Giardia lamblia medical parasitology for medical lab

THIS TOPIC IS FOR MEDICAL PARASITOLOGY DIPLOMA STUDENTS

1. Giardia lamblia

2. Introduction Giardia lamblia , a flagellate, is the only common pathogenic protozoan found in the duodenum and jejunum of humans . It is the cause of giardiasis . Giardia duodenalis is another name commonly ascribed to the parasite that causes human giardiasis ; the term Giardia intestinalis is frequently used in Europe and Lamblia intestinalis in the former USSR. Giardia lamblia is a flagellate of worldwide distribution. It is more common in warm climates than moderate climates. It is the most common flagellate of the intestinal tract, causing Giardiasis . Humans are the only important reservoir of infection. Infection is most common in parts of the world where sanitation levels are the lowest . Giardiasis is an infection of the upper small intestine, which may cause diarrhoea . Only Giardia spreads disease.

3. Morphology:

4. The trophozoite of G lamblia is a heart-shaped, symmetric organism 10-20 m in length. There are four pairs of flagella, two nuclei with prominent central karyosomes , and two axostyles (rod-like supporting organelles ). A large concave sucking disk in the anterior portion occupies much of the ventral surface. The swaying or dancing motion of giardia trophozoites in fresh preparations is unmistakable. As the parasites pass into the colon, they typically encyst . Cysts are found in the stool-often in enormous numbers. They are thick-walled, highly resistant, 8-14 m in length, and ellipsoid and contain two nuclei as immature, four as mature cysts.

5. Life Cycle of Giardia :

6. Infection occurs by ingestion of cysts (generally from fecally contaminated food or water) Excystation occurs in the small intestine Trophozoites multiply by binary fission in the small intestine. G. lamblia attach to the mucosal surface by means of its adhesive disk. Cyst formation is triggered by the dehydration of gut contents moving through the large intestine . Encystation : is the process of forming the cyst or the process becoming enclosed in a capsule). This event takes place in the rectum of the host as feces are dehydrated or soon after the feces have been excreted. Excystation : produces a trophozoite from the cyst stage, and it takes place in the Upper Small Intestine of the host after the cyst has been ingested.

7. Cysts are resistant forms and are responsible for transmission of giardiasis . Both cysts and trophozoites can be found in the feces (diagnostic stages) . The cysts are hardy and can survive several months in cold water. Infection occurs by the ingestion of cysts in contaminated water, food, or by the fecal-oral route (hands or fomites ) . In the small intestine, excystation releases trophozoites (each cyst produces two trophozoites ) . Trophozoites multiply by longitudinal binary fission, remaining in the lumen of the proximal small bowel where they can be free or attached to the mucosa by a ventral sucking disk . Encystation occurs as the parasites transit toward the colon. The cyst is the stage found most commonly in nondiarrheal feces . Because the cysts are infectious when passed in the stool or shortly afterward, person-to-person transmission is possible. While animals are infected with Giardia , their importance as a reservoir is unclear.

8. Pathogenesis: Giardiasis : • Most common causative agent of epidemic & endemic diarrhoea throughout the world • Prevalence - 2-5% in industrialised countries 20-30% in developing countries • Caused by Giardia intestinalis / Giardia lamblia • Man is the main reservoir • Inhabit duodenum, jejunum & upper ileum • G. intestinalis exists in 2 stages – trophozoite &cyst

9. • Infective form – mature cyst passed in feces of man • Routes of transmission – Feco -oral • ingestion of contaminated water – most important • Ingestion of contaminated food – Person to person – day care, nursing homes, mental asylums (poor hygiene) • Do not invade tissues • Feed on mucous secretions • May localise in biliary tract to avoid the acidity of duodenum

10. • Cause inflammation of duodenum & jejunum • Cause malabsorption as the parasite coats the mucosa & damage epithelial brush border • Stool contains large amounts of mucous & fat but no blood  Asymptomatic : largest group  Acute : self-limiting infection, acute watery diarrhoea , abdominal cramps, bloating, flatulence  Stool is profuse & watery in earlier disease  Voluminous, foul smelling & greasy ( steatorrhoea ) later  Chronic : chronic diarrhoea with malabsorption syndrome, steatorrhoea

11. laboratory diagnosis: Samples • Stool • Duodenal contents – Duodenal fluid ( Entero test ) – Duodenal/ jejunal biopsy Microscopy: Direct Wet Mount • Trophozoite with falling leaf motility in saline mount • Cyst in iodine mount Stained stool smears • Trichrome • Iron haemotoxylin

12. Antigen detection ( Coproantigen ) •ELISA • Sensitivity & specificity high Culture • Not done routinely • Diamond’s medium Serodiagnosis •ELISA • Epidemiological purpose Molecular diagnosis • DNA probes & PCR for research purpose

13. prevention and control of: • Avoid food & water that might be contaminated – filtration of water (be sure filter is fine enough to trap the cysts) – boiling water – addition of a tincture of iodine are effective in killing cysts (chlorination of water does not effect the cysts) • Practice good hygiene – Wash hands thoroughly with soap and water • after using the toilet • before handling or eating food

14. Treatment: Metronidazole Tinidazole