Giardia intestinalis

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Giardia intestinalis

Introduction

Location and host

These parasites occur in small intestine of dog, primates, cat, livestock, rodents as well as human

Morphology

Trophozoite has pyriform to ellipsoidal, bilaterally symmetrical body, measuring 12-15 x 5-9 µm.
Dorsal side is convex and large sucking disc is present on ventral side
Two anterior nuclei, two slender axostyles, eight flagella in four pairs and pair of darkly staining median bodies
Median bodies are curved bars, resembling the claws of hammers
Cysts are ovoid, 8-12 x 7-10 µm and contain four nuclei.

Giardiasis intenstinalis: symptoms | transferability | treatment |

Fig: Giardia lamblia (Intestinalis)

Fig: Oocyst of Giardia intestinalis

Life cycle

Life cycle is simple and complex in single host
Infection is acquired orally by ingestion of cyst from contaminated food or water
Excystation occurs in stomach and duodenum in presence of gastric acid, pancreatic enzyme. pH: 1.3-2.7 is required for excystation
Each cyst excyst to produce two trophozoites
Trophozoites multiplies in intestine by binary fission, adhere to enterocytes through help of ventral sucker
Some trophozoites pass down into large intestine where they again encyst in presence of neutral pH and bile salts
Encyst trophozoites undergo nuclear division and produce Quadri nucleated mature cyst. These are excreted in faeces.
Encystation begins with appearance of encystation specific secretory vesicles (ESVs) in cytoplasm of trophozoites followed by production of cyst wall within 15 hours.
Within 24 hours after appearance of ESV; trophozoites covered with cyst wall proteins, resulting in formation of cyst. Cyst formation begins by shortening of flagellum followed by condensation of cytoplasm and finally secretion of thick hyaline cyst wall.

Mode of transmission

Transmission is mainly by ingestion of cyst contaminated food and water.
Transmission is also possible from person to person or animal to animal due to poor hygiene in animal care center, nursing homes.

Pathogenesis

Disease caused by this parasite is called giardiasis
More pathogenic in human being, especially in children
They do not invade intestine and transfer to blood. Lesion are confined to intestine
After excystation, trophozoite released uses flagella to swim to micro villi covered surface of duodenum and jejunum. There, they attach to enterocytes using adhesive disc
Lectins present on surface of giardia binds to receptor present on surface of the enterocytes. This attachment process damage microvilli.
Rapid multiplication of trophozoites creates physical barrier between enterocytes and intestinal lumen. This results in interference of nutrient absorption. This leads to damage in enterocytes, atrophy of villi, hyperplasia of crypt, intestinal hypermeability and brush border damage that causes reduction in disaccharide enzyme secretion.
Decreased jejunal electrolyte water and glucose absorption and damage to intestinal epithelium leads to malabsorption of electrolyte and fluids, resulting in osmotic diarrhea. This is known as giardiasis.

Clinical signs

Diagnosis

Detection of cyst in faeces through direct examination of fecal smears or fecal concentration by formalin-ethyl acetate or zinc-sulphate methods
Three consecutive samples should be examined as cysts are excreted intermittently.

Treatment

Treatment are similar to amoebiasis
Several benzimidazole antihelmintics (albendazole, mebendazole) and nitroimidazole (metronidazole, tinidazole) are effective
Metronidazole @ 100 ng thrice a day for 3-5 days
Chloroquine 300 mg daily for 5 days un human and pig.
Emetine hydrogen chloride @ 0.5-1 gm intramuscular of sub cutaneous injection for 10 days.
Quinacrine is given orally @ 50-100 mg twice daily for 2-3 days ( in case of dogs)

Control

Good hygiene and frequent check up help in control of disease
Vaccine based on disrupted axenically cultured trophozoites is available commercially ( Giardia vax) for use in dogs and cats.

G. canis

G. bovis