1
|
Abstract
At the cellular and molecular levels, the small and simpler nervous systems of invertebrates do not differ fundamentally from the larger more complex ones of vertebrates. It seems therefore that the special properties of the human brain arise more from the fact that it has ten trillion cellular components than from any unusual properties of the components themselves. By studying invertebrates we can gain insight into what basic functions are performed by the cells and molecules of the nervous system and this will contribute to a more fundamental understanding of what goes on in a system in which the same functions are performed by uncountable numbers of neurones. Invertebrate studies are also important for an entirely different reason; they are interesting and important in their own right. Moreover, a relatively small number of invertebrates are pests; either parasites, vectors of serious parasitic diseases or pests of our agricultural production. It is no accident that most of the methods that are used to control such organisms act on their nervous system. That is because the nervous system is a complex chemical machine which works through a great variety of chemical interactions between a wide diversity of receptors and ligands. Many currently used control methods work because they disrupt these interactions. For this reason I would imagine that the new generation of compounds developed to control invertebrates will depend for their activity on interactions with the nervous system. Since most of the chemical effectors (transmitters, modulators and hormones) in the nervous system are peptides, a number of these newly developed approaches will depend upon a fundamental knowledge of peptidergic systems in parasites. This essay is about peptidergic systems and indicates how we might exploit their vulner-ability to interference.
Collapse
|
2
|
Abstract
Although parasitic helminths are a very heterogeneous group of organisms, they share many interesting properties in their energy metabolism. In certain stages of their life cycle, they all have a large capacity for anaerobic functioning. In other stages, an aerobic energy metabolism prevails. Parasites have to adapt to different environments in which the availability of oxygen and food varies widely. These variations in their external conditions strongly influence their energy metabolism. Here, Louis Tielens presents an introduction to the current ideas on the bioenergetics of parasitic helminths, focusing on the differences in energy metabolism between various stages (free-living and parasitic), and paying special attention to the mechanisms involved in the transitions between the different methods of energy generation.
Collapse
Affiliation(s)
- A G Tielens
- Laboratory of Veterinary Biochemistry, Utrecht University, PO Box 80176, TD Utrecht, The Netherlands
| |
Collapse
|
3
|
Morley NJ, Irwin SWB, Lewis JW. Pollution toxicity to the transmission of larval digeneans through their molluscan hosts. Parasitology 2004; 126 Suppl:S5-26. [PMID: 14667169 DOI: 10.1017/s0031182003003755] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The increased occurrence of pollutants in ecosystems is a continuing area of concern. It is known that numerous diseases of wild aquatic animals can occur with decreased or increased prevalences in areas associated with high or chronic levels of pollution. This may have serious implications for environmental health. There has consequently been an increasing number of laboratory and field studies on disease transmission under polluted conditions, especially focusing on digeneans of medical or economic importance. The effect of pollutants to the transmission of larval digeneans (miracidia, cercariae, metacercariae) and snail-digenean interactions is therefore considered. An overview and interpretation of the published literature on laboratory and field studies is provided. It is apparent from these studies that the influence of pollutants on digenean transmission is highly complex with much of the observed effects in the laboratory often masked by a complexity of other factors in the field. Future studies would benefit from a standardisation of experimental procedures, increasing the number of combined laboratory and field studies, and increasing the complexity of the experiments undertaken.
Collapse
Affiliation(s)
- N J Morley
- School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, UK.
| | | | | |
Collapse
|
4
|
Abstract
Tenebrio molitor is an intermediate host for the rat tapeworm, Hymenolepis diminuta. Parasite oncospheres hatch in the beetle midgut and burrow through into the haemocoel, where they rapidly grow and mature into metacestodes. Repair of damage incurred during invasion and the nutritional demands of the parasites are likely to impose costs on the host. Despite these costs, there is an overall very highly significant difference in survival time (p < 0.001) between infected and control populations of beetles, with a hazard ratio of 2.35 (control versus infected). Infected females showed a 40% increase in survival time to 50% mortality and males showed a 25% increase in survival time to 50% mortality. This parasite-induced increase in host longevity is discussed in the light of changes in resource allocation that may occur in infected beetles. Previous findings have demonstrated that reproductive success is significantly reduced in infected females. The outcome of changes in the reproductive effort made by male beetles is less clear. We suggest that the optimum trade-off between reproduction and longevity may be altered to favour longer host survivorship, which is likely to enhance parasite transmission.
Collapse
Affiliation(s)
- H Hurd
- Centre for Applied Entomology and Parasitology, School of Life Sciences, Keele University, Keele, Staffordshire ST5 5BG, UK.
| | | | | |
Collapse
|
5
|
Webb TJ, Hurd H. Direct manipulation of insect reproduction by agents of parasite origin. Proc Biol Sci 1999. [DOI: 10.1098/rspb.1999.0812] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- T. J. Webb
- Centre for Applied Entomology and Parasitology, School of Biological Sciences, Keele University, Keele, Staffordshire ST5 5BG, UK
| | - H. Hurd
- Centre for Applied Entomology and Parasitology, School of Biological Sciences, Keele University, Keele, Staffordshire ST5 5BG, UK
| |
Collapse
|
6
|
Abstract
Host fertility is often curtailed as a result of parasitic infection. The hypothesis that this may confer an adaptive advantage upon the symbionts if nutrients are directed from reproduction and made available for host/parasite maintenance is explored. The suggestion is made that an understanding of the mechanisms underlying the pathophysiology of fecundity reduction may shed light upon the evolutionary implications of this strategy for both parasite and host. To illustrate this the down-regulation of egg production is explored with reference to a particular model system, the association between metacestodes of the rat tapeworm, Hymenolepis diminuta and the mealworm beetle, Tenebrio molitor. Several aspects of host reproductive behavior and physiology are affected by infection in this association, including vitellogenesis. Metacestodes directly inhibit the fat body synthesis of vitellogenin in a stage-specific, density-dependent manner. This inhibition is likely to be orchestrated by a modulator molecule, produced by the parasite. In the ovarian follicles, juvenile hormone III binding to a specific follicular membrane-binding protein is inhibited in infected beetles, resulting in the down-regulation of a cascade of events which enables vitellogenin to pass into the developing oocyte. Data to support the proposed existence of a parasite-induced antigonadotrophin, of host origin, are discussed. Evidence that similar mechanisms operate in Plasmodium-infected anopheline mosquitoes and Onchocerca-infected blackflies is presented in support of the possibility that a parasite-induced reduction in host reproductive fitness is an adaptive strategy and an assessment of who is manipulating whom is made.
Collapse
Affiliation(s)
- H Hurd
- Department of Biological Sciences, Keele University, Staffordshire, UK
| |
Collapse
|
7
|
Nishina M, Matsushita K, Kato K, Takahashi M, Kono Y. Characterization of tissue water in Tribolium confusum parasitized by metacestodes of Hymenolepis diminuta. J Invertebr Pathol 1998; 72:93-5. [PMID: 9647708 DOI: 10.1006/jipa.1998.4766] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- M Nishina
- Department of Medical Zoology, Saitama Medical School, 38 Morohongo Moroyama, Iruma-gun, Saitama, 350-04, Japan
| | | | | | | | | |
Collapse
|
8
|
Izvekova GI, Kuperman BI, Kuz'mina VV. Digestion and digestive-transport surfaces in cestodes and their fish hosts. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. PART A, PHYSIOLOGY 1997; 118:1165-71. [PMID: 9505426 DOI: 10.1016/s0300-9629(97)00040-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The structural and functional organization of digestive-transport surfaces in some lower cestodes and their fish hosts was studied. It has been shown that the ultrastructure of cestode microtriches and fish enterocyte microvilli being the basis of membrane-linked digestion is quite similar. These organelles increase the digestive-transport surfaces both in helminths and fishes. However, the hydrolytic enzyme activity in helminths is usually 2-4 times lower than that of the fishes. Desorption (adsorption) characteristics of various hydrolases in helminths and fishes are also different. In helminths the easily desorbed fraction of each enzyme is always more abundant than in fishes. In contrast, the intensity of transport processes in helminths is higher when compared with fishes. The adaptation of digestive-transport surfaces and enzyme systems to feeding conditions is discussed.
Collapse
Affiliation(s)
- G I Izvekova
- Laboratory of Ecological Parasitology, I.D. Papanin Institute of Biology of Inland Waters, Russian Academy of Sciences, Borok, Yaroslavl Prov., Russia
| | | | | |
Collapse
|
9
|
Kearns JY, Hurd H, Pullin AS. Effect of metacestodes of Hymenolepis diminuta on storage and circulating carbohydrates in the intermediate host, Tenebrio molitor. Parasitology 1994; 108 ( Pt 4):473-8. [PMID: 8008461 DOI: 10.1017/s0031182000076034] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The metamorphosis of oncospheres of the rat tapeworm, Hymenolepis diminuta, to mature metacestodes induces several pathophysiological effects in the intermediate host, Tenebrio molitor (Coleoptera). Previous investigations have failed to elucidate the mechanism responsible for changes in the host reproductive physiology and behaviour. This work forms part of an assessment of the degree to which nutrient resource management may be involved in these interactions. We report that developing metacestodes exert a pronounced effect upon host carbohydrate reserves and also alter circulating carbohydrate titres at some stages post-infection. Biochemical studies of fat body glycogen demonstrated a significant depletion of reserves as early as 3 days post-infection in males and 5 days post-infection in females. Gas chromatography revealed trehalose to be the predominant haemolymph carbohydrate, titres being significantly elevated in male beetles 5 and 9 days post-infection and in females 12 days post-infection. Metacestodes had no effect on glucose concentrations in male or female beetles.
Collapse
Affiliation(s)
- J Y Kearns
- Department of Biological Sciences, Keele University, Staffordshire, UK
| | | | | |
Collapse
|
10
|
Rosen R, San ML, Denton ME, Wolfe JM, Uglem GL. The rapid development of the glucose transport system in the excysted metacestode of Hymenolepis diminuta. Parasitology 1994; 108 ( Pt 2):217-22. [PMID: 8159466 DOI: 10.1017/s0031182000068311] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Temporal changes in glucose transport capacity in excysted scoleces of Hymenolepis diminuta were examined. Assays involved incubation for 1 min in [3H]glucose after pre-incubation for 1 min to 8 h in saline. There were two abrupt increases in uptake velocity, a relatively small one between 15 and 75 min, and a large one between 5 and 6 h, during which the Vmax increased from 0.36 to 2.49 nmol/25 larvae/h. The second increase was unaffected when the pre-incubation saline contained 5 mM glucose, but it was completely blocked when the excysted larvae were pre-incubated in Ca(2+)-free saline. Abrupt glucose transport changes did not occur in intact cysticercoids or in scoleces when the substrate was [3H]leucine or [3H]uracil. Arrhenius plots (log V versus 1/temperature, 10-42 degrees C) were linear for intact cysticercoids, but were biphasic for both scoleces and adults with discontinuities at 20 +/- 1 degrees C. Thus, 'activation' of the excysted scolex seemed to involve a specific, Ca(2+)-dependent increase in number of glucose transporters functioning in the worm surface. The Arrhenius plots indicated that development in the final host does not involve a major change in lipid composition of the parasite's membranes.
Collapse
Affiliation(s)
- R Rosen
- Department of Biology, Berea College, Kentucky 40404
| | | | | | | | | |
Collapse
|
11
|
Wastling JM, Chappell LH. Cyclosporin A: drug treatment in vivo affects the kinetics of [14C]glucose transport in Hymenolepis microstoma in vitro. Parasitology 1994; 108 ( Pt 2):223-8. [PMID: 8159467 DOI: 10.1017/s0031182000068323] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The transport of [14C]glucose by Hymenolepis microstoma in vitro following in vivo treatment with cyclosporin A (CsA) was determined over a range of concentrations. For untreated (control) worms glucose uptake showed saturation kinetics with a small diffusion component. Estimates of the maximum velocity of glucose uptake (Vmax) and the affinity of substrate for the glucose transporter (Kt) revealed that untreated 8-day-old worms had a Vmax twice that of 15-day-old worms and that younger worms had a lower Kt. An inverse relationship was demonstrated between log10 worm weight and the rate of uptake of [14C]glucose, reflecting the relatively greater number of glucose transporters due to the larger surface area:volume ratio of smaller worms. Treatment of H. microstoma with CsA in vivo significantly increased the diffusion component of glucose uptake in vitro. Parasites from drug-treated mice had a significantly lower Vmax for glucose uptake than size-matched controls. The affinity of glucose for its transporter in CsA-treated worms (Kt) was not significantly different from size-matched controls. Both juvenile and adult worms underwent transient depletion in total glycogen content after CsA treatment in vivo. The data confirm that CsA treatment in vivo disrupts the functional integrity of the worm tegument, one facet of which is impaired acquisition of glucose.
Collapse
Affiliation(s)
- J M Wastling
- Department of Zoology, University of Aberdeen, Scotland
| | | |
Collapse
|
12
|
Leducq R, Gabrion C. Developmental changes of Echinococcus multilocularis metacestodes revealed by tegumental ultrastructure and lectin-binding sites. Parasitology 1992; 104 Pt 1:129-41. [PMID: 1614730 DOI: 10.1017/s003118200006087x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Ultrastructural investigations (SEM, TEM) combined with lectin-binding analysis, have revealed concurrent modifications in tegumentary structure and surface glycoconjugates during the establishment and differentiation of Echinococcus multilocularis metacestodes in jirds. The laminated layer, which is amorphous and rich in polysaccharides when initially secreted by the young cyst, takes on a different appearance and has a different glycoconjugate composition according to whether the cyst becomes fertile or sterile. The laminated layer of fertile cysts transforms into a microfibrillar matrix, the protein content of which may increase while sugar content decreases during protoscolex differentiation. Independently of this structure, brood capsules, from which arise protoscoleces, are formed by invagination of the cyst tegument. The intense secretion of glycoconjugates from the brood capsule wall during invagination may serve to interact with host factors passing through the laminated layer. The combined use of ultrastructural study and lectin labelling has allowed the demonstration of an ultrastructural and biochemical gradient of differentiation of the protoscolex. Seven stages of differentiation have been described. The possibility that the excreted-secreted tegumentary glycoconjugates, revealed by lectin labelling during protoscolex differentiation, might be the gradual biochemical expression of one or several stimuli implicated in the phenomenon of protoscolex maturation, is discussed.
Collapse
Affiliation(s)
- R Leducq
- Laboratoire de Parasitologie Comparée, U.S.T.L. Montpellier II, France
| | | |
Collapse
|
13
|
Abstract
The uptake of glucose by Acanthocheilonema viteae was studied in vitro. The process was selective for the D-isomer and saturatable with a Km of 2 mM. The rate of glucose transport/utilization was inhibited by 2-deoxyglucose, mannose, 5-thioglucose and dipyridamole but, unlike mammalian systems, was not impaired by cytochalasin B, phloretin, phloridzin, 3-O-methylglucose and 4,6-ethylideneglucose. A potential chemotherapeutic advantage of selectively inhibiting filarial glucose transport exists for the following reasons. (1) The glucose transporter present in A. viteae was shown to be different from the one present in some mammalian systems. (2) Incubation under glucose-free conditions led to glycogen depletion, loss of motility and worm death. (3) Worms maintained in vitro for more than 18 h without glucose did not survive when implanted into gerbils.
Collapse
Affiliation(s)
- D J Hayes
- Wellcome Research Laboratories, Beckenham, Kent
| | | |
Collapse
|
14
|
Hurd H. Physiological and behavioural interactions between parasites and invertebrate hosts. ADVANCES IN PARASITOLOGY 1990; 29:271-318. [PMID: 2181829 DOI: 10.1016/s0065-308x(08)60108-6] [Citation(s) in RCA: 78] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- H Hurd
- Parasitology Research Laboratory, University of Keele, Staffordshire, UK
| |
Collapse
|