Worms, parasitic

Parasitic worms are multicellular organisms, which are not always microscopic and are difficult to eliminate by the immune system. They do elicit an immune reaction, mostly by production of immunoglobulin E (IgE) and attack by eosinophils, which can be harmful to the host. With few exceptions, the reproductive stage is either free in the environment or in another host, for example insects or snails. This means that in humans most infestations, in terms of numbers, are self-limiting. 

Worms are known as helminths and the majority is not parasitic. Classes of worms that parasitize man are round worms (nematodes) and flat worms (platyhelminths). The flat worms are divided into tapeworms (cestodes) and flukes (trematodes). Only a few human parasitic worms are common in the United Kingdom, for example threadworms and round worms. In tropical and subtropical parts of the world, where abundant water and high temperatures provide an optimal environment for the larvae and intermediate hosts, parasitic worms are common and widespread. Table 9.8 lists some parasitic worms that can infect man, their effect and drugs used to treat them. 

Ascaris lumbricoides Intestinal obstruction possible Levamisole  

Necator americanus Draw blood, can cause anaemia  

Ancylostoma duodenale Infection by larvae in soil through skin  

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Many parasitic worms cause systemic infections outside the gastrointestinal tract. These include Strong loides stercoralis (threadworm), Trichinella spiralis Dracunculus medinensis and the several species of nematodes that cause filariasis (Mansonellaperstans and Onchocerca volvulus). 

Antihelmintic (Anthelmintic). An agent that is useful in the control of parasitic worms. 

In Hawaii, Faust (2000) contended that the hair sheep, St Croix breed, not only has a unique resistance to parasitic worms but also keeps the coffee, avocado and citrus orchards free of tropical weeds. 

Day, T.A. and Maule, A.G. (1999) Parasitic peptides The structure and function of neuropeptides in parasitic worms. Peptides 20, 999-1019. 

Figure 17.34 Kitting of targe parasites by eosinophib. A parasite worm is surrounded by eosinophils which bind to the IgE molecules that are bound to the worm. The eosinophils kill the parasite worm by release of the contents of their lysosomes.

Figure 17.35 Rote of IgE and mast cetts in kitting targe parasites. The parasitic worm binds to IgE antibodies that are attached to a mast cell, which then releases its granules, the contents of which kill the parasite.

Rodriguez, E., Gavin, J. C., and West, J. E. (1982). The possible role of Amazonian psychoactive plants in the chemotherapy of parasitic worms a hypothesis. Journal of Ethnopharmacology 6,303-309. 

Paragonimus spp. Parasitic worm found in crabs and crayfish in Asia 0.1 In vitro minimum effective dose... 

Gnathostoma spinigerum Parasitic worm found in raw, undercooked or fermented fish 7 Reduces worm recovery rate in mice... 

Charles Pfizer, a German chemist who founded the pharmaceutical company Pfizer in 1849. After immigrating to the United States, he and Charles Erhardt borrowed 2,500 to establish their new chemical business in Brooklyn, New York. Their first success was to make a palatable form of the drug santonin used to treat parasitic worms, a common problem in the 1800s. Over the next century and a half, the company grew into the world s largest pharmaceutical maker. 

Infestations with parasitic worms and flukes are widespread both in humans and in animals, and their treatment requires drugs that act in a different manner from antibacterial and antiprotozoal agents. It is desirable for worms to be expelled from the body intact since the presence of dead worms in the tissues can provoke severe reactions. Such reactions are seen when filarial worms which circulate in the blood and lymph are killed by diethylcar-bamazine (264). Intestinal worms may be expelled when they are paralyzed by neuromuscular blockers such as piperazine citrate or pyrantel (265), or their metabolism may be disrupted by the anthelmintic drugs tetramisole and thiabendazole (266) which inhibit fumarate reductase, or mebendazole (267) which prevents glucose uptake by the worms. The anthelmintic activity of tetramisole is due to its laevo isomer levamisole (186). The dextro isomer has antidepressant activity. 

Anthelmintic. A drug used to remove or destroy parasitic worms. 

In addition to the one-celled anaerobes, certain parasitic worms, such as Ascaris, are thought to use anaerobic metabolism, to a certain extent at least. Living in the intestine of higher animals these worms have little access to free oxygen. 

Trouve, S., Morand, S. and Gabrion, C. (2003) Asexual multiplication of larval parasitic worms a predictor of adult life-history traits in Taeniidae Parasitology Research 89, 81-88. 

Williams, H.H. and Jones, A. (1 994) Parasitic Worms of Fishes. Taylor Francis, London. 

Brooks, D. and Isaac, R.E. (2002) Functional genomics of parasite worms the dawn of a new era. Parasitology International 51, 319-325. 

Mansour, T.E. (1 984) Serotonin receptors in parasitic worms. Advances in Parsitology 23, 1-36. 

Parasitic stages, on the other hand, generally do not use oxygen as the final electron acceptor but use fermentative processes to obtain most of their ATP. For these stages, an uneconomical energy metabolism is not detrimental, as the host provides the nutrients. Most adult flatworms inside the final host produce end products of a fermentative carbohydrate breakdown, such as succinate, acetate, propionate and lactate. These end products are formed via malate dismutation, a fermentative pathway, which is present in all types of parasitic worms (flatworms as well as many nematodes), but which is also present in animals like freshwater snails, mussels, oysters and other marine organisms. Malate dismutation is linked to a specially... 

Infection from helminths, or parasitic worms, is the most common form of disease in the world.41,44 There are several types of worms that may invade and subsist... 

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