What is giardiasis?

 

What is giardiasis?

Giardiasis is an infection in your small intestine. It’s caused by a microscopic parasite called Giardia lamblia. Giardiasis spreads through contact with infected people. And you can get giardiasis by eating contaminated Food  or drinking contaminated water. Pet dogs and cats also frequently contract giardia.

 

Cysts are resistant forms and are responsible for transmission of giardiasis. Both cysts and trophozoites can be found in the feces (diagnostic stages)

1.     . The cysts are hardy and can survive several months in cold water. Infection occurs by the ingestion of cysts in contaminated water, food, or by the fecal-oral route (hands or fomites) 

2.     . In the small intestine, excystation releases trophozoites (each cyst produces two trophozoites) 

3.     . Trophozoites multiply by longitudinal binary fission, remaining in the lumen of the proximal small bowel where they can be free or attached to the mucosa by a ventral sucking disk 

4.     . Encystation occurs as the parasites transit toward the colon. The cyst is the stage found most commonly in non diarrheal feces

5.     .  Because the cysts are infectious when passed in the stool or shortly afterward, person-to-person transmission is possible. While animals are infected with Giardia, their importance as a reservoir is unclear.

 

 

 

 

 

 

Causes of giardiasis

People with Giardia parasites in their faeces can infect others if they do not wash their hands properly after going to the toilet. Contaminated hands can then spread the parasites to food that may be eaten by other people or to surfaces that may be touched by other people. Hands can also become contaminated when changing the nappy of an infected infant or handling infected animals. 

Giardiasis can be spread by contaminated drinking water. It can also be spread by faecal contamination of water supplies or recreational swimming areas, such as pools and spas. People who have had giardiasis should not use swimming pools until at least one week after their symptoms have ceased, but may then swim again provided they shower carefully beforehand.

 

 

 

 

 

Symptoms Giardiasis 

Some people with giardia infection never develop signs or symptoms, but they still carry the parasite and can spread it to others through their stool. For those who do get sick, signs and symptoms usually appear one to three weeks after exposure and may include:

·         Watery, sometimes foul-smelling diarrhea that may alternate with soft, greasy stools

·         Fatigue

·         Stomach cramps and bloating

·         Gas

·         Nausea

·         Weight loss

Signs and symptoms of giardia infection may last two to six weeks, but in some people they last longer or recur.

 

 

 

Laboratory Diagnosis

 

Cysts of G. duodenalis (lower right) and Cryptosporidium (upper left) labeled with commercially available immunofluorescent antibodies.

Giardiasis is diagnosed by the identification of cysts or trophozoites in the feces, using direct mounts as well as concentration procedures. Cysts are typically seen in wet mount preparations, while trophozoites are seen in permanent mounts (i.e. trichrome). Repeated samplings may be necessary. In addition, samples of duodenal fluid (e.g., Enterotest) or duodenal biopsy may demonstrate trophozoites. Alternate methods for detection include antigen detection tests by enzyme immunoassays, and detection of parasites by immunofluorescence. Both methods are available in commercial kits.

 

Direct Immunofluorescence Assay (DFA)

A direct immunofluorescence assay (DFA) is available for diagnosing Giardia duodenales infections. Antibodies tagged with fluorescent markers are added to stool and incubated. Visualization under a fluorescent microscope shows the Giardia cysts as green, glowing ovoid objects. This test includes antibodies for Cryptosporidium and both diseases can be tested for simultaneously.

·         Enzyme immunoassay for antigen or molecular test for parasite DNA in stool

·         Microscopic examination of stool

Enzyme immunoassay to detect parasite antigen in stool is more sensitive than microscopic examination. Characteristic trophozoites or cysts in stool are diagnostic, but parasite excretion is intermittent and at low levels during chronic infections. Thus, microscopic diagnosis may require repeated stool examinations.

Sampling of the upper intestinal contents can also yield trophozoites but is seldom necessary.

Molecular tests for parasite DNA in stool are available.

 

 

Treatment of Giardiasis

·         Tinidazole, metronidazole, or nitazoxanide

For symptomatic giardiasis, tinidazole, metronidazole, or nitazoxanide are used. Treatment failures and resistance can occur with any of them.

Tinidazole is as effective as metronidazole, but tinidazole is better tolerated and administered as a single dose as follows:

·         Adults: 2 g orally once 

·         Children: 50 mg/kg [maximum 2 g] orally once

Metronidazole is given as follows:

·         Adults: 250 mg orally 3 times a day for 5 to 7 days

·         Children: 5 mg/kg orally 3 times a day for 5 to 7 days

Adverse effects of metronidazole include nausea and headaches. Metronidazole and tinidazole should not be given to pregnant women. Alcohol must be avoided because these drugs have a disulfiram-like effect. In terms of gastrointestinal adverse effects, tinidazole is generally better tolerated than metronidazole.

Nitazoxanide is given orally for 3 days as follows:

·         Age 1 to 3 years: 100 mg 2 times a day

·         Age 4 to 11 years: 200 mg 2 times a day

·         Age > 12 years (including adults): 500 mg 2 times a day

Nitazoxanide is available in liquid form for children. 

The safety of nitazoxanide during pregnancy has not been assessed. If therapy cannot be delayed because of symptoms, the nonabsorbable aminoglycoside paromomycin (8 to 11 mg/kg orally 3 times a day for 5 to 10 days) is an option if the benefit outweighs the risk.

Furazolidone, quinacrine, or albendazole are rarely used because of potential toxicity, lower efficacy, or cost.

 

 

Prevention of giardiasis

·         Appropriate public water treatment

·         Hygienic food preparation

·         Appropriate fecal-oral hygiene

·         Thorough handwashing after contact with feces 

Water can be decontaminated by boiling. Giardiacysts resist routine levels of chlorination. Disinfection with iodine-containing compounds is variably effective and depends on the turbidity and temperature of the water and duration of treatment. Some handheld filtration devices can remove Giardia cysts from contaminated water, but the efficacy of various filter systems has not been fully assessed.