Host-parasite hormonal relationships: a common theme?

Elucidating the molecular and developmental biology of parasitic nematodes: Moving to a multiomics paradigm

In the past two decades, significant progress has been made in the sequencing, assembly, annotation and analyses of genomes and transcriptomes of parasitic worms of socioeconomic importance. This progress has somewhat improved our knowledge and understanding of these pathogens at the molecular level. However, compared with the free-living nematode Caenorhabditis elegans, the areas of functional genomics, transcriptomics, proteomics and metabolomics of parasitic nematodes are still in their infancy, and there are major gaps in our knowledge and understanding of the molecular biology of parasitic nematodes. The information on signalling molecules, molecular pathways and microRNAs (miRNAs) that are known to be involved in developmental processes in C. elegans and the availability of some molecular resources (draft genomes, transcriptomes and some proteomes) for selected parasitic nematodes provide a basis to start exploring the developmental biology of parasitic nematodes. Indeed, some studies have identified molecules and pathways that might associate with developmental processes in related, parasitic nematodes, such as Haemonchus contortus (barber's pole worm). However, detailed information is often scant and 'omics resources are limited, preventing a proper integration of 'omic data sets and comprehensive analyses. Moreover, little is known about the functional roles of pheromones, hormones, signalling pathways and post-transcriptional/post-translational regulations in the development of key parasitic nematodes throughout their entire life cycles. Although C. elegans is an excellent model to assist molecular studies of parasitic nematodes, its use is limited when it comes to explorations of processes that are specific to parasitism within host animals. A deep understanding of parasitic nematodes, such as H. contortus, requires substantially enhanced resources and the use of integrative 'omics approaches for analyses. The improved genome and well-established in vitro larval culture system for H. contortus provide unprecedented opportunities for comprehensive studies of the transcriptomes (mRNA and miRNA), proteomes (somatic, excretory/secretory and phosphorylated proteins) and lipidomes (e.g., polar and neutral lipids) of this nematode. Such resources should enable in-depth explorations of its developmental biology at a level, not previously possible. The main aims of this review are (i) to provide a background on the development of nematodes, with a particular emphasis on the molecular aspects involved in the dauer formation and exit in C. elegans; (ii) to critically appraise the current state of knowledge of the developmental biology of parasitic nematodes and identify key knowledge gaps; (iii) to cover salient aspects of H. contortus, with a focus on the recent advances in genomics, transcriptomics, proteomics and lipidomics as well as in vitro culturing systems; (iv) to review recent advances in our knowledge and understanding of the molecular and developmental biology of H. contortus using an integrative multiomics approach, and discuss the implications of this approach for detailed explorations of signalling molecules, molecular processes and pathways likely associated with nematode development, adaptation and parasitism, and for the identification of novel intervention targets against these pathogens. Clearly, the multiomics approach established recently is readily applicable to exploring a wide range of interesting and socioeconomically significant parasitic worms (including also trematodes and cestodes) at the molecular level, and to elucidate host-parasite interactions and disease processes.

Dafachronic acid promotes larval development in Haemonchus contortus by modulating dauer signalling and lipid metabolism

Here, we discovered an endogenous dafachronic acid (DA) in the socioeconomically important parasitic nematode Haemonchus contortus. We demonstrate that DA promotes larval exsheathment and development in this nematode via a relatively conserved nuclear hormone receptor (DAF-12). This stimulatory effect is dose- and time-dependent, and relates to a modulation of dauer-like signalling, and glycerolipid and glycerophospholipid metabolism, likely via a negative feedback loop. Specific chemical inhibition of DAF-9 (cytochrome P450) was shown to significantly reduce the amount of endogenous DA in H. contortus; compromise both larval exsheathment and development in vitro; and modulate lipid metabolism. Taken together, this evidence shows that DA plays a key functional role in the developmental transition from the free-living to the parasitic stage of H. contortus by modulating the dauer-like signalling pathway and lipid metabolism. Understanding the intricacies of the DA-DAF-12 system and associated networks in H. contortus and related parasitic nematodes could pave the way to new, nematode-specific treatments.

In the present study, using an integrative multi-omics approach, we show that dafachronic acid (DA) plays a critical functional role in the developmental transition in larvae of the parasitic nematode Haemonchus contortus (barber’s pole worm) by modulating the dauer-like signalling pathway and lipid metabolism. The DA-DAF-12 signalling module in H. contortus provides a paradigm to explore its developmental and reproductive biology at the molecular level, to study physiochemical cross-talk between the parasite and its hosts, and to discover novel anthelmintic targets.

Prevalence of a nematode castrator of the carrot weevil and impact on fecundity and survival

Bradynema listronoti is a parasitic nematode described from infected specimens of the carrot weevil Listronotus oregonensis. Prevalence of infection by B. listronoti under field conditions was followed over a period of 16 years in an untreated carrot field. Susceptibility of different carrot weevil life stages was evaluated as well as the impact of infection on fecundity and mortality. Gene expression in infected and uninfected carrot weevils was also compared to evaluate the impact of the parasite on the host transcriptome. Prevalence of B. listronoti in carrot weevil populations was sustained over the years ranging from 20 to 63%. All the weevil stages exposed to B. listronoti inoculum were susceptible to infection, larvae being more vulnerable (59 ± 8% infected) compared with pupae (4 ± 3% infected) and adults (7 ± 3% infected). The fecundity of infected female weevils was greatly reduced (60-fold) due to an inhibition of the maturation of the reproductive system. Transcriptomic analyses revealed that this parasitic castration may have been triggered by the inhibition of reproductive hormone production. The B. listronoti-L. oregonensis interaction represents a case of parasitic castration with a unique potential for biological control of an important pest of carrots.

Nancy E. Beckage (1950-2012): pioneer in insect host-parasite interactions

Nancy E. Beckage is widely recognized for her pioneering work in the field of insect host-parasitoid interactions beginning with endocrine influences of the tobacco hornworm, Manduca sexta, host and its parasitoid wasp Apanteles congregatus (now Cotesia congregata) on each other's development. Moreover, her studies show that the polydnavirus carried by the parasitoid wasp not only protects the parasitoid from the host's immune defenses, but also is responsible for some of the developmental effects of parasitism. Nancy was a highly regarded mentor of both undergraduate and graduate students and more widely of women students and colleagues in entomology. Her service both to her particular area and to entomology in general through participation on federal grant review panels and in the governance of the Entomological Society of America, organization of symposia at both national and international meetings, and editorship of several different journal issues and of several books is legendary. She has left behind a lasting legacy of increased understanding of multilevel endocrine and physiological interactions among insects and other organisms and a strong network of interacting scientists and colleagues in her area of entomology.

Molecular characterization of thyroid hormone receptor beta from Schistosoma japonicum and assessment of its potential as a vaccine candidate antigen against schistosomiasis in BALB/c mice

Background

Thyroid hormones (TH) modulate growth, development and differentiation and metabolic processes by interacting with thyroid hormone receptors (THRs). The purpose of this study was to identify a novel thyroid hormone receptor beta encoding gene of Schistosoma japonicum (SjTHRβ) and to investigate its potential as a vaccine candidate antigen against schistosomiasis in BALB/c mice.

Methods

The full-length cDNA sequence of SjTHRβ, its gene organization, and its transcript levels were characterized, and the phylogenetic relationship between THR, RAR and RXR from other organisms were analysis, the ability of this protein binding to a conserved DNA core motif, and its potential as a vaccine candidate antigen against schistosomiasis in BALB/c mice were evaluated.

Results

The SjTHRβ cDNA was cloned, verified by 5’ and 3’ Rapid Amplification of cDNA Ends and shown to be polyadenylated at the 3’end, suggesting the transcript is full-length. SjTHRβ is homologous to THRs from other species and has a predicted conservative DNA binding domain and ligand binding domain that normally characterizes these receptors. A comparative quantitative PCR analysis showed that SjTHRβ was the highest expressed in 21d worms and the lowest in 7 d and 13 d schistosomula. The cDNA corresponding to DNA binding domain (SjTHRβ-DBD) and ligand binding domain (SjTHRβ-LBD) were cloned and subsequently expressed in E coli. The expressed proteins were used to immunize mice and generate specific serum against recombinant SjTHRβ (rSjTHRβ). Western blotting revealed that anti-rSjTHRβ-LBD serum recognized two protein bands in extracts from 21 d worm with molecular sizes of approximately 95 kDa and 72 kDa. Electrophoretic mobility shift assay (EMSA) analysis showed that rSjTHRβ-DBD could bind to a conserved DNA core motif. Immunization of BALB/c mice with rSjTHRβ-LBD could induce partial protective efficacy(27.52% worm reduction and 29.50% liver eggs reduction)against schistosome infection. Enzyme-linked immunosorbent assay showed that mice vaccinated with recombinant SjTHRβ-LBD (rSjTHRβ-LBD) generated increased levels of specific IgG, IgG1 and IgG2a antibody. Bio-plex analysis demonstrated that rSjTHRβ-LBD induced considerably higher levels of T helper 1 cytokines (IL-2, IL-12 and TNF-α) than T helper 2 cytokines (IL-10, IL-4), suggesting that rSjTHRβ-LBD vaccination could stimulate mixed Th1/Th2 types with Th1 dominant immune responses.

Conclusions

Our study presented here identified SjTHRβ as a new schistosome THR that might play an important role in host-parasite interaction and be a vaccine candidate for schistosomiasis.

Environmental risk and toxicology of human and veterinary waste pharmaceutical exposure to wild aquatic host-parasite relationships

Pollution of the aquatic environment by human and veterinary waste pharmaceuticals is an increasing area of concern but little is known about their ecotoxicological effects on wildlife. In particular the interactions between pharmaceuticals and natural stressors of aquatic communities remains to be elucidated. A common natural stressor of freshwater and marine organisms are protozoan and metazoan parasites, which can have significant effects on host physiology and population structure, especially under the influence of many traditional kinds of toxic pollutants. However, little is known about the effects of waste pharmaceuticals to host-parasite dynamics. In order to assess the risk waste pharmaceuticals pose to aquatic wildlife it has been suggested the use of toxicological data derived from mammals during the product development of pharmaceuticals may be useful for predicting toxic effects. An additional similar source of information is the extensive clinical studies undertaken with numerous classes of drugs against parasites of human and veterinary importance. These studies may form the basis of preliminary risk assessments to aquatic populations and their interactions with parasitic diseases in pharmaceutical-exposed habitats. The present article reviews the effects of the most common classes of pharmaceutical medicines to host-parasite relationships and assesses the risk they may pose to wild aquatic organisms. In addition the effects of pharmaceutical mixtures, the importance of sewage treatment, and the risk of developing resistant strains of parasites are also assessed.

Schistosoma mansoni (Platyhelminthes, Trematoda) nuclear receptors: Sixteen new members and a novel subfamily

Nuclear receptors (NRs) are important transcriptional modulators in metazoans. Sixteen new NRs were identified in the Platyhelminth trematode, Schistosoma mansoni. Three were found to possess novel tandem DNA-binding domains that identify a new subfamily of NR. Two NRs are homologues of the thyroid hormone receptor that previously were thought to be restricted to chordates. This study brings the total number of identified NR in S. mansoni to 21. Phylogenetic and comparative genomic analyses demonstrate that S. mansoni NRs share an evolutionary lineage with that of arthropods and vertebrates. Phylogenic analysis shows that more than half of the S. mansoni nuclear receptors evolved from a second gene duplication. As the second gene duplication of NRs was thought to be specific to vertebrates, our data challenge the current theory of NR evolution.

Regulation of the immune response to cestode infection by progesterone is due to its metabolism to estradiol

The aim of this work was to investigate the role of progesterone during Taenia crassiceps cysticercosis, and the immunological mechanisms involved in its effects, by relating progesterone treatment to whole parasite counts, to host humoral and cellular immune response, to the presence or absence of nuclear receptors to sex steroids in splenocytes, and to serum sex steroid levels in infected mice of both genders. Progesterone treatment increased parasite loads two-fold in females and three-fold in males compared with control mice. The expression of the Th2 cytokine profile (IL-4, IL-6 and IL-10) was markedly increased in infected mice of both genders, while progesterone treatment returned this expression to basal levels. However, the Th1 cytokine profile (IFN-gamma and TNF-alpha) was not affected by infection, whilst progesterone treatment increased the expression of both cytokines two-fold compared to uninfected, infected and placebo-treated mice. Testosterone serum levels decreased in infected male mice by 95%, and treatment with progesterone did not affect them. In females, no change in testosterone levels was observed. Progesterone levels increased three-fold only in progesterone-treated infected mice of both sexes, while estradiol levels in female and male progesterone-treated infected mice increased two-fold compared to infected control mice. The infection markedly induced the expression of progesterone receptor (PR) isoforms A and B in splenocytes of infected mice of both genders (five-fold). Metabolism of progesterone to estradiol was demonstrated by the use of the anti-estrogen tamoxifen, which reduced parasite loads 100% in infected mice of both sexes treated with progesterone. These results suggest that progesterone, possibly through its metabolism to estradiol, affects establishment, growth and reproduction of the helminth parasite T. crassiceps.

Steroid hormone production by parasites: the case of Taenia crassiceps and Taenia solium cysticerci

Many examples of reciprocal endocrine interactions between parasites and hosts have been found in insects, arthropods and mammals. Cysticercosis produced by Taenia solium metacestodes is a widely distributed parasite infection that affects the human and the pig. Taenia crassiceps experimental murine cysticercosis has been used to explore the role of biological factors involved in host-parasite interactions. We had shown that T. crassiceps cysticercosis affects the serum concentration of steroid hormones and the reproduction behavior of the male mice host. In an effort to understand the biology of the parasite, we had investigated the parasite capacity to produce sex steroids. For this purpose, T. crassiceps cysticerci were incubated in the presence of different steroid precursors. TLC and recrystallization procedures showed that testosterone is produced from 3H-androstenedione in cysticerci. The conversion of 3H-testosterone to androstenedione, although present is much less significant. In addition, we had studied the production of testosterone by T. solium cysticerci. For this purpose, cysticerci were dissected from pork meat and incubated as above described. The results showed that T. solium cysticerci also produce testosterone. We have speculated about the importance of androgens in the growth of T. crassiceps cysticerci and found that the addition of the antiandrogen flutamide to the culture media of the parasites significantly decreased 3H-thymidine incorporation. We therefore hypothesized, that the ability of cysticerci to produce testosterone from steroid precursors might be important for the parasite growth and development.

Entomogenous fungus Nomuraea rileyi inhibits host insect molting by C22-oxidizing inactivation of hemolymph ecdysteroids

The entomogenous fungus Nomuraea rileyi reportedly secretes a proteinaceous substance inhibiting larval molt and metamorphosis in the silkworm Bombyx mori. We studied the possibility that N. rileyi controls B. mori development by inactivating hemolymph molting hormone, ecdysteroids. Incubation of ecdysone (E) and 20-hydroxyecdysone (20E) in fungal-conditioned medium resulted in their rapid modification into products with longer retention times in reverse-phase HPLC. Each modified product from E and 20E was purified by HPLC, and identified by NMR as 22-dehydroecdysone and 22-dehydro-20-hydroxyecdysone. Some other ecdysteroids with a hydroxyl group at position C22 were also modified. Injection of the fungal-conditioned medium into Bombyx mori larvae in the mid-4th instar inhibited larval molt but induced precocious pupal metamorphosis, and its injection into 5th instar larvae just after gut purge blocked pupal metamorphosis. In hemolymph of injected larvae, E and 20E disappeared and, in turn, 22-dehydroecdysone and 22-dehydro-20-hydroxyecdysone accumulated. These results indicate that N. rileyi secretes a specific enzyme that oxidizes the hydroxyl group at position C22 of hemolymph ecdysteroids and prevents molting in B. mori larvae.

Castration and pregnancy of rural pigs significantly increase the prevalence of naturally acquired Taenia solium cysticercosis

Cuentepec is a rural village of central Mexico, where 1300 pigs were bred at the time of the study in conditions that favor Taenia solium transmission. The tongues of 1087 (84%) of these pigs were visually examined and 33% were found to be cysticercotic. Castration of male pigs increased prevalence from 23 to 50% (P < 0.001) and pregnancy in sows also increased their prevalence from 28 to 59% (P < 0.001). Thus, endocrinological conditions characterized by low levels of androgens or high levels of female hormones probably influence the susceptibility of pigs to T. solium cysticercosis as observed in mice infected with Taenia crassiceps. Delaying castration of male pigs and confinement of sows during pregnancy might significantly decrease the prevalence of pig-cysticercosis and help curb transmission without much cost or difficulty.

Taenia crassiceps: androgen reconstitution of the host leads to protection during cysticercosis

The effects of testosterone, dihydrotestosterone, and 17beta-estradiol in castrated mice of both sexes infected with Taenia crassiceps cysticerci were studied. The results showed that castration and treatment with either testosterone or dihydrotestosterone before infection decreased parasite loads by 50 and 70%, respectively, while the treatment with 17beta-estradiol increased it by three times in both genders, as compared with control mice. The specific splenocyte cell proliferation and IL-2 and IFN-gamma production were depressed in infected-castrated mice of both genders, while treatment with testosterone or dihydrotestosterone produced a significant proliferation recovery and enhanced production of IL-2 and IFN-gamma. On the other hand, the humoral response was unaffected with testosterone or dihydrotestosterone restitution, while the treatment with estradiol in both genders augmented the levels of anti-cysticerci IgG, as well as IL-6 and IL-10 production. These results suggest a protective role for androgens, possibly through the stimulation of the specific cellular immunity.

Metabolic cues for puberty onset in free grazing Holstein heifers naturally infected with nematodes

Leptin is a new plausible candidate for the molecular link between nutritional status and the reproductive axis. In previous studies we described that continuous natural nematode infections in heifers retarded growth and delayed the onset of puberty, and that the insulin-like growth factor I (IGF-I) was involved. In the present study we monitored the leptin levels during development in heifers naturally parasitized versus those chronically treated with ivermectin and we investigated whether growth hormone (GH) accounted for the differences in IGF-I previously noted. Insulin levels were also measured. Prolactin hormone was recorded as an indicator of immune system activation. We found a direct correlation between leptin and body weight during development and a prepubertal surge of the hormone 2 weeks before the first progesterone peak that indicates the onset of puberty. This suggests that leptin may act as a signal for this event. Insulin did not vary during growth and prepuberty. On the other hand, GH as not responsible for diminished IGF-I levels in parasitized animals as levels were similar in both groups. The GH levels were high at birth and then diminished rapidly and remained constant during development and puberty. The last hormone studied, prolactin, followed seasonal changes of sunlight duration and presented sporadic bursts in infected animals. These were related to high nematode infection and are probably involved in the immune response of the host.

Sex steroids and parasitism: Taenia crassiceps cisticercus metabolizes exogenous androstenedione to testosterone in vitro

Sex hormones are known to modulate immune responses and may be implicated in sex associated susceptibilities to infections. Taenia crassiceps cysticerci grow to larger numbers in female mice than in males. Gonadectomy alters the course of this infection and hormone replacement with 17beta-estradiol increases the parasite numbers. However, in chronic Taenia crassiceps cysticercosis the sex-hormone profile of males becomes more like that of the females' and progressively loose their sexual behavior. To have further insight in these outstanding endocrinological effects induced by the parasite upon the host, we investigated the parasite's capacity to produce sex steroids. In vitro experiments showed that Taenia crassiceps cysticerci transform 3H-Androstenedione to 3(H)-Testosterone, but not 3H-Pregnenolone. The production of 3H-Testosterone increased when the parasite numbers doubled. A recrystallisation procedure demonstrated that the metabolite identified by TLC was in fact testosterone. Thus, the cysticercus has the ability to use 3H-Androstenedione to make Testosterone possibly by a 17beta-Hydroxysteroid deshidrogenase-like activity in the parasite. In vivo, the parasite could use steroid precursors from the host to produce sex hormones, either accidentally or as needed for its own development, and thus alters the host's normal environment with sexual and immunological repercussions.

Hormones and nuclear receptors in schistosome development

A substantial but disparate body of evidence suggests that hormones affect the development of schistosomes within their definitive hosts. Here, Raymond Pierce and colleagues review such evidence for host steroid and thyroid hormones, and for ecdysteroids, and link this to the expanding knowledge of the nuclear receptors for these hormones. Phylogenetic analysis of the nuclear receptor superfamily and the characterization of the first schistosome nuclear receptors suggest that steroids and thyroid hormone probably act indirectly, or by pathways not involving the control of gene transcription. However, the probability that schistosome nuclear receptors exist for a variety of unique ligands opens up exciting possibilities for targeted drug development.

Mass dynamics of the spleen and other organs in geese: measures of immune relationships to helminths?

The spleen is an important organ of avian immune systems. We examined whether helminth loads were related to spleen mass in the lesser snow goose, Chen caerulescens caerulescens. On 27 collecting occasions, 744 geese were obtained at 13 different locations in a south-north gradient in midcontinental North America. The masses of the spleen, caecum, small intestine, large intestine, pancreas, heart, and crop of all geese were determined, and intestinal and caecal helminths were counted. Seventy-eight percent of geese harbored at least one helminth species. For analyses, helminths were grouped as cestodes (26% prevalence), trematodes (19% prevalence), and nematodes (70% prevalence). After sample location and time, host age, host sex, and host body size were controlled for in a multivariate analysis of covariance, nematodes were the only helminth group associated with variation in organ masses. Greater nematode loads were weakly associated with lower spleen, higher caecum, lower large intestine, and lower heart masses. When uninfected individuals were excluded from the analysis, greater nematode loads were no longer associated with variation in spleen size but were associated with higher crop mass, and greater cestode loads were associated with higher heart mass. In neither of these analyses were any other cestode-organ or trematode-organ associations significant. Geese carrying two or more helminth groups had lower spleen masses than did geese infected with no or one helminth group. When we interchanged response and explanatory variables from the preceding analyses and retained the same covariates, the same organ mass - helminth associations tended to remain significant. Nonetheless, the small variation in helminth loads explained by variation in spleen mass (or vice versa) provided only weak support for the hypothesis that intraspecifically, wild individuals with lower investment in immunity are more susceptible to nematode infections.

Manipulation of fifth-instar host (Manduca sexta) ecdysteroid levels by the parasitoid wasp Cotesia congregata

Although 5th (last) instar parasitized Manduca sexta larvae undergo developmental arrest and do not wander, they exhibit a small hemolymph ecdysteroid peak (300-400pg/&mgr;l) which begins one day prior to the parasitoid's molt to the 3rd (last) instar and concomitant emergence from the host. Ecdysteroids present in this peak were 20-hydroxyecdysone, 20,26-dihydroxyecdysone and one or more very polar ecdysteroids, as well as small amounts of 26-hydroxyecdysone and ecdysone. In parasitized day-1 and -2 5th instars ligated just behind the 1st abdominal proleg, hemolymph ecdysteroid levels increased in both anterior and posterior portions (100-500pg/&mgr;l), while in unparasitized larvae, hormone levels only increased in the anterior portion (100-350pg/&mgr;l). Thus, the ecdysteroid peak observed in host 5th instars was probably produced, at least in part, by the parasitoids. It may serve to promote Cotesia congregata's molt from the second to the third instar and/or to facilitate parasitoid emergence from the host. In parasitized day-1 and -2 5th instars ligated between the last thoracic and 1st abdominal segments, hemolymph ecdysteroid titers reached much higher levels (500-3500pg/&mgr;l) in the anterior portion (no parasitoids present) than in the posterior portion (150-450pg/&mgr;l). Therefore, it appears that the parasitoid's regulation of hemolymph ecdysteroid titers occurs at two levels. First, parasitization neutralizes the host's ability to maintain its normal hemolymph ecdysteroid levels. Second, in a separate action, the parasitoid manipulates the ecdysteroid-producing machinery so that hemolymph levels are maintained at the 200-400pg/&mgr;l characteristic of day 3-4 hosts. This is the first report of a parasitoid's ability to interfere with the normal inhibitory mechanisms which prevent prothoracic gland production of ecdysteroid at inappropriate periods of insect growth and development.

"Adaptive" changes in the behaviour of parasitized animals: a critical review

Changes in host behaviour following infection with parasites are frequently reported in the literature, and are often hypothesized to be adaptive for either host or parasite. However, investigators of such phenomena often use the "adaptation" label for host behavioural changes based on their intuition and not on rigorous criteria. Alterations in host behaviour following infection can only be considered adaptive if they satisfy certain conditions: (1) they must be complex; (2) they must show signs of a purposive design; (3) they are more likely to be adaptations if they have arisen independently in several lineages of hosts or parasites; and (4) they must be shown to increase the fitness of either the host or the parasite. A survey of published examples of host behavioural changes indicates that while some are spectacularly complex and are extremely well-fitted to their presumed function, most are simple increases or decreases in an activity performed prior to infection. There are some suggestions of convergent evolution in behavioural change in distantly related host or parasite groups but more evidence is needed. Finally, most known behavioural changes have not been demonstrated to lead to fitness gains in either hosts or parasites. Few known examples satisfy more than two of the above criteria, and, in general, the adaptive function of changes in host behaviour following infection is in need of more solid proof.

Sex hormone changes induced by the parasite lead to feminization of the male host in murine Taenia crassiceps cysticercosis

Female mice are more susceptible to Taenia crassiceps (TC) infection than males. However, after a month parasite load increases massively in both genders reaching thousands of parasites per host. The possibility of hormonal changes in the infected mice was envisaged. Sex hormones levels were assayed after different periods of infection, the parasites present in the peritoneal cavity were collected and gonads, uterus and seminal vesicles were weighed. In male mice, serum estradiol increased to levels 200 times their normal values whilst those of testosterone decreased 90% relative to controls. The weight of seminal vesicles was significantly diminished. Infected female mice also showed a slight increase in estrogen blood levels after 8 weeks of infection and the weight of the uterus was significantly increased relative to controls. Serum estradiol and testosterone were almost undetectable after gonadectomy. Cytokines such as IL-6 are capable of stimulating aromatase activity and we found that splenocytes from infected mice produced amounts of IL-6 higher than control as measured by ELISA. In conclusion T. crassiceps infection triggers a feminization process in the infected hosts. The gonads are required for the parasite to induce higher estrogen synthesis. IL-6 could be involved in the immunoendocrine mechanism used by the parasite to maintain a highly permissive environment for its rapid growth.

Leprosy in women: characteristics and repercussions

"Health is often measured in terms of low mortality; nevertheless, merely being alive is not a measure of the quality of life" H. Méndez Castellanos. Physiological, socioeconomic and cultural factors play important roles in the response of women to Mycobacterium leprae and in the impact of leprosy on their lives. They appear to develop stronger immunological responses to M. leprae than men, as suggested by lower incidence and less severe clinical forms of disease in most areas of the world, as well as stronger reactions of cell-mediated immunity after prophylactic vaccination. Genetic factors and physiological status including pregnancy, intercurrent infection and malnutrition might be among the factors which modulate this response. Women in leprosy-endemic areas of the world, with few exceptions, suffer from marked economic and social dependency and inferiority which can only be heightened by the social stigma associated with leprosy. Nevertheless, they bear an enormous responsibility for the health of their families, often as head of the household, and they often possess a unique capacity to influence community opinion. With the introduction of multidrug therapy, leprosy control throughout the world is no longer an unrealistic goal. Active vaccination may constitute the other factor necessary for eventual eradication of the disease. The incorporation of women at all levels into active roles in health care programs may constitute one of the decisive factors in the success or failure of leprosy control.

Effects of parasitism by the braconid wasp Cotesia congregata on host hemolymph proteins of the tobacco hornworm, Manduca sexta

Parasitism by the braconid wasp Cotesia congregata causes major alterations in the hemolymph proteins of host tobacco hornworm larvae. Earlier studies showed that the total amount of hemolymph protein is reduced during parasitism, beginning almost immediately after the host is parasitized. Simultaneously, parasitism induces synthesis of large amounts of novel proteins that appear in the blood as early as 1-2 h post-parasitization. The present report confirms earlier studies describing the presence of novel proteins in last instar hosts, and also characterizes the effects of parasitism in altering the titers of several endogenous host hemolymph proteins normally produced by the fat body and other tissues. Analysis of hemolymph plasma using SDS-PAGE and densitometry, as well as immunodiffusion assays, showed that in terminal stage fifth instar host larvae, the titers of serpins and arylphorin were dramatically reduced relative to the levels of these proteins detected in nonparasitized gate II fifth instar larvae of the same age. The relative differences between parasitized and nonparasitized larvae increased with time following ecdysis to the fifth instar, so that the day 4 nonparasitized larvae had arylphorin titers of c. 30 mg/ml, whereas parasitized day 4 larvae with newly emerged wasps had only one sixth that amount of storage protein circulating in the hemolymph. Similarly, in nonparasitized larvae the hemolymph serpin concentration increased from c. 200 micrograms/ml (on day 0) to > 600 micrograms/ml (on day 4) in prewandering gate II larvae, but in parasitized larvae the hemolymph serpin concentration was maintained in the range of 100-200 micrograms per ml hemolymph until the pharate third instar parasites emerged from the host larva on day 4. In contrast, the level of hemolymph lipophorin was unaffected by parasitism, and lipophorin increased from c. 1.3 to > 3 mg/ml during the time interval between days 0 and 4 in both nonparasitized and parasitized larvae. Hemolymph titers of insecticyanin also were not significantly different in parasitized vs nonparasitized larvae, and in both types of larvae the concentration of this pigment decreased by c. 50% during the same time interval when lipophorin was increased significantly. Instead of causing a generalized inhibition of host hemolymph protein synthesis, parasitism causes a complex array of changes in the hemolymph protein profile of Manduca sexta, possibly via the mediation of hormonal modulators of host protein synthesis, or transcriptional or translational regulation of host gene expression by factors associated with the polydnavirus or molecules secreted by the parasites.(ABSTRACT TRUNCATED AT 400 WORDS)