Giardia lamblia

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Giardia lamblia
Giardia cell, SEM
Scientific classification
Kingdom: Protista Phylum: Metamonada Genus: Giardia Species: G. lamblia
Binomial name
Giardia lamblia (Kunstler, 1882)

This page is about microbiologic aspects of the organism(s).  For clinical aspects of the disease, see Giardiasis.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

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

Natural Reservoir

• Giardia affects humans and animals, such as cats, dogs, cows, beavers, deer, and sheep.

Microbiological Characteristicsc

• 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.

Genome

• 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’).

Life cycle

Parasite life cycle.

Giardia belongs among the diplomonads.

Non-infective Cyst

• 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.

Trophozoite

• 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).

Differential diagnosis

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

Cause	History	Laboratory findings	Diagnosis	Treatment
Diverticulitis	Bloody diarrhea Left lower quadrant abdominal pain Abdominal tenderness on physical examination Low grade fever	Leukocytosis Elevated serum amylase and lipase Sterile pyuria on urinalysis	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
Ulcerative colitis	Diarrhea mixed with blood and mucus, of gradual onset. Signs of weight loss Rectal urgency Tenesmus Blood is often noticed on underwear Different degrees of abdominal pain	Anemia Thrombocytosis A high platelet count Elevated ESR (>30mm/hr) Low albumin	Endoscopy	Induction of remission with mesalamine and corticosteroids followed by the administration of sulfasalazine and 6-Mercaptopurine depending on the severity of the disease.
Entamoeba histolytica	Abdominal cramps Diarrhea Passage of 3 - 8 semiformed stools per day Passage of soft stools with mucus and occasional blood Fatigue Intestinal gas (excessive flatus) Rectal pain while having a bowel movement (tenesmus) Unintentional weight loss	cysts shed with the stool	detects ameba DNA in feces	Amebic dysentery Metronidazole 500-750mg three times a day for 5-10 days Tinidazole 2g once a day for 3 days is an alternative to metronidazole Luminal amebicides for E. histolytica in the colon: Paromomycin 500mg three times a day for 10 days Diloxanide furoate 500mg three times a day for 10 days Iodoquinol 650mg three times a day for 20 days For amebic liver abscess: Metronidazole 400mg three times a day for 10 days Tinidazole 2g once a day for 6 days is an alternative to metronidazole Diloxanide furoate 500mg three times a day for 10 days must always be given afterwards.