Protozoa pathogenicity

Protozoa pathogenic to man which can be transmitted by contaminated water (Entamoeba histolytica, Giardia lamblia, Naegleria gruberi and Acan-thamoeba) are described in Section 4.2.7. 

Bacteria are smaller than protozoa and are responsible for many diseases, such as typhoid fever, cholera, diarrhea, and dysentery. Pathogenic bacteria range in size from 0.2 to 0.6 /tm, and a 0.2 /tm filter is necessary to prevent transmission. Contamination of water supplies by bacteria is blamed for the cholera epidemics, which devastate undeveloped countries from time to time. Even in the U.S., E. coli is frequently found to contaminated water supplies. Fortunately, E. coli is relatively harmless as pathogens go, and the problem isn t so much with E. coli found, but the fear that other bacteria may have contaminated the water as well. Never the less, dehydration from diarrhea caused by E. coli has resulted in fatalities. 

Viruses are the 2nd most problematic pathogen, behind protozoa. As with protozoa, most waterborne viral diseases don t present a lethal hazard to a healthy adult. Waterborne pathogenic viruses range in size from 0.020-0.030 jtim, and are too small to be filtered out by a mechanical filter. All waterborne enteric viruses affecting humans occur solely in humans, thus animal waste doesn t present much of a viral threat. At the present viruses don t present a major hazard to people drinking surface water in the U.S., but this could change in a survival situation as the level of human sanitation is reduced. Viruses do tend to show up even in remote areas, so a case can be made for eliminating them now. 

Antiparasitic drugs are used for the treatment of parasitic infections caused by pathogenic protozoa or helminths (worms). 

Increased amounts of faecal-oral water-borne pathogens (virus, bacteria and protozoa) and microbial indicators (bacterial and viral) have been reported in groundwater bodies [18], karst springs [19, 20], surface freshwater [21-26], marine waters used for bathing [27-29] and shellfish growing [30] as well as tap water [31]. 

Moulds and yeasts show varying responses to biocides. These organisms are often important in the pharmaceutical context because they may cause spoilage of formulated products. Various types of protozoa are potentially pathogenic and inactivation by biocides may be problematic. Viral response to biocides depends upon the type and structure of the virus particle and on the nature of the biocide. 

Human infections with Salmonella spp. and E. coli 0157 H7 are a common worldwide phenomenon. Livestock may serve as a source of several relevant human pathogenic microorganisms (Table 19.2). The most prevalent group is the enteric pathogens which include bacteria, viruses and parasites (i.e. protozoa and helminths). Animals may shed pathogens through excreta without... 

Faeces from colonised cows may contain from 102 to 107 colony-forming units (CFU) of Salmonella cells per gram of faeces. Particularly calves and heifers colonised with E. coli 0157 H7 may shed the bacteria at levels ranging from 102 to 105 CFU g 1 (Himathongham el al., 1999). Furthermore, calves younger than four months are the main domestic animals that excrete pathogenic protozoa like Giardia and Cryptosporidia. 

The immune system protects humans and animals from microbial infections by such infectious agents as bacteria, yeasts and fungi, viruses and protozoa. These differ greatly not only in their size but in their structural and molecular properties, as well as in the ways in which they seek to infect our bodies. Some of these pathogens infect bodily fluids, some penetrate tissues and some even survive and multiply within individual host cells. These intracellular pathogens include viruses, some parasitic protozoa (such as Plasmodium, the causative agent of malaria, which infects erythrocytes) and... 

It is of historical interest that Tetrahymena gelii, whose metabolism has been described in detail [387], is inhibited by 8-azaguanine [388] and other purine analogues [389, 390]. Of more importance to chemotherapy is the fact that pathogenic protozoa such as the trypanosomes respond in vitro to a number of... 

The most widespread protozoan infections caused by pathogenic protozoa are malaria, leishmaniasis, and trypanosoma, as well as trichomonas, amebiasis, giardia, and toxoplasmosis. All types of protozoa are single-cell organisms that can adapt to various conditions. They are much more versatile than bacteria. They have a fairly complex life cycle, and therefore they exist in many forms. These forms require different approaches when treating patients that have protozoan infections. Protozoa are typical parasites that occupy host cells, multiply in them, and then destroy them. 

Human pathogenic protozoa such as Giardia, Entamoeba, Toxoplasma, Sarcocystis, Isopora, Cryptosporidium, Eimeria, and Cyclospora can be transferred via fecally contaminated water or vegetables (Armon et al., 2002). 

Similar to enteric viruses, protozoa require a suitable host for replication but can persist within nonhost environments for significant time periods (Sidhu and Toze, 2009). The main source of human protozoan is from direct contact with humans although foodbome sources can also represent a significant vehicle (Sidhu and Toze, 2009 Thompson et al., 2008). All of these human pathogenic protozoa cause diarrhea-like symptoms except Toxoplasma, which causes fetal damage and glandular fever-like syndrome (Dumetre and Darde, 2003). 

The persistence of enteric pathogens in soil is dependent on several factors. For example, the survival of E. coli is prolonged in clay soils where absorption of cells to the soil particles provides protection against protozoa (Lang and Smith, 2007 Mosaddeghi et al., 2009 Wong et al., 2008). 

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