Surface carbohydrate changes on Onchocerca lienalis larvae as they develop from microfilariae to the infective third-stage in Simulium ornatum

The Functional Parasitic Worm Secretome: Mapping the Place of Onchocerca volvulus Excretory Secretory Products

Nematodes constitute a very successful phylum, especially in terms of parasitism. Inside their mammalian hosts, parasitic nematodes mainly dwell in the digestive tract (geohelminths) or in the vascular system (filariae). One of their main characteristics is their long sojourn inside the body where they are accessible to the immune system. Several strategies are used by parasites in order to counteract the immune attacks. One of them is the expression of molecules interfering with the function of the immune system. Excretory-secretory products (ESPs) pertain to this category. This is, however, not their only biological function, as they seem also involved in other mechanisms such as pathogenicity or parasitic cycle (molting, for example). We will mainly focus on filariae ESPs with an emphasis on data available regarding Onchocerca volvulus, but we will also refer to a few relevant/illustrative examples related to other worm categories when necessary (geohelminth nematodes, trematodes or cestodes). We first present Onchocerca volvulus, mainly focusing on the aspects of this organism that seem relevant when it comes to ESPs: life cycle, manifestations of the sickness, immunosuppression, diagnosis and treatment. We then elaborate on the function and use of ESPs in these aspects.

Use of microarray hybridization to identify Brugia genes involved in mosquito infectivity

Brugia malayi and Brugia pahangi microfilariae (mf) require a maturation period of at least 5 days in the mammalian host to successfully infect laboratory mosquitoes. This maturation process coincides with changes in the surface composition of mf that likely are associated with changes in gene expression. To test this hypothesis, we verified the differential infectivity of immature (< or =3 day) and mature (>30 day) Brugia mf for black-eyed Liverpool strain of Aedes aegypti and then assessed transcriptome changes associated with microfilarial maturation by competitively hybridizing microfilarial cDNAs to the B. malayi oligonucleotide microarray. We identified transcripts differentially abundant in immature (94 in B. pahangi and 29 in B. malayi) and mature (64 in B. pahangi and 14 in B. malayi) mf. In each case, >40% of Brugia transcripts shared no similarity to known genes or were similar to genes with unknown function; the remaining transcripts were categorized by putative function based on sequence similarity to known genes/proteins. Microfilarial maturation was not associated with demonstrable changes in the abundance of transmembrane or secreted proteins; however, immature mf expressed more transcripts associated with immune modulation, neurotransmission, transcription, and cellular cytoskeleton elements, while mature mf displayed increased transcripts potentially encoding hypodermal/muscle and surface molecules, e.g., cuticular collagens and sheath components. The results of the homologous B. malayi microarray hybridization were validated by quantitative reverse transcriptase polymerase chain reaction. These findings preliminarily lend support to the underlying hypothesis that changes in microfilarial gene expression drive maturation-associated changes that influence the parasite to develop in compatible vectors.

Introduction to neuropeptides: perspectives for the parasitologist

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.

Surface carbohydrate composition of a tapeworm in its consecutive intermediate hosts: Individual variation and fitness consequences

Carbohydrates on parasite surfaces have been shown to play an important role in host-parasite coevolution, mediating host non-self recognition and parasite camouflage. Parasites that switch hosts can change their surface molecules to remain undetected by the diverse immune systems of their different hosts. However, the question of individual variation in surface sugar composition and its relation to infectivity, virulence, immune evasion and growth of a parasite in its different hosts is as yet largely unexplored. We studied such fitness consequences of variation in surface sugars in a sympatric host-parasite system consisting of the cestode Schistocephalus solidus and its intermediate hosts, a copepod and the three-spined stickleback. Using lectins to analyse the sugar composition, we show that the tapeworm changes its surface according to the invertebrate or vertebrate host. Importantly, sugar composition seems to be genetically variable, as shown by differences among tapeworm sibships. These differences are related to variation in parasite fitness in its second intermediate host, i.e. infectivity and growth. Surface sugar composition may thus be a proximate correlate of the evolutionarily relevant variability in infectivity and virulence of parasites in different hosts.

Lectin-parasite interactions

Lectins are proteins that bind specifically to carbohydrate residues and are widely distributed in Nature. All parasites have such residues which vary in their configurations. Here, Jake Jacobson and Ron Doyle review the application of lectins in defining the developmental stages of parasites and the characterization, localization and structural composition of parasite glycoconjugates. The lectins of some parasites and lectin-mediated host-parasite interaction are also discussed.

Mechanisms of resistance to Onchocerca infection in blackflies

In this article Peter Ham, Hans Hagen, Andrea Baxter and Jorg Grunewald focus on the susceptibility of blackflies to parasitic filarial infection (particularly Onchocera spp, most of the vectors of which belong to the genus Simulium). They outline what is known about, as well as speculating on, the various defence mechanisms of these insects. Investigations have involved the use of natural and surrogate vectors of bovine onchocerciasis as models for the human vector-parasite relationship.

Developmental changes of Echinococcus multilocularis metacestodes revealed by tegumental ultrastructure and lectin-binding sites

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.