Helminth parasites, control

Roepstorff, A., Monrad, J., Sehested, J., Spegaard, K. and Danielsen, V. (2002). Mixed grazing with sows and heifers - as a mean of parasite control , in Novel Approaches Meeting III - A Workshop Meeting on Helminth Control in Livestock in the New Millenium. Third International conference, 1-5 July 2002, 41. 

Ecdysteroids are the most widespread and probably oldest steroidal hormone. Recent investigations suggest that the lower animals, namely Annelida, Nematoda and Mollusca might also use ecdysteroids to control certain vital processes in their life cycle. Ecdysteroids have been found in helminth parasites of humans and livestock (trematodes, filarial nematodes and cestodes [188]. 

Taken as a whole, these observations show that parasite lines differ in an immune-dependent manner in their infection/expulsion kinetics. Furthermore, there is heritable variation in survival and fecundity in previously exposed hosts and quantitative variation in the immune response that selected parasite lines elicit. Again, taken as a whole, these observations have the necessary corollary that variation in these traits exists not only in laboratory-maintained isolates but also in helminth species in nature. The phenotypes under consideration here (infection/expulsion kinetics, survival, fecundity) are multifactorial life-history traits. Understanding the basis of variation in the components and interplay of these complex, immune-responsive phenotypes must be of crucial relevance to understanding the immunology of infections of parasitic nematodes. This is of particular relevance in view of current attempts to develop immunological methods of nematode control. 

Other contributions to this book have taken a molecular view of parasitic nematodes, yet molecules make only a rather brief appearance here. This chapter has tried to show that parasitic nematodes are fascinatingly and tantalizingly diverse at a phenotypic level. It has focused particularly on diversity in phenotypes that are apparent in response to environmental conditions within or outside a host. The interaction of parasites with within-host factors is a major current research effort. However, helminth immunology is particularly notable for its inattention to diversity, especially when compared with the immunology of parasitic protozoa (Read and Viney, 1996). Observations of the interaction of host immunity with subsequent development in S. ratti show the potential power of such interactions. It is also clear that a principal mechanism of the action of host immune responses is against nematode fecundity (Stear et al., 1997). This is likely to be a molecularly complex interaction. Understanding this interaction, as well as variation in the interaction is interesting, but could also form the basis of control by transmission-reduction rather than eradication per se. 

Pritchard, D.I., Hewitt, C. and Moqbel, R. (1997) The relationship between immunological responsiveness controlled by T helper 2 lymphocytes and infections with parasitic helminths. Parasitology S33-S44. 

The initial objective of the search was an anthelmintic with properties radically different from those of known anthelmintics. What was found was an anthelmintic whose properties were indeed markedly different — not only in terms of chemical structure and efficacy against helminths, but also in the extension of the potential utility of the class to the control of arthropod parasites of animals. Further, the compounds turned out to have striking activity against a variety of free-living and plant-parasitic nematodes and arthropods — and so it has come about that a new livestock anthelmintic has become an agenda item in this symposium on agricultural pesticides. 

The major phosphagens found in nature are arginine and creatine but parasitic helminths are unusual in that they possess no detectable phosphagens and none occurs in Hymenolepis diminuta, Moniezia expansa, Ligula intestinalis or Schistocephalus solidus (44). This absence of phosphagens has implications for control of metabolism in cestodes. If... 

In spite of the widespread occurrence of slgA, not only in cestode infections, but in all other helminth intestinal infections, the role played by IgA remains unknown (921). In relation to this, it has been speculated (53) that IgA antibody is relevant in the control of the uptake of parasite antigens, their clearance from the circulation and in the modulation of the activities of various cells in the inflammatory events associated with infections this may involve enhancement of cytotoxic functions or the minimization of potentially pathogenic reactions. ... 

Since a variety of en2ymatic reactions control the energy metabolism in parasitic helminths, the following biochemical targets may be utilized for effective design of new anthelmintics. 

Even if it could seem bizarre nowadays, live parasites or their antigens would work for ameriolating immunological disorders, like allergies or autoimmune diseases. Helminth infection can control concomitant immune disease modulat-... 

It is difficult to title correctly a discussion that attempts to deal with the broad area of drugs utilized to treat all the types of infections that parasitize humanity. Antiparasitic might be technically more correct because it would include all organisms from the microscopic in size to the 75-foot tapeworm, but the term parasite has acquired a much narrower meaning as commonly used. The title antimicrobial was selected even though drugs controlling helminthic (worm) infestations will be considered. Similarly, antiviral compounds will also be discussed, even if viruses are not microbes as commonly viewed. 

Aoki, T. and Oya, H. (1979) Glutamine-dependent carbamoyl-phosphate synthetase and control of pyrimidine biosynthesis in the parasitic helminth Schistosoma mansoni. Comp. Biochem. Physiol. 63-B 511-515. 

Araujo MIAS, Hoppe B, Medeiros M Jr et al 2004 Impaired T helper 2 response to aeroallergen in helminth-infected patients with asthma. J Infect Dis 190 1797—1803 Babu S, Blauvelt CP, Kumaraswami V, Nutman TB 2006 Regulatory networks induced by live parasites impair both Thl and Th2 pathways in patent lymphatic filariasis implications for parasite persistence.] Immunol 176 3248-3256 Belkaid Y, Piccirillo CA, Mendez S, Shevach EM, Sacks DL 2002 004 0025" regulatory T cells control l eishmania persistence and immunity. Nature 420 502—507 Bluestone JA, Abbas AK 2003 Natural versus adaptive regulatory T cells. Nat Rev Immunol 3 253-257... 

The host immune response to helminths is partially controlled by cytokines as immune cell signalii molecules, and chemokines to induce cell-specific chemotaxis, in order to ehcit the appropriate antihelminthic response. Prolonged co-existence of helminths and their hosts have resulted in parasite developing homologues to human cytokines and chemokines that manipulates the host immune response in such a way as to prolong parasite infestation. Examples of helminth cytokine and chemokine homologues are shown in Table 6 and described herein. 

It thus appears that for some helminths infesting some animal hosts there are limiting factors in the host s diet which control the establishment and development of the parasite. This seems to apply to carbohydrate for rat tapeworms and to calcium and phosphorus for chick round-worms. Some factor or factors in the B complex vitamins may limit the development of rat tapeworms also. 

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