating giardiasis, especially in children, as it has fewer adverse effects than other drugs. It is given at a dose of 100 mg four times a day for 7 to 10 days.
• Fluids and electrolytes: Patients with giardiasis may lose fluids and electrolytes due to diarrhea and vomiting. Therefore, it is important to drink plenty of fluids while sick to avoid dehydration (loss of fluids). Infants and pregnant women may be more likely to become dehydrated from diarrhea caused by Giardia infection. Dehydration can be life-threatening for infants, so it is especially important to talk to a doctor about treatment options if your infant is sick. Oral rehydration solutions (ORS) are recommended for replacing fluids and electrolytes lost due to diarrhea. ORS are available over-the-counter or can be made at home by mixing one liter of boiled or treated water with six level teaspoons of sugar and half a teaspoon of salt. ORS should be given frequently and in small amounts until diarrhea stops. In severe cases of dehydration, intravenous fluids may be needed.
• Nutrition: Patients with giardiasis may have difficulty absorbing nutrients from food due to damage to the intestinal lining caused by the parasite. This can lead to malnutrition and weight loss. Therefore, it is important to eat a balanced diet that provides adequate calories, protein, vitamins and minerals. Foods that are easy to digest and do not aggravate diarrhea, such as rice, bananas, toast, applesauce and yogurt, are recommended. Foods that are high in fat, fiber, lactose or spices should be avoided, as they may worsen diarrhea or cause gas and bloating. Some patients may develop lactose intolerance due to reduced lactase activity in the intestine. Lactose intolerance is the inability to digest lactose, a sugar found in milk and dairy products. Symptoms of lactose intolerance include abdominal pain, gas, bloating and diarrhea after consuming lactose-containing foods. Patients with lactose intolerance should avoid or limit dairy products or use lactase supplements or lactose-free products. Vitamin B12 and folic acid supplements may also be needed in some cases of malabsorption.

• Prevention: Giardiasis can be prevented by avoiding exposure to contaminated water and food and practicing good hygiene. The following are some of the measures to prevent giardiasis:

  • Proper disposal of wastewater and feces.
  • The practice of personal hygiene like hand-washing before eating and proper disposal of diapers.
  • Prevention of food and water contamination.
  • Community chlorination of water is ineffective for inactivating cysts.
  • Boiling or filtering of potentially contaminated water.
  • Avoiding drinking untreated water from lakes, rivers, streams or wells.
  • Avoiding eating raw or undercooked food that may be contaminated with feces.
  • Avoiding contact with animals that may carry Giardia, such as dogs, cats, beavers and sheep.
  • Avoiding sharing personal items such as towels, cups or utensils with someone who has giardiasis.

Prophylaxis of Giardia duodenalis

Giardia duodenalis infection can be prevented by avoiding exposure to contaminated water, food, and fecal matter. The following measures can help reduce the risk of acquiring or transmitting giardiasis :

• Boil or filter water before drinking or using it for cooking, especially if the source is uncertain or potentially contaminated by animals or humans.
• Wash hands thoroughly with soap and water after using the toilet, changing diapers, handling pets, or before preparing or eating food.
• Wash fruits and vegetables with clean water before eating them raw, and peel them if possible.
• Avoid eating raw or undercooked meat, fish, or shellfish that may be contaminated by animal feces.
• Avoid swallowing water when swimming in pools, lakes, rivers, or other recreational water sources that may be contaminated by human or animal feces.
• Use condoms during sexual contact that involves oral-anal contact or exposure to fecal matter.
• If traveling to areas where giardiasis is endemic or where sanitation is poor, follow the above precautions and consider taking prophylactic medication such as metronidazole or nitazoxanide.
• If infected with Giardia duodenalis, seek medical attention and complete the prescribed course of treatment to avoid relapse and transmission to others. Do not return to work, school, daycare, or swimming until at least 24 hours after the last episode of diarrhea.
• In addition to the above measures, some studies have suggested that probiotics may have a beneficial role in the prevention and treatment of giardiasis by modulating the intestinal microbiota and enhancing the immune response. However, more research is needed to confirm the efficacy and safety of probiotics for giardiasis.

Giardia duodenalis infection can be prevented by avoiding exposure to contaminated water, food, and fecal matter. The following measures can help reduce the risk of acquiring or transmitting giardiasis :

• Boil or filter water before drinking or using it for cooking, especially if the source is uncertain or potentially contaminated by animals or humans.
• Wash hands thoroughly with soap and water after using the toilet, changing diapers, handling pets, or before preparing or eating food.
• Wash fruits and vegetables with clean water before eating them raw, and peel them if possible.
• Avoid eating raw or undercooked meat, fish, or shellfish that may be contaminated by animal feces.
• Avoid swallowing water when swimming in pools, lakes, rivers, or other recreational water sources that may be contaminated by human or animal feces.
• Use condoms during sexual contact that involves oral-anal contact or exposure to fecal matter.
• If traveling to areas where giardiasis is endemic or where sanitation is poor, follow the above precautions and consider taking prophylactic medication such as metronidazole or nitazoxanide.
• If infected with Giardia duodenalis, seek medical attention and complete the prescribed course of treatment to avoid relapse and transmission to others. Do not return to work, school, daycare, or swimming until at least 24 hours after the last episode of diarrhea.
• In addition to the above measures, some studies have suggested that probiotics may have a beneficial role in the prevention and treatment of giardiasis by modulating the intestinal microbiota and enhancing the immune response. However, more research is needed to confirm the efficacy and safety of probiotics for giardiasis.

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