Enteric parasites

Development of new molecular techniques that can be applied to a wide variety of food items has dramatically increased the sensitivity and specificity of detection of human enteric parasites in the tissue of molluscan shellfish (Schwab et al., 1998, 2000 citations in Table I). 

In general, the flow rate F(t) consists of the following additive components the controlled flow rate Fd of the entering gas, the flow rate Fi which is due to parasitic leaks and/or diffusion, and the flow rate Fw resulting from possible adsorption-desorption processes on the system walls (in Section I, references are given to papers dealing with the elimination or control of the wall effects in the flash filament technique). In each of these flow rate components a particular ratio of the investigated adsorbate and of the inert gas exists and all these components contribute to the over-all mean values Fh(t) and F (t). 

The Great Lakes have suffered the invasion of numerous exotic species of which the smelt, alewife and sea lamprey are probably the best known. More recently, two more species have entered the lakes probably via ballast water from foreign ships. The ruffe (Gymnocephalus cemuus) a small percid, feeds on the eggs and larvae of other percids and whitefish. The ruffe is currently considered to be a threat to Lake Superior s 5- 10 million whitefish fishery. The zebra mussel (Dreissena polymorpha) was discovered in Lake St. Clair in 1985 (31). It has subsequently been discovered at locations throughout the Great Lakes and is of major concern not only environmentally but economically. It has already colonized numerous industrial and domestic water intakes in sufficient numbers to entirely block water flow and is also an intermediate host to parasites which eventually invade fish. 

Giardia lamblia (also known as G. intestinalis or G. duode-nalis), an enteric protozoan, is the most common intestinal parasite responsible for diarrheal syndromes throughout the world. Giardia is the most frequently identified intestinal parasites in the United States, with a prevalence rate of 5% to 15% in some areas. G. lamblia has been identified as the first enteric pathogen seen in children in developing countries, with prevalence rates between 15% and 30%. 

Fig. 11.4. Model for cholinergic signalling in the intestinal mucosa, providing a possible rationale for AChE secretion by parasitic nematodes. ACh released from enteric cholinergic motor neurons stimulates chloride secretion, mucus secretion and Paneth cell exocytosis through muscarinic receptors. Secretory responses may be modulated by mast cell mediators, either directly or via the induction of neural reflex programmes. The role of muscarinic receptor-positive cells in the lamina propria of rats infected with N. brasiliensis is undetermined, as are potential mechanisms of trans-epithelial transport of the enzymes. Adapted from Cooke (1984).

McKay, D.M., Benjamin, M., Baca-Estrada, M., D Inca, R., Croitoru, K. and Perdue, M.H. (1995) Role of T lymphocytes in secretory response to an enteric nematode parasite. Studies in athymic rats. Digestive Disease Sciences 40, 331-337. 

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... 

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. 

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