Capillaria hepatica (syn. Calodium hepaticum) infection and factors influencing infection carriage in rats (Rattus spp.) in Hong Kong

Capillaria hepatica (syn. Calodium hepaticum) (Bancroft, 1893) is a nematode, which colonises the liver of a wide range of hosts including humans. The worldwide prevalence of infection in the genus Rattus can be as high as 100% and the Norway rat (R. norvegicus) and black rat (R. rattus) are considered the main host species. This study is the first to investigate the epidemiology of C. hepatica infection in wild rats trapped in various geographical locations in Hong Kong. Four species of trapped rats were identified, with 65% being R. norvegicus, followed by 30% R. tanezumi (Asian house rat), 4% R. andamanensis (Sikkim rat), and 1% Niviventer huang (South China white-bellied rat). The overall prevalence of C. hepatica infection was 36.7% (81/221) (95% CI 30.4-43.4) and R. norvegicus was the most common rat species trapped during this study, with the highest prevalence of C. hepatica infection. Two risk factors for host infection were skin wounds and geographical region, whilst sex, body weight, stage of development, and presence of ectoparasites were not risk factors for this infection. Gross hepatic lesions were absent in 17% of infected rats and when present, were not pathognomonic for the infection. Infected rats lacked severe hepatic inflammation or fibrosis, indicating that rats tolerate the infection well. Egg production was observed in the livers of 69% of infected rats, which emphasizes their role as reservoirs of this zoonotic parasite. Several infected rats in this study were trapped inside residential buildings, which highlights the zoonotic risk of C. hepatica to humans following the potential ingestion of embryonated eggs from contaminated food, water, or soil.

The rebalancing of the immune system at the maternal-fetal interface ameliorates autism-like behavior in adult offspring

Maternal immune activation (MIA) is critical for imparting neuropathology and altered behaviors in offspring; however, maternal-fetal immune cell populations have not been thoroughly investigated in MIA-induced autism spectrum disorders (ASDs). Here, we report the single-cell transcriptional landscape of placental cells in both PBS- and poly(I:C)-induced MIA dams. We observed a decrease in regulatory T (Treg) cells but an increase in the M1 macrophage population at the maternal-fetal interface in MIA dams. Based on the Treg-targeting approach, we investigate an immunoregulatory protein, the helminth-derived heat shock protein 90α (Sjp90α), that induces maternal Treg cells and subsequently rescues the autism-like behaviors in adult offspring. Furthermore, in vivo depletion of maternal macrophages attenuates placental inflammatory reaction and reverses behavioral abnormalities in adult offspring. Notably, Sjp90α induces CD4+ T cell differentiation via scavenger receptor A (SR-A) on the macrophage in vitro. Our findings suggest a maternal Treg-targeted approach to alleviate MIA-induced autism-like behavior in adult offspring.

Entomopathogenic nematodes in insect pest biocontrol: Diversity and function of excretory/secretory proteins

Entomopathogenic nematodes (EPNs) are obligate parasitic "biopesticides" that play a vital role in pest management. A thorough understanding of their pathogenic mechanisms is essential for promoting their widespread use in agricultural pest control. The pathogenicity of EPNs arises from two key factors: the pathogenicity of their symbiotic bacteria and the nematodes' intrinsic pathogenic mechanisms. This review concentrates on the latter, offering an exploration of the excretory/secretory products of EPNs, along with their pathogenic mechanisms and key components. Particular attention is given to specific excretory/secretory proteins (ESPs) identified in various EPN species. The aim is to provide a foundational reference for comprehending the role of these ESPs in pest control. Furthermore, the review discusses the potential of these findings to advance the development of eco-friendly biopesticides, thereby supporting sustainable agricultural practices.

The Secretome of Adult Murine Hookworms Is Shaped by Host Expression of STAT6

Co-evolutionary adaptation of hookworms with their mammalian hosts has been selected for immunoregulatory excretory/secretory (E/S) products. However, it is not known whether, or if so, how host immunological status impacts the secreted profile of hematophagous adult worms. This study interrogated the impact of host Signal transducer and activator of transcription 6 (STAT6) expression during the experimental evolution of hookworms through the sequential passage of the life cycle in either STAT6 deficient or WT C57BL/6 mice. Proteomic analysis of E/S products by LC-MS showed increased abundance of 15 proteins, including myosin-3, related to muscle function, and aconitate hydratase, related to iron homeostasis. However, most E/S proteins (174 of 337 unique identities) were decreased, including those in the Ancylostoma-secreted protein (ASP) category, and metallopeptidases. Several identified proteins are established immune-modulators such as fatty acid-binding protein homologue, cystatin, and acetylcholinesterase. Enrichment analysis of InterPro functional categories showed down-regulation of Cysteine-rich secretory proteins, Antigen 5, and Pathogenesis-related 1 proteins (CAP), Astacin-like metallopeptidase, Glycoside hydrolase, and Transthyretin-like protein groups in STAT6 KO-adapted worms. Taken together, these data indicate that in an environment lacking Type 2 immunity, hookworms alter their secretome by reducing immune evasion proteins- and increasing locomotor- and feeding-associated proteins.

A biological invasion modifies the dynamics of a host-parasite arms race

By imposing novel selection pressures on both participants, biological invasions can modify evolutionary 'arms races' between hosts and parasites. A spatially replicated cross-infection experiment reveals strong spatial divergence in the ability of lungworms (Rhabdias pseudosphaerocephala) to infect invasive cane toads (Rhinella marina) in Australia. In areas colonized for longer than 20 years, toads are more resistant to infection by local strains of parasites than by allopatric strains. The situation reverses at the invasion front, where super-infective parasites have evolved. Invasion-induced shifts in genetic diversity and selective pressures may explain why hosts gain advantage over parasites in long-colonized areas, whereas parasites gain advantage at the invasion front.

Transcriptomic profiling of different developmental stages reveals parasitic strategies of Wohlfahrtia magnifica, a myiasis-causing flesh fly

BACKGROUND

Wohlfahrtia magnifica is an obligatory parasite that causes myiasis in several warm-blooded vertebrates. Adult females deposit the first-stage larvae directly onto wounds or natural body orifices (e.g., genitalia) of the host, from where they quickly colonize the host tissue and feed on it for development. The infestation of W. magnifica can lead to health issues, welfare concerns, and substantial economic losses. To date, little is known about the molecular mechanisms of the W. magnifica-causing myiasis.

RESULTS

In this study, we collected parasitic-stage larvae of W. magnifica from wounds of naturally infested Bactrian camels, as well as pupae and adult flies reared in vitro from the wound-collected larvae, for investigating the gene expression profiles of the different developmental stages of W. magnifica, with a particular focus on examining gene families closely related to the parasitism of the wound-collected larvae. As key proteins related to the parasite-host interaction, 2049 excretory/secretory (ES) proteins were identified in W. magnifica through the integration of multiple bioinformatics approaches. Functional analysis indicates that these ES proteins are primarily involved in cuticle development, peptidase activity, immune response, and metabolic processes. The global investigation of gene expression at different developmental stages using pairwise comparisons and weighted correlation network analysis (WGCNA) showed that the upregulated genes during second-stage larvae were related to cuticle development, peptidase activity, and RNA transcription and translation; during third-stage larvae to peptidase inhibitor activity and nutrient reservoir activity; during pupae to cell and tissue morphogenesis and cell and tissue development; and during adult flies to signal perception, many of them involved in light perception, and adult behavior, e.g., feeding, mating, and locomotion. Specifically, the expression level analysis of the likely parasitism-related genes in parasitic wound-collected larvae revealed a significant upregulation of 88 peptidase genes (including 47 serine peptidase genes), 110 cuticle protein genes, and 21 heat shock protein (hsp) genes. Interestingly, the expression of 2 antimicrobial peptide (AMP) genes, including 1 defensin and 1 diptericin, was also upregulated in the parasitic larvae.

CONCLUSIONS

We identified ES proteins in W. magnifica and investigated their functional distribution. In addition, gene expression profiles at different developmental stages of W. magnifica were examined. Specifically, we focused on gene families closely related to parasitism of wound-collected larvae. These findings shed light on the molecular mechanisms underlying the life cycle of the myiasis-causing fly, especially during the parasitic larval stages, and provide guidance for the development of control measures against W. magnifica.

Proteomic differences between extracellular vesicles and extracellular vesicle-depleted excretory/secretory products of barber's pole worm

BACKGROUND

Components of excretory/secretory products (ESPs) of helminths have been proposed as vaccine targets and shown to play a role in modulating host immune responses for decades. Such research interest is further increased by the discovery of extracellular vesicles (EVs) in the ESPs of parasitic worms. Although efforts have been made to reveal the cargos of EVs, little is known about the proteomic differences between EVs and canonical ESPs released by parasitic worms from animals.

METHODS

The total ESPs of Haemonchus contortus (barber's pole worm) were obtained by short-term in vitro culturing of young adult worms, and small EVs were isolated from ESPs using an ultracentrifugation method. Data-dependent acquisition (DDA) label-free Nano-LC-MS/MS was used to quantify the proteomic difference between small EVs and EV-depleted ESPs of H. contortus. Functional annotation and enrichment of the differential proteins were performed regarding cellular components, molecular functions, pathways, and/or biological processes.

RESULTS

A total of 1697 proteins were identified in small EVs and EV-depleted ESPs of H. contortus adult worms, with 706 unique proteins detected in the former and 597 unique proteins in the latter. It was revealed that proteins in small EVs are dominantly cytoplasmic, whereas proteins in EV-depleted ESPs are mainly extracellular; canonical ESPs such as proteases and small GTPases were abundantly detected in small EVs, and SCP/TAP-, DUF-, and GLOBIN domain-containing proteins were mainly found in EV-depleted ESPs. Compared with well-characterised proteins in small EVs, about 50% of the proteins detected in EV-depleted ESPs were poorly characterised.

CONCLUSIONS

There are remarkable differences between small EVs and EV-depleted ESPs of H. contortus in terms of protein composition. Immune modulatory effects caused by nematode ESPs are possibly contributed mainly by the proteins in small EVs.

Parasitic nematode secreted phospholipase A2 suppresses cellular and humoral immunity by targeting hemocytes in Drosophila melanogaster

A key aspect of parasitic nematode infection is the nematodes' ability to evade and/or suppress host immunity. This immunomodulatory ability is likely driven by the release of hundreds of excretory/secretory proteins (ESPs) during infection. While ESPs have been shown to display immunosuppressive effects on various hosts, our understanding of the molecular interactions between individual proteins released and host immunity requires further study. We have recently identified a secreted phospholipase A2 (sPLA2) released from the entomopathogenic nematode (EPN) Steinernema carpocapsae we have named Sc-sPLA2. We report that Sc-sPLA2 increased mortality of Drosophila melanogaster infected with Streptococcus pneumoniae and promoted increased bacterial growth. Furthermore, our data showed that Sc-sPLA2 was able to downregulate both Toll and Imd pathway-associated antimicrobial peptides (AMPs) including drosomycin and defensin, in addition to suppressing phagocytosis in the hemolymph. Sc-sPLA2 was also found to be toxic to D. melanogaster with the severity being both dose- and time-dependent. Collectively, our data highlighted that Sc-sPLA2 possessed both toxic and immunosuppressive capabilities.

An informatic workflow for the enhanced annotation of excretory/secretory proteins of Haemonchus contortus

Major advances in genomic and associated technologies have demanded reliable bioinformatic tools and workflows for the annotation of genes and their products via comparative analyses using well-curated reference data sets, accessible in public repositories. However, the accurate in silico annotation of molecules (proteins) encoded in organisms (e.g., multicellular parasites) which are evolutionarily distant from those for which these extensive reference data sets are available, including invertebrate model organisms (e.g., Caenorhabditis elegans - free-living nematode, and Drosophila melanogaster - the vinegar fly) and vertebrate species (e.g., Homo sapiens and Mus musculus), remains a major challenge. Here, we constructed an informatic workflow for the enhanced annotation of biologically-important, excretory/secretory (ES) proteins ("secretome") encoded in the genome of a parasitic roundworm, called Haemonchus contortus (commonly known as the barber's pole worm). We critically evaluated the performance of five distinct methods, refined some of them, and then combined the use of all five methods to comprehensively annotate ES proteins, according to gene ontology, biological pathways and/or metabolic (enzymatic) processes. Then, using optimised parameter settings, we applied this workflow to comprehensively annotate 2591 of all 3353 proteins (77.3%) in the secretome of H. contortus. This result is a substantial improvement (10-25%) over previous annotations using individual, "off-the-shelf" algorithms and default settings, indicating the ready applicability of the present, refined workflow to gene/protein sequence data sets from a wide range of organisms in the Tree-of-Life.

PD-L2 Blockade Exacerbates Liver Lesion in Mice Infected with Capillaria hepatica through Reducing Alternatively Activated Macrophages

Capillaria hepatica is a seriously neglected zoonotic parasite, which infects the liver of mammalian hosts, causing fibrosis or even hepatic failure. At present, the immune responses elicited by C. hepatica are not fully understood, and the role(s) of the programmed death 1 (PD-1) signaling pathway in the context of C. hepatica-induced pathology are not known. In this study, we identify that the late stage of infection with C. hepatica-especially the egg-derived antigens-modulates the host immune responses to promote alternatively activated macrophage (M2) polarization and programmed death ligand 2 (PD-L2) expression. The PD-L2-expressing alternatively activated M2 macrophages play an important role in maintaining Th2-biased regulatory immune responses, which may facilitate the survival of parasitic worms or eggs within the infected liver and reduce the liver pathology caused by the egg granulomas. Treatment with anti-PD-L2 antibody had no effect on the survival of parasitic eggs but deteriorated the pathology of egg granulomas. The obtained results suggest that PD-1/PD-L2 signaling, which is involved in alternative macrophage polarization, determines the immune response pattern and the immunopathology, consequently determining the outcome of the parasitic infection.

Excreted secreted products from the parasitic nematode Steinernema carpocapsae manipulate the Drosophila melanogaster immune response

Steinernema carpocapsae is an entomopathogenic nematode (EPN) that rapidly infects and kills a wide range of insect hosts and has been linked to host immunosuppression during the initial stages of infection. The lethal nature of S. carpocapsae infections has previously been credited to its symbiotic bacteria; however, it has become evident that the nematodes are able to effectively kill their hosts independently through their excretion/secretion products (ESPs). Here we examined how the adult Drosophila melanogaster immune system is modulated in response to S. carpocapsae ESPs in an attempt to ascertain individual pathogenic contributions of the isolated compound. We found that the S. carpocapsae ESPs decrease the survival of D. melanogaster adult flies, they induce the expression of certain antimicrobial peptide-encoding genes, and they cause significant reduction in phenoloxidase enzyme activity and delay in the melanization response in males flies. We also report that S. carpocapsae ESPs affect hemocyte numbers in both male and female individuals. Our results indicate the manipulative role of EPN ESPs and reveal sex-specific differences in the host response against nematode infection factors. These findings are beneficial as they promote our understanding of the molecular basis of nematode pathogenicity and the parasite components that influence nematode-host interactions.