Giardia lamblia

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Giardia lamblia
Giardia cell, SEM
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%).[1]
  • The genome pairs are distributed across five linear chromosomes.[1]
  • Similar to other eukaryotes, each chromosome is flanked by the telomere sequence (5’TAGGG3’).[1]

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.


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[3][4][5][6][6]

Cause History Laboratory findings Diagnosis Treatment
Diverticulitis 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 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 cysts shed with the stool detects ameba DNA in feces Amebic dysentery

Luminal amebicides for E. histolytica in the colon:

For amebic liver abscess:

References

  1. 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. 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)".
  3. Konvolinka CW (1994). "Acute diverticulitis under age forty". Am J Surg. 167 (6): 562–5. PMID 8209928.
  4. 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.
  5. 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. 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.

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