Protozoa cysts

Identification may be by gross examination for adult helminths or, more commonly, by microscopic examination for protozoa, helminth eggs, and larvae. The diagnostic forms of some parasites, such as the eggs of Ascaris spp., are present on a regular basis. Other forms, such as malaria parasites, Taenia eggs, or Giardia cysts, vary from day to day. 

The direct wet mount made from unconcentrated fresh feces is most useful for the detection of the motile trophozoites of intestinal protozoa and the motile larvae of Strongyloides spp. It is also useful for the detection of protozoan cysts and helminth eggs. For fixed feces, the direct wet mount may allow the detection of parasites which do not concentrate well. This method is also useful for the examination of specific portions of feces, such as flecks of blood or mucus. 

In an ideal stain, the cytoplasm of cysts and trophozoites is blue-green tinged with purple. Entamoeba coli cyst cytoplasm is often more purple than that of other species. Nuclear chromatin, chromatoid bodies, erythrocytes, and bacteria stain red or purplish red. Other ingested particles such as yeasts often stain green. Parasite eggs and larvae usually stain red. Inflammatory cells and tissue cells stain in a fashion similar to that of protozoa. Color reactions may vary from the above. 

While Giardia is sensitive to freezing of soil, Cryptosporidium is more resistant. Mahdy et al. (2008) reported Giardia cysts in soil were inactivated after 7 days at -4 °C, but Cryptosporidium could survive for >12 weeks. However, persistence of both protozoa was reduced to 8 weeks at 4 °C and 4 weeks at 25 °C (Mahdy et al., 2008). Cryptosporidium have been shown to be particularly sensitive to drying. Various studies have shown less than 5% viability following 4 h of air drying at room temperature (Anderson, 1986 Nasser et al., 2007 Robertson et al, 1992). 

Protozoa are microscopic animals consisting of single eukaryotic cells and classified on the bases of morphology, means of locomotion, presence or absence of chloroplasts, presence or absence of shells, and ability to form cysts. Several devastating human diseases, including malaria, sleeping sickness, and some kinds of dysentery, are caused by parasitic protozoa. Parasitic protozoa can cause debilitating, even fatal, diseases in livestock and wildlife. 

As opposed to the prokaryotic bacteria, protozoa are a diverse set of eukaryotic organisms, often with complex life cycles. These entities exist in various forms, from proliferative trophozoites through to dormant cysts, and some spending their... 

When adverse conditions prevail, the protozoa become inactive, transforming into a rounded form, and eventually developing a protective cell wall. Under the safety inside the cell wall, the organism may live for a long time and resist any destructive insult from the environment. This transformation is called a cyst. 

Cyst—A transformation protozoa undergo when adverse conditions prevail. 

Intestinal protozoa are common throughout the world and particularly in areas where food and water sources are subject to contamination from animal and human waste. Typically, protozoa that infect their host through water or food do so while in an inactive state, called a cyst, where they have encased themselves in a protective outer membrane and are released through the digestive tract of a previous host. Once inside the host, they develop into a mature form that feeds and reproduces. 

Protozoa are unicellular organisms with a well-defined cell nucleus. Some species are capable of sexual reproduction, while others reproduce asexually. In addition to their vegetative (usually motile) forms, most protozoa also develop cysts as a permanent state under unfavourable external conditions. They move with the aid of flagella or cilia, by amoeboid locomotion, or in a winding, gliding manner. 

On the whole, which are the infectious forms of foodbome parasites Main infectious stages (to humans) of coccidian parasites are either highly resistant oocysts (monoxenous species), like Cryptosporidium, or tissue zoites (heteroxenous species), contained in tissue cysts, like those of Toxoplasma. Other parasitic Protozoa develop resistant cystic forms in their life cycle, like Giardia. 

Amebiasis ajfects 10% of the world s population. In the U.S., amebiasis is usually seen in those living in crowded, unsanitary conditions. Entamoeba dispar accounts for 90% of human infections and E. histolytica/or only 10%, but only E. histolytica causes human disease. Humans are the only known hosts for these protozoa, which are transmitted almost exclusively by the fecal-oral route. E. histolytica cysts ingested from contaminated food or water transform into trophozoites that reside in the large intestine. Many individuals infected with E. histolytica are asymptomatic but excrete infectious cysts, making them a source for further infections. In others, E. histolytica trophozoites invade the colonic mucosa with resulting colitis and bloody diarrhea (amebic dysentery). Rarely, E. histolytica trophozoites invade through the colonic mucosa and reach the liver via the portal circulation, where they establish an amebic liver abscess. 

Certain treatment processes are less effective in reducing enteric viruses and protozoan cysts than enteric bacteria. Different treatment processes are differently able to remove and to inactivate viruses, bacteria, antinomycetes, algae, protozoa, filamentous fungi and yeasts in drinking water. 

Protozoa may become another problem of water treatment. Usually, removal or inactivation of Entamoeba has been the central problem, but recent investigations also concerns Giardia [43]. Proper coagulation, flocculation, sedimentation, and filtration can remove up to 99% of protozoan cysts slow sand filtration can remove Giardia cysts [16]. Improper operation of treatment facilities can cause outbreaks of water-borne illnesses caused by protozoa [44]. Chlorination and disinfectants such as chloramines and ozone can further reduce levels of protozoa [45-47]. 

The activated sludge process is effective in reducing the number of co-liform organisms, Salmonella, Shigella and Mycobacterium tuberculosis by 85 to 99%, polio virus type I by 90% and Coxsackie A9 virus by 98%. The process does not have a great effect on the cysts of parasitic protozoa. 

Corliss, J.O., Esser, S.C. (1974). Role of cyst in Ufe-cycle and survival of free-living protozoa. Transactions of the American Microscopical Society 93,578-593. 

In Europe tests with rotifers, cysts from aquatic invertebrates (Calleja et al., 1994), development of onion roots have been tried but none have been accepted (Persoone et al., 1994 Snell and Persoone, 1989 Fresjog, 1985 Gaggi et al. 1995). Jaffe (1995) has proposed a method using the survival of a protozoan. Toxic chemicals kill the protozoa. The test requires a Coulter particle counter to determine the numbers of viable protozoa. 

These rely on the small pore size of the ceramic material, are inexpensive and more effective water filter, to filter dirt, debris, and bacteria, protozoa, and microbial cyst etc. out of water. But again, this is not effective against viruses since they are of smaller size than the pores and can pass through to the other clean side of the filter. To overcome this, CWF are treated with silver in a form that will not leach away helps to kill or incapacitate bacteria and prevent the growth of algae in the body of the filter. 

---