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Giardia intestinalis
This scanning electron micrograph (SEM) revealed some of the external ultrastructural details displayed by a flagellated Giardia lamblia protozoan parasite. G. lamblia is the organism responsible for causing the diarrheal disease "giardiasis". Once an animal or person has been infected with this protozoan, 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. 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 non-diarrheal 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. Photo credit: CDC / Janice Haney Carr, via Wikimedia Commons. This image is a work of the Centers for Disease Control and Prevention, part of the United States Department of Health and Human Services, taken or made as part of an employee's official duties. As a work of the U.S. federal government, the image is in the public domain.

The genome sequence and gene models of Giardia intestinalis were not determined by the Joint Genome Institute (JGI), but were downloaded from NCBI on May 29, 2018. In order to allow comparative analyses with other genomes sequenced by the JGI, a copy of this genome is incorporated into the JGI Genome Portal. JGI tools were used to automatically annotate predicted proteins. Please note that this copy of the genome is not maintained by NCBI and is therefore not automatically updated.

The following text comes from NCBI Genome:

Giardia intestinalis

Giardia lamblia, also referred to as Giardia intestinalis, is a common cause of diarrhea (giardiasis) in humans and other mammals throughout the world. It is the most common cause of waterborne outbreaks of diarrhea in the United States and is occasionally seen as a cause of food-borne diarrhea. The prevalence of giardiasis in many developing countries in tropical regions is very high. G. lamblia is a single-celled eukaryotic organism which lacks organelles that are nearly universal in eukaryotes, such as nucleoli, peroxisomes and mitochondria. It also lacks the components of oxidative phosphorylation. It is not clear why G. lamblia maintains a polyploid genome with two apparently identical nuclei. The sequencing of this organism's genome will certainly provide insights into the selective advantage conferred by the two nuclei. The study of other unique features of this protist may provide information on eukaryotic evolution and should facilitate the understanding of this organism's biology and pathogenicity.

Genome Reference(s)