Parasitization host larva

Another interesting observation is that several species of filarial nematodes have been shown to express chitinase (Fuhrman, 1995). Indeed the chitinase of A. viteae infective stage larvae (L3) is the main target of the protective humoral immune response when jirds are vaccinated with irradiated attenuated L3s (Adam et al., 1996 see also Chapter 10). It remains to be established whether there is an interaction between the parasite s oligo-chitin A-glycans and chitinase and whether such an interaction has a role to play in parasite-host interaction. 

Parasitoid wasps are the most widely studied group of insect parasites. Female wasps lay an egg(s) on or in an insect and the progeny develop utilizing that insect as their sole food source, eventually killing the host. Female parasitoids tend to be host specific and typically exploit a specific host immature life stage (e.g., egg, larvae, or pupae). Most parasitoid wasps are relatively small. Females actively seek out multiple hosts and can find and parasitize host insects in cryptic habitats. There is a wide range of species that attack stored-product insects and a considerable body of research on these natural enemies, only some of which are covered here [see Godfray (1994) for more information on parasitoids and Brower et al. (1995) and Scholler and Flinn (2000) for reviews of information specifically on stored product parasitoids]. 

Because of the previously described problems in culture of parasitic nematodes, investigation of sterol metabolism in these organisms has been largely limited to comparison of the sterol compositions of host and parasite. For example, lathosterol and cholesterol were the major sterols of N. carpocapsae DD-136 propagated in wax moth larvae, organisms that contained cholesterol as their principal sterol. Radiolabeled cholesterol injected into host larvae was recovered as radiolabeled lathosterol and cholesterol in the nematode (19). 

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. 

In some helminth infections, a migration through various body tissues is essential for maturation, as in ascarasis or schistosomiasis, whereas in other infections, the larva leaves the egg and simply matures in the intestinal tract, as in trichuriasis and enterobiasis. Host tissues involved vary depending upon the parasite. In severely immunocompromised patients, sites may be involved that are not involved in normal hosts. 

Current understanding of parasitism by T. spiralis is compartmentalized, and so glycoprotein function has been considered in the context of one compartment or another. However, LI larvae of T. spiralis have evolved under selective pressure to parasitize both intestine and muscle. Biological economy may require a duality of function in larval glycoproteins such that they are able to perform distinct roles in each of the two niches. Dualism is common in proteins, and elucidation of such properties in parasitic nematode products would provide unique insights into the basis of host adaptation. 

Another fascinating aspect of trichinellosis is the muscle phase of the infection, which will be the focus of this chapter. From an epidemiological perspective, it is the muscle phase which serves as a reservoir for parasite transmission. Muscle larvae are infective to the next host upon ingestion, and the muscle phase is chronic, lasting months to years. From a biological perspective, the mechanisms by which the parasite establishes this reservoir are most intriguing. 

The muscle phase of the infection is initiated by newborn larvae (immature LI larvae). These larvae originate from female worms located in the small intestine of the host. On recognition of skeletal muscle cells, larvae invade and initiate the processes that culminate in long-term intracellular infection of these cells. Following infection, both the parasite and host muscle cell undergo significant changes, over the course of the first 15 days (referred to here as the initiation phase), which is followed by... 

In contrast to NA which remain largely uncharacterized, better defined parasite proteins have been identified for which localization and interactions within the host cell remain ill-defined. Despite results from irradiated newborn larva experiments, a- and p-stichocyte proteins cannot be excluded from a regulatory role in host muscle cells. For instance, p43 was described as having a potential helix-loop-helix (HLH) motif (Vassilatis et al., 1992). In a manner similar to the inhibitor of DNA binding (ID) (Benezra et al., 1990), this motif in p43 might antagonize the... 

Two additional parasite proteins with apparent HLH binding properties were identified, based on the idea that direct antagonism of host HLH transcription factors might be responsible for muscle cell subversion. One is a MyoDdike protein (Connolly el al., 1996) and another (110 kDa) is located in the vicinity of the hypodermis or somatic musculature of muscle larvae (Lindh el al., 1998). Secretion of these proteins into the infected cell has not been reported. 

Dropkin, V.H. and Boone, W.R. (1966) Analysis of host-parasite relations of root-knot nematodes by single larva inoculations of excised tomato roots. 

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