Evidence of opiates and opioid neuropeptides and their immune effects in parasitic invertebrates representing three different phyla: Schistosoma Mansoni, Theromyzon Tessulatum, Trichinella Spiralis

Neuroimmune Pain and Its Manipulation by Pathogens

Recent studies highlight extensive crosstalk that exists between sensory neurons responsible for pain and the immune system. Cutaneous pain neurons detect harmful microbes, recruit immune cells, and produce anticipatory immunity in nearby tissues. These complementary systems generally protect hosts from infections. At the same time, neuroimmune pain is vulnerable to manipulation. Some pathogens evade immunity activated by nociceptors by producing opioid analogs and by interfering with sensory nerve function. Other organisms manipulate neuroimmune pain by increasing it. Hosts may gain protection from interference by adjusting pain sensitivity. Nociceptive sensitization follows expectations of signal detection theory and the smoke detector principle, allowing pain to be more easily triggered in response to microbial threats and damage. However, pain sensitization at the spinal level and cortical responses to pain are themselves the target of manipulation by parasites and other organisms. Here we review examples of parasites, bacteria, and other medically important organisms that interfere with pain signaling and describe their implications for public health, infectious disease, and the treatment of pain.

Impact of parasitic infection on mental health and illness in humans in Africa: a systematic review

A growing body of research implicates inflammation as a potential pathway in the aetiology and pathophysiology of some mental illnesses. A systematic review was conducted to determine the association between parasitic infection and mental illnesses in humans in Africa and reviewed the state of the evidence available. The search focused on publications from Africa documenting the relationship between parasites from two parasite groups, helminths and protozoans, and four classifications of mental illness: mood affective disorders, neurotic and stress-related disorders, schizotypal disorders and unspecified mental illnesses. In the 26 reviewed papers, the prevalence of mental illness was significantly higher in people with parasitic infection compared to those without infection, i.e., 58.2% vs 41.8% (P < 0.001). An overall odds ratio found that the association of having a mental illness when testing positive for a parasitic infection was four times that of people without infection. Whilst the study showed significant associations between parasite infection and mental illness, it also highlights gaps in the present literature on the pathophysiology of mental illness in people exposed to parasite infection. This study highlighted the importance of an integrated intervention for parasitic infection and mental illness.

Behavioural alterations in female Aedes aegypti mosquito in response to entomopathogenic fungal infections

BACKGROUND

Due to the rapid rise in arboviral disease cases, there is a need for alternative methods of vector control since fast growing insecticides resistance is a matter of great concern. Recent studies have shown the potential of entomopathogenic fungi in controlling mosquito vectors, but behavioural responses of the mosquitoes encountering with entomopathogenic fungi are still unclear.

RESULTS

In this study, behavioural responses induced by the entomopathogenic fungus Metarhizium anisopliae (Metschnikoff) Sorokin in adult female Aedes aegypti mosquito were evaluated. The survival of female mosquitoes was significantly reduced after exposure to medium and high concentrations of fungal conidia. A significant increase in frequencies and durations of different self-grooming types was observed in mosquitoes exposed to medium or high concentrations of fungal conidia. Mosquitoes were able to differentiate between active and inactive fungal conidia as application of inactive conidia showed non-significant effect on survival and self-grooming parameters. A concentration-specific reduction in flight locomotor activity of the female mosquitoes was found after fungal treatments. Fungal-exposed mosquitoes showed significantly higher antifungal activity 72 h post-application.

CONCLUSION

These findings provide greater understanding of behavioural responses of the mosquitoes to resist fungal infections and suggest that mosquitoes can remove the lower amounts of fungal conidia through self-grooming behaviour, which they encounter within natural field conditions.

The interplay of helminthic neuropeptides and proteases in parasite survival and host immunomodulation

Neuropeptides comprise a diverse and broad group of neurotransmitters in vertebrates and invertebrates, with critical roles in neuronal signal transduction. While their role in controlling learning and memory in the brains of mammals is known, their extra-synaptic function in infection and inflammation with effects on distinct tissues and immune cells is increasingly recognized. Helminth infections especially of the central nervous system (CNS), such as neurocysticercosis, induce neuropeptide production by both host and helminth, but their role in host-parasite interplay or host inflammatory response is unclear. Here, we review the neurobiology of helminths, and discuss recent studies on neuropeptide synthesis and function in the helminth as well as the host CNS and immune system. Neuropeptides are summarized according to structure and function, and we discuss the complex enzyme processing for mature neuropeptides, focusing on helminth enzymes as potential targets for novel anthelminthics. We next describe known immunomodulatory effects of mammalian neuropeptides discovered from mouse infection models and draw functional parallels with helminth neuropeptides. Last, we discuss the anti-microbial properties of neuropeptides, and how they may be involved in host-microbiota changes in helminth infection. Overall, a better understanding of the biology of helminth neuropeptides, and whether they affect infection outcomes could provide diagnostic and therapeutic opportunities for helminth infections.

Immunity, host physiology, and behaviour in infected vectors

When infection alters host behaviour such that the pathogen benefits, the behaviour is termed a manipulation. There are several examples of this fascinating phenomenon in many different systems. Vector-borne diseases are no exception. In some instances, as the term implies, pathogens directly interfere with host processes to control behaviour. However, host response to infection and host physiology are likely to play important roles in these phenotypes. We highlight the importance of considering host response and physiology from recent work on altered host-seeking in malaria parasite-infected mosquitoes and argue that this general approach will provide useful insights across vector-borne disease systems.

Impacts of a newly identified behaviour-altering trematode on its host amphipod: from the level of gene expression to population

Changes to host behaviour induced by some trematode species, as a means of increased trophic transmission, represents one of the seminal examples of host manipulation by a parasite. The amphipod Echinogammarus marinus (Leach, 1815) is infected with a previously undescribed parasite, with infected individuals displaying positive phototaxic and negative geotaxic behaviour. This study reveals that the unknown parasite encysts in the brain, nerve cord and the body cavity of E. marinus, and belongs to the Microphallidae family. An 18 month population study revealed that host abundance significantly and negatively correlated with parasite prevalence. Investigation of the trematode's influence at the transcriptomic level revealed genes with putative neurological functions, such as serotonin receptor 1A, an inebriated-like neurotransmitter, tryptophan hydroxylase and amino acid decarboxylase, present consistent altered expression in infected animals. Therefore, this study provides one of the first transcriptomic insights into the neuronal gene pathways altered in amphipods infected with a trematode parasite associated with changes to its host's behaviour and population structure.

Effect of nematode Trichinella infection on glucose tolerance and status of macrophage in obese mice

We investigated the effect of Trichinella infection on glucose tolerance and (pro- or anti-inflammatory) macrophage status in adipose tissue. Ob/ob mice and high fat-fed mice (obesity model) and C57/BL mice (control mice) were orally infected with (infected group) or without (uninfected group) 400 Trichinella per mouse. Four weeks later, the mice were subjected to investigation, which showed that fasting plasma glucose levels decreased in the infected group of C57/BL and ob/ob mice. Glucose tolerance, evaluated with intraperitoneal GTT, improved in the infected group of ob/ob mice and high fat-fed mice compared with the uninfected groups. Additional assay included anti-inflammatory macrophage (M2) markers and pro-inflammatory macrophage (M1) markers, with the aim to explore the effect of Trichinella infection on adipose tissue inflammation, since our previous study identified anti-inflammatory substances in secreted proteins by Trichinella. The result showed that mRNA levels of M2 markers, such as CD206, arginase and IL-10, increased, whereas M1 markers, such as CD11c, iNOS and IL-6, decreased in the stromal vascular fraction (SVF) isolated from epididymal fat in ob/ob mice. Residential macrophages obtained from the peritoneal lavage exhibited lower M1 markers and higher M2 markers levels in the infected group than in the uninfected group. Trichinella infection increases the ratio of M2/M1 systemically, which results in an improvement in pro-inflammatory state in adipose tissue and amelioration of glucose tolerance in obese mice.

Parasites: evolution’s neurobiologists

For millions of years, parasites have altered the behaviour of their hosts. Parasites can affect host behaviour by: (1) interfering with the host’s normal immune–neural communication, (2) secreting substances that directly alter neuronal activity via non-genomic mechanisms and (3) inducing genomic- and/or proteomic-based changes in the brain of the host. Changes in host behaviour are often restricted to particular behaviours, with many other behaviours remaining unaffected. Neuroscientists can produce this degree of selectivity by targeting specific brain areas. Parasites, however, do not selectively attack discrete brain areas. Parasites typically induce a variety of effects in several parts of the brain. Parasitic manipulation of host behaviour evolved within the context of the manipulation of other host physiological systems (especially the immune system) that was required for a parasite’s survival. This starting point, coupled with the fortuitous nature of evolutionary innovation and evolutionary pressures to minimize the costs of parasitic manipulation, likely contributed to the complex and indirect nature of the mechanisms involved in host behavioural control. Because parasites and neuroscientists use different tactics to control behaviour, studying the methods used by parasites can provide novel insights into how nervous systems generate and regulate behaviour. Studying how parasites influence host behaviour will also help us integrate genomic, proteomic and neurophysiological perspectives on behaviour.

The effect of opioids and their antagonists on the nocifensive response of Caenorhabditis elegans to noxious thermal stimuli

Opiates modulate nociception in vertebrates. This has also been demonstrated in a number of invertebrate models. Herein, the effect of the opiate morphine and opioid neuropeptides Endomorphin 1 and 2 on the thermal avoidance (Tav) behavior of Caenorhabditis elegans is explored. Adult wild-type C. elegans N2 were collected from NGM plates using M9 buffer and exposed to morphine and endomorphine 1 and 2 in concentrations between 10(-8) and 10(-4) M (2.5 pmol/mg to 25 nmol/mg) for 30 min and tested for Tav. The opioid receptor antagonists Naloxone and CTOP were tested in combination with the drugs. Forty-seven percentage of the morphine exposed worms exhibited a class I response versus 76% of the control group (P < 0.001). Endomorphin 1 and 2 also caused a statistically significant reduction in class I responses, 36 and 39%, respectively. These effects were reversed with Naloxone and CTOP. Thermonocifensive behavior in C. elegans is modulated by opioids.

A worm's eye view of the immune system: consequences for evolution of human autoimmune disease

Humans and the many parasites that we can host have co-evolved over millions of years. This has been compared to an arms race in which the immune armoury of the human has evolved to deal with potential pathogens and the pathogen has evolved strategies to evade, and in some cases use, the immune system of the human host. Recently, there have been marked changes in the exposure of individuals in the developed world to both microorganisms and metazoan parasites, so the immune stimuli such organisms provide no longer have a role in our lives. As we discuss here, this is a marked perturbation, and the absence of the associated immunomodulation might have led to the increased emergence of autoimmune diseases.

An opioid peptide from synganglia of the tick, Amblyomma testindinarium

An opioid peptide, which shares similarity with mammalian hemorphins, has been identified from the synganglia (central nervous system) of the hard tick, Amblyomma testindiarium. Its primary sequence was established as LVVYPWTKM that contains a tetrapeptide sequence Tyr-Pro-Trp-Thr of hemorphin-like opioid peptides. By hot-plate bioassay, the purified peptide and synthetic peptide displayed dose-related antinociceptive effect in mice, as observed for other hemorphin-like opioid peptides. This is the first opioid peptide identified from ticks. Ticks may utilize the opioid peptide in their strategy to escape host immuno-surveillance as well as in inhibiting responses directed against themselves.

Opiate alkaloids and nitric oxide production in the nematode Ascaris suum

The tissue distribution, course of secretion, and sex differences of morphine were delineated in Ascaris suum. Nitric oxide (NO) release in various tissues in response to morphine and its metabolite morphine-6-glucuronide (M6G) were also examined. Ascaris suum of both sexes along with their incubation fluid were analyzed for morphine concentrations by high-performance liquid chromatography (HPLC) over a 5-day period. Various tissues were also dissected for HPLC and NO analysis. Morphine was found to be most prevalent in the muscle tissue, and there is significantly more morphine in females than males, probably because of the large amounts present in the female uterus. Morphine (10(-9) M) and M6G (10(-9) M) stimulated the release of NO from muscles. Naloxone (10(-7) M) and N-nitro-L-arginine methyl ester (10(-6) M) blocked (P < 0.005) morphine-stimulated NO release from A. suum muscle tissue. D-Phe-Cys-Tyr-D-Trp-Om-Thr-Pen-Thr-NH2 (CTOP) (10(-7) M) did not block morphine's NO release. However, naloxone could not block M6G-stimulated NO release by muscles, whereas CTOP (10(-7) M) blocked its release. These findings were in seeming contradiction to our earlier inability to isolate a mu opiate receptor messenger RNA by reverse transcriptase-polymerase chain reaction using a human mu primer. This suggests that a novel mu opiate receptor was possibly present and selective toward M6G.

Transcriptome analysis of the acoelomate human parasite Schistosoma mansoni

Schistosoma mansoni is the primary causative agent of schistosomiasis, which affects 200 million individuals in 74 countries. We generated 163,000 expressed-sequence tags (ESTs) from normalized cDNA libraries from six selected developmental stages of the parasite, resulting in 31,000 assembled sequences and 92% sampling of an estimated 14,000 gene complement. By analyzing automated Gene Ontology assignments, we provide a detailed view of important S. mansoni biological systems, including characterization of metazoa-specific and eukarya-conserved genes. Phylogenetic analysis suggests an early divergence from other metazoa. The data set provides insights into the molecular mechanisms of tissue organization, development, signaling, sexual dimorphism, host interactions and immune evasion and identifies novel proteins to be investigated as vaccine candidates and potential drug targets.

Molecular expression and characterization of a homologue of host cytokine macrophage migration inhibitory factor from Trichinella spp

A homologue of cytokine macrophage migration inhibitory factor (MIF) from complementary DNA (cDNA) of Trichinella spiralis and Trichinella pseudospiralis was expressed in Escherichia coli and characterized. The sequence analysis indicated that the predicted amino acid sequence has an identity of 57 and 44% with the MIF of nematodes Trichuris trichiura and Brugia malayi respectively, and 41 and 40% with that of a human and a mouse, respectively. The identity in sequences of cDNA and amino acids between T. spiralis and T. pseudospiralis was 91 and 86%, respectively. Western blot analysis showed that anti-MIF antibodies positively stained proteins from the extracts of adult worms or muscle larvae migrating at about 12.5 kDa (3 isoforms with isoelectric point 5.23, 5.72, and 6.29). Semiquantitative reverse transcriptase-polymerase chain reaction revealed that the gene was expressed in various developmental stages, including in adult worms, newborn larvae, precyst muscle larvae, and postcyst muscle larvae, although there was difference in the expression level among these stages. The immunohistochemical analysis showed the MIF exists in the muscle cells of the body wall and some stichocytes of larvae. Histopathology of T. spiralis-infected muscles revealed an accumulation of mononuclear cells around the worms, and immunocytochemical staining showed these cells were not macrophages. Mononuclear cells, including macrophages, were, however, observed in cardiac muscles where the parasite did not encyst. Macrophages accumulated around the Sephadex beads transplanted in mice subcutaneously, but this accumulation was profoundly inhibited when the beads were pretreated with MIF recombinant protein.

Human proprotein convertase 2 homologue from a plant nematode: cloning, characterization, and comparison with other species

Proprotein convertases (PCs) are evolutionarily conserved enzymes responsible for processing the precursors of many bioactive peptides in mammals. The invertebrate homologues of PC2 play important roles during development that makes the enzyme a good target for practical applications in pest management. Screening of a plant nematode Heterodera glycines cDNA library resulted in isolation of a full-length clone encoding a PC2-like precursor. The deduced protein (74.2 kD) exhibits strong amino acid homology to all known PC2s, including human, and shares the main structural characteristics: signal peptide; prosegment; catalytic domain, with D/H/S catalytic triad, PC2-specific residues, and 7B2 binding sites; P domain (with RRGDT pentapeptide); and carboxyl terminus. Comparative analysis of PC2s from 15 species discloses the presence of an insert in the catalytic domain unique to nematodes. Expression of PC2-like mRNA found in eggs and juveniles was undetectable in adult stages of H. glycines. Nucleotide analysis reveals distinctive differences in base composition and codon usage between H. glycines and Caenorhabditis elegans PC2s. The H. glycines cDNA clone encoding PC2 is the first one isolated from plant-parasitic nematodes.

Expression of excretory and secretory protein genes of Trichinella at muscle stage differs before and after cyst formation

By adapting a semi-quantitative reverse transcriptase-PCR (RT-PCR) method, we investigated kinetics of gene expression at different developmental stages of Trichinella spiralis and T. pseudospiralis. The analyzed genes included four kinds of excretory and secretory (ES) proteins, a heat shock protein (HSP) and a DNA binding protein and showed that T. spiralis and T. pseudospiralis expressed ES proteins in a stage-specific manner. The gene encoding a 43 kDa ES protein was expressed by muscle larvae, either pre-cyst or post-cyst larvae. The genes encoding: the 53 kDa ES protein of T. spiralis; 53 kDa ES protein of T. pseudospiralis; and 19.6 kDa ES protein of T. spiralis were expressed by post-cyst larvae and adult worms, but not expressed by pre-cyst larvae or newborn larvae. The results showed that pre-cyst larvae and post-cyst larvae are similar but different in the expression of 53 and 19.6 kDa ES proteins. On the other hand, genes of housekeeping proteins, such as HSP and the DNA binding protein, were expressed at all stages although there were some differences in the expression level.