Morphology and Classification of the Giardialamblia - Article Example

Giardialamblia Morphology and ification of the organism: Giardialambia is a protozoan with flagella and is d after the French biologist Alfred Giard.(www.lowchensaustralia.com). The Giardia micro-organism exists primarily in two forms (a) the mobile form - trophozoite and (b) the immobile cyst. The trophozoits have four pairs of flagella which help them to move and are largely comprised of adhesive disks that comprise the ventral surface of the microorganism. It is dorsoventrally flattened and piriform. (www.lowchensaustralia.com). The internal structure of the mobile flagellate protozoan is unique with two nuclei and in between them, there are two pairs of recurrent flagella that run within the organism and are known as axonemes. The trophozoite form of Giardia measures 9 to 21 mu-m long, 5 to 15 mu-m wide and 2 to 4 mu-m thick (www.lowchensaustralia.com). However, while the trophozoites have nuclei and a well developed cytoskeleton, they lack mitochondria, peroxisomes and components of oxidative phosphorylation.(Adam, 2001) They are akin to primitive eukaryotes, with an endomembrane system and some of the characteristics of golgi bodies and an encoplasmic reticulum. As opposed to the dorsoventral flattening of the trophozoite form, the cysts, which are the source of infection, are oval and have thick, refractile walls. They measure 8 to 12 mu-m in length and are 7 to 10 mu-m wide with two nuclei present in recently formed cysts and four nuclei present in well developed cysts.(www.lowchensaustralia.com) The encoplasmic reticulum is more extensive in the cysting organism.(Adam 2001). Studies have been revealing that the microorganism also has a genetic structure. The giardia lamblia is estimated to have a ploidy of 4 and a genome size of about 10 to 12 Mb which may be distributed among five separate chromosomes. Within the trophozoites, there is antigenic variation of cysteine rich surface proteins and allele specific genetic expression appears to vary from one gene to the other.(Adam, 2001). Growth conditions: The microorganism has a direct life cycle. It exists as immobile cysts that are excreted in feaces and transmission of the disease caused by Giardia lamblia occurs through the oral fecal route. The cyst is the immobile form in which the organism survives in the outside environment, however it may enter the bodies of humans or mammals through the ingestion of feaces or through drinking water contaminated with faeces. Once the cyst has entered the intestine of the host mammal, then it becomes active and the cyst attaches to the wall of the duedonum, where it excysts and then begins to grow successfully under in vitro conditions (www.lowchensaustralia.com). The cyst form changes into the trophozoic form and this metamorphosis is aided by a low gastric pH and the presence of pancreatic enzymes such as chymotrypsin and trypsin. During the process of excystation, each mature cyst that has four nuclei within it breaks up into two trophozoiutes, each of which has two nuclei. The large disk of the trophozoite form also has an adhesive surface, so that it is able to attach itself easily to the walls of the duodenum or jejunum and survive within the intestine. Once they have been established within the intestine, the trophozoites then begin to reproduce rapidly, through an asexual method of reproduction – binary fission. Some of them are passed out in the faeces where they reform into cysts and survive until they infect another victim. Within the intestine, it has not yet been clearly established exactly how these flagellate protozoa actually cause diarrhoea, although low pH may play a role. A study by Echmann et al (2000) which tested alkaline conditions within the intestine suggested that gastric pH may play a role in providing the right environmental conditions for the giardial differentiation from the inactive cyst to the active trophozoites to take place. Gillin and Diamond (1981) found that metronidazole inhibited the clonal growth of giardia lambia in the semi solid media, when used in a concentration of 2 to 4 mg per litre. The parasite was killed rapidly – 50% of the microorganisms were destroyed in the space of 5 to 7 hours at 2 mg per litre or in one hour at 10 mg per litre. This study also tested susceptibility to quinacrine and the microorganism was found to be more sensitive to quinacrine than to inhibitors of protein synthesis. Echmann et al(2000) examined whether the presence of nitric oxide within the human intestine could be a potentially limiting factor in the growth of the giardia microorganism. Since nitric oxide is produced by the intestinal wall where the giardia cysts and trophozoites attach themselves, and since the end products of nitric oxide are nitrites and nitrates, these may constitute a defense against the microorganism. However, their study suggested that there were slim grounds to support the hypothesis that nitric oxide might be toxic to the giardia microorganism. Rather the micro organism may have already devised strategies to avoid the effects of nitric oxide and its compounds in the human intestine in order to evade this potential host defense against infection. Classification of organism: On the basis of the above, the giardia organism may therefore be classified as a protozoan and represents the eukaryptic form. Moreover, it is definitely a pathogenic or disease producing organism, since it causes diarrhoea in both humans and several species of mammals such as dog, cat, deer, mouse, squirrel, swine and guinea pigs among others. (lowchensaustralia.com) Disease caused by giardia lambia: Giardia is responsible for the intestinal disorders and is a common cause for diarrhea in animals and other mammals throughout the world. Both the genotypes of Giardia lamblia – the trophozoites and the cysts infect humans (Adam, 2001). There are no forewarning signs before the onset of the disease. The most notable symptom of infection is foul smelling diarrhoea which may be continuous or intermittent. The stools are not bloody, but they are light in color, greasy and mixed with plenty of mucus. (www.lowchensaustralia.com). The diarrhoea is not watery, but it does produce listlessness ands weight loss. In its more serious manifestations, it may result in the diarrhoea becoming chronic and the passage of excessive amounts of mucus, or in tenesmus or hematochezia. Treatment: In treating the symptoms of diarrhoea induced by giardia lambia, the same chemicals that have been identified as retarding its growth are used in treatment. As a result, metronidazole is the drug of choice to be used because it kills the giardia microorganism quickly, especially in larger doses. Other drugs that destroy the microorganism are quinacrine or furazolidone (www.lowchensaustralia.com). The disease can also be prevented, since a vaccine is now available in the United States to kill microorganisms and prevent the disease. Methods of identification: The most common and best method that is used to identify the microorganism is through the identification cysts present in the faeces. In some rare instances, there may also be trophozoites present in fecal specimens. Smears are taken of the diarrhoeal feces and zinc sulphate is then used for fecal flotation in order to concentrate the cysts so that they can be clearly identified. Another method to identify the presence of giardia lambia is by using Lugol’s iodine solution for staining the fecal specimens, which makes them easy to identify. The third method is to detect the presence of Giardia antigens in the fecal matter of an infected person by using immunoflourescent assays, both using monoclonal antibodies as well as by using direct florescent assays. (www.lowchensaustralia.com). Humans may be sensitive to these assays so they may need to be used with care or only as a last resort. Another such method for identifying the presence of Giardia is through immunoflouresence. A real time PCR assay is also very useful in detecting Giardia differentiation in specimens of human stool. References: * Adam, Rodney D, 2001. “Biology of Giardia Lamblia” Clinical Microbiology Reviews, 14(3): 447-475 * Echmann, Lars, Fabrice, Laurent, Langford, Dianne T, Hetsko, Michael L, Smith, Jennifer R, Kagnoff, Martin F and Gillin, Francis D, 2000. “Nitric oxide production by human intestinal epithelial cells and competition for arginine as potential determinants of host defense against the lumen dwelling pathogen Giardia lamblia.” The Journal of Immunology, 164: 1478-1487 * Gillin, Francis D and Diamond, Louis, S, 1981. “Inhibition of clonal growth of Giardia lambia and Entamoeba histolytica by metronidazole, quinacrine and other microbial agents.” Journal of Antimicrobial Chemotherapy, 8 : 305-316 * “Intestinal giardiasis in the dog” [online] available at: lowchensaustralia.com/health/giardia.htm Read More