Giardia: Introduction, morphology, Life cycle, pathogenecity , lab diagnosis and treatment

Giardia lamblia

Introduction of Giardia 

Giardia is a  genus of anaerobic flagellated protozoan parasites of the phylum metamonad that colonies and reproduce in the small intestines of several vertebrates, causing giardiasis. Their life cycle alternates between a swimming trophozoite and an infective, resistant cyst. Giardia were first described by the  Dutch micrscopist Antonie van Leuwenhoek  in 1681.  The genus is named after French zoologist Alfred Mathieu Gird. Giardia lamblia is also known as:
Giardia intestinalis or
Lamblia intestinalis and
Giardia duodenalis.

Geographical distribution:  It is cosmopolitan in distribution (Worldwide) and most common in warm climates.

Habitat: Duodenum and the upper part  of the jejunum of man

Morphology

Giardia lamblia has two forms, cyst, and trophozoite.

Cyst 

Oval shaped

12 µm long and 7 µm broad

Axostyle lie diagonally

4 nuclei

Remaining flagella and margin of the sucking disc

Trophozoites

In flat view racket -shaped

Side view resembles a split pear

Dorsal surface convex

Ventral view concave with sucking disc

14µm long and 7µm broad

Anterior end broad

Contains two axostyles, two nuclei, and four pairs of flagella

Life cycle of Giardia

Unfavorable conditions of duodenum, encystment occur in the intestine. Ingestion of contaminated food containing cyst of Giardia. Within 30 minutes cyst hatches out 2 trophozoites. From stomach to the duodenum where cyst divides giving rise to 2 trophozoites.  In the duodenum, multiplication of trophozoites occurs and colonization occurs.

Mode of transmission

Cysts
Direct transmission
Fomites
Contaminated water and/or food
Ingested cysts release trophozoites
Trophozoites multiply and encyst in intestines
Excreted in feces

Survival
Cysts
Survive well in cool, moist conditions
Remain viable for months in cold water
Two months at 8°C
One month at 21°C
Can also survive freezing
Susceptible to desiccation and direct sunlight

Pathogenicity of Giardia

Trophozoite attaches to the convex surface of epithelial cells of the intestine leading to disturbances of absorption function causing malabsorption of fat. There is also looseness of the bowel and steatorrhea. Trophozoite may cause the following effects toxic effects, traumatic and irritative effects.

Incubation period: 1-25 days

Clinical features

It may show the following features-

Asymptomatic

Intestinal symptoms – It may be further

acute enterocolitis and chronic enteritis

General features- Symptoms of clinical disease is of the following types-

  • Mild to severe gastrointestinal sign
  • Sudden onset diarrhea
  • Foul-smelling stools
  • Abdominal cramps
  • Bloating, flatulence
  • Nausea, fatigue
  • Weight loss
  • anemia
  • Allergic manifestation
  • Chronic cholecystography

Laboratory Diagnosis of Giardia

Microscopic examination

Stool (freshly passed)

Direct observation in feces
Trophozoites
“Teardrop” shape
Two nuclei and tumbling mobility
Cysts
Approximately 13 microns long
Oval, with 2-4 nuclei
Immunofluorescence
ELISA,
PCR

Note-Trophozoite may also see in

Bile aspirated from the duodenum

Bile from bile duct

Treatment of  Giardia

Following antiprotozoal drugs are useful to treat giardiasis and they are-

Anti-protozoal drugs
Metronidazole
Tinidazole
Ornidazole

Chloroquine

Secnidazole

Chronic cases
Maybe resistant
Prolonged therapy may be necessary.

Prevention and Control

Water
Do not drink contaminated water from the sources like
untreated lakes, rivers, shallow wells.
Treat potentially contaminated water
Heat (rolling boil for one minute)
Filter (absolute pore size of one micron)
Chlorinate
Food
Wash raw fruits and vegetables

Practice good hygiene
Hand washing
Don’t swim in recreational waters for at least two weeks after symptoms end
Avoid fecal exposure

Limit environmental contamination
Clean and promptly remove feces from surface

Note: For the visual cyst of Giardia lamblia  (focus at center), click on this title and similarly,  for the trophozoite of Giardia lamblia too.

Further Readings

  1. Isenberg clinical microbiology procedures Handbook
    2nd edition. Vol. 2
  2. Merkel and Voge’s medical parasitology
    9th edition.
  3. Parasitology: 12th edition
    By K. D. Chatterjee
  4. District laboratory practice in Tropical countries –Part-I.
    By Monica Chesbrough.
  5. Atlas of Medical Helminthology and protozoology -4th edn  -P.L.  Chiodini, A.H. Moody, D.W. Manser
  6. Medical Parasitology by Abhay R. Satoskar, Gary L. Simon, Peter J. Hotez and Moriya Tsuji

 

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