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microbiologyparasitic InfectionsParasitology

Giardia Lamblia, Giardiasis, Lifecycle, Symptoms, diagnosis and Treatment

Giardia lamblia, giardiasisGiardia lamblia is a parasite which is found in 30% of developing countries and 3-7% of United States Population. Thus, living standards have a definite effect on the prevalence of Giardiasis. In this article we will discuss, the morphology of Giardia lamblia, its life cycle, habitat, transmission, how does Giardia cause disease, Clinical signs and symptoms, Diagnosis and Treatment.

Morphology of Giardia lamblia

1. Morphology of Trophozoite

  • Shape: It has a pear-like shape.
  • Nuclei: It contains two nuclei, one on each side of the body
  • Flagella: It has four pairs of flagella, which help in locomotion.
  • Sucking Disc: It has a circular sucking disc, which is situated on the ventral surface. Giardia attaches to the intestinal wall with the help of this sucking disc.

2. Morphology of Giardia Cyst

It is oval in shape and contains four nuclei. Each organism of giardia contains two nuclei, so when a cyst hatches it releases two trophozoites.

Life Cycle of Giardia Lamblia

Giardia lamblia is found in the digestive tracts of many animals (vertebrates) as well as humans. Infection is more common in the season of Summer. Infection in human starts when an individual ingests something that is contaminated with the cysts of giardia, When cysts reach duodenum and upper part of jejunum, under normal conditions each cyst hatches to release two trophozoites within 30 minutes of ingestion. Trophozoites multiply in number and colonize in the duodenum, proximal jejunum and biliary tract and produce inflammation of the intestinal walls.
Under unfavourable conditions, the Giardia trophozoites move to the large intestine where they are encysted. During the process of encystation a thick, resistant wall is secreted around the trophozoite. After encystation, the cell divides into two and cyst passes out along with the stool. And the cycle starts again when it reaches the mouth of the human through any mean.
Life cycle of giardia lamblia, giardiasis

Habitat of Giardia Lamblia

Cysts are found in the large intestine of human and contaminated materials, faeces etc. It remains infectious for 3 months in cold water.  Trophozoites are found in the duodenum, biliary tract and jejunum.

Transmission of Giardia Lamblia

Cysts are released in the environment along with the faeces. The route of transmission is faecal-oral. For example, If an animal has defecated on a grassy soil and another animal feeds on that grass or human touches that soil and then immediately his mouth, so the infection may transmit this way. .

How does Giardia cause disease?

The trophozoites of Giardia attach themselves to the wall of intestine with the help of sucking discs and induce a sub-acute, low-grade inflammatory reaction in the jejunal and duodenal mucosa, it causes hypertrophy of the crypts and atrophy of villi. Villous atrophy causes mal-absorption and chronic diarrhoea. Giardia doesn’t invade the intestinal wall.

What are the clinical features of giardiasis?

Patient of giardiasis have following complains;
  • Non-bloody, foul-smelling diarrhoea, Acute or chronic in nature.
  • Malabsorption of fats causes steatorrhoea
  • Malaise
  • Generalized weakness
  • Weight loss due to mal-absorption and chronic diarrhoea
  • Abdominal cramps
  • Flatulence and abdominal distension, a feeling of heaviness in the abdomen.
  • Nauseous feeling and sometimes vomiting.
  • Gall bladder and bile duct problems if an organism chooses to live in the biliary tract.

How to diagnose Giardiasis in the laboratory.

  • Stool samples or duodenal aspirates are examined for the presence of cysts and trophozoites respectively. Formed and solid stool usually reveals cysts. The loose or watery stool may reveal both cysts and trophozoites.
  • A gelatin capsule which is attached to a thread on one side and its open side is kept in the mouth while the capsule is ingested. Trophozoites attach to the capsule in the duodenum. Capsule is removed after some time by pulling the thread out of the mouth and washed with saline solution and this saline is then examined under the microscope in order to reveal any trophozoites if present.
  • ELISA has also 90% sensitivity and can be used.

Treatment of Giardiasis

Giardiasis usually remains un-diagnosed in most of the cases, because the disease is not so severe and self-limiting. But acute cases, where the patient has troublesome symptoms and also giardiasis has been diagnosed then drugs like metronidazole, tinidazole and albendazole can be used.
  • Metronidazole is taken three times a day for 10 days.
  • Tinidazole is taken once a day for 10 days
  • Albendazole is taken once a day for 10 days.
So Tinidazole and albendazole have better drug compliance and albendazole has better tolerability. But any of the above drugs can be used to treat giardiasis.

Dr. Adil Ramzan, MBBS, Dated, 19 Oct. 2014

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