Giardia lamblia On the Web
American Roentgen Ray Society Images of Giardia lamblia
Giardia cell, SEM
Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Giardia lamblia (synonymous with Lamblia intestinalis and Giardia duodenalis) is a flagellated protozoan parasite that is responsible for the development of giardiasis.
Higher Order Classification
Eukaryota, Diplomonadida group, Diplomonadida, Hexamitidae, Giardiinae, Giardia, G. lamblia
- Giardia affects humans and animals, such as cats, dogs, cows, beavers, deer, and sheep.
- Giardia lamblia is a flagellated, microaerophilic parasite.
- The trophozoite form of G. lamblia is pear-shaped and has a unique morphology that includes two identical nuclei, a ventral disc for adhesion to the host intestine, and flagella.
- G. lamblia genome consists of 1.2 million base pairs (average GC content: 46%).
- The genome pairs are distributed across five linear chromosomes.
- Similar to other eukaryotes, each chromosome is flanked by the telomere sequence (5’TAGGG3’).
Giardia belongs among the diplomonads.
- The life cycle begins with a noninfective cyst being excreted with faeces of an infected individual. Once out in the environment, the cyst becomes infective.
- A distinguishing characteristic of the cyst is 4 nuclei and a retracted cytoplasm.
- Once ingested by a host, the trophozoite emerges to an active state of feeding and motility.
- After the feeding stage, the trophozoite undergoes asexual replication through longitudinal binary fission.
- The resulting trophozoites and cysts then pass through the digestive system in the feces.
- While the trophozoites may be found in the feces, only the cysts are capable of surviving outside of the host.
- Distinguishing features of the trophozoites are large karyosomes and lack of peripheral chromatin, giving the two nuclei a halo appearance.
SEM depicts the dorsal surface of a Giardia protozoan, isolated from a rat’s intestine. From Public Health Image Library (PHIL). 
SEM depicts the mucosal surface of the small intestine of a gerbil infested with Giardia sp. protozoa. From Public Health Image Library (PHIL). 
SEM depicts a Giardia lamblia protozoan in a late stage of cell division that was about to become two separate organisms, producing a heart-shaped form. From Public Health Image Library (PHIL). 
SEM depicts the ventral surface of a Giardia muris trophozoite. From Public Health Image Library (PHIL). 
SEM depicts dorsal surface of a Giardia protozoan, isolated from a rat’s intestine. From Public Health Image Library (PHIL). 
SEM depicts some of the ultrastructural morphologic details of an oblong-shaped Giardia sp. protozoan cyst. From Public Health Image Library (PHIL). 
SEM depicts the ventral surface of a Giardia muris trophozoite that had settled atop the mucosal surface of a rat’s intestine. From Public Health Image Library (PHIL). 
SEM depicts a Giardia lamblia protozoan that was about to become two separate organisms, as it was caught in a late stage of cell division. From Public Health Image Library (PHIL). 
SEM depicts a Giardia muris protozoan adhering itself to the microvillous border of an intestinal epithelial cell. From Public Health Image Library (PHIL). 
This photomicrograph depicts Giardia lamblia parasites using indirect immunofluorescence test for giardiasis. From Public Health Image Library (PHIL). 
Giardia lamblia infection must be differentiated from other causes of viral, bacterial, and parasitic gastroentritis.
|Organism||Age predilection||Travel History||Incubation Size (cell)||Incubation Time||History and Symptoms||Diarrhea type8||Food source||Specific consideration|
|Fever||N/V||Cramping Abd Pain||Small Bowel||Large Bowel||Inflammatory||Non-inflammatory|
|Viral||Rotavirus||<2 y||-||<102||<48 h||+||+||-||+||+||-||Mostly in day cares, most common in winter.|
|Norovirus||Any age||-||10 -103||24-48 h||+||+||+||+||+||-||Most common cause of gastroenteritis, abdominal tenderness,|
|Adenovirus||<2 y||-||105 -106||8-10 d||+||+||+||+||+||-||No seasonality|
|Astrovirus||<5 y||-||72-96 h||+||+||+||+||+||Seafood||Mostly during winter|
|Bacterial||Escherichia coli||ETEC||Any age||+||108 -1010||24 h||-||+||+||+||+||-||Causes travelers diarrhea, contains heat-labile toxins (LT) and heat-stable toxins (ST)|
|EPEC||<1 y||-||10†||6-12 h||-||+||+||+||+||Raw beef and chicken||-|
|EIEC||Any ages||-||10†||24 h||+||+||+||+||+||Hamburger meat and unpasteurized milk||Similar to shigellosis, can cause bloody diarrhea|
|EHEC||Any ages||-||10||3-4 d||-||+||+||+||+||Undercooked or raw hamburger (ground beef)||Known as E. coli O157:H7, can cause HUS/TTP.|
|EAEC||Any ages||+||1010||8-18 h||-||-||+||+||+||-||May cause prolonged or persistent diarrhea in children|
|Salmonella sp.||Any ages||+||1||6 to 72 h||+||+||+||+||+||Meats, poultry, eggs, milk and dairy products, fish, shrimp, spices, yeast, coconut, sauces, freshly prepared salad.||Can cause salmonellosis or typhoid fever.|
|Shigella sp.||Any ages||-||10 - 200||8-48 h||+||+||+||+||+||Raw foods, for example, lettuce, salads (potato, tuna, shrimp, macaroni, and chicken)||Some strains produce enterotoxin and Shiga toxin similar to those produced by E. coli O157:H7|
|Campylobacter sp.||<5 y, 15-29 y||-||104||2-5 d||+||+||+||+||+||Undercooked poultry products, unpasteurized milk and cheeses made from unpasteurized milk, vegetables, seafood and contaminated water.||May cause bacteremia, Guillain-Barré syndrome (GBS), hemolytic uremic syndrome (HUS) and recurrent colitis|
|Yersinia enterocolitica||<10 y||-||104 -106||1-11 d||+||+||+||+||+||Meats (pork, beef, lamb, etc.), oysters, fish, crabs, and raw milk.||May cause reactive arthritis; glomerulonephritis; endocarditis; erythema nodosum.
can mimic appendicitis and mesenteric lymphadenitis.
|Clostridium perfringens||Any ages||> 106||16 h||-||-||+||+||+||Meats (especially beef and poultry), meat-containing products (e.g., gravies and stews), and Mexican foods.||Can survive high heat,|
|Vibrio cholerae||Any ages||-||106-1010||24-48 h||-||+||+||+||+||Seafoods, including molluscan shellfish (oysters, mussels, and clams), crab, lobster, shrimp, squid, and finfish.||Hypotension, tachycardia, decreased skin turgor. Rice-water stools|
|Parasites||Protozoa||Giardia lamblia||2-5 y||+||1 cyst||1-2 we||-||-||+||+||+||Contaminated water||May cause malabsorption syndrome and severe weight loss|
|Entamoeba histolytica||4-11 y||+||<10 cysts||2-4 we||-||+||+||+||+||Contaminated water and raw foods||May cause intestinal amebiasis and amebic liver abscess|
|Cryptosporidium parvum||Any ages||-||10-100 oocysts||7-10 d||+||+||+||+||+||Juices and milk||May cause copious diarrhea and dehydration in patients with AIDS especially with 180 > CD4|
|Cyclospora cayetanensis||Any ages||+||10-100 oocysts||7-10 d||-||+||+||+||+||Fresh produce, such as raspberries, basil, and several varieties of lettuce.||More common in rainy areas|
|Helminths||Trichinella spp||Any ages||-||Two viable larvae (male and female)||1-4 we||-||+||+||+||+||Undercooked meats||More common in hunters or people who eat traditionally uncooked meats|
|Taenia spp||Any ages||-||1 larva or egg||2-4 m||-||+||+||+||+||Undercooked beef and pork||Neurocysticercosis: Cysts located in the brain may be asymptomatic or seizures, increased intracranial pressure, headache.|
|Diphyllobothrium latum||Any ages||-||1 larva||15 d||-||-||-||+||+||Raw or undercooked fish.||May cause vitamin B12 deficiency|
8Small bowel diarrhea: watery, voluminous with less than 5 WBC/high power field
Large bowel diarrhea: Mucousy and/or bloody with less volume and more than 10 WBC/high power field
† It could be as high as 1000 based on patient's immunity system.
The table below summarizes the findings that differentiate inflammatory causes of chronic diarrhea
||Abdominal CT scan with oral and intravenous (IV) contrast||bowel rest, IV fluid resuscitation, and broad-spectrum antimicrobial therapy which covers anaerobic bacteria and gram-negative rods|
||Endoscopy||Induction of remission with mesalamine and corticosteroids followed by the administration of sulfasalazine and 6-Mercaptopurine depending on the severity of the disease.|
||cysts shed with the stool||detects ameba DNA in feces||Amebic dysentery
Luminal amebicides for E. histolytica in the colon:
For amebic liver abscess:
- ↑ 1.0 1.1 1.2 Le Blancq SM, Kase RS, Van der Ploeg LH (1991). "Analysis of a Giardia lamblia rRNA encoding telomere with [TAGGG]n as the telomere repeat". Nucleic Acids Res. 19 (20): 5790. PMC 328996. PMID 1840670.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 "Public Health Image Library (PHIL)".
- ↑ Konvolinka CW (1994). "Acute diverticulitis under age forty". Am J Surg. 167 (6): 562–5. PMID 8209928.
- ↑ Silverberg MS, Satsangi J, Ahmad T, Arnott ID, Bernstein CN, Brant SR; et al. (2005). "Toward an integrated clinical, molecular and serological classification of inflammatory bowel disease: report of a Working Party of the 2005 Montreal World Congress of Gastroenterology". Can J Gastroenterol. 19 Suppl A: 5A–36A. PMID 16151544.
- ↑ Satsangi J, Silverberg MS, Vermeire S, Colombel JF (2006). "The Montreal classification of inflammatory bowel disease: controversies, consensus, and implications". Gut. 55 (6): 749–53. doi:10.1136/gut.2005.082909. PMC 1856208. PMID 16698746.
- ↑ 6.0 6.1 Haque R, Huston CD, Hughes M, Houpt E, Petri WA (2003). "Amebiasis". N Engl J Med. 348 (16): 1565–73. doi:10.1056/NEJMra022710. PMID 12700377.