The peritrophic membrane: its formation, structure, chemical composition and permeability in relation to vaccination against ectoparasitic arthropods

Three-dimensional correlative microscopy of the Drosophila female reproductive tract reveals modes of communication in seminal receptacle sperm storage

In many taxa, females store sperm in specialized storage organs. Most insect sperm storage organs have a tubular structure, typically consisting of a central lumen surrounded by epithelial cells. These specialized tubules perform the essential tasks of transporting sperm through the female reproductive tract and supporting long-term sperm survival and function. Little is known about the way in which female sperm storage organs provide an environment conducive to sperm survival. We address this using a combined light microscopy, micro computed tomography (microCT), and Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) approach for high-resolution correlative three-dimensional imaging to advance our understanding of sperm-female interactions in Drosophila melanogaster. Using this multimodal approach, we were able to scan the lower female reproductive tract and distal portion of the seminal receptacle at low magnification, and to subsequently zoom in for further analysis on an ultrastructural level. Our findings highlight aspects of the way in which the seminal receptacle keeps sperm viable in the lumen, and set the stage for further studies. The methods developed are suitable not only for Drosophila but also for other organisms with soft, delicate tissues.

Peritrophin-like Genes Are Associated with Delousing Drug Response and Sensitivity in the Sea Louse Caligus rogercresseyi

Caligus rogercresseyi is the main ectoparasite that affects the salmon industry in Chile. The mechanisms used by the parasite to support its life strategy are of great interest for developing control strategies. Due to the critical role of insect peritrophins in host–parasite interactions and response to pest control drugs, this study aimed to identify and characterize the peritrophin-like genes present in C. rogercresseyi. Moreover, the expression of peritrophin-like genes was evaluated on parasites exposed to delousing drugs such as pyrethroids and azamethiphos. Peritrophin genes were identified by homology analysis among the sea louse transcriptome database and arthropods peritrophin-protein database obtained from GenBank and UniProt. Moreover, the gene loci in the parasite genome were located. Furthermore, peritrophin gene expression levels were evaluated by RNA-Seq analysis in sea louse developmental stages and sea lice exposed to delousing drugs deltamethrin, cypermethrin, and azamethiphos. Seven putative peritrophin-like genes were identified in C. rogercresseyi with high homology with other crustacean peritrophins. Differences in the presence of signal peptides, the number of chitin-binding domains, and the position of conserved cysteines were found. In addition, seven peritrophin-like gene sequences were identified in the C. rogercresseyi genome. Gene expression analysis revealed a stage-dependent expression profile. Notably, differential regulation of peritrophin genes in resistant and susceptible populations to delousing drugs was found. These data are the first report and characterization of peritrophin genes in the sea louse C. rogercresseyi, representing valuable knowledge to understand sea louse biology. Moreover, this study provides evidence for a deeper understanding of the molecular basis of C. rogercresseyi response to delousing drugs.

Effects of chitin from Daphnia similis and its derivative, chitosan on the immune response and disease resistance of white shrimp, Litopenaeus vannamei

Daphnia similis chitin and its derivative chitosan were prepared as immunostimulants to boost the immune response and determine the ability to control infectious disease caused by Vibrio alginolyticus in white shrimp, Litopenaeus vannamei. Three experimental diets supplemented with 0% chitin or chitosan (control) and 0.4% chitin or 0.4% chitosan were fed to shrimp for 56 days. Dietary inclusion of 0.4% chitosan accelerated shrimp growth compared to chitin and control. The survival and disease resistance of shrimp increased significantly when fed chitin and chitosan diets, after pathogenic injection, as indicated by the up-regulated immune responses in respiratory burst (RB), superoxide dismutase (SOD), and phagocytic activity (PA). There were no significant differences in the total haemocyte count (THC), phenoloxidase (PO)activity, and lysozyme (LYZ) activity among the groups. No significant differences were observed for prophenoloxidase system-related gene expressions among groups. However, shrimp fed chitin, and chitosan expressed significantly higher levels of antimicrobial proteins (penaeidin 3a, crustin, and anti-lipopolysaccharide factor 2) in the haemocytes than in control. The gene expressions of catalase and heat shock protein 70 increased in the hepatopancreas of shrimp fed chitosan diet compared to the chitin and control diet. The O-linked N-acetylglucosamine transferase (ogt) was significantly higher in the haemocytes of shrimp fed chitosan and chitin than the control, but ogt was only significantly higher in the hepatopancreas of shrimp fed chitosan. Dietary chitin and chitosan also showed positive effects on the transcription of peritrophin-like protein. These findings suggest that both chitin and chitosan from D. similis are efficacious at boosting the immunity of shrimp by preventing and controlling infectious diseases caused by Vibrio and have great potential to be used as a feasible immunostimulant that significantly contributes to the circular economy.

Chitin Synthases Are Critical for Reproduction, Molting, and Digestion in the Salmon Louse (Lepeophtheirus salmonis)

Chitin synthase (CHS) is a large transmembrane enzyme that polymerizes Uridine diphosphate N-acetylglucosamine into chitin. The genomes of insects often encode two chitin synthases, CHS1 and CHS2. Their functional roles have been investigated in several insects: CHS1 is mainly responsible for synthesizing chitin in the cuticle and CHS2 in the midgut. Lepeophtheirus salmonis is an ectoparasitic copepod on salmonid fish, which causes significant economic losses in aquaculture. In the present study, the tissue-specific localization, expression, and functional role of L. salmonis chitin synthases, LsCHS1 and LsCHS2, were investigated. The expressions of LsCHS1 and LsCHS2 were found in oocytes, ovaries, intestine, and integument. Wheat germ agglutinin (WGA) chitin staining signals were detected in ovaries, oocytes, intestine, cuticle, and intestine in adult female L. salmonis. The functional roles of the LsCHSs were investigated using RNA interference (RNAi) to silence the expression of LsCHS1 and LsCHS2. Knockdown of LsCHS1 in pre-adult I lice resulted in lethal phenotypes with cuticle deformation and deformation of ovaries and oocytes in adult lice. RNAi knockdown of LsCHS2 in adult female L. salmonis affected digestion, damaged the gut microvilli, reduced muscular tissues around the gut, and affected offspring. The results demonstrate that both LsCHS1 and LsCHS2 are important for the survival and reproduction in L. salmonis.

Molecular tools-advances, opportunities and prospects for the control of parasites of veterinary importance

The recent advancement in genome sequencing facilities, proteomics, transcriptomics, and metabolomics of eukaryotes have opened door for employment of molecular diagnostic techniques for early detection of parasites and determining target molecules for formulating control strategies. It further leads to the introduction of several purified vaccines in the field of veterinary parasitology. Earlier, the conventional diagnostic methods was entirely based upon morphological taxonomy for diagnosis of parasites but nowadays improved molecular techniques help in phylogenetic study and open an another area of molecular taxonomy of parasites with high precision. Control measures based upon targeting endosymbionts in parasites like Dirofilaria immitis is also under exploration in veterinary parasitology. Metagenomics have added an inside story of parasites bionomics which have created havoc in human and animals population since centuries. Omics era is playing a key role in opening the new approaches on parasite biology. Various newer generations of safer vaccines like edible vaccines and subunit vaccines and diagnostic techniques based upon purified immunologically active epitopes have become commercially available against the parasites (helminths, protozoa and arthropod borne diseases). Nowadays, a transgenic and gene knock out studies using RNA interference and CRISPR are also helping in understanding the functions of genes and screening of target genes, which are not available before the advent of molecular tools. Molecular techniques had paramount impact on increasing the sensitivity of diagnostic tools, epidemiological studies and more importantly in controlling these diseases. This review is about the advancements in veterinary parasitology and their impact on the control of these pathogens.

Molecular drug targets for scabies: a medicinal chemistry perspective

Sarcoptes scabiei is a causative organism for scabies that affects an estimated global population of 300 million and remains a disease of significant concern. Recently, a number of potential drug targets were identified for scabies, including hydrolytic enzymes, inactivated paralogues of hydrolytic enzymes, inhibitors of host proteolytic enzymes and other proteins of interest. These discoveries remain confined to academic laboratories and institutions, failing to attract interest from researchers in commercial drug development. Here, we summarize the latest developments in the scabies mite biology and the drug targets that were subsequently identified, and we propose several peptide and nonpeptide ligands targeting the hot spots for protein-protein interactions. We also identify gaps in the development of ligands as inhibitors or modulators of these macromolecules.

The Effect of Diet on Midgut and Resulting Changes in Infectiousness of AcMNPV Baculovirus in the Cabbage Looper, Trichoplusia ni

Insecticide resistance has been reported in many important agricultural pests, and alternative management methods are required. Baculoviruses qualify as an effective, yet environmentally benign, biocontrol agent but their efficacy against generalist herbivores may be influenced by diet. However, few studies have investigated the tritrophic interactions of plant, pest, and pathogen from both a gene expression and physiological perspective. Here we use microscopy and transcriptomics to examine how diet affects the structure of peritrophic matrix (PM) in Trichoplusia ni larvae and consequently their susceptibility to the baculovirus, AcMNPV. Larvae raised on potato leaves had lower transcript levels for chitinase and chitin deacetylase genes, and possessed a thicker and more multi-layered PM than those raised on cabbage or artificial diet, which could contribute to their significantly lower susceptibility to the baculovirus. The consequences of these changes underline the importance of considering dietary influences on pathogen susceptibility in pest management strategies.

A VP24-truncated isolate of white spot syndrome virus is inefficient in per os infection

White spot syndrome virus (WSSV) is a major pathogen of penaeid shrimp. Here we identified a new WSSV strain, WSSV-CN04, from naturally infected Marsupenaeus japonicus. Whole genomic sequencing results indicate that the WSSV-CN04 genome was 281 054 bp in length, and encoded 157 hypothetic proteins. The genome sequence of WSSV-CN04 was most closely related to the low-virulent strain WSSV-CN03, sharing 97.5% sequence identity. Notably, in WSSV-CN04, the major envelop protein VP24 was not only truncated but also absent in the virions. Since VP24 was previously reported to be essential for WSSV per os infection by mediating WSSV-chitin interaction, we further analyzed the peroral infection of WSSV-CN03 and -CN04 in Litopenaeus vannamei, and show that the infectivity of WSSV-CN04 was significantly lower than that of WSSV-CN03. When compared with WSSV-CN03-infected shrimp, fewer virions were detected in the digestive tract tissues of WSSV-CN04-infected shrimp at 4 hours post-infection (hpi), and the viral titers in the animals at 24 hpi were much lower. Moreover, a peptide corresponding to VP24 chitin-binding domain reduced the amount of WSSV-CN03 in the midgut to a level similar to that of WSSV-CN04 at 4 hpi. These findings indicate that the truncation of VP24 may attenuate the peroral infectivity of WSSV-CN04, and therefore verify the important role of VP24 in WSSV per os infection.

An update on mechanism of entry of white spot syndrome virus into shrimps

Host-parasite relationships can be best understood at the level of protein-protein interaction between host and pathogen. Such interactions are instrumental in understanding the important stages of life cycle of pathogen such as adsorption of the pathogen on host surface followed by effective entry of pathogen into the host body, movement of the pathogen across the host cytoplasm to reach the host nucleus and replication of the pathogen within the host. White Spot Disease (WSD) is a havoc for shrimps and till date no effective treatment is available against the disease. Moreover information regarding the mechanism of entry of White Spot Syndrome Virus (WSSV) into shrimps, as well as knowledge about the protein interactions occurring between WSSV and shrimp during viral entry are still at very meagre stage. A cumulative and critically assessed information on various viral-shrimp interactions occurring during viral entry can help to understand the exact pathway of entry of WSSV into the shrimp which in turn can be used to device drugs that can stop the entry of virus into the host. In this context, we highlight various WSSV and shrimp proteins that play role in the entry mechanism along with the description of the interaction between host and pathogen proteins.

The Battle Against Flystrike - Past Research and New Prospects Through Genomics

Flystrike, or cutaneous myiasis, is caused by blow fly larvae of the genus Lucilia. This disease is a major problem in countries with large sheep populations. In Australia, Lucilia cuprina (Wiedemann, 1830) is the principal fly involved in flystrike. While much research has been conducted on L. cuprina, including physical, chemical, immunological, genetic and biological investigations, the molecular biology of this fly is still poorly understood. The recent sequencing, assembly and annotation of the draft genome and analyses of selected transcriptomes of L. cuprina have given a first global glimpse of its molecular biology and insights into host-fly interactions, insecticide resistance genes and intervention targets. The present article introduces L. cuprina, flystrike and associated issues, details past control efforts and research foci, reviews salient aspects of the L. cuprina genome project and discusses how the new genomic and transcriptomic resources for this fly might accelerate fundamental molecular research of L. cuprina towards developing new methods for the treatment and control of flystrike.

Origin, evolution and function of the hemipteran perimicrovillar membrane with emphasis on Reduviidae that transmit Chagas disease

The peritrophic matrix is a chitin-protein structure that envelops the food bolus in the midgut of the majority of insects, but is absent in some groups which have, instead, an unusual extra-cellular lipoprotein membrane named the perimicrovillar membrane. The presence of the perimicrovillar membrane (PMM) allows these insects to exploit restricted ecological niches during all life stages. It is found only in some members of the superorder Paraneoptera and many of these species are of medical and economic importance. In this review we present an overview of the midgut and the digestive system of insects with an emphasis on the order Paraneoptera and differences found across phylogenetic groups. We discuss the importance of the PMM in Hemiptera and the apparent conservation of this structure among hemipteran groups, suggesting that the basic mechanism of PMM production is the same for different hemipteran species. We propose that the PMM is intimately involved in the interaction with parasites and as such should be a target for biological and chemical control of hemipteran insects of economic and medical importance.

Understanding the biology and control of the poultry red mite Dermanyssus gallinae: a review

Dermanyssus gallinae, the poultry red mite (PRM), is a blood-feeding ectoparasite capable of causing pathology in birds, amongst other animals. It is an increasingly important pathogen in egg layers and is responsible for substantial economic losses to the poultry industry worldwide. Even though PRM poses a serious problem, very little is known about the basic biology of the mite. Here we review the current body of literature describing red mite biology and discuss how this has been, or could be, used to develop methods to control PRM infestations. We focus primarily on the PRM digestive system, salivary glands, nervous system and exoskeleton and also explore areas of PRM biology which have to date received little or no study but have the potential to offer new control targets.

VP24 Is a Chitin-Binding Protein Involved in White Spot Syndrome Virus Infection

Oral ingestion is the major route of infection for the white spot syndrome virus (WSSV). However, the mechanism by which virus particles in the digestive tract invade host cells is unknown. In the present study, we demonstrate that WSSV virions can bind to chitin through one of the major envelope proteins (VP24). Mutagenesis analysis indicated that amino acids (aa) 186 to 200 in the C terminus of VP24 were required for chitin binding. Moreover, the P-VP24186-200 peptide derived from the VP24 chitin binding region significantly inhibited the VP24-chitin interaction and the WSSV-chitin interaction, implying that VP24 participates in WSSV binding to chitin. Oral inoculation experiments showed that P-VP24186-200 treatment reduced the number of virus particles remaining in the digestive tract during the early stage of infection and greatly hindered WSSV proliferation in shrimp. These data indicate that binding of WSSV to chitin through the viral envelope protein VP24 is essential for WSSV per os infection and provide new ideas for preventing WSSV infection in shrimp farms.

IMPORTANCE

In this study, we show that WSSV can bind to chitin through the envelope protein VP24. The chitin-binding domain of VP24 maps to amino acids 186 to 200 in the C terminus. Binding of WSSV to chitin through the viral envelope protein VP24 is essential for WSSV per os infection. These findings not only extend our knowledge of WSSV infection but also provide new insights into strategies to prevent WSSV infection in shrimp farms.

Envelope Proteins of White Spot Syndrome Virus (WSSV) Interact with Litopenaeus vannamei Peritrophin-Like Protein (LvPT)

White spot syndrome virus (WSSV) is a major pathogen in shrimp cultures. The interactions between viral proteins and their receptors on the surface of cells in a frontier target tissue are crucial for triggering an infection. In this study, a yeast two-hybrid (Y2H) library was constructed using cDNA obtained from the stomach and gut of Litopenaeus vannamei, to ascertain the role of envelope proteins in WSSV infection. For this purpose, VP37 was used as the bait in the Y2H library screening. Forty positive clones were detected after screening. The positive clones were analyzed and discriminated, and two clones belonging to the peritrophin family were subsequently confirmed as genuine positive clones. Sequence analysis revealed that both clones could be considered as the same gene, LV-peritrophin (LvPT). Co-immunoprecipitation confirmed the interaction between LvPT and VP37. Further studies in the Y2H system revealed that LvPT could also interact with other WSSV envelope proteins such as VP32, VP38A, VP39B, and VP41A. The distribution of LvPT in tissues revealed that LvPT was mainly expressed in the stomach than in other tissues. In addition, LvPT was found to be a secretory protein, and its chitin-binding ability was also confirmed.

Identification and molecular characterization of a peritrophin-like gene, involved in the antibacterial response in Chinese mitten crab, Eriocheir sinensis

Peritrophin was first isolated from insect peritrophic membrane (PM) and was thought to protect insects from invasion of microorganisms and to stimulate digestion of food. In this study, a peritrophin-like gene (EsPT) was obtained from Eriocheir sinensis. The full length cDNA of EsPT was 1232 bp, which contained 1005 bp ORF encoding a protein of 334 amino acids, including a 22 amino acid signal peptide, and 3 conserved chitin binding type 2 domains (ChtBD2) characterized by having a 6-cysteine motif. Phylogenetic analysis showed that EsPT was clustered together with 2 insect peritrophin-44-like proteins (MdP44L from Musca domestica and CcP44L from Ceratitis capitata), an insect chitin binding peritrophin-A domain containing protein (CfPT from Coptotermes formosanus) and a crustacean peritrophin (MnPT from Macrobrachium nipponense). Tissue distribution analysis revealed that EsPT was mainly expressed in hepatopancreas, intestine and hemocytes. The expression of EsPT is regulated by lipopolysaccharide, peptidoglycan, Staphylococcus aureus, Vibrio parahaemolyticus and Aeromonas hydrophila challenge. The recombinant EsPT could bind to different microbes, and enhanced the clearance of V. parahaemolyticus in vivo. In crabs, silencing of EsPT by siRNA suppressed the elimination of V. parahaemolyticus and increasing number of bacteria, finally upregulated the expression of anti-lipopolysaccharide factor (ALF) and clip domain serine proteases (cSP). The results might indicate that EsPT was involved in the anti-bacterial innate immunity of crabs.

The immunobiology of myiasis infections--whatever happened to vaccination?

The current state of myiasis vaccine technologies are reviewed mainly in the primary research genera of Lucilia and Hypoderma. The importance of myiasis flies as primary causes of morbidity and mortality in agricultural species and man has not diminished despite the existence of good control strategies. However, the development of vaccines against myiasis infections has been relatively quiescent for more than 10 years despite the rapid development of genomic and proteomic analysis and of skills in data interpretation. The value of vaccine research in an era of chemical primacy is analysed. In fact, recent findings of drug resistance and the impact of animal welfare concerns should mean a renewed interest in alternative controls. The reasons that this has not been true to date are explored and new possibilities discussed.

Peritrophic membrane origin in adult bees (Hymenoptera): immunolocalization

The midgut is a region of the digestive tract of bees with the lumen lined by a peritrophic membrane that is composed of chitin and proteins (peritrophins). The origin of the peritrophins in the midgut of adult bees is unknown. This study used an anti-peritrophin 55-kDa antibody to immunolocalize the sites of the peritrophic membrane synthesis in nine species of adult bees' representatives of different families and sociability levels. In all studied species the peritrophin-55 is produced by digestive cells in the entire midgut in the rough endoplasmic reticulum following transference to Golgi apparatus and released by secretory vesicles, which fuses with the plasma membrane and microvilli. Thus, in the representatives of different groups of bees, the PM is of type I.

Ectoparasite performance when feeding on reproducing mammalian females: an unexpected decrease when on pregnant hosts

Reproduction is an energy-demanding activity in mammalian females, with increased energy requirements during pregnancy and, especially, during lactation. To better understand the interactions between parasitism and host reproduction, we investigated feeding and reproductive performance of fleas (Xenopsylla ramesis) parasitizing non-reproducing, pregnant or lactating gerbilline rodents (Meriones crassus). Based on energetic considerations, we predicted that feeding and reproductive performance of fleas would be lowest on non-breeding females, moderate on pregnant females and highest on lactating females. We estimated feeding performance of the fleas via absolute and mass-specific bloodmeal size and reproductive performance via egg production and latency to peak oviposition. Host reproductive status had no effect on either absolute or mass-specific bloodmeal size or the day of peak oviposition, but significantly affected the daily number of eggs produced by a female flea. Surprisingly, and contrary to our predictions, egg production of fleas fed on pregnant rodents was significantly lower than that of fleas on non-reproducing and lactating rodents, while no difference in egg production between fleas feeding on non-reproducing and lactating hosts was found. Our results suggest that differences in parasite reproduction when feeding on hosts of different reproductive status are not associated with the different energy requirements of the hosts at non-breeding, pregnancy and lactation but rather with variation in hormonal and/or immune status during these periods.

A new shrimp peritrophin-like gene from Exopalaemon carinicauda involved in white spot syndrome virus (WSSV) infection

Peritrophin was first separated from insect peritrophic membrane (PM), and it played an important role in stimulating the digestion of food and protecting insects from invasion by microorganisms. In this study, a full-length cDNA of a new peritrophin-like protein (EcPT) was cloned from the ridgetail white shrimp Exopalaemon carinicauda, which was an excellent experimental animal for shrimp. The full length cDNA comprised 1235 bp including an 873 bp open reading frame encoding 291 amino acids. The deduced amino acid sequence contained a segment of signal peptide and three conserved chitin binding type 2 domains (ChtBD2) characterized by having a 6-cysteine motif. Tissue expression analysis revealed that EcPT was mainly expressed in stomach and gills, which were also the two main target tissues of WSSV infection. The transcription levels of EcPT in both stomach and gills were found to have significantly changed upon WSSV infection by real-time PCR. Silencing EcPT by dsRNA interference led to higher survival rate of shrimp against WSSV challenge, which suggested that EcPT might be involved in WSSV infection.

Mucosal immunity in the gut: the non-vertebrate perspective

Much is now known about the vertebrate mechanisms involved in mucosal immunity, and the requirement of commensal microbiota at mucosal surfaces for the proper functioning of the immune system. In comparison, very little is known about the mechanisms of immunity at the barrier epithelia of non-vertebrate organisms. The purpose of this review is to summarize key experimental evidence illustrating how non-vertebrate immune mechanisms at barrier epithelia compare to those of higher vertebrates, using the gut as a model organ. Not only effector mechanisms of gut immunity are similar between vertebrates and non-vertebrates, but it also seems that the proper functioning of non-vertebrate gut defense mechanisms requires the presence of a resident microbiota. As more information becomes available, it will be possible to obtain a more accurate picture of how mucosal immunity has evolved, and how it adapts to the organisms' life styles.

Structure and partial protein profiles of the peritrophic membrane (PM) from the gut of the shrimp Litopenaeus vannamei

Peritrophic membrane (PM) is a non-cellular structure surrounding the food bolus in invertebrate's midgut. In this study, the shrimp Litopenaeus vannamei was found continuously secreting a tube-like PM enclosing the fecal pellets. The PM structure was membranous in this penaeid shrimp which was similar to that in Sicyonia ingentis studied and was primarily composed of chitin and proteins. Chitin was detected along the whole PM. By using the approach of gel electrophoresis and mass spectrometry of tryptic peptides, the most extracted proteins from the shrimp PMs were identified mainly including digestion-related, immune-related, antioxidant proteins and proteins related to PM structure. This suggests that PM may participate in modulating its permeability and immobilizating the digestive enzymes, actively protect the gut from pathogen contact, and play an important role in the gut immune system.

The role of peritrophic membrane in the resistance of Anticarsia gemmatalis larvae (Lepidoptera: Noctuidae) during the infection by its nucleopolyhedrovirus (AgMNPV)

The aim of this study was to analyze morphologically the peritrophic membrane (PM) of Anticarsia gemmatalis larvae resistant (RL) and non-resistant (susceptible) (SL) to the A. gemmatalis multicapsid nucleopolyhedrovirus (AgMNPV), in the presence of viral infection. Also, in this investigation the results between SL and RL were compared to improve the understanding of the resistance mechanisms to the virus. The PM of SL of A. gemmatalis was less efficient as a barrier against the viral infection since it was found to be more fragile than the PM of RL. The lower chitin content as seen from weaker fluorescent staining in SL as well as the abundance of non-solubilized vesicular materials in the ectoperitrophic space, would cause the malformation of this membrane, facilitating the passage of the virus toward the epithelium of the midgut. On the other hand, in RL, the intensity of WGA (wheat germ agglutinin)-conjugated FITC (fluorescein) reaction of the PM was greater than in SL, making this insect more resistant to infection. We can conclude that the effectiveness of the PM in protecting against pathogens is dependent on the integrity of the epithelial cells of the midgut and of the structural preservation of the PM, being directly implicated in the resistance of A. gemmatalis larvae to AgMNPV.

Live imaging reveals a biphasic mode of dissemination of Borrelia burgdorferi within ticks

Lyme disease is caused by transmission of the spirochete Borrelia burgdorferi from ticks to humans. Although much is known about B. burgdorferi replication, the routes and mechanisms by which it disseminates within the tick remain unclear. To better understand this process, we imaged live, infectious B. burgdorferi expressing a stably integrated, constitutively expressed GFP reporter. Using isolated tick midguts and salivary glands, we observed B. burgdorferi progress through the feeding tick via what we believe to be a novel, biphasic mode of dissemination. In the first phase, replicating spirochetes, positioned at varying depths throughout the midgut at the onset of feeding, formed networks of nonmotile organisms that advanced toward the basolateral surface of the epithelium while adhering to differentiating, hypertrophying, and detaching epithelial cells. In the second phase of dissemination, the nonmotile spirochetes transitioned into motile organisms that penetrated the basement membrane and entered the hemocoel, then migrated to and entered the salivary glands. We designated the first phase of dissemination "adherence-mediated migration" and provided evidence that it involves the inhibition of spirochete motility by one or more diffusible factors elaborated by the feeding tick midgut. Our studies, which we believe are the first to relate the transmission dynamics of spirochetes to the complex morphological and developmental changes that the midgut and salivary glands undergo during engorgement, challenge the conventional viewpoint that dissemination of Lyme disease-causing spirochetes within ticks is exclusively motility driven.

Susceptibility/resistance of Anticarsia gemmatalis larvae to its nucleopolyhedrovirus (AgMNPV): Structural study of the peritrophic membrane

This investigation compares the peritrophic membrane (PM) morphology along the midgut of susceptible (SL) and resistant (RL) Anticarsia gemmatalis larvae to the AgMNPV. The PM increased the thickness from the anterior to the posterior midgut region in both insects strain; however, the intensity of FITC-WGA reaction of the PM in the RL were greater than in SL. The PM in RL was ultrastructurally constituted by several layers of fibrous/vesicular materials in comparison with the few ones in SL. Our results showed that the structure of PM in the RL could be one of the resistance barriers to AgMNPV.

Peritrophic membrane of the penaeid shrimp Sicyonia ingentis: structure, formation, and permeability

Peritrophic membranes (PTMs) are secreted acellular layers that separate ingested materials from the gut epithelium in a variety of invertebrates. In insects and crustaceans, PTMs are produced in the midgut trunk (MGT, or intestine), but the MGT in decapod crustaceans, unlike that of insects, is not involved with digestion or absorption of food. We demonstrate that the PTM in the penaeid shrimp Sicyonia ingentis is similar to that in other crustaceans that have been studied and is primarily composed of chitin. The lectin WGA binds only to the PTM and glycocalyx along the microvilli of the midgut cells, which is consistent with the suggestion that the chitin is synthesized along the microvilli. The PTM is only permeable to inert particles smaller than 20 nm. We also describe the secretion of granules, which fill the apices of the epithelial cells, into the ectoperitrophic space. Although their function is not clear, they do not contribute to the PTM.

Progress and opportunities in the development of vaccines against mites, fleas and myiasis-causing flies of veterinary importance

Despite the potential benefits offered by vaccination against ectoparasites, there have been few commercial successes with this strategy, in spite of sustained efforts using increasingly sophisticated techniques. This review outlines the progress and challenges offered by recent research into vaccination against some of the major ectoparasites of veterinary importance, and provides an insight into the opportunities arising from our increased understanding of the immunology of host-parasite relationships and the potential for exploitation of this knowledge and that arising from new genomic data provided by expressed sequence tag projects.

Sex-biased parasitism, seasonality and sexual size dimorphism in desert rodents

We investigated seasonality of gender differences in the patterns of flea infestation in nine rodent species to test if sex-biased parasitism in terms of mean abundance, species richness, prevalence and the level of aggregation (a) varies among hosts and between seasons, and (b) is linked to sexual size dimorphism. Sexual size differences were significant in both summer and winter in Acomys cahirinus, Gerbillus pyramidum and Meriones crassus, and in winter only in Acomys russatus, Gerbillus dasyurus, Gerbillus nanus and Sekeetamys calurus. Sexual size dimorphism was male biased except for A. russatus in which it was female biased. Manifestation of sexual differences in flea infestation was different among hosts between seasons. A significant effect of sex on mean flea abundance was found in six hosts, on mean flea species richness in five hosts and on prevalence in two hosts. Male-biased parasitism was found in summer in one host only and in winter in five hosts. Female-biased parasitism occurred in winter in A. russatus. Gender differences in the slopes of the regressions of log-transformed variances against log-transformed mean abundances occurred in three hosts. No relationship was found between sexual size dimorphism and any parasitological parameter in any season using both conventional regressions and the method of independent contrasts. Our results suggest that sex-biased parasitism is a complicated phenomenon that involves several different mechanisms.

Modeling the structure of the type I peritrophic matrix: characterization of a Mamestra configurata intestinal mucin and a novel peritrophin containing 19 chitin binding domains

Twelve to fourteen integral proteins were found to reside in the Type I peritrophic matrix (PM) of Mamestra configurata (bertha armyworm) larvae. Several methods were employed, including de novo peptide sequencing, the generation of a midgut-specific EST database and immunological screening, which led to the isolation of cDNAs encoding two integral PM proteins. McPM1, the largest PM protein described to date at 202 kDa, was comprised of a concatamer of 19 chitin binding domains (CBD), 12 of which resided within a central repetitive region consisting of six iterations of a two CBD module. The protein was found to reside within the PM primarily as several lower molecular weight, presumably proteolytically processed, forms. McMUC1 was similar in structure to other insect intestinal mucins (IIM) and was highly glycosylated. The expression of both proteins was restricted to the larval midgut. Lower molecular weight proteins that may represent non- and partially glycosylated forms of McMUC1 were also recognized by an anti-McMUC1 antiserum. These were preferentially degraded upon ingestion of M. configurata multi-capsid nucleopolyhedrovirus by larvae, possibly by a viral-encoded metalloprotease. A molecular model of PM structure is presented featuring the interaction of McPM1 with chitin inter-fibril junctions and McMUC1 with the extended chains in the internodal regions. The potential for interaction between PM proteins via intermolecular disulfide bond formation and through association of CBD with N-linked glycans is discussed.

Immune responses to fleas in two rodent species differing in natural prevalence of infestation and diversity of flea assemblages

We studied in vivo immune response to fleas in two gerbils, Gerbillus dasyurus and Gerbillus andersoni allenbyi, which differed in their natural species richness of flea assemblages and prevalence of infestation. G.dasyurus is parasitized naturally by several flea species, but the prevalence of infestation is low, whereas G. a. allenbyi is parasitized by a single flea species, with high prevalence of infestation. We hypothesized that immunological parameters and the cell-mediated specific immune response to an antigen from an unfamiliar flea species differ between the two gerbil species. Parasitized and control gerbils of both species demonstrated similar, relatively low levels of spontaneous glucose consumption. The same was true for the phytohemagglutinin treatment. Responses to antigen from unfamiliar flea species were higher than both spontaneous glucose consumption and response to phytohemagglutinin in parasitized and control G. a. allenbyi and parasitized G. dasyurus. However, no significant difference in the spontaneous blast transformation index and responses to both phytohemagglutinin and flea antigen was found in control G. dasyurus. The number of white blood cells was significantly lower in control than in parasitized G. dasyurus, whereas no difference in the number of white blood cells was found between control and parasitized G. a. allenbyi. The levels of circulating immune complexes and concentrations of immunoglobulins did not differ between parasitized and control individuals in both species. Phagocytic activity was significantly higher in males than in females of G. a. allenbyi but not of G. dasyurus. In addition, phagocytes of G. dasyurus appeared to be significantly more active than those of G. a. allenbyi.

Immune response to fleas in a wild desert rodent: effect of parasite species, parasite burden, sex of host and host parasitological experience

We studied immune responses of the jird Meriones crassus to different flea species belonging to the same family. We used jirds maintained in an outdoor enclosure (enclosure; N=18) and parasitized by fleas Xenopsylla conformis mycerini and Xenopsylla ramesis, and also jirds born in the laboratory to previously parasitized mothers(laboratory animals; N=23). We asked (i) whether cross-immunity to different fleas occurs, (ii) whether there is a sex difference in immune responses to flea parasitism and (iii) whether the severity of the immune responses depends on parasite load. In the enclosure animals, immune response to antigen from the unfamiliar flea Synosternus cleopatrae pyramidisdid not differ from those to antigens from the familiar fleas. In contrast,laboratory rodents demonstrated no difference in the immune response between S. c. pyramidis antigen and either the phytohemagglutinin treatment or controls, although their responses to antigens of fleas familiar to their mothers (X. c. mycerini and X. ramesis) were significantly higher than those to antigen of S. c. pyramidis and phytohemagglutinin. The results clearly demonstrated that (i) cross-reactivity in rodent responses to different flea species occurred for enclosure but not for laboratory jirds and (ii) immune-naïve animals whose mothers were parasitized by fleas had some degree of immunity against fleas. The only sex difference in immunological parameters was the higher level of circulating immune complexes in females than in males. Only phagocytic activity was affected by flea burden, decreasing with an increase in flea numbers.

Cloning and characterization of five cDNAs encoding peritrophin-A domains from the cat flea, Ctenocephalides felis

Five cDNAs encoding peritrophin-A domains were identified as expressed sequence tags (ESTs) from flea hindgut and Malpighian tubule (HMT) cDNA libraries. The full-length cDNAs for each were subsequently isolated and sequenced. Three of the encoded proteins were similar to published peritrophin sequences, and thus were called "peritrophin-like", or PL1, PL2, and PL3. The other two sequences had similarity to both mucin and peritrophin proteins, and were called "mucin/peritrophin-like", or MPL1 and MPL2. The predicted protein sequences encoded by these cDNAs all contained a signal sequence and one or more peritrophin-A domains, which have been shown in other proteins to bind chitin. Aside from the peritrophin-A domains, the sequences shared little or no similarity to each other or to other proteins in the GenBank non-redundant database. The predicted protein sequences were variable in size, ranging in length from 81 to 453 amino acids. The two MPL proteins contained putative N-linked and O-linked glycosylation sites, including a region of seven nearly perfect tandem repeats in the MPL1 protein sequence. Northern blot analysis of different flea lifestages and fed adult timepoints showed distinct mRNA expression patterns for each gene, although all five transcripts were primarily or exclusively detected in the HMT tissues in adults. The PL1 protein was detected by immuno-blot in soluble and insoluble protein extracts from unfed and fed adult fleas. The PL1 protein from the insoluble fractions appeared to be approximately 1 kDa larger than the PL1 protein from the soluble protein fractions. Immunohistochemistry performed on flea thin sections revealed that the PL1 protein was detected in the Malpighian tubules, hindgut, rectum, and trachea. Unpurified native PL1 protein from both soluble and insoluble protein fractions was tested for chitin-binding activity but did not bind to chitin under the conditions tested. These results show that the flea peritrophin-like proteins may have biological functions that are distinct from the peritrophic matrix and from the binding of chitin.

Histochemical localization of N-acetyl-galactosamine in the midgut Lutzomyia longipalpis (Diptera: Psychodidae)

The binding of lectins to the midgut of the female sand fly Lutzomyia longipalpis (Lutz & Neiva) was investigated using lectin-gold conjugates. Midguts from laboratory-reared flies provided fructose solution and/or blood fed on hamster were dissected at 6, 24, and 48 h and at 5 and 7 d after feeding. Before examination by transmission electron microscopy, each midgut was sectioned, incubated with lectins from four sources (Canavalia ensiformis [ConA], Helix pomata agglutinin [HPA], peanut agglutinin [PNA], and wheat germ agglutinin [WGA] ), then conjugated with colloidal gold. Only HPA, which is specific for N-acetyl-galactosamine (GalNAc), bound to the midgut. Binding sites were cytoplasmic secretory granules and microvilli throughout the length of the midgut epithelium. Binding occurred in sand flies fed fructose as well as in flies receiving a blood meal. The presence of GalNAc on the midgut microvilli of sand flies before, during, and after blood feeding indicates this amino-sugar is not altered by digestion. As a structural component, GalNAc may represent a terminal on a receptor molecule. The failure of the sand fly peritrophic matrix to bind WGA by N-acetylglucosamine may be caused by the complex composition of the membrane, which renders N-glycan inaccessible to the lectin-gold conjugate.

The peritrophic matrix of hematophagous insects

The peritrophic matrix (PM) is an extracellular envelope that lines the digestive tract of most insects. It is thought to play key roles in protecting insects from pathogens and facilitating digestion. Until recently, little information was available on the molecular composition of the PM. This review summarizes recent progress in the study of the PM from hematophagous insects, with emphasis on molecular and physiological aspects. Topics discussed include the presence of chitin and protein diversity in the PM, cloning and characterization of genes encoding PM proteins, PM permeability, and the role of the PM as a barrier for pathogens.

The intrinsic peritrophic matrix protein peritrophin-95 from larvae of Lucilia cuprina is synthesised in the cardia and regurgitated or excreted as a highly immunogenic protein

The intrinsic peritrophic matrix glycoprotein, peritrophin-95, from the midgut of larvae of Lucilia cuprina can only be solubilized from the matrix using strong denaturants. This suggests that the protein has a structural role in the matrix. Consistent with this is the finding that immuno-gold and immuno-fluorescence localizations of the protein showed a uniform distribution within the peritrophic matrix. RT-PCR demonstrated that expression of peritrophin-95 mRNA was restricted to the larval cardia, a small organ located in the anterior midgut from which the type 2 peritrophic matrix originates. Immuno-blots and ELISAs demonstrated that the sera from sheep infested naturally or artificially with these larvae recognised peritrophin-95. This indicates that peritrophin-95 stimulates the ovine immune system during larval infestation even though the protein is firmly attached to the peritrophic matrix in the larval midgut and seemingly "concealed" from the ovine immune surveillance system. Analyses of larval regurgitated or excreted material by immuno-blots, immuno-affinity purification and amino-terminal sequencing demonstrated the presence of soluble monomeric peritrophin-95. These results indicate that peritrophin-95, a candidate vaccine antigen for use in sheep is not a "concealed" antigen as previously thought. The presence of soluble peritrophin-95 in the regurgitated/excreted material from larvae suggests that this protein may be involved in a maturation phase of peritrophic matrix production, a by-product of which is the excretion or regurgitation of soluble peritrophin-95.

Immunological control of ectoparasites: past achievements and future research priorities

Recombinant vaccines are available for the control of the tick Boophilus microplus, while progress has been made in the development of vaccines against Lucilia cuprina and Chrysomya bezziana. Literature suggests that the control of other ectoparasites is feasible, either through the duplication in a vaccine of naturally acquired immunity or through 'concealed' antigen vaccines. Major deficiencies in our current knowledge however point to possible research opportunities for the future. The identification of protective antigens from all species is proceeding slowly, particularly for the antigens of naturally acquired immunity. Our capacity to produce effective recombinant antigens has progressed greatly, though there remains a major difficulty where some or all of the protective effect is due to immunogenic oligosaccharide. Our understanding of protective mechanisms is limited. The delivery of the appropriate immunological response remains difficult. Nevertheless, some of the most critical areas of ignorance are in basic biological issues: factors which affect the susceptibility of particular pest species to immunological attack and the implications of vaccine-induced effects for pest and disease control under field conditions. Increasingly too, effective pest control is likely to demand the integration of a variety of control technologies. The study of this integration is in its infancy.

Digestion of host immunoglobulin and activity of midgut proteases in the buffalo fly Haematobia irritans exigua

The digestion of blood by the buffalo fly (Haematobia irritans exigua) was monitored for 6h at 33 degrees C after a single meal. Following the meal, the concentration of soluble protein within the midgut increased to a peak at 2 hours then decreased steadily over the next 4h. The magnitude of the increase in soluble protein at 2h indicated a release of protein from another source; most likely from lysed red blood cells. The immunoglobulin (IgG) fraction of the blood meal was digested rapidly (50% within one hour of feeding) and fully digested within 4h. This is indicative of its accessibility to digestive enzymes within the midgut. In contrast, when flies had continuous access to blood, the concentration of IgG in the midgut remained at a more constant level. The loss of antigen-binding activity of a specific antibody was more rapid than complete degradation of the IgG, with 70% of binding activity lost within one hour of feeding. The level of trypsin activity in the midgut increased from pre-feeding levels to reach a peak at 2h before returning to basal levels after 6h. The pattern of trypsin activity follows closely that of the concentration of soluble protein in the midgut (r=0.88). The activity of leucine aminopeptidase in the midgut also increased immediately after feeding and remained elevated for 4 h before declining to a basal level after 6h. The rapid digestion of IgG and subsequent loss of antibody activity suggests that for a specific anti-buffalo fly antibody to be effective it would need to be able to either evade the digestive system or induce a rapid response.

Vaccination of sheep against larvae of the sheep blowfly (Lucilia cuprina)

Four first stage larval antigens from the sheep blowfly were identified using supernatants from cultures of antibody secreting cells. These partially purified larval antigens, when added to Montanide ISA-25 containing recombinant ovine IL-1 beta (rovIL-1 beta) were used to successfully vaccinate sheep against larvae of the sheep blowfly. Significantly less strikes were recorded on vaccinated sheep compared to controls (P < 0.033) with surviving larvae from vaccinated sheep up to 85% smaller than larvae from control sheep. RovIL-1 beta was found to be an important component of the vaccine. Vaccinated sheep showed both humoral and cellular immune responses to the larval antigens. Antibody levels generally correlated directly with delayed-type hypersensitivity (DTH) responses, but neither antibody nor DTH correlated positively with protection in vaccinated sheep. Skin sections removed from individual sheep immediately after challenge revealed aggregations of CD4+, gamma delta-TCR+ and CD1+ cells located directly under the epidermis in vaccinated sheep.

The effect of immune and inflammatory mediators on growth of Lucilia cuprina larvae in vitro

Immune and inflammatory responses occurring during dermal infestation by larvae of Lucilia cuprina can retard larval growth and development. This study examined the effect of 4 classes of humoral inflammatory mediators on larval growth in an in vitro assay. Mediators of plasma leakage (histamine, bradykinin, platelet-activating factor and serotonin), leucocyte chemotactic agonists (activated complement, leukotriene B4 and interleukin-8), effector molecules of immune responses (interleukin-1 beta, tumour necrosis factor-alpha and interferon-gamma) and endotoxin all failed to inhibit larval growth. In contrast, immunoglobulins isolated from immune serum caused marked retardation of larval growth. The results suggest that humoral mediators of inflammatory and immune responses do not play a role in immune defence against Lucilia cuprina.