Pathogen Project PathogensGiardia lamblia

Pathogen Project PathogensGiardia lamblia - Causative agent...

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Causative agent: Giardia lamblia Category : Parasite Kingdom: Protozoa Phylum: Sarcomastigophora Subphylum: Mastigophora Class: Zoomastigophora Order: Diplomonadida Family: Hexamitidae Genus: Giardia Species : lamblia Disease: Giardiasis (GEE-are-DYE-uh-sis) is a diarrheal illness caused by a one-celled, microscopic parasite, Giardia intestinalis (also known as Giardia lamblia). Once an animal or person has been infected with Giardia intestinalis, the parasite lives in the intestine and is passed in the stool. Because the parasite is protected by an outer shell, it can survive outside the body and in the environment for long periods of time. During the past 2 decades, Giardia infection has become recognized as one of the most common causes of waterborne disease (found in both drinking and recreational water) in humans in the United States . Giardia are found worldwide and within every region of the United States. Symptoms of giardiasis normally begin 1 to 2 weeks (average 7 days) after becoming infected. Giardia has one of the simplest life cycles of all human parasites. The life cycle is composed of 2 stages, (1) the trophozoite, which exists freely in the human small intestine and (2) the cyst, which is passed into the environment. No intermediate hosts are required. Upon ingestion of the cyst contained in contaminated water or food, excystation occurs in the stomach and duodenum in the presence of acid and pancreatic enzymes. The trophozoites pass into the small bowel where they multiply rapidly, with a doubling time of 9-12 hours. As trophozoites pass into the large bowel, encystation occurs in the presence of neutral pH and secondary bile salts. Cysts are passed into the environment, and the cycle is repeated. The trophozoite form of G lamblia is teardrop-shaped and measures 9-21 micrometers long by 5-15 micrometers wide. The trophozoite has a convex dorsal surface and a flat ventral surface that contains the ventral disk, a rigid cytoskeleton composed of microtubules and microribbons. The trophozoite also contains 4 pairs of flagella, directed posteriorly, that aid the parasite in moving. Two symmetric nuclei with prominent karyosomes produce the characteristic face-like image that appears on stained preparations. The cyst form of the protozoan is smooth-walled and oval in shape, measuring 8-12 micrometers long by 7-10 micrometers wide. As the cyst matures, nuclear division occurs and readies the cyst to release 2 trophozoites upon excystation. Once the host is infected, trophozoites may appear in the duodenum within minutes. Excystation occurs within 5 minutes of exposure of the cysts to an environment with a pH between 1.3 and 2.7.After infection, the trophozoites attach to the enterocytes via
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This note was uploaded on 05/11/2011 for the course BIO 31 taught by Professor Silva during the Spring '11 term at Reedley.

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Pathogen Project PathogensGiardia lamblia - Causative agent...

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