Giardia & Giardiasis
(Intestinal flagellate)
Dr. Aye Mya Thu
Demonstrator
Department of Microbiology
University of Medicine 1
Genus Giardia
• move by means of flagella
• Giardiasis : infection caused by Giardia intestinalis
Aetiology
• Agent : Giardia intestinalis (Giardia lamblia)
• Habitat : duodenum & upper part of jejunum of man
• Morphology : two phases trophozoite & cyst
Trophozoites
• Size : 14 um long x 7 um broad
• Shape : on front view : tennis or badminton racket
: on lateral view : longitudinally split pear
• Movement : swaying or dancing movement
• Body : bilaterally symmetrical
: organs are paired
(2 axostyles, 2 nuclei, 4 pair of flagella)
• Dorsal surface : convex
• Ventral surface : concave with a sucking disc
• Anterior end : broad & rounded
• Posterior end : tapers to a sharp point
Cyst
•Size : 12 um long x 7 um broad
•Shape : oval
•Cyst wall : thick, well defined
: 4 nuclei – clustered at one end (or) lie in pairs
at opposite poles
: flagella & sucking disc seen inside the cytoplasm
An acid environment causes parasite to encyst
Cultivation
•Enriched medium containing chick embryo
•Enriched human serum
•Tryptic meat digest & Hank’s solution
•With Candida quillermondi
Resistance to physical & chemical agents
• Trophozoites : die outside the host within half an hour
• Cyst : survive for 10 days in moist stool, up to
3 months in water
• Killed by drying & heating
• Can survive in chlorinated water
Pathogenicity
•Weakly pathogenic or non pathogenic for man
•Cyst found in large no. in stool of asymptomatic carrier
not invasive but exert pathogenic effects by
mechanical interference
Transmission & life cycle
• Source of infection : infected persons
• MOT : ingestion of cysts
• Within 30 min of ingestion, cyst 2 trophozoites
multiply in numerous no. colonize in the duodenum
• To avoid the high acidity of duodenum, localizes in the
biliary tract (gall bladder)
• Multiply by binary fission & encystment occurs under
unfavourable conditions, usually in the large intestine
• During encystment, thick resistant wall is secreted & cell
divides within the cyst
• Cysts are excreted along with faeces
• Food & drinks contaminated with giardia cysts are
ingested, the cycle is repeated
Pathogenesis
• Infective form : Cyst
• Portal of entry : GI tract
• Mode of infection : by ingestion of contaminated food &
drink
• With the help of sucking disc, parasite attaches to
epithelial cells in the intestine disturbance of intestinal
function malabsorption of fat (persistent loose motion &
mild steatorrhoea)
• Toxic effect (allergy), traumatic & irritative effect as well
as by spoliative action
Clinical conditions
1. Asymptomatic infection
2. Clinical infection young children (6-10 yrs)
water born outbreaks in USA
2.1 Acute & chronic enteritis
• irritation & low grade inflammation of the mucosa
acute or chronic diarrhoea & steatorrhoea
• Stools watery, semi-solid, greasy, bulky, foul-smelling
(Fatty stool) due to malabsorption of fat
• Impair fat soluble vitamins A, D, E, K leads to vitamin
deficiency especially Vit A
2.2 Acute enterocolitis
• Involvement of large intestine as well as diarrhoea with
superimposed dysenteric attack
2.3 Cholangitis & cholecystitis
• Catarrhal inflammation of bile duct & gall bladder
2.4 Generalised clinical manifestations
• Fever, anaemia & allergic manifestation
2.5 Chronic cholecystopathy
• Trophozoites of G. intestinalis revealed tissue invasion
found in the mucosal tissue
Lab Diagnosis
1. Examination of stool for trophozoites & cysts
1.1 Stool RE – a series of 3 or more stool RE on
alternate days
1.2 Microscopic examination of stained smear
1.3 Concentration method for cysts (in suspected chronic
giardiasis)
• Zinc sulphate floatation method
• Formal ether sedimentation method
to detect asymptomatic infection
1.4 Cultural method difficult to grow them
2. Examination of duodenal aspirate for trophozoites
Specimen is collected by Ryle’s tube
3. String test (entero-test) involves a gelatin capsule
connected to a weighted nylon
4. Stool ELISA : rapid diagnostic test
Treatment
•Quinacrine, Metronidazole
Prevention & Control
• Specific No specific measure
• General For personal prophylaxis
Use of boiled drinking water
Protection of all food & drink from contamination
To wash raw vegetables & fruits thoroughly before use
Personal hygiene
For community prophylaxis
• Effective sanitary disposal of faeces
• Protection of water supplies from faecal pollution
• Avoidance of use of human excreta as fertilizer
• Detection & isolation of carriers
