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

Giardia lamblia

Introduction of Giradia 

Giardia is a  genus of  anaerobic flagellated protozoan parasites of the phylum  metamonad that colonies and reproduce in the small intestines of several vertebrate, 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 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 sucking disc

Trophozoites

In flat view racket -shaped

Side view resemle 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

Unfavourable conditions of duodenum, encystment occurs in intestine. Ingestion of contaminated food containig cyst of Giardia. Within 30 minutes cyst hatches out 2 trophozoites. From stomach to duodenum where cyst divides giving rise to 2 trophozoites.  In 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

Pathogenecity  of Giardia

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

Incubation period: 1-25 days

Clinical features

It may show following features like-

Asymptomatic

Intestinal symptoms – It may be further

acute enterocolitis and chronic enteritis

General features- Symptoms of clinical disease is of 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 cholecystopathy

Laboratory Diagnosis of Giardia

Microscopic examination

Stool (freshly passed)

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

Note-Trophozoite may also seen in

Bile aspirated from 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

Choloquine

Secnidazole

Chronic cases
May be 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 minutes)
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 visual cyst of Giardia lamblia  (focus at centre),click on this title and  similarly,  for trophozoite of Giardia lamblia too.

References

  1. Isenberg clinical microbiology procedures Handbook
    2nd edition. Vol. 2
  2. Merkell 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 cheesbrough.
  5. Atlas of Medical Helminthology and ptotozoology -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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