Giardia lamblia

• The trophozoite is bilateral symetrical• Pear-shaped flagellate, 12-15 µ, with a broad,

rounded anterior and and a tapering posterior extremity

• The dorsal surface is convex• An ovoid concave sucking disk occupies about

three fourth of the flat ventral surface

• There are two nuclei with large central karyosome, two axonemes, two blepharoblasts, two deeply staining bars considered to be parabasal bodies, and four pairs of flagella

• Although five flagella have been demonstrated

• The ellipsoidal cyst 9-12 µ has smooth, well-defined wall and contains two to four nuclei and many of the structures of the trophozoite

• The flagellate inhabits the duodenum and upper jejunum and at times possibly the bile ducts and gallbladder

• The lashing flagella propel the trophozoite with a rapid, jerky, twisting motion

• The sucking disk enables the trophozoites to resist ordinary peristalsis

• Hence, they are rarely found except in fluid stools

• Food is absorbed from the intestinal content , although the parasite may possibly obtain nourishment form the epithelial cells through its sucking disk

• Multiplication occurs by mitotic division during encystment followed by separation into daughter trophozoites after excystation

• Longitudinal binary fission has been observed in trophozoites

• An alkaline environment and rich carbohydrate diet favor multiplication

• Under moist conditions, cysts may viable for months outside the host

• Humanity is the natural host of Giardia lamblia

• But morphologically identical species of Giardia are found in variety of animals

• Transmission is through food and water cantaminated with sewage, flies, or food handlers, and by hand-to-mouth

• Infection is more common in children than in adults, particularly in the 6-10 year age group

• Outbreaks of giardiasis has been described in day care centers and nurseries

• In poulations group practiticing oral-anal intercourse Giardia is encountered more frequently than in general population

• Large number of cysts are passed intermittently in the feces, but relatively few trophozoites are passed except in diarrheic stools

• When ingested by a new host the cysts pass unharmed through the gastric juices and undergo excystation in the duodenum

• The prepatent period ranged from 6-15 days• Infections usually lasted up to 41 days,

although several continued for as long as 4 months

• Although Giardia lamblia is found in stool of many children and adults without current or recent symptoms, it is now clear that the parasite can cause diarrheal disease and intestinal malabsorption

• Small bowel aspirates and biopsies of symptomatic patients have demonstrated large numbers of trophozoites in the duodenum and proximal jejunum, and attachment of the organisms to the intestinal mucosa

• Mast-cell-mediated reactions probably contribute to inflamation and edema seen in the mucosa and lamina propria

• However, the principal lesion is dearangement of normal vilous architecture, with shortening of villi and inflamatory foci in the crypts and lamina propria as seen in other type of malabsorption syndromes

• Wether the mucosal abnormalities produced by Giardia are due to mechanical, toxic or some other factors is unknown

• Functionally, the patient with giardial diarrhea may exhibit steatorrhea, impaired absorption of carotene, folate and vitamin B12

• Production of disaccharidases and other mucosal enzymes can also be greatly reduced

• Uptake of bile salts by Giardia may inhibit normal biologic activity of pancreatic lipase

• This abnormalities of small bowel function are referred to collectively as malabsorption syndrome

• Symptomatic manifestations of the syndrome are flatulence, abdominal distention, nausea, and anorexia, passage of foul-smelling and bulky stools, and eventual weight loss

• A helpful different point is that the stool in giardiasis does not contain blood or increase in polymorphonuclear as is seen in some of the bacterial dysentries

• Wether Giardia is causing diarrhea in a homosexual male can be difficult to determine because of multiple causes of diarrhea in this population

• The possible role of increased bacterial growth in the small bowel in association with giardiasis is still controversial; it may be contributing factor in some cases

• Both the functional and morphologic abnormalities of the small bowel are reversible after treatment of the giardiasis

• A variety of immune responses to Giardia infection, in experimental animals as well as in humans, have been described

• Symptomatic disease ultimately subsides without treatment in most infected individuals, even though cysts excretion continues

• Therefore, the immune process must modify or eliminate pathologic change produced by the organism without eradicating it

• Initial IgM and later IgG antibodies to crude parasite antigens are demonstrable in serum of infected patients, but presence of these antibodies does not necessarily affect excretion of cysts

• Secretory IgA antibodies which might be expected to play an important role in mucosal immunity, have been describe in animal model but their function is diificult to investigate in human infections

Diagnosis

• Diagnosis is usually made by finding cysts in formed stools and trophozoites and cysts in diarrheic feces

• The distinctive morphology of Giardia lamblia in saline and iodine mounts and in stained smears distinguished it from other intestinal protozoa

• To find trophozoites, one must examine specimens without delay before they disintegrate

• Concentration methods increase the chances of detection of cysts

• Immunologic tests for detection of Giardia antigen in the stool are quite sensitive and specific

Treatment

• Quinacrine HCl is given to adults, 100 mg t.i.d for 5-7 days

• For children the dosage is 6 mg per kg dailyfor 5 days. The maximum daily dose is 300 mg

• Metronidazole is equally effective. The dosage for adults is 250 mg t.i.d for 7 days

• Children younger than 2 years are given 125 daily for 5 days

• Otherwise, the pediatric dosage is 15 mg/days divided into 3 doses

• Since as few as 10 cysts can initiate infection, giardiasis can be acquired as a result of minimal fecal contamination by the direct fecal-oral route, via water, or even food