Chemical communication in helminths

Influence of Asafoetida Extract on the Virulence of the Entomopathogenic Nematode Steinernema carpocapsae and Its Symbiotic Bacterium Xenorhabdus nematophila in the Host Pyrrhocoris apterus

Nematode-microbe symbiosis plays a key role in determining pathogenesis against pests. The modulation of symbiotic bacteria may affect the virulence of entomopathogenic nematodes (EPNs) and the biological management of pests. We tested the influence of asafoetida (ASF) extract on the virulence of Steinernema carpocapsae and its symbiotic bacterium, Xenorhabdus nematophila, in Pyrrhocoris apterus. A total of 100 mg of ASF killed 30% of EPNs in 48 h, while P. apterus remained unaffected. The EPNs pre-treated with 100 mg of ASF influenced P. apterus's mortality by 24-91.4% during a period of 24 to 72 h. The topical application of ASF acted as a deterrent to S. carpocapsae, lowering host invasion to 70% and delaying infectivity with 30% mortality for 168 h. Interestingly, Steinernema's symbiotic bacterium, Xenorhabdus, remained unaffected by ASF. An in vitro turbidity test containing 100 mg of ASF in a medium increased the growth rate of Xenorhabdus compared to a control. A disc diffusion assay confirmed the non-susceptibility of Xenorhabdus to ASF compared to a positive control, streptomycin. Pro-phenol oxidase (PPO) and phenol oxidase (PO) upregulation showed that ASF influences immunity, while EPN/ASF showed a combined immunomodulatory effect in P. apterus. We report that ASF modulated the virulence of S. carpocapsae but not that of its symbiotic bacterium, X. nematophila, against P. apterus.

Intra- and interspecific pairing of rediae and sporocysts of five species of digenetic trematodes

In vitro pairing studies on rediae of Echinostoma trivolvis, E. caproni, Zygocotyle lunata, Ribeiroia sp. and sporocysts from a species of armatae cercaria were undertaken at 22°C in a Petri dish bioassay containing an agar substratum and a Locke's 1:1 overlay. Pairing was arbitrarily defined as larvae in contact or within 1 mm of each other. Intraspecific and interspecific pairing occurred in the bioassay using several larval combinations initially placed 5 or 10 mm apart. Intraspecific pairing occurred with the rediae of Ribeiroia sp. and interspecific pairing was seen between E. trivolvis or E. caproni and Ribeiroia sp. A previous study documented intraspecific and interspecific pairing between rediae of E. trivolvis and E. caproni. Armatae sporocysts did not pair intraspecifically or interspecifically when matched with either E. caproni or E. trivolvis rediae. Intraspecific pairing of Z. lunata or interspecific pairing between Z. lunata rediae and echinostome rediae did not occur. The significance of redial pairing remains unclear.

Angiostrongylus costaricensis: complete redescription of the migratory pathways based on experimental Sigmodon hispidus infection

Angiostrongylus costaricensis lives in the cecal and mesenteric arteries of its vertebrate hosts, and causes an inflammatory disease in humans. To investigate unknown aspects of the abdominal angiostrogyliasis pathogenesis, infected Sigmodon hispidus were sequentially studied in different times of infection. The study revealed that L3 goes alternatively through two migratory courses during its development into an adult worm: lymphatic/venous-arterial and venous portal pathways. The former is considered the principal one, because it is used by most of the larvae. Like other metastrongylides, A. costaricensis passes over the pulmonary circulation to migrate from the lymphatic system to the arterial circulation, where they circulate during some days before reaching their definitive habitat. The oviposition by mature females began on 15th day. Eggs and L1 were detected mainly in the intestine and stomach, surrounded by inflammatory reaction constituted by macrophages, monocytes, and eosinophils. They were also spread to the lungs, mesenteric lymph nodes, pancreas, spleen, and kidneys. The larvae (L1) exhibited the centripetal capacity to invade the lymphatic and venous vessels of the intestine and mesentery. Adult worms that developed in the venous intrahepatic pathway migrated downstream to reach the mesenteric veins and laid eggs that embolized in the portal hepatic vessels.

Schistosoma mansonimale–female interactions

Schistosome parasites are muticellular eucaryotic organisms with a complex life cycle that involves mammalian and snail hosts. Unlike other trematode parasites, schistosomes (along with the Didymozoidae) have evolved separate sexes or dioecy. Sex is determined by a chromosomal mechanism. The dioecious state created an opportunity for the sexes to play a role in schistosome evolution that has resulted in an interesting interplay between the sexes. The classical observation, made more than 50 years ago, is that female schistosomes do not develop unless a male worm is present. Studies up through the 1990s focused on dissecting the role of the sexes in mate attraction, mate choice, mating behavior, female growth, female reproductive development, egg production, and other sex-evolved functions. In the mid-1980s, studies began to address the molecular events of male–female interactions. The classic morphological observation that female schistosomes do not complete reproductive development unless a male worm is present has been redefined in molecular terms. The male by an unknown mechanism transduces a signal that regulates female gene expression in a stage-, tissue-, and temporal-specific manner. A number of female-specific genes have been identified, along with signaling pathways and nuclear receptors, that play a role in female reproductive development. In addition, a number of host factors such as cytokines have also been demonstrated to affect adult male and female development and egg production. This review focuses on the biological interactions of the male and female schistosome and the role of parasite and host factors in these interactions as they contribute to the life cycle of Schistosoma mansoni.

Evidence of a mate-finding cue in the hermaphrodite nematode Caenorhabditis elegans

When males of the roundworm Caenorhabditis elegans come into association with their hermaphroditic counterparts they cease foraging behavior and begin to mate. Here we detail several assays used to demonstrate that a diffusible cue is correlated with this process. This cue is sexually dimorphic, given off only by the hermaphrodite and eliciting a response only in the male. Males are attracted to, reverse direction of movement frequently, and remain in regions of agar conditioned with hermaphrodites. From our studies we suggest a form of kinesis that works by attracting males to their mating partners from a distance and functions, once males arrive, in holding attracted males in close proximity. The hermaphrodite vulva is not required for the cue. Males from general sensory mutants osm-5 and osm-6 fail to respond to the cue, whereas male-specific mutants lov-1 and pkd-2 respond. Finally, that males from multiple isolates of C. elegans also respond similarly to this cue indicates that this cue is robust and has been maintained during recent evolution.

Chemical communication and mate attraction in echinostomes

Mate attraction is widespread among animals and appears to facilitate mating and to prevent hybridisation between closely related species. In this study we investigated mate preference between two geographical isolates of Echinostoma caproni (Trematoda, Platyhelminth) and another species of the genus Echinostoma E. sp. Because previous experiments showed a partial reproductive isolation between echinostome isolates, we examined the possibility that such isolation resulted from differential mate attraction. We compared intra-isolate, inter-isolate and interspecific pairings using two in vitro experimental designs. In the first experiment we compared mate attraction of two individuals belonging to or not belonging to the same isolate, while in the second experiment we examined mate choice when individuals were in the presence of individuals from both the same isolate and from a different isolate or a different species. Distances between worms were measured over a period of 90 min. Results from both experiments suggested that mate attraction was similar for intra-isolate, inter-isolate or interspecific combinations. This lack of mate preference in vitro would therefore support an alternative hypothesis of a reproductive isolation through sperm selection.

Physico-chemical properties of the female sex pheromone of Heterodera schachtii (Nematoda: Heteroderidae)

Several physico-chemical properties of the female sex pheromone of the beet cyst nematode Heterodera schachtii were elucidated. At least one component of the pheromone can be extracted from aqueous solutions with diethyl ether. However, the pheromone has a higher solubility in water, as most of the pheromone activity remained in the water fraction. Ion exchange chromatography revealed that the pheromone or at least one of its components is positively charged, whereas another pheromone component may be negatively charged. Fractional distillation of pheromone extracts showed that it is, indeed, composed of at least two components. These components may interact additively rather than synergistically.

Schistosoma mansoni: females enhance [14C]-tyrosine incorporation in males maintained in vitro

Incorporation of radiolabelled tyrosine was examined in males of Schistosoma mansoni maintained in vitro. Adult worms were recovered from mice and only those that were paired were used. Males and females were separated and placed in 4 degrees C RPMI 1640 containing 10% fetal calf serum (FCS). Individual males were incubated for 1 h either alone or with a female. Other males were incubated in a medium containing 40 ng ml-1 recombinant tumour necrosis factor alpha (rTNF alpha). Subsequently, males were incubated with or without females for 1 h in a medium containing 20 muCi ml-1 [14C]-tyrosine. All incubations were carried out in RPMI 1640 containing 10% FCS at 37 degrees C under 5% CO2. Untreated single males incorporated small amounts of labelled tyrosine. Pretreatment of single males with rTNF alpha did not affect their tyrosine incorporation (P = 0.693). However, males maintained in vitro with females incorporated 221% more tyrosine than the controls (P = 0.00008), suggesting that a chemical stimulus from the female affects tyrosine incorporation in males.

Schistosoma mansoni: effect of recombinant tumor necrosis factor alpha on fecundity and [14C]-tyrosine uptake in females maintained in vitro

It has been reported that recombinant tumor necrosis factor alpha (rTNF alpha) stimulates egg-laying in Schistosoma mansoni females. Because tyrosine requirement is increased in female undergoing sexual maturation in preparation for oogenesis and tyrosine is a major component of eggshell protein, we wanted to determine whether females treated with rTNF alpha would also incorporate more tyrosine. Adult females were first treated with 10, 20 or 40 ng/ml rTNF alpha for 1, 3 or 6 hr in RPMI 1640 containing 10% fetal calf serum (FCS). Another two groups of females were each exposed either to males or to male excretory-secretory (ES) products for 1 hr. They were then exposed to 20 microCi/ml-1 [14C]-tyrosine for 1 hr in RPMI 1640 containing 10% FCS. All females were incubated individually unless indicated otherwise. Females incorporated more tyrosine after exposure to males or their ES products. They incorporated significantly more tyrosine when treated with rTNF alpha for 1 hr; the increased uptake correlated with increasing amounts of rTNF alpha used. Although after a 3-hr treatment with 10 ng/ml rTNF alpha females incorporated slightly more tyrosine than controls, increasing amounts of rTNF alpha had an adverse effect. Females treated with rTNF alpha for 6 hr incorporated less tyrosine than controls and those treated for 1 hr. SDS-PAGE and fluorography did not reveal any differences in polypeptide profiles of untreated and rTNF alpha-treated females. These unexpected results led us to study the effect of rTNF alpha on fecundity in females. Contrary to the published report, we observed a sharp decline in egg-laying in females when exposed to increasing concentrations of rTNF alpha in vitro.

Chemoreception in plant parasitic nematodes

The role and functioning of the anterior chemosensory organs of plant parasitic nematodes is examined, with particular emphasis on the amphids. The morphology of the amphids is discussed primarily in the context of the changes in the ultrastructure associated with different life stages. The involvement of amphidial secretions in chemoreception and the behavioral and electrophysiological analyses of nematode responses to semiochemicals are discussed with special reference to research on sex pheromones. These research techniques, combined with the use of lectins and antibodies, provide information on nematode sensilla that may lead to novel control strategies for economically important plant parasitic nematodes based on perturbing nematode sensory perception to prevent host or mate location.

Infectivity, growth, distribution and fecundity of a six versus twenty-five metacercarial cyst inoculum of Echinostoma caproni in ICR mice

Female ICR mice, 6-8 weeks old, were exposed to 6 (group A) or 25 (group B) metacercarial cysts/host of Echinostoma caproni to determine the effects of these cyst dosages on infectivity, growth, distribution and fecundity of worms in the small intestines. All 30 mice exposed (15 in group A and 15 in group B) were infected and there was no significant difference in the percentage of worm recovery between group A and B at 2, 4 and 8 weeks postinfection (PI). Growth was rapid in both groups with worm body areas increasing from about 3mm2 at 2 weeks PI to about 7 mm2 at 8 weeks PI. More worms from group B were in the anterior sections of the small intestines at 2 and 4 weeks PI than those from group A. However, at 8 weeks PI more worms from Group A were in the anterior sections of the small intestines than those from group B. There were marked differences in our findings on infectivity, growth and distribution of E. caproni in ICR mice using 6 and 25 cyst inocula compared to a previous study using the same echinostome and cyst inocula in NMRI mice, presumably related to the mouse strain. Fecundity studies were somewhat comparable in both studies showing an approximate three to four times increase in the average number of eggs/gram of faeces in mice receiving 25 versus 6 cyst inocula.

Optimal habitat selection by helminths within the host environment

Helminth parasites of vertebrates usually select very specific regions or habitats in their hosts, and this is often preceded by a tortuous migration through various host organs. However, the proximate mechanisms of migration and habitat selection have remained enigmatic despite considerable effort by parasitologists. In this paper a new approach to studying helminth behaviour in the host is proposed. The core idea is that behaviour strategies must be considered from the perspective of the parasites and their perceptions of their environment. A guiding principle is that the environmental features to which an animal responds, and the actions which are required for responding to the environment, form a fundamental unit of behaviour. Thus, we can deduce an animal's behavioural strategy from the details of its response to environmental signals and from its sensory capabilities. The evidence presented suggests that helminth behaviours in the host often occur as fixed (or modal) action patterns which are usually seen in response to constant, or predictable environmental features. Thus, a working hypothesis is that the mechanisms of physiological and biochemical homeostasis within the host provide an extremely predictable environment for the parasite. Under these conditions, a parasite needs to perceive only small subsets of the total information available from the environment to respond appropriately. Studies on sensory and nervous systems of these organisms are critical to understanding parasite perception, but there are formidable technical obstacles that prevent easy access to parasite nervous systems. Therefore, a multidisciplinary approach, using ideas from parasitology, ecology, evolutionary biology and neuroethology, is considered requisite for reconstructing the parasites' behaviour strategies. It is suggested that future directions should pursue integration of studies on sensory physiology with the behavioural ecology of these organisms.

The ecology of host-finding behaviour and parasite transmission: past and future perspectives

Host location by parasites can be achieved by either active or passive mechanisms. In spite of their significance, the efficacy of these methods has been little researched. High fecundity in parasites is discussed in terms of the role it plays in dispersal and transmission. Some concepts developed by mainstream behavioural ecologists are outlined and their relevance to parasitology is indicated. 'Reproductive value' is recommended as an appropriate measure of the costs and benefits of behavioural cts. Although costs of reproduction have been rarely studied in parasites, they are likely to occur in cosexual insects, nematodes and crustaceans. Experiments using captive hosts and/or in vitro cultivation could help in the construction of realistic optimality models. We suggest that r- and K-selection theory could assist in the study of the evolution of parasite behaviour. We discuss how parasite populations are dispersed and controlled and consider the implications of overdispersion. We outline three sources of signals to which parasites may respond and suggest that understanding evolutionary mechanisms and community organisation of parasites and hosts requires evaluation of fundamental behavioural responses to environmental signals. The study of closely related groups of parasites and their hosts may advance our knowledge of the evolution of parasite life cycles and the evolutionary costs and benefits of behavioural acts.

Schistosoma mansoni: a chemoattractive factor released by males and its receptor in females

Chemoattraction between developing (23- to 28-day-old) and adult (10- to 12-week-old) Schistosoma mansoni males and females has been described previously. We report here on in vitro attraction of mature worms to released products of worms of the opposite sex. In the absence of a stimulus worms migrated randomly and did not show any preference in their orientation. Males were not significantly attracted to released products of females. Females exhibited greatest attraction to released products of males, and some attraction to the lipid fraction of released products of males. The aqueous fraction of male-released products slightly repelled females. Prior exposure to released products of males rendered females unresponsive to subsequent exposure, suggesting receptor saturation. These findings have important potential implications for the control of schistosomiasis by intercepting attraction and mating between males and females.

Schistosoma japonicum: changes in lipase activity in adults maintained in vitro

Schistosoma japonicum (Chinese strain) adult worm pairs (10-12 weeks old) were fixed in 4 degrees C absolute acetone or neutral buffered formalin either immediately after recovery from mice, or following incubation for 0.5 or 1.0 h. Males and females were incubated individually in Earle's balanced salt solution at 37 degrees C. Lipase activity was determined in frozen sections by Gomori's method using Tween 80 as substrate. In unincubated males, lipase activity was localized only in the parenchyma; in females it was present in the vitellaria and parenchyma subjacent to the tegument. After 0.5 h incubation, males showed less lipase activity in the parenchyma than unincubated males, and females showed increased activity in the parenchyma subjacent to the tegument, but not in the vitellaria. Following 1.0 h incubation, males showed less lipase activity than previously, and females showed a marked increase in activity, particularly in the parenchyma subjacent to the tegument.

Thin-layer and liquid column chromatographic analyses of the lipids of adult Onchocerca gibsoni

Lipids were extracted from adult Onchocerca gibsoni with chloroform/methanol and the total lipid content was characterized. Glycolipids were isolated from other lipid classes by Florisil column chromatography and were then fractionated by DEAE-Sephadex ion-exchange chromatography. HPTLC revealed the presence of 9 neutral glycolipid bands and of 15 acidic glycolipid bands that stained for sialic acid with resorcinol. Lipids that contained no carbohydrates were analyzed by a combination of TLC and amino column chromatography. Triacylglycerols, cholesterol, cholesterol esters, and free fatty acids were found to be major components of the neutral lipid fraction, and diacylglycerols and monoacylglycerols were minor components. Phosphatidylethanolamine and phosphatidylcholine were the predominant phospholipids. Phosphatidylserine, phosphatidylinositol, sphingomyelin, lysophosphatidylcholine, and lysophosphatidylethanolamine were also present in significant amounts, whereas only traces of cardiolipin and phosphatidic acid were detected. Several minor lipids and phospholipids remained unidentified. These results indicate that adult O. gibsoni have a nonglycosylated lipid composition resembling that of other parasitic nematodes as well as a substantial repertoire of glycolipids, including many with the characteristics of gangliosides.

Evidence that a 16-kilodalton integral membrane protein antigen from Schistosoma japonicum adult worms is a type A2 phospholipase

Type A2 phospholipase (PLA2) activity has been observed in integral membrane protein extracts of Schistosoma japonicum. Antiserum raised against bee venom PLA2 recognized a single 16-kDa band in the parasite extracts; it also localized to antigen in the gut lining of fixed adult schistosomes as shown by immunofluorescence techniques. Evidence was obtained that the molecule was expressed at low levels in comparison with other integral membrane proteins and was weakly immunogenic in rabbits. Two oligonucleotide probes were constructed on the basis of highly conserved regions between the nucleotide sequences of rat, bovine, rattlesnake, and bee venom PLA2; these probes were used to isolate S. japonicum genomic DNA phage clones. A 1.8-kb FnuD2 fragment was shown by Southern blot analysis to strongly hybridize with the 5' 32P-labeled PLA2 oligonucleotides in both S. japonicum genomic DNA and DNA from one of the phage clones. The nucleotide and predicted amino acid sequences of this fragment revealed homology with the C terminus of PLA2s from different species.

Single- and five-worm infections of Echinostoma caproni (Trematoda) in the ICR mouse

Twenty-nine (64%) of 44 ICR mice fed a single metacercarial cyst of Echinostoma caproni and all of 23 mice each fed five cysts were infected with ovigerous worms at necropsy 2-4 weeks post-infection. Each host fed five cysts had two to five worms at necropsy, and all worms were either paired or clustered. Distribution of worms in the small intestine was similar in single- and five-worm infections and all worms were located 17-20 cm anterior to the ileo-cecal valve. Both single and multiple worms produced eggs with fully-developed miracidia. The number of eggs per uterus in 2-week-old multiple worms was almost twice that of single worms. The body area of 3- and 4-week-old multiple worms was significantly greater than that of single worms of the same age.