Pathogens enteric viruses

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. 

This article provides an overview of the epidemiological impact, pathogenesis and new approaches to the management of enteric infections. Although several enteric viruses are important causes of diarrhea in both developed and developing country, we will focus this overview on bacterial and selected parasitic pathogens. 

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). 

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... 

Some diseases caused by viruses are communicable and easily transferred from an infected individual to anyone in close proximity. Typically, this occurs when the infected individual coughs or sneezes creating an infectious aerosol. These aerosols enter the body of a new host through inhalation and /or contact of the aerosol with the mucous membranes of the eyes, nose, or mouth. In addition, although intact skin is an effective barrier against most pathogens, abrasions, or lacerations circumvents this protective barrier and allows entry of the pathogen into the body. 

Drugs are also used to inhibit the enzymatic reactions of foreign pathogens that enter the human body. An example is the use of reverse transcriptase inhibitor and protease inhibitor for combating the human immunodeficiency virus (HIV), as shown in Exhibit 2.12. Some new inhibitors are used to block HIV from attaching to the human cell, CD4, thus stopping replication and infection of other cells, as presented in Exhibit 2.13. 

Pathogens that have entered the body—e.g., viruses (top)—are taken up by antigen-presenting cells (APCs) and proteolytically degraded (1). The viral fragments produced in this way are then presented on the surfaces of these cells with the help of special membrane proteins (MHC proteins see p. 296) (2). The APCs include B lymphocytes, macrophages, and dendritic cells such as the skin s Langer-hans cells. 

Carter, M. J. (2005). Enterically infecting viruses Pathogenicity, transmission and significance for food and waterborne infection. J. Appl. Microbiol. 98,1354 1380. 

HSE occurs in a certain percentage of mice or rabbits following infecdon. The frequency of HSE in experimental infec dons is dependent on the pathogenic po ten dal of the HSV-1 and the mouse sd ain used for experimental infecdon. For HSE to occur after ocular infecdon, the virus must enter the TG, and then spread to the CNS, or the virus directly gains access into the brain via the opdc nerve. Models have also been developed in which the virus is directly inoculated into the brain. In this model, d ansport from the peripheral dssue the peripheral nervous system the CNS is not important. Thus, viral genes necessary for neuronal d ansport and spread are not crucial for virus infecdon if the brain is inoculated. 

The kidneys attempt to excrete, via the urine, toxins that have found their way into the blood. Toxins can enter the body from the air we breathe, the food we eat, or the beverages we drink. Toxins can also be created within the body as the by-products of normal metabolism or as a result of excess stress hormones linked to a chronically stressful life. Toxins may also be the by-products of viruses, bacteria, fungi, or other pathogens that inhabit our bodies (more on this topic later). 

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