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Giardia lamblia

الكلية كلية التمريض     القسم قسم العلوم الطبية الاساسية     المرحلة 2
أستاذ المادة ميس هادي جبر       20/02/2019 08:57:37
L4: A:Class:Mastigophara(Flagellates)
Giardia lamblia
Trophzoite
The typical Giardia lamblia trophozoite ranges from 8 to 20 ?m in length by 5 to 16 ?m in width. The average G. lamblia trophzoite, however, measures 10 to 15 ?m long. The G. lamblia trophzoite is described as pear or tear – drop in shape. The broad anterior end of the organism tapers off at the posterior end. The G. lamblia trophozoite characteristically exhibits motility that resembles a falling leaf. The trophzoite is bilaterally symmetrical, containing two ovoid to spherical nuclei, each with a large karyosome, usually centrally located. The trophozoite is supported by an axostyle made up of two axonemes. Two slightly curved rod – like structures, known as median (parabasal) bodies, sit on the axonemes posterior to the nuclei .The typical G. lamblia trophzoite has four pairs of flagella. One pair of flagella originates from the antrior end, and one pair extends from the posterior end. The remaining two pairs of flagella are located laterally, extending from the axonemes in the center of the body. The G. lamblia trophozoite is equipped with a sucking disc. Covering one half to three quarters of the ventral surface, the sucking disc serves as the nourishment point of entry by attaching to the intestinal villi of an infected human (Fig 10).






Table (10) : Giardia lamblia trophozoite : Typical characteristics
Size range 8 to 20 ?m long
5 to 16 ?m wide
Shape Pear / tear drop
Motility “ Falling leaf “
Appearance Bilaterally symmetrical
Nuclei Two ovoid – shaped , each with a large karyosome No peripheral chromatin
Flagella Four pair , origination of each : One pair anterior end One pair posterior end
Two pair central laterally
Other structure Two median bodyies , two axonemes , sucking disc
Cyst

The typical ovoid G. lamblia cyst ranges in size from 8 to 17 ?m long by 6 to 10 ?m wide, with an average length of 10 to 12 ?m . The colorless and smooth cyst wall is prominent and distinct from the interior of the organism. The cytoplasm is often retracted away from the cyst wall, creating a clearing zone. This phenomenon is especially possible after being preserved in formalin. The immature cyst contains two nuclei and two median bodies. Four nuclei, which may be seen in iodine wet preparations as well as on permanent stains, and four median bodies are present in the fully mature cysts. In addition, mature cysts contain twice as many interior flagellar structures.





Table (10) : Giardia lamblia cyst : Typical characteristics
Size range
8 to 17 ?m long , 6 to 10?m wide
Shape Ovoid
Nuclei Immature cyst – 2, Mature cyst – 4
Central karyosomes, No peripheral chromatin
Cytoplasm Retracted from cell wall
Other structures Median bodies , two or four , Interior flagellar structures

Life cycle

Upon ingestion, the infective G. lamblia cysts enter the stomach. The digestive juices, particularly gastric acid, stimulate the cysts to excyst in the duodenum. the resulting trophozoites become established and multiply approximately every 8 hours via longitudinal binary fission . The trophozoites feed by attaching their sucking discs to the mucosa of the duodenum. Trophozoites may also infect the common bile duct and the gallbladder. Changes resulting in an unacceptable environment for trophozoite multiplication stimulate encystation, which occurs as the trophozoites migrate into the large bowel. The cysts enter the outside environment via the feces and may remain viable for as long as 3 months in water.



Clinical symptoms
Giardiasis (“Traveler’s Diarrhea”). Symptomatic infections with Giardia lamblia may be characterized by a wide variety of clinical symptoms, ranging from mild diarrhea, abdominal cramps, anorexia, and flatulence to tenderness of the epigastric region steatorrhea, and malabsorption syndrome. Patients suffering from a severe case of giardiasis produce light – colored stools with a light fat content that may be caused by secretions produced by the irritated mucosal lining. Fat soluble vitamin deficiencies, folic acid deficiencies, hypoproteinemia with hypogammaglobulinemia, and structural changes of the intestinal villi may also be observed in such cases.

Laboratory diagnosis
The specimen of choice for the traditional recovery technique of G. lamblia trophozoites and cysts is stool. In addition, doudenal contents obtained by aspiration, as well as upper small intestine biopsies, may also be collected for examination. Several other diagnostic techniques are available for identifying G. lamblia, including Countercurrent Immunoelectrophoresis (CIE), which detects the G. lamblia fecal antigen, immunofluorescence and Enzyme – Linked Immunosorbent Assay (ELISA).


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