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Giardia lamblia
1. Name of the Organism: |
Giardia lamblia (intestinalis) is a single celled animal, i.e., a protozoa, that moves with the aid of five flagella. In Europe, it is sometimes referred to as Lamblia intestinalis. |
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Giardiasis is the most frequent cause of non-bacterial diarrhea in North America. |
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Organisms that appear identical to those that cause human illness have been isolated from domestic animals (dogs and cats) and wild animals (beavers and bears). A related but morphologically distinct organism infects rodents, although rodents may be infected with human isolates in the laboratory. Human giardiasis may involve diarrhea within 1 week of ingestion of the cyst, which is the environmental survival form and infective stage of the organism. Normally illness lasts for 1 to 2 weeks, but there are cases of chronic infections lasting months to years. Chronic cases, both those with defined immune deficiencies and those without, are difficult to treat. The disease mechanism is unknown, with some investigators reporting that the organism produces a toxin while others are unable to confirm its existence. The organism has been demonstrated inside host cells in the duodenum, but most investigators think this is such an infrequent occurrence that it is not responsible for disease symptoms. Mechanical obstruction of the absorptive surface of the intestine has been proposed as a possible pathogenic mechanism, as has a synergistic relationship with some of the intestinal flora. Giardia can be excysted, cultured and encysted in vitro; new isolates have bacterial, fungal, and viral symbionts. Classically the disease was diagnosed by demonstration of the organism in stained fecal smears. Several strains of G. lamblia have been isolated and described through analysis of their proteins and DNA; type of strain, however, is not consistently associated with disease severity. Different individuals show various degrees of symptoms when infected with the same strain, and the symptoms of an individual may vary during the course of the disease. Infectious Dose - Ingestion of one or more cysts may cause disease, as contrasted to most bacterial illnesses where hundreds to thousands of organisms must be consumed to produce illness. |
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Giardia lamblia is frequently diagnosed by visualizing the organism, either the trophozoite (active reproducing form) or the cyst (the resting stage that is resistant to adverse environmental conditions) in stained preparations or unstained wet mounts with the aid of a microscope. A commercial fluorescent antibody kit is available to stain the organism. Organisms may be concentrated by sedimentation or flotation; however, these procedures reduce the number of recognizable organisms in the sample. An enzyme linked immunosorbant assay (ELISA) that detects excretory secretory products of the organism is also available. So far, the increased sensitivity of indirect serological detection has not been consistently demonstrated. |
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Giardiasis is most frequently associated with the consumption of contaminated water. Five outbreaks have been traced to food contamination by infected or infested food handlers, and the possibility of infections from contaminated vegetables that are eaten raw cannot be excluded. Cool moist conditions favor the survival of the organism. |
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Giardiasis is more prevalent in children than in adults, possibly because many individuals seem to have a lasting immunity after infection. This organism is implicated in 25% of the cases of gastrointestinal disease and may be present asymptomatically. The overall incidence of infection in the United States is estimated at 2% of the population. This disease afflicts many homosexual men, both HIV-positive and HIV-negative individuals. This is presumed to be due to sexual transmission. The disease is also common in child day care centers, especially those in which diapering is done. |
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About 40% of those who are diagnosed with giardiasis demonstrate disaccharide intolerance during detectable infection and up to 6 months after the infection can no longer be detected. Lactose (i.e., milk sugar) intolerance is most frequently observed. Some individuals (less than 4%) remain symptomatic more than 2 weeks; chronic infections lead to a malabsorption syndrome and severe weight loss. Chronic cases of giardiasis in immunodeficient and normal individuals are frequently refractile to drug treatment. Flagyl is normally quite effective in terminating infections. In some immune deficient individuals, giardiasis may contribute to a shortening of the life span. |
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Giardiasis occurs throughout the population, although the prevalence is higher in children than adults. Chronic symptomatic giardiasis is more common in adults than children. |
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Food is analyzed by thorough surface cleaning of the suspected food and sedimentation of the organisms from the cleaning water. Feeding to specific pathogen-free animals has been used to detect the organism in large outbreaks associated with municipal water systems. The precise sensitivity of these methods has not been determined, so that negative results are questionable. Seven days may be required to detect an experimental infection. |
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Literature references can be found at the links below. |
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Major outbreaks are associated with contaminated water systems that do not use sand filtration or have a defect in the filtration system. |
In April 1988, the Albuquerque Environmental Health Department and the New Mexico Health and Environment Department investigated reports of giardiasis among members of a church youth group in Albuquerque. The first two members to be affected had onset of diarrhea on March 3 and 4, respectively; stool specimens from both were positive for Giardia lamblia cysts. These two persons had only church youth group activities in common. |
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On August 8, 1983, the Utah Department of Health was notified by the Tooele County Health Department (TCHD) of an outbreak of diarrheal illness in Tooele, Utah, possibly associated with a contaminated public water supply that resulted from flooding during Utah's spring thaw. |
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For more information on recent outbreaks see the CDC. |
Giardia lamblia
source: http://www.biosci.ohio-state.edu/~parasite/giardia.html
Giardia lamblia
(giardiasis)
Giardia lamblia trophozoites live in the small intestine of the host. Cysts, which are resistant to adverse environmental conditions, are passed in the feces of an infected host, and the next host is infected when it ingests cysts in food or water contaminated with feces ( view a diagram of the life cycle). Giardiasis is diagnosed by finding cysts or trophozoites in the feces, and both life cycle stages have a characteristic appearance. The trophozoites average about 15 µm in length, have a distinct "tear-drop" shape and two nuclei at the anterior end. The characteristic shape of the trophozoite is particularly interesting when they are viewed with an scanning electron microscope ( view SEM). People who see G. lamblia under the microscope often say that it appears that the trophozoites are "staring back at them." The trophozoites also contain a dark transverse rod, the axostyle, which seems to be a supportive element. The cysts average about 13 µm in length, are oval, and contain two nuclei and remnants of the axostyle. Because of these unique characteristics, G. lamblia is one of the easiest intestinal protozoans of humans to diagnose.
Unlike Entamoeba histolytica which can invade the tissues of the large intestine, G. lamblia does not invade the tissues of the small intestine. However, the trophozoites do adhere closely to the lining of the small intestine, and in heavy infections much of the lining of the small intestine can be covered with trophozoites. The symptoms associated with giardiasis range from none (in light infections) to severe, chronic diarrhea (in heavy infections), but not dysentery.
One person can pass millions of G. lamblia cysts each day, and most infections probably result from ingestion of water or food contaminated with human sewage. Open sewers in city streets and contamination of drinking water with this sewage undoubtedly results in many infections. However, in some countries the use of human fecal material ("night soil") as a fertilizer is also an important source of infection. Many cases of "traveler's diarrhea" are caused by Giardia. Even in developed countries potable water can be contaminated with small amounts of sewage, especially when septic systems are built too close to wells. Thus, it is not surprising that G. lamblia is found throughout the world.
Every year many people return from camping trips to find that they are suffering from giardiasis, but the source of these infections remains uncertain. Some authorities believe that Giardia infects a number animals other than humans, particularly beavers, and that campers contract giardiasis from drinking stream water contaminated with cysts from beavers (hence, "beaver fever"). Other authorities, however, believe that these cases result from streams contaminated with human feces. Although mountain streams may appear to be "sparkling clean," some camper upstream may be using your drinking water as a toilet! Thus, no matter what it looks like, stream water should be treated before drinking. Boiling will kill Giardia cysts, and there are commercially available filters that will remove the cysts from water.
Giardia lamblia trophozoite; approximate size = 14 µm. The two nuclei and clearly visible, but the characteristic "tear-drop" shape is not visible in this plane of focus.
Another example of a Giardia lamblia troph. The two nuclei are easy to see in this image. (Original image from a Japanese language site tentatively titled "Internet Atlas of Human Parasitology."
Giardia lamblia cyst; approximate size = 14 µm. The nuclei and axostyles are clearly visible.
Giardia lamblia cyst; approximate size = 16 µm.
Giardiasis
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In the United States , nationally distributed brands of bottled or canned carbonated soft drinks are safe to drink. Commercially packaged non-carbonated soft drinks and fruit juices that do not require refrigeration until after they are opened (those that are stored unrefrigerated on grocery shelves) also are safe.
If you are unable to avoid using or drinking water that might be contaminated, then you can make the water safe to drink by doing one of the following:
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Avoid food that might be contaminated.
Avoid fecal exposure during sexual activity.
It depends. You should consider having your well water tested if you can answer “yes” to any of the following questions:
Tests used to specifically identify Giardia are often expensive, difficult, and usually require hundreds of gallons of water to be pumped through a filter. If you answered “yes” to the above questions, consider generally testing your well for fecal contamination by testing it for the presence of coliforms or E. coli instead of Giardia . Although tests for fecal coliforms or E. coli do not specifically tell you whether Giardia is present, these tests will show whether your well water has been contaminated by fecal matter.
These tests are only useful if your well is not routinely disinfected with chlorine, since chlorine kills fecal coliforms and E. coli . If the tests are positive, it is possible that the water may also be contaminated with Giardia or other harmful bacteria and viruses. Contact your county health department, your county cooperative extension service, or a local laboratory to find out who offers water testing in your area. If the fecal coliform test comes back positive, indicating that your well is fecally contaminated, stop drinking the well water and contact your local water authority for instructions on how to disinfect your well.
This fact sheet is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health care provider. If you have any questions about the disease described above or think that you may have a parasitic infection, consult a health care provider.
Revised Summer 2004
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Home | Professional Info | Public Info CDC Home | CDC Search | CDC Health Topics A-Z This page last reviewed September 17, 2004 Centers for Disease Control and Prevention |
Giardia lamblia:
cell biology and microscopy
of one of the most primitive eukaryotes.
Giardia, a protist, is providing new insights into the evolution
of the eukaryotic cell and of endoplasmic reticulum,
microtubules and mitochondria
SUMMARY
Here you will learn some of the new and exciting things about the biology of protists, the most primitive eukaryotic, or non-bacterial, organisms. Recent discoveries concerning Giardia lamblia are emphasized and microscopic imaging of this organism and its subcellular organelles using both fluorescence and electron microscopy is a major highlight. There is also a tribute page in honor of Keith Porter, pioneer of electron microscopy, which features comparative microscopic imaging of mammalian cells, including human cells, which in contrast to Giardia represent the most highly evolved eukaryotic organisms.
CONTENTS
II. Identification and characterization of Giardia's endomembranes
III. Identity and organization of Giardia's cytoskeleton
IV. Did Giardia lose mitochondria in evolution?
VI. Links and recommended books
As a primitive eukaryote, understanding how Giardia performs basic cellular functions will be helpful in elucidating the mechanisms present in all higher eukaryotic cells (3, 4). In comparison, a model organism such as yeast, which many scientists study, is actually a higher eukaryote and provides information about only relatively recent evolutionary developments. Also, the giardial genome is not much more complex than that of yeast, making its complete sequencing a feasible and deserving objective (4). There are also applied reasons for studying Giardia. Giardia is of significant environmental and medical importance worldwide, being a waterborne pathogen and an important intestinal parasite in humans (5, 6) .
A few basic facts about Giardia should be mentioned. The life cycle of Giardia alternates between trophozoite and cyst. Giardia lacks mitochondria and peroxisomes and until recently (see below) was reported to also lack a Golgi apparatus and endoplasmic reticulum. The dormant water-resistant cyst causes infection while the rapidly dividing trophozoite causes the symptoms of giardiasis. The processes of encystation and excystation are both problems in cell differentiation. Giardia is relatively easy to culture and work with in the laboratory. Encystation can be artificially induced in culture. De novo assembly of endomembranes has been suggested to occur during encystation, correlated with regulated secretion of cyst wall proteins. (3, 4).
All the fluorescence and electron microscopic imaging shown on this website comes from my own laboratory research while I was a postdoctoral researcher in the Department of Biochemistry at McMaster University ( Hamilton, Ontario, Canada). I have published fundamental studies that deal with different aspects of Giardia cell biology (7-9). These studies identify three important areas of current basic research on this organism.
II. IDENTIFICATION AND CHARACTERIZATION OF GIARDIA ENDOMEMBRANES.
Despite there having already been 30 years of research on Giardia's subcellular structure, I and Rad Gupta have provided the first definitive evidence for the presence of endoplasmic reticulum (ER) in this organism (Reference 7). You may click on electron microscopic (EM) pictures or you can read the actual publication. Permission to make these items available on the Internet was obtained from the Journal of Cell Science and the Company of Biologists Ltd.
1.Low magnification EM of Giardia.
2.Higher magnification EM showing ER membranes. The ER is labelled with antibody against the ER protein called Bip. The antibody is bound to colloidal gold markers, which in EM appear as black dots.
3.Read the actual publication.You will need Adobe Acrobat Reader.
For a review of this study, see the ‘Headlines' article which appeared in Trends in Cell Biology (7). This work depended on (i) the use of cryotechniques to preserve endomembranes and (ii) raising an antibody against recombinant giardial Bip, the hsp70 homolog resident in ER in higher eukaryotes, to serve as a definitive molecular label. This work confirmed a central dogma in cell biology, namely that the endomembrane system and nucleus co-evolved in the same evolutionary event and that all eukaryotic cells would possess both. In addition to characterizing the structural organization of the ER, this study also identified membrane systems in trophozoites which appeared to represent a Golgi apparatus. Although a Golgi apparatus was previously reported by others to form uniquely during encystation (4), our studies led us to conclude that a Golgi apparatus is present throughout the life cycle but in functionally different forms. Further confirmation of this will require molecular labels which specifically identify the Golgi. Giardia should prove to be an excellent model system for studies into developmental changes in Golgi structure and function, vesicular transport and regulated versus constitutive secretion, with the changes that occur during encystation and excystation serving as models of cell differentiation.
III. IDENTITY AND ORGANIZATION OF THE GIARDIA CYTOSKELETON.
The processes of cytokinesis and cell differentiation are driven by dramatic restructuring of cytoskeletal structures. I have published a detailed study of the organization of the microtubule-based cytoskeleton in trophozoites (8) which also included a partial investigation of postranslational tubulin modifications (postranslational modifications are chemical reactions that change the biological activity and/or localization of a protein). In the case of tubulin, postranslational modifications may alter the assembly/disassembly dynamics of microtubules. You can click on some fluorescence or electon microscopic pictures:
1.Immunofluorescence micrograph of Giardia microtubules. Cells were labeled with a fluorescent antibody against acetylated tubulin.
2. Electron micrographs of flagellar axonemes and the median body. Microtubules in these structures, which look like railroad tracks when viewed longitudinally (A and B) or as circles when viewed in cross section (C),are labeled with antibody against acetylated tubulin bound to colloidal gold markers, which appear as black dots.
3. Flagella microtubules in cross section Giardia flagella have the typical 9(2)+2 axonemal structure found in higher eukaryotes (nine sets of two microtubules arranged in a circle with two microtubules in the center) and not a more primitive version.
4. Longitudinal sections of cytoplasmic axonemes Kinetosomes from which microtubules are nucleated are seen at the top of part B.
5. Electron micrographs showing labeling of the adhesive disk with antibody to acetylated tubulin. The adhesive disk is a microtubule-based structure only found in Giardia.
Since postranslational modifications of tubulin are known to significantly alter microtubule assembly-disassembly dynamics, further investigation of these throughout the life cycle are warranted. Thus far, the cytoskeleton of trophozoites appears to be a rather stable structure, with all microtubules being acetylated . Future work should include examination of cytoskeleton dynamics during encystation and excystation, when dramatic structural rearrangements occur. Moreover, mitosis in Giardia has not yet been adequately described. Since it is no doubt the simplest mitosis in all eukaryotes, Giardia may be an excellent model system for understanding mitosis in general. The mitotic spindle is also a potential target for therapeutic intervention in cases of giardiasis, and tests of anti-mitotic drugs would benefit from an understanding of Giardia's mitotic spindle physiology.
IV. DID GIARDIA LOSE MITOCHONDRIA?
A large number of protists, including Giardia, lack mitochondria. In the past this has been taken as evidence that these organisms existed before the endosymbiosis event which led to mitochondria, and hence were more primitive than other protists. In endosymbiosis, a theory made popular in its modern version by Dr. Lynn Margulis 30 years ago, oxygen respiring bacteria invaded a host cell and formed a permanent relationship living within it, evolving into mitochondria. This endosymbiotic event is thought to have occured more than 1000 million years ago [our planetary system formed 4600 million years ago; the first bacterial cell appeared 3900 million years ago; the first protists appeared 2000 milllion years ago; man's ancestors appeared 4 million years ago]. Mitochondria in cells actually still look like bacteria and grow and divide at their own pace. They even have their own DNA, although most genes over time have been transferred to the nucleus.
Despite the fact that Giardia lacks mitochondria, I and Rad Gupta published work showing the presence of a protein related to mitochondrial hsp60 in Giardia (9). The evidence included biochemical immunoblot detection of a protein of the correct molecular weight and both immunoflourescence and electron microscopic localization of reactivity at discrete sites in the cytoplasm.
1.Immunofluorescence micrograph of Giardia.Cells were labeled with antibody against mammalian hsp60. Hsp60 is considered a mitochondrial protein in higher eukaryotes. The fluorescent dots throughout the cytoplasm are suggestive of organelle labeling.
2. Double label immunofluorescence.Hsp60 antibody labeling in A is compared with anti-tubulin labeling of the same cells in B. Some microtubule structures are identified in B: MB=median body, AF=anterior flagella, AD=adhesive disk.
Electron microscopic localization of hsp60 showed that hsp60 labeling was in the cytoplasm and was not associated with any type of membranous structure (not shown). To explain the findings we suggested that Giardia originally had mitochondria but lost them in evolution. More recent studies in the higher protist Trichomonas vaginalis, which contain hydrogenosomes but no mitochondria, showed molecular evidence for the presence of mitochondrial heat shock proteins within hydogenosomes (the hydrogenosome is a double membraned redox organelle found in certain anaerobic protists). Palmer et al (10) have reviewed this work. The results led to the suggestion that hydogenosomes evolved (or de-evolved, depending on how you look at it) from mitochondria by a process of reductive, as opposed to acquisitive, evolution. Since Giardia has been regarded as the most primitive eukaryote in existence, Palmer et al (10) also cite our work as evidence from diplomonads to support the idea that the earliest eukaryotic cell contained mitochondria which were subsequently lost. Thus, the timing for the endosymbiotic event that gave rise to mitochondria is currently being pushed backwards. We are faced with the possibility that no representative of the premitochondrial stage of eukaryotic evolution may be alive today. The endosymbiotic event that gave rise to mitochondria in fact may have occurred as far back as the very origin of the first eukaryotic cell. The key to resolving this issue would be to obtain further molecular data in Giardia. The cloning of a variety of mitochondrial proteins will be necessary. It may be very difficult, however, to exclude lateral gene transfer of proteins from another species, particularly bacterial. The proteins would have to contain mitochondrial targeting sequences to definitively distinquish them from prokaryotic homologs.
Material presented here is protected by copyright.
V. GIARDIA REFERENCES
1. Sogin, ML 1991. Early evolution and the origin of eukaryotes. Current Opinion in Genetics and Development 1:457-463.
2. Nasmuth, K 1996. A homage to Giardia. Current Biology 6:1042.
3. Gillin, F et al.1996. Cell biology of the primitive eukaryote Giardia lamblia. Annual Review of Microbiology 50, 679-705.
4. Lujan, HD, Mowatt, MR and Nash, TE 1997. Mechanisms of Giardia lamblia differentiation into cysts. Microbiology and Molecular Biology Review. 61:294-304.
5. Marshall , MM, et al. 1997. Waterborne protozoan pathogens. Clinical Microbiology Review 10:67-85.
6. Finch, GR 1996. Water industry challenge waterborne parasites Part II. Environmental Science and Engineering 9:35,36,38.
7.Soltys, BJ, Falah, M and RS Gupta. 1996. Identification of endoplasmic reticulum in the primitive eukaryote Giardia lamblia using cryoelectron microscopy and antibody to Bip. Journal of Cell Science 109:1909-1917 .*See also the ‘Headlines' article entitled ‘The Primitive ER' which reviews this work in Trends in Cell Biology 1996. 6:378.
8. Soltys, BJ and RS Gupta. 1994. Immunoelectron microscopy of Giardia lamblia cytoskeleton using antibody to acetylated alpha tubulin. Journal of Eukaryotic Microbiology 41: 625-632.
9. Soltys, BJ and RS Gupta. 1994. Presence and cellular distribution of a 60-kDa protein related to mitochondrial hsp60 in Giardia lamblia. Journal of Parasitology 80: 580-590.
10. Palmer, JD 1997. Organelle genomes: going, going, gone! Science 275:790-791.
11. Roger AJ, Svard SG, Tovar J, Clark CG, Smith MW, Gillin FD, Sogin ML 1998 A mitochondrial-like chaperonin 60 gene in Giardia lamblia: evidence that diplomonads once harbored an endosymbiont related to the progenitor of mitochondria. Proc Natl Acad Sci USA 95: 229-34.
VI. RECOMMENDED BOOKS AND LINKS
A. LINKS
For links to websites on other protists, its a must to check out Protist Image Data
This site is a featured website at YAHOO! where you can find links to other sites on model systems and microorganisms:
1. http://dir.yahoo.com/Science/Research/Model_Systems/
2. http://dir.yahoo.com/Science/Biology/Microbiology/Microorganisms/
B. BOOKS FOR STUDENTS, HOBBYISTS AND AMATEUR SCIENTISTS
1. Explore the World Using Protozoa by R.O. Anderson and M. Druger
Paperback (1997) Natl Science Teachers Assn; ISBN: 0873551591; highly recommended.
2. Guide to Microlife by K.G. Rainis and B.J. Russell
Paperback (1997) Franklin Watts, Inc.; ISBN: 0531112667
3. How to Know the Protozoa by Theodore L. Jahn
Paperback 2nd edition (1979) WCB/McGraw-Hill; ISBN: 0897047598
4. A World in a Drop of Water : Exploring With a Microscope by A. Silverstein, V.B. Silverstein
Paperback (1998) Dover Pubns; ISBN: 0486403815; Under $4!
5. Antoni Van Leeuwenhoek : First to See Microscopic Life (Great Minds of Science series) by L. Yount
Library Binding (1996) Enslow Publishers, Inc.; ISBN: 0894906801
6. Five Kingdoms : An Illustrated Guide to the Phyla of Life on Earth by L. Margulis, K.V. Schwartz, S.J. Gould
Paperback 3rd edition (1998) W H Freeman & Co; ISBN: 0716730278
C. BOOKS FOR GRADUATE STUDENTS AND PROFESSIONAL SCIENTISTS
1. Protozoa and Other Protists by Michael A. Sleigh
Hardcover 3rd edition (1999) Edward Arnold; ISBN: 0521573629
2. Protoctista Glossary by L. Margulis, H.I. McKhann, L. Olendzenski
Hardcover (1999) Jones & Bartlett Pub; ISBN: 0867200812
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Giardiasis
Giardiasis
Giardiasis
