Protozoa protection

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... 

Myeloperoxidase is an extremely potent, antimicrobial protein that is present in neutrophils at up to 5% of the total cell protein. Its role in the killing of a wide range of bacteria, fungi, viruses, protozoa and mammalian cells (e.g. tumour cells) is well established from in vitro studies. It also plays an important role in the inactivation of toxins and the activation of latent proteases, as well as in other functions described in section 5.4.1. In view of this apparent central role in neutrophil function during host defence, one would think that any deficiencies in this enzyme would have disastrous consequences on the ability of the host to combat infections. Until the early 1980s, this key role for myeloperoxidase in host protection seemed substantiated by the extremely low incidence of reports of patients with deficiencies of this enzyme. Indeed, up to this time, only 15 cases from 12 families had been reported worldwide. Sometimes these patients were asymptomatic but often suffered Candida infections, particularly if their myeloperoxidase deficiency was also associated with diabetes mellitus. 

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). 

Packaged as a commercial product, NPVs have a remarkable shelf life. The occluded virions, within the protective inclusion-body protein, are among the most stable entomopathogens, compared with other microorganisms and microparasites, such as bacteria, fungi, protozoa, and nematodes. In the laboratory, lyophilized, frozen, or simply refrigerated NPV inclusion bodies, stored in darkness, remain active for many years, even decades... 

In addition to specific chemical substances, a variety of other determinations is very important and is often required for environmental studies and protection programs. These include identifications and measurements of bacteria, viruses, protozoa, and minerals such as asbestos fibers. Measurements of meteorological conditions, particulate matter in air by size, water turbidity, biological oxygen demand, chemical oxygen demand, and radioactivity are also very important. These and other similar determinations are beyond the scope of this chapter and the reader should consult other reference books for information about these topics. 

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. 

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. 

Bacteria have no mitochondria. In them, the mitochondrial functions described earlier are all carried out within the plasma membrane, where all the needed enzymes are anchored. This relatively poor protection of the enzyme systems (compared with the host s cell) is the likely reason for the selective toxicity of these agents. The situation in protozoa is somewhat different. Some species have a few mitochondria more often, some contain simpler tubules rather than cristae. 

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