Dynamic Interplay of Metabolic and Transcriptional Responses in Shrimp during Early and Late Infection Stages of Enterocytozoon hepatopenaei (EHP)

Enterocytozoon hepatopenaei (EHP) is a microsporidian parasite that infects Litopenaeus vannamei, causing severe hepatopancreatic microsporidiosis (HPM) and resulting in significant economic losses. This study utilizes a combined analysis of transcriptomics and metabolomics to unveil the dynamic molecular interactions between EHP and its host, the Pacific white shrimp, during the early and late stages of infection. The results indicate distinct immunological, detoxification, and antioxidant responses in the early and late infection phases. During early EHP infection in shrimp, immune activation coincides with suppression of genes like Ftz-F1 and SEPs, potentially aiding parasitic evasion. In contrast, late infection shows a refined immune response with phagocytosis-enhancing down-regulation of Ftz-F1 and a resurgence in SEP expression. This phase is characterized by an up-regulated detoxification and antioxidant response, likely a defense against the accumulated effects of EHP, facilitating a stable host-pathogen relationship. In the later stages of infection, most immune responses return to baseline levels, while some immune genes remain active. The glutathione antioxidant system is suppressed early on but becomes activated in the later stages. This phenomenon could facilitate the early invasion of EHP while assisting the host in mitigating oxidative damage caused by late-stage infection. Notably, there are distinctive events in polyamine metabolism. Sustained up-regulation of spermidine synthase and concurrent reduction in spermine levels suggest a potential role of polyamines in EHP development. Throughout the infection process, significant differences in genes such as ATP synthase and hexokinase highlight the continuous influence on energy metabolism pathways. Additionally, growth-related pathways involving amino acids such as tryptophan, histidine, and taurine are disrupted early on, potentially contributing to the growth inhibition observed during the initial stages of infection. In summary, these findings elucidate the dynamic interplay between the host, Litopenaeus vannamei, and the parasite, EHP, during infection. Specific phase differences in immune responses, energy metabolism, and antioxidant processes underscore the intricate relationship between the host and the parasite. The disruption of polyamine metabolism offers a novel perspective in understanding the proliferation mechanisms of EHP. These discoveries significantly advance our comprehension of the pathogenic mechanisms of EHP and its interactions with the host.

A comparative transcriptome analysis of how shrimp endure and adapt to long-term symbiosis with Enterocytozoon hepatopenaei infection

Enterocytozoon hepatopenaei (EHP) is a prevalent microsporidian pathogen responsible for hepatopancreatic microsporidiosis (HPM) in Litopenaeus vannamei. This infection not only leads to slowed growth in shrimp abut aslo inflicts substantial economic losses in the global aquaculture industry. However, the molecular mechanisms by which EHP influences the host during various infection stages remain unclear. This study employed comparative transcriptomics to examine the effects of EHP infection on Litopenaeus vannamei between early and late stage of infection groups. Utilizing transcriptomic approaches, we identified differentially expressed genes (DEGs) with notable biological significance through the COG, GO, KEGG, GSEA, and Mufzz time-series methodologies. The results reveal that EHP infection considerably influences host gene expression, with marked differences between early and late infection across distinct timeframes. Key processes such as detoxification, cell apoptosis, and lipid metabolism are pivotal during host-parasite interactions. Hexokinase and phosphatidic acid phosphatase emerge as key factors enabling invasion and sustained effects. Cytochrome P450 and glucose-6-phosphate dehydrogenase could facilitate infection progression. EHP significantly impacts growth, especially through ecdysteroids and 17β-estradiol dehydrogenase. By delineating stage-specific effects, we gain insights into interaction between EHP and Litopenaeus vannamei, showing how intracellular pathogens reprogram host defenses into mechanisms enabling long-term persistence. This study provides a deeper understanding of host-pathogen dynamics, emphasizing the interplay between detoxification, metabolism, immunity, apoptosis and growth regulation over the course of long-term symbiosis.

Metagenomic Studies Reveal the Evidence of Akkermansia muciniphila and Other Probiotic Bacteria in the Gut of Healthy and Enterocytozoon hepatopenaei (EHP)-Infected Farmed Penaeus vannamei

Penaeus vannamei (whiteleg shrimp) is the most widely cultured shrimp globally. Enterocytozoon hepatopenaei (EHP), a microsporidian parasite, infects P. vannamei and causes severe growth retardation, subsequent production, and economic losses in the shrimp culture. The influence of EHP infection in the shrimp gut microbiota is poorly studied, and this would be an interesting area to investigate since the gut microbiome of shrimp influences a number of key host processes such as digestion and immunity. In this study, a metagenomic approach was followed to compare the overall species richness of the gut microbiota of EHP-infected and healthy P. vannamei. Bacterial genomic DNA from the healthy and EHP-infected gut sample were profiled for the bacterial 16S rRNA gene, targeting the V3-V4 conserved region. Operational taxonomic units (OTUs), an approximation of definitive taxonomic identity, were identified based on the sequence similarity within the sample reads and clustered together using a cut-off of 97% identity using UCLUST. The OTUs were then used for the computation of alpha diversity and beta diversity for each sample. EHP-infected gut sample showed lower bacterial abundance throughout the family, class, order, genus, and species levels when compared to healthy gut sample. This study shows that the shrimp gut microbiota is sensitive and exhibits a high level of plasticity during a microsporidian infection like EHP. Furthermore, Akkermansia muciniphila, a novel probiotic bacterium, has been reported in the shrimp gut for the first time.

Application of PCR-based diagnostic tools that target Enterocytozoon hepatopenaei for the molecular detection of a Vittaforma-like microsporidium that infects Penaeus vannamei from Costa Rica

Several PCR methodologies are available for the detection of Enterocytozoon hepatopenaei (EHP) that target the SSU rRNA gene. However, these methodologies are reported as unsuitable for the detection of EHP due to specificity issues. Here, we report the applicability of two commonly used SSU rRNA methodologies for the detection of additional microsporidia from the genus Vittaforma that is present in cultured Penaeus vannamei from Costa Rica. The molecular detection of DNA of the novel microsporidia can only be achieved using SSU rRNA targeting methodologies and does not cross-react with the highly specific spore wall protein gene PCR detection method.

Molecular characterization of turtle-like protein in whiteleg shrimp (Litopenaeus vannamei) and its role in Enterocytozoon hepatopenaei infection

Enterocytozoon hepatopenaei (EHP) is a microsporidian parasite that infects shrimp hepatopancreas, causing growth retardation and disease susceptibility. Knowledge of the host-pathogen molecular mechanisms is essential to understanding the microsporidian pathogenesis. Turtle-like protein (TLP) is part of the immunoglobulin superfamily of proteins, which is widely distributed in the animal kingdom. TLP has multiple functions, such as cell surface receptors and cell adhesion molecules. The spore wall proteins (SWPs) of microsporidia are involved in the infection mechanisms. Some SWPs are responsible for spore adherence, which is part of the activation and host cell invasion processes. Previous studies showed that TLP from silkworms (Bombyx mori) interacted with SWP26, contributing to the infectivity of Nosema bombycis to its host. In this study, we identified and characterized for the first time, the Litopenaeus vannamei TLP gene (LvTLP), which encodes an 827-aa protein (92.4 kDa) composed of five immunoglobulin domains, two fibronectin type III domains, and a transmembrane region. The LvTLP transcript was expressed in all tested tissues and upregulated in the hepatopancreas at 1 and 7 days post-cohabitation (dpc) and at 9 dpc in hemocytes. To identify the LvTLP binding counterpart, recombinant (r)LvTLP and recombinant (r)EhSWP1 were produced in Escherichia coli. Coimmunoprecipitation and enzyme-linked immunosorbent assays demonstrated that rLvTLP interacted with rEhSWP with high affinity (KD = 1.20 × 10-7 M). In EHP-infected hepatopancreases, LvTLP was clustered and co-localized with some of the developing EHP plasmodia. Furthermore, LvTLP gene silencing reduced the EHP copy numbers compared with those of the control group, suggesting the critical role of LvTLP in EHP infection. These results provide insight into the molecular mechanisms of the host-pathogen interactions during EHP infection.

Natural Antimicrobials Block the Host NF-κB Pathway and Reduce Enterocytozoon hepatopenaei Infection Both In Vitro and In Vivo

The objective of this work was to investigate, for the first time, the antioxidant effect of a mixture of natural antimicrobials in an Enterocytozoon hepatopenaei (EHP) shrimp-gut model of infection and the biological mechanisms involved in their way of action. The study approach included investigations, firstly, in vitro, on shrimp-gut primary (SGP) epithelial cells and in vivo by using EHP-challenged shrimp. Our results show that exposure of EHP spores to 0.1%, 0.5%, 1%, and 2% AuraAqua (Aq) significantly reduced spore activity at all concentrations but was more pronounced after exposure to 0.5% Aq. The Aq was able to reduce EHP infection of SGP cells regardless of cells being pretreated or cocultured during infection with Aq. The survivability of SGP cells infected with EHP spores was significantly increased in both scenarios; however, a more noticeable effect was observed when the infected cells were pre-exposed to Aq. Our data show that infection of SGP cells by EHP activates the host NADPH oxidases and the release of H₂O₂ produced. When Aq was used during infection, a significant reduction in H₂O₂ was observed concomitant with a significant increase in the levels of CAT and SOD enzymes. Moreover, in the presence of 0.5% Aq, the overproduction of CAT and SOD was correlated with the inactivation of the NF-κB pathway, which, otherwise, as we show, is activated upon EHP infection of SGP cells. In a challenge test, Aq was able to significantly reduce mortality in EHP-infected shrimp and increase the levels of CAT and SOD in the gut tissue. Conclusively, these results show, for the first time, that a mixture of natural antimicrobials (Aq) can reduce the EHP-spore activity, improve the survival rates of primary gut-shrimp epithelial cells and reduce the oxidative damage caused by EHP infection. Moreover, we show that Aq was able to stop the H₂O₂ activation of the NF-κB pathway of Crustins, Penaeidins, and the lysozyme, and the CAT and SOD activity both in vitro and in a shrimp challenge test.

Role of hemocytin from Litopenaeus vannamei in immune response against microsporidian, Enterocytozoon hepatopenaei

Hemocytin, a multidomain hemostasis-related protein, is a homologous protein of hemolectin in Drosophila melanogaster and von Willebrand factor (vWF) in humans. The vWF type D (VWD) domain in hemocytin is thought to be a major mediator of hemocyte aggregation and the prophenoloxidase (proPO) activation system. Here, we report for the first time the role of hemocytin from Litopenaeus vannamei (LvHCT) against Enterocytozoon hepatopenaei (EHP), the pathogenic microsporidian causing hepatopancreatic microsporidiosis in Pacific white shrimp (L. vannamei). The LvHCT gene contains 58,366 base pairs consisting of 84 exons encoding for 4267 amino acids. Multiple sequence alignment and phylogenetic analysis revealed that LvHCT was clustered with crustacean hemocytins. Gene expression analysis by quantitative real-time RT-PCR showed that LvHCT in hemocytes was significantly upregulated at 9 and 11 days post-EHP cohabitation, which was consistent with EHP copy numbers in the infected shrimp. To further investigate the biological function of LvHCT in EHP infection, a recombinant protein containing an LvHCT-specific VWD domain (rLvVWD) was expressed in Escherichia coli. In vitro agglutination assays showed that rLvVWD was functionally representative of LvHCT and induced aggregation of pathogens, including Gram-negative and -positive bacteria, fungi, and EHP spore. LvHCT suppression resulted in higher EHP copy numbers and proliferation due to the lack of hemocytin-mediated EHP spore aggregation in LvHCT-silenced shrimp. Moreover, immune-related genes in the proPO-activating cascade and Toll, IMD and JAK/STAT signaling pathways were upregulated to eliminate the over-controlled EHP in LvHCT-silenced shrimp. Furthermore, the impaired phenoloxidase activity due to LvLGBP suppression was recovered after rLvVWD injection, suggesting that LvHCT may be directly involved in phenoloxidase activation. In conclusion, a novel LvHCT is involved in shrimp immunity against EHP via EHP spore aggregation and possible activation of the proPO-activating cascade.

Analysis of differentially expressed proteins after EHP-infection and characterization of caspase 3 protein in the whiteleg shrimp (Litopenaeus vannamei)

Whiteleg shrimp (Litopenaeus vannamei) is the most important species of shrimp farmed worldwide in terms of its economic value. Enterocytozoon hepatopenaei (EHP) infects the hepatopancreas, resulting in the hepatopancreatic microsporidiosis (HPM) of the host, which causes slow growth of the shrimp and poses a threat to the farming industry. In this study, differentially expressed proteins (DEPs) between EHP-infected and uninfected shrimp were investigated through proteomics sequencing. A total of 9908 peptides and 2092 proteins were identified. A total of 69 DEPs were identified in the hepatopancreas (HP), of which, 28 were upregulated and 41 were downregulated. Our results showed that the differences among the level of multiple proteins involved in the apoptosis were significant after the EHP infection, which indicated that the apoptosis pathway was activated in whiteleg shrimp. In addition, expression leve of caspase 3 gene were identified related to the EHP infection. Furthermore, predictions of spatial structure, analysis of phylogeny and chromosome-level linearity of the caspase 3 protein were performed as well. In conclusion, a relatively complete proteomic data set of hepatopancreas tissues in whiteleg shrimp were established in this study. Findings about genes involved in the apoptosis here will provide a further understanding of the molecular mechanism of EHP infection in the internal immunity of whiteleg shrimp.

An isothermal enzymatic recombinase amplification (ERA) assay for rapid and accurate detection of Enterocytozoon hepatopenaei infection in shrimp

Enterocytozoon hepatopenaei (EHP) is a kind of microsporidian parasite belonging to fungi, and poses a serious threat to prawn farmers. Due to the lack of effective treatments for EHP, the establishment of a rapid and sensitive detection method would be beneficial to the control and prevention of this prawn parasitic disease. In this study, an isothermal enzymatic recombinase amplification (EHP-ERA) assay that could diagnose EHP within 20 min at 42 °C was developed and evaluated. The determined final concentrations of primers and probe in the reaction system were 400 nM and 120 nM, respectively. EHP-ERA was carried out within 13 min (24.31 ± 0.37 Ct) with a detection limit of 10 copies/μL. The results of specificity test showed that EHP-ERA had no cross-reactivity with white spot syndrome virus (WSSV), Vibrio parahaemolyticus strain causing acute hepatopancreatic necrosis disease (VpAHPND), and infectious hypodermal and hematopoietic necrosis virus (IHHNV) and specific pathogen free (SPF) shrimp. Using 32 clinical samples, the practical diagnostic results of EHP-ERA was consistent with nested PCR and real-time PCR (qPCR) under the premise of less time-consuming and simpler operation. In summary, we established a simple, rapid, and effective ERA assay for the detection of EHP, which had great potential to be widely used in both lab and practical usage.

Comparative transcriptome analysis of non-germinated and germinated spores of Enterocytozoon hepatopenaei (EHP) in vitro

Enterocytozoon hepatopenaei (EHP), an obligate intracellular parasite classified as microsporidia, is an emerging pathogen with a significant impact on the global shrimp aquaculture industry. The understanding of how microsporidia germinate has been a key factor in exploring its infection process. However, the germination process of EHP was rarely reported. To gain insight into the germination process, we conducted a high-throughput sequencing analysis of purified EHP spores that had undergone in vitro germination treatment. This analysis revealed 137 differentially expressed genes, with 84 up-regulated and 53 down-regulated genes. While the functions of some of the genes remain unknown, this study provides important data on the transcriptomic changes before and after EHP germination, which can aid in further studies on the EHP infection mechanism.

Transcriptome analysis of the hepatopancreas in Penaeus vannamei under experimental infection with Enterocytozoon hepatopenaei (EHP)

Enterocytozoon hepatopenaei (EHP) is a specialized intracellular parasite that mainly resides in the hepatopancreas of shrimp, causing significant growth retardation in shrimp. In this study, Penaeus vannamei was infected with EHP through an artificial challenge experiment, and the different genes and pathways in the hepatopancreas between EHP-infected and healthy shrimp were analyzed by transcriptome sequencing. The results showed that a total of 240 significantly differentially expressed genes were obtained, including 99 up-regulated genes and 141 down-regulated genes. Immune-related genes such as Astakine, lysozyme, NACHT, LRR, and PYD domains-containing protein 3 (NLRP3), and macrophage mannose receptor 1-like (MMR) were up-regulated, and the expression levels of lipid metabolism-related genes pancreatic lipase-related protein 2 (PLRP2), lysosomal acid lipase (LIPA), and adiponectin receptor protein (AdipoR) were also increased. However, several genes were down-regulated in carbohydrate and protein metabolism, such as glyceraldehyde-3-phosphate dehydrogenase (GAPDH), trypsin-1, and delta-1-pyrroline-5-carboxylate synthase (ALDH18A1). The results suggested that EHP infection of shrimps could significantly activate the immune system, but the energy and material metabolism processes were disturbed. This study identified a substantial number of genes and pathways associated with EHP infection, providing a valuable resource for revealing the molecular mechanism of growth retardation in shrimp.

Pyrococcus furiosus Argonaute Combined with Recombinase Polymerase Amplification for Rapid and Sensitive Detection of Enterocytozoon hepatopenaei

Enterocytozoon hepatopenaei (EHP) is one of the most serious pathogens in shrimp farming. This study combines recombinase polymerase amplification (RPA) with the Argonaute from Pyrococcus furiosus (PfAgo) and establishes a sensitive and reliable method for on-site detection of EHP. With careful screening of gDNA and optimization of the reaction, the method shows a good specificity and reaches a sensitivity of single copy per reaction, which is higher than the sensitivity of the currently available molecular assays. The whole procedure can be finished within 1.5 h including the sample processing time and only requires minimum laboratory support, which is user-friendly for on-site environments. This is the first application of PfAgo for the diagnosis of infectious diseases in seafood supply chains. It provides a reliable method for on-site detection of EHP in shrimp farms and establishes a groundwork for multiplex detection of important pathogens in seafood farming using PfAgo.

Identification of Potential Druggable Targets and Structure-Based Virtual Screening for Drug-like Molecules against the Shrimp Pathogen Enterocytozoon hepatopenaei

Enterocytozoon hepatopenaei (EHP) causes slow growth syndrome in shrimp, resulting in huge economic losses for the global shrimp industry. Despite worldwide reports, there are no effective therapeutics for controlling EHP infections. In this study, five potential druggable targets of EHP, namely, aquaporin (AQP), cytidine triphosphate (CTP) synthase, thymidine kinase (TK), methionine aminopeptidase2 (MetAP2), and dihydrofolate reductase (DHFR), were identified via functional classification of the whole EHP proteome. The three-dimensional structures of the proteins were constructed using the artificial-intelligence-based program AlphaFold 2. Following the prediction of druggable sites, the ZINC15 and ChEMBL databases were screened against targets using docking-based virtual screening. Molecules with affinity scores ≥ 7.5 and numbers of interactions ≥ 9 were initially selected and subsequently enriched based on their ADMET properties and electrostatic complementarities. Five compounds were finally selected against each target based on their complex stabilities and binding energies. The compounds CHEMBL3703838, CHEMBL2132563, and CHEMBL133039 were selected against AQP; CHEMBL1091856, CHEMBL1162979, and CHEMBL525202 against CTP synthase; CHEMBL4078273, CHEMBL1683320, and CHEMBL3674540 against TK; CHEMBL340488, CHEMBL1966988, and ZINC000828645375 against DHFR; and CHEMBL3913373, ZINC000016682972, and CHEMBL3142997 against MetAP2.The compounds exhibited high stabilities and low binding free energies, indicating their abilities to suppress EHP infections; however, further validation is necessary for determining their efficacy.

First Report of Enterocytozoon hepatopenaei Infection in Giant Freshwater Prawn (Macrobrachium rosenbergii de Man) Cultured in the Republic of Korea

In the Republic of Korea, Enterocytozoon hepatopenaei (EHP) was first isolated from Pacific whiteleg shrimp in April 2020; however, there are no existing reports of EHP infection in other shrimp or prawns. Here, we aimed to investigate EHP infection and its prevalence in giant freshwater prawn farms in the Republic of Korea. We tested prawns from 22 farms for EHP infection, and samples from eight farms showed positive EHP infection results in 2021. In EHP-infected prawn farms, the prevalence ranged from 4.9% to 18.2%. The prevalence of EHP infection in the Republic of Korea, derived from the prevalence in prawn farms, was estimated to be 0.8% in 2021. The proliferation of EHP was observed within the hepatopancreatic epithelial cells of prawns using H&E and Giemsa staining. Mature EHP was observed in the sinus between epithelial cells of the digestive tubules. Phylogenetic analysis revealed a clade distinct from the previously reported EHP in Pacific whiteleg shrimps. This is the first report of EHP infection in a giant freshwater prawn in the Republic of Korea, where the prevalence of EHP infection is not high, but it is recognized as an emerging disease that requires periodic monitoring and quarantine management in giant freshwater prawns.

Down-Regulation of Lipid Metabolism in the Hepatopancreas of Shrimp Litopenaeus vannamei upon Light and Heavy Infection of Enterocytozoon hepatopenaei: A Comparative Proteomic Study

Enterocytozoon hepatopenaei (EHP) is the pathogen of hepatopancreatic microsporidiosis (HPM) in shrimp. The diseased shrimp Litopenaeus vannamei exhibits a slow growth syndrome, which causes severe economic losses. Herein, 4D label-free quantitative proteomics was employed to analyze the hepatopancreas of L. vannamei with a light (EHPptp2 < 103 copies/50 ng hpDNA, L group) and heavy (EHPptp2 > 104 copies/50 ng hpDNA, H group) load of EHP to better understand the pathogenesis of HPM. Exactly 786 (L group) and 1056 (H group) differentially expressed proteins (DEPs) versus the EHP-free (C group) control were mainly clustered to lipid metabolism, amino acid metabolism, and energy production processing. Compared with the L group, the H group exhibited down-regulation significantly in lipid metabolism, especially in the elongation and degradation of fatty acid, biosynthesis of unsaturated fatty acid, metabolism of α-linolenic acid, sphingolipid, and glycerolipid, as well as juvenile hormone (JH) degradation. Expression pattern analysis showed that the degree of infection was positively correlated with metabolic change. About 479 EHP proteins were detected in infected shrimps, including 95 predicted transporters. These findings suggest that EHP infection induced the consumption of storage lipids and the entire down-regulation of lipid metabolism and the coupling energy production, in addition to the hormone metabolism disorder. These were ultimately responsible for the stunted growth.

Enterocytozoon hepatopenaei real-time and Shrimp MultiPathTM PCR assay validation for South-East Asian and Latin American strains of Penaeid shrimp

Enterocytozoon hepatopenaei (EHP) infections are a global challenge for the Penaeid shrimp industry with a sharp rise in prevalence over the last 10 yr. EHP is known to cause sub-optimal growth, large size variation and reduced survival of shrimp. Molecular methods development has mainly focussed on 18S rRNA or spore wall protein 1 (SWP1). Due to the specificity and sensitivity issues with previously designed assays for both targets, new molecular assays are needed by the global shrimp industry and regulators to help manage the risks posed by EHP. This paper describes new real-time PCR (qPCR) methods developed for the novel EHP gene targets polar tube protein 2 (PTP2) and spore wall protein 26 (SWP26), whilst also presenting performance metrics of the new Shrimp MultiPathTM technology EHP assay. qPCR assays PTP2G and SWP26G show high amplification efficiency, a limit of detection (LOD) of between 1 and 4 copies, low assay variation and high diagnostic sensitivity (DSe) and specificity (DSp) compared to imperfect reference assays. Similar performance is seen with Shrimp MultiPathTM EHP showing an LOD of 8 copies, low assay variation and high DSe and DSp. These novel molecular targets for EHP and Shrimp MultiPathTM EHP strengthen global efforts to monitor and mitigate risks of EHP infections and outbreaks. Moreover, this study presents novel data on distribution of EHP in shrimp populations from South-East Asia and Latin America, and how sequence variations need to be considered when monitoring EHP in different geographies.

Early responses in Penaeus vannamei during experimental infection with Enterocytozoon hepatopenaei (EHP) spores by injection and oral routes

Hepatopancreatic microsporidiosis caused by Enterocytozoon hepatopenaei (EHP) is associated with severe production losses in Penaeus vannamei farming. Early responses in P. vannamei experimentally infected with EHP was assessed in this study by feeding infected hepatopancreatic tissue and by injecting purified EHP spores (∼1 × 10⁵ Spores/shrimp). Immune responses to EHP infection were assessed in the haemolymph by analysing the total haemocyte count (THC), superoxide dismutase (SOD) activity, prophenoloxidase activity (proPO), respiratory burst activity (RBA), catalase activity (CAT), lysozyme activity (LYS) and Toll gene expression in hepatopancreas at 0, 6, 12, 24, 36, 48, 60 and 72 h post-infection (hpi). Experimental infection with EHP resulted in a significant (p < 0.05) reduction in the immune parameters such THC, CAT and LYS at 6, 24 and 24 hpi respectively while there was a significant increase (p < 0.05) in the levels of SOD, proPO and RBA at 6 hpi. The expression of the Toll gene was significantly upregulated (p < 0.05) after experimental infection with EHP from 6 hpi. These findings on immune responses in P. vannamei during EHP infection will assist in the development of suitable management measures to reduce the negative impacts of EHP in P. vannamei farming. This is the first report on early responses in P. vannamei during EHP infection.

Development of a PCR assay for the effective detection of Enterocytozoon hepatopenaei (EHP) and investigation of EHP prevalence in Shandong Province, China

Enterocytozoon hepatopenaei (EHP), a recently reported pathogen in the penaeid shrimp, is spreading widely and seriously threatening Penaeus (Litopenaeus) vannamei aquaculture. This study aimed to develop a new and more sensitive polymerase chain reaction (PCR) method for the effective detection of EHP. An EHP PCR assay with a pair of primers specifically amplifying a 358 bp EHP DNA fragment was developed, which was demonstrated to be capable of detecting as low as 2 × 10¹ copies of EHP and is specific for EHP without cross reaction with DNA samples prepared from five common shrimp pathogens, including white spot syndrome virus (WSSV), infectious hypodermal and haematopoietic virus (IHHNV), hepatopancreatic parvovirus (HPV), infectious myonecrosis virus (IMNV), and yellow head virus (YHV). This new assay is more specific and more sensitive than the previously published EHP PCR methods. With the PCR assay developed in this study, we investigated the prevalence of EHP in four areas of Shandong, China by testing a total of 639 shrimp samples collected from Yantai, Binzhou, Dongying, and Weifang. The results showed that the EHP positive rate reached 51.2%, indicating that EHP is prevalent in shrimp culture in China.

Closed-tube field-deployable loop-mediated isothermal amplification (LAMP) assay based on spore wall protein (SWP) for the visual detection of Enterocytozoon hepatopenaei (EHP)

Hepatopancreatic microsporidiosis (HPM) is an infectious shrimp disease caused by the microsporidian Enterocytozoon hepatopenaei (EHP). In recent years, the widespread occurrence of EHP poses a significant challenge to the shrimp aquaculture industry. Early, rapid and accurate diagnosis of EHP infection is very much essential for the control of HPM crop-related losses. Loop-mediated isothermal amplification (LAMP) is a robust, sensitive, cost-effective disease diagnostic technique. Here, we demonstrate an improved, simple, closed-tube, colorimetric EHP LAMP diagnostic assay. LAMP assay was illustrated with the specific EHP spore wall protein (SWP) gene primers. Naked eye visual detection of LAMP amplicons was achieved using Hydroxy naphthol blue (HNB) or Phenol red dye without opening the tubes. This LAMP assay is efficient in detecting the EHP pathogen in all clinical samples include shrimp hepatopancreas, FTA card samples, feces, pond water, and soil. Also, the elution of EHP DNA from FTA cards was demonstrated within 17 min using a simple dry bath. In clinical evaluation, the visual LAMP assay established 100% diagnostic sensitivity and 100% diagnostic specificity. The visual LAMP assay is rapid, can detect the EHP pathogen within 40 min using a simple dry bath, and does not require any expensive instruments and technical proficiency. In conclusion, this visual LAMP protocol is a user-friendly, specific assay that can be conceivably operated at the farm-site/ resource-limited settings by the farmer himself with simple equipment.

Occurrence of Enterocytozoon hepatopenaei (EHP) infection on Penaeus vannamei in one rearing cycle

The microsporidian parasite Enterocytozoon hepatopenaei (EHP) is an emerging problem in the marine shrimp industry, primarily in Asian countries such as China, Thailand, India, Malaysia, Indonesia, and Vietnam. A screening was conducted to investigate the prevalence of EHP after a fixed period of culturing for 1 rearing cycle in 3 states of Malaysia. The screening stages covered Penaeus vannamei post larvae (PL) and after 14-30, 31-50, 51-70, and 71-90 d of culture in 1 production cycle. A total of 279 samples were amplified using a PCR assay targeting the gene encoding a spore wall protein (SWP) of EHP. The EHP infection was initially detected in the hatchery and increased to 96.6% after the shrimp were transferred to the pond. The positive EHP sequence showed 91 to 100% similarity to sequences from India, Thailand, Vietnam, Indonesia, and Latin America. EHP infection increased throughout 1 rearing cycle due to factors such as the cannibalistic feeding habits of shrimp and the presence of unknown vectors or carriers of EHP in the culture ponds. Hence, the finding from the current study will be fundamental for other studies concerning EHP.

Rapid Detection of Enterocytozoon hepatopenaei Infection in Shrimp With a Real-Time Isothermal Recombinase Polymerase Amplification Assay

Enterocytozoon hepatopenaei (EHP) infection has become a significant threat in shrimp farming industry in recent years, causing major economic losses in Asian countries. As there are a lack of effective therapeutics, prevention of the infection with rapid and reliable pathogen detection methods is fundamental. Molecular detection methods based on polymerase chain reaction (PCR) and loop-mediated isothermal amplification (LAMP) have been developed, but improvements on detection speed and convenience are still in demand. The isothermal recombinase polymerase amplification (RPA) assay derived from the recombination-dependent DNA replication (RDR) mechanism of bacteriophage T4 is promising, but the previously developed RPA assay for EHP detection read the signal by gel electrophoresis, which restricted this application to laboratory conditions and hampered the sensitivity. The present study combined fluorescence analysis with the RPA system and developed a real-time RPA assay for the detection of EHP. The detection procedure was completed in 3–7 min at 39°C and showed good specificity. The sensitivity of 13 gene copies per reaction was comparable to the current PCR- and LAMP-based methods, and was much improved than the RPA assay analyzed by gel electrophoresis. For real clinical samples, detection results of the real-time RPA assay were 100% consistent with the industrial standard nested PCR assay. Because of the rapid detection speed and the simple procedure, the real-time RPA assay developed in this study can be easily assembled as an efficient and reliable on-site detection tool to help control EHP infection in shrimp farms.

The effect of salinity on enterocytozoon hepatopenaei infection in Penaeus vannamei under experimental conditions

Background

Enterocytozoon hepatopenaei (EHP) is an enteric pathogen that affects Penaeus vannamei and Penaeus monodon shrimp in many SE Asian countries. In the western hemisphere, EHP was reported for the first time in 2016 in farmed P. vannamei in Venezuela. Anecdotal evidence suggests that EHP is more prevalent in grow-out ponds where the salinity is high (> 15 parts per thousand (ppt)) compared to grow-out ponds with low salinities (< 5 ppt). Considering that P. vannamei is an euryhaline species, we were interested in knowing if EHP can propagate in P. vannamei in low salinities.

Results

In this study, we described an experimental infection using fecal strings as a source inoculum. Specific Pathogen Free (SPF) P. vannamei were maintained at three different salinities (2 ppt, 15 ppt, and 30 ppt) while continuously challenged using feces from known EHP-infected P. vannamei over a period of 3 weeks. The fecal strings, used as a source of EHP inocula in the challenges, was sufficient to elicit an infection in shrimp maintained at the three salinities. The infectivity of EHP in shrimp reared at 2 ppt, 15 ppt, and 30 ppt salinities was confirmed by PCR and histopathology. The prevalence and the severity of the EHP infection was higher at 30 ppt than at 2 ppt and 15 ppt.

Conclusion

The data suggests that fecal strings are a reliable source of EHP inoculum to conduct experimental challenges via the fecal-oral route. An EHP infection can occur at a salinity as low as 2 ppt, however, the prevalence and the severity of the EHP infection is higher at a salinity of 30 ppt.

Evidences supporting Enterocytozoon hepatopenaei association with white feces syndrome in farmed Penaeus vannamei in Venezuela and Indonesia

White feces syndrome (WFS) is an emerging and poorly described disease characterized by the presence of floating white fecal strings in shrimp (Penaeus monodon and P. vannamei) grow-out ponds. WFS has been associated with several pathogens, including Enterocytozoon hepatopenaei. This association is based on the fact that in areas where E. hepatopenaei has been reported, there was also a high WFS prevalence. E. hepatopenaei is an emerging pathogen that has affected cultured shrimp in Indonesia, Vietnam, China, Thailand, and India. In 2016, we reported the presence of E. hepatopenaei in farmed P. vannamei in Venezuela. In this study, we describe the first case of WFS in Venezuela associated with E. hepatopenaei. The white fecal strings and shrimp displaying white feces along the gastrointestinal tract observed in this study were similar to the gross signs found in WFS-impacted P. vannamei in SE Asian countries. Furthermore, we describe a strong association between WFS and E. hepatopenaei in the samples obtained from Venezuela and Indonesia. Quantification of E. hepatopenaei in WFS-affected ponds, ponds with a history of WFS, and ponds with no WFS showed that E. hepatopenaei loads were significantly higher in WFS-affected ponds. Furthermore, these findings constitute the first report of WFS being associated with E. hepatopenaei in farmed shrimp in Latin America. Additionally, we propose that the gross signs of WFS such as floating whitish fecal strings can be used as an indicator of the presence of E. hepatopenaei in countries where E. hepatopenaei is endemic.

Integrated qPCR and Staining Methods for Detection and Quantification of Enterocytozoon hepatopenaei in Shrimp Litopenaeus vannamei

Enterocytozoon hepatopenaei (EHP) is an obligate, intracellular, spore-forming parasite, which mainly infects the gastrointestinal tract of shrimp. It significantly hinders the growth of shrimp, which causes substantial economic losses in farming. In this study, we established and optimized a SYBR Green I fluorescent quantitative PCR (qPCR) assay based on the polar tube protein 2 (PTP2) gene for the quantitative analysis of EHP-infected shrimp. The result showed that the optimum annealing temperature was 60 °C for the corresponding relation between the amplification quantitative (Cq) and the logarithmic of the initial template quantity (x), conformed to Cq = −3.2751x + 31.269 with a correlation coefficient R² = 0.993. The amplification efficiency was 102%. This qPCR method also showed high sensitivity, specificity, and repeatability. Moreover, a microscopy method was developed to observe and count EHP spores in hepatopancreas tissue of EHP-infected shrimp using Fluorescent Brightener 28 staining. By comparing the PTP2-qPCR and microscopy method, the microscopic examination was easier to operate whereas PTP2-qPCR was more sensitive for analysis. And we found that there was a correspondence between the results of these two methods. In summary, the PTP2-qPCR method integrated microscopy could serve for EHP detection during the whole period of shrimp farming and satisfy different requirements for detecting EHP in shrimp farming.

CRISPR-Cas fluorescent cleavage assay coupled with recombinase polymerase amplification for sensitive and specific detection of Enterocytozoon hepatopenaei

Enterocytozoon hepatopenaei (EHP) is a parasite that infects pacific whiteleg shrimp, Penaeus vannamei, causing growth retardation and uneven size distributions that lead to severe losses in shrimp productivity. Routine monitoring is crucial to timely prevention and management of EHP, but field-deployable diagnostic kits for EHP are still scarce. Here, we proposed the use of recombinase polymerase amplification (RPA) and CRISPR-Cas12a fluorescence assay, henceforth RPA-Cas12a, for detection of EHP. Targeting ptp2 gene, RPA-Cas12a could detect as few as 50 copies of DNA and showed no reactivity with closely related microsporidia. The entire procedure could be performed at a temperature close to 37 °C within 1 h. Naked eye visualization was possible with UV/blue-light excitation or lateral flow detection. Thus, RPA-Cas12a is a rapid, sensitive and specific detection platform that requires no sophisticated equipment and shows promise for on-site surveillance of EHP.

The shrimp microsporidian Enterocytozoon hepatopenaei (EHP): Biology, pathology, diagnostics and control

Disease is a major limiting factor in the global production of cultivated shrimp. The microsporidian parasite Enterocytozoon hepatopenaei (EHP) was formally characterized in 2009 as a rare infection of the black tiger shrimp Penaeus monodon. It remained relatively unstudied until mid-2010, after which infection with EHP became increasingly common in the Pacific whiteleg shrimp Penaeus vannamei, by then the most common shrimp species farmed in Asia. EHP infects the hepatopancreas of its host, causing hepatopancreatic microsporidiosis (HPM), a condition that has been associated with slow growth of the host in aquaculture settings. Unlike other infectious disease agents that have caused economic losses in global shrimp aquaculture, EHP has proven more challenging because too little is still known about its environmental reservoirs and modes of transmission during the industrial shrimp production process. This review summarizes our current knowledge of the EHP life cycle and the molecular strategies that it employs as an obligate intracellular parasite. It also provides an analysis of available and new methodologies for diagnosis since most of the current literature on EHP focuses on that topic. We summarize current knowledge of EHP infection and transmission dynamics and currently recommended, practical control measures that are being applied to limit its negative impact on shrimp cultivation. We also point out the major gaps in knowledge that urgently need to be bridged in order to improve control measures.

A staining method for detection of Enterocytozoon hepatopenaei (EHP) spores with calcofluor white

A fluorescent stain, calcofluor white (CFW), was used for detection of spores of the microsporidium Enterocytozoon hepatopenaei (EHP). EHP spores in suspension, in feces, or in the infected hepatopancreas of the shrimp Penaeus vannamei, can be easily stained with this chitin and cellulose binding dye to show distinct blue-white fluorescent oval walls. The dye does not stain the host tissues. EHP spores showed orange-red spots by staining with hematoxylin and phloxine (H&P) in the section. CFW staining provides a simple and rapid method for determining the presence of EHP spores in fecal or tissue samples.

A comparative study of Enterocytozoon hepatopenaei (EHP) challenge methods in Penaeus vannamei

The microsporidium Enterocytozoon hepatopenaei (EHP) is considered as an emerging pathogen threating the shrimp industry worldwide. It is an intracellular parasite that has been associated with retarded growth syndrome and white feces syndrome in shrimp. Although the impact of EHP to the shrimp industry is well known, many aspects of host-pathogen interactions are not well understood. A major limitation in the study of EHP is the lack of a reliable method to produce large quantities of inoculum rapidly and reproducibly. The present study was designed to compare different challenge methods including intramuscular injection, oral administration, co-habitation, hepatopancreas (HP) injection and reverse gavage. The results showed that the HP injection and the reverse gavage are two promising methods to infect shrimp rapidly and generate inoculum in a reproducible manner starting with a limited amount of inoculum. Therefore, the HP injection and reverse gavage were chosen for a scale-up study. Histopathology results showed that EHP proliferated in the epithelial cells of the HP in shrimp challenged via direct injection of inoculum into HP and reverse gavage treatments. In accordance with the histopathology results, the qPCR data showed that EHP loads in the challenged shrimp increased significantly with the HP injection and reverse gavage methods. Furthermore, the histopathological and quantification results indicate that HP injection and reverse gavage are two novel methods that can be used in EHP-challenge studies and for rapidly generating viable EHP inoculum.

Quantification of Enterocytozoon hepatopenaei (EHP) in Penaeid Shrimps from Southeast Asia and Latin America Using TaqMan Probe-Based Quantitative PCR

We developed a qPCR assay based on the β-tubulin gene sequence for the shrimp microsporidian parasite Enterocytozoon hepatopenaei (EHP). This assay reacted with the hepatopancreas (HP) of EHP-infected shrimps, and the highest copy numbers were found in HP and feces samples from Southeast Asian countries (10⁶-10⁸ copies mg^-1), while HP samples from Latin America, Artemia, and EHP-contaminated water showed lower amounts (10¹-10³ copies mg^-1 or mL^-1 of water). No false positive was found with the normal shrimp genome, live feeds, or other parasitic diseases. This tool will facilitate the management of EHP infection in shrimp farms.

Proteomic and metabolomic responses in hepatopancreas of whiteleg shrimp Litopenaeus vannamei infected by microsporidian Enterocytozoon hepatopenaei

Enterocytozoon hepatopenaei (EHP) causes hepatopancreatic microsporidiosis (HPM) in shrimp. HPM is not normally associated with shrimp mortality, but is associated with significant growth retardation. In this study, the responses induced by EHP were investigated in hepatopancreas of shrimp Litopenaeus vannamei using proteomics and metabolomics. Among differential proteins identified, several (e.g., peritrophin-44-like protein, alpha2 macroglobulin isoform 2, prophenoloxidase-activating enzymes, ferritin, Rab11A and cathepsin C) were related to pathogen infection and host immunity. Other proteomic biomarkers (i.e., farnesoic acid o-methyltransferase, juvenile hormone esterase-like carboxylesterase 1 and ecdysteroid-regulated protein) resulted in a growth hormone disorder that prevented the shrimp from molting. Both proteomic KEGG pathway (e.g., "Glycolysis/gluconeogenesis" and "Glyoxylate and dicarboxylate metabolism") and metabolomic KEGG pathway (e.g., "Galactose metabolism" and "Biosynthesis of unsaturated fatty acids") data indicated that energy metabolism pathway was down-regulated in the hepatopancreas when infected by EHP. More importantly, the changes of hormone regulation and energy metabolism could provide much-needed insight into the underlying mechanisms of stunted growth in shrimp after EHP infection. Altogether, this study demonstrated that proteomics and metabolomics could provide an insightful view into the effects of microsporidial infection in the shrimp L. vannamei.

Real-time loop-mediated isothermal amplification for rapid detection of Enterocytozoon hepatopenaei

Background

Enterocytozoon hepatopenaei (EHP) is a newly emerged microsporidian parasite that causes retarded shrimp growth in many countries. But there are no effective approaches to control this disease to date. The EHP could be an immune risk factor for increased dissemination of other diseases. Further, EHP infection involves the absence of obvious clinical signs and it is difficult to identify the pathogen through visual examination, increasing the risk of disease dissemination. It is urgent and necessary to develop a specific, rapid and sensitive EHP-infected shrimp diagnostic method to detect this parasite. In the present study, we developed and evaluated a rapid real-time loop-mediated isothermal amplification (real-time LAMP) for detection of EHP.

Methods

A rapid and efficient real-time LAMP method for the detection of EHP has been developed. Newly emerged EHP pathogens in China were collected and used as the sample, and three sets of specificity and sensitivity primers were designed. Three other aquatic pathogens were used as templates to test the specificity of the real-time LAMP assay. Also, we compared the real-time LAMP with the conventional LAMP by the serial dilutions of EHP DNA and their amplification curves. Application of real-time LAMP was carried out with clinical samples.

Results

Positive products were amplified only from EHP, but not from other tested species, EHP was detected from the clinical samples, suggesting a high specificity of this method. The final results of this assay were available within less than 45 min, and the initial amplification curve was observed at about 6 min. We found that the amplification with an exponential of sixfold dilutions of EHP DNA demonstrated a specific positive signal by the real-time LAMP, but not for the LAMP amplicons from the visual inspection. The real-time LAMP amplification curves demonstrated a higher slope than the conventional LAMP.

Discussion

In this study, pathogen virulence impacts have been increased in aquaculture and continuous observation was predominantly focused on EHP. The present study confirmed that the real-time LAMP assay is a promising and convenient method for the rapid identification of EHP in less time and cost. Its application greatly aids in the detection, surveillance, and prevention of EHP.

Identification, characterization and heparin binding capacity of a spore-wall, virulence protein from the shrimp microsporidian, Enterocytozoon hepatopenaei (EHP)

Background

The microsporidian Enterocytozoon hepatopenaei (EHP) is a spore-forming, intracellular parasite that causes an economically debilitating disease (hepatopancreatic microsporidiosis or HPM) in cultured shrimp. HPM is characterized by growth retardation and wide size variation that can result in economic loss for shrimp farmers. Currently, the infection mechanism of EHP in shrimp is poorly understood, especially at the level of host-parasite interaction. In other microsporidia, spore wall proteins have been reported to be involved in host cell recognition. For the host, heparin, a glycosaminoglycan (GAG) molecule found on cell surfaces, has been shown to be recognized by many parasites such as Plasmodium spp. and Leishmania spp.

Results

We identified and characterized the first spore wall protein of EHP (EhSWP1). EhSWP1 contains three heparin binding motifs (HBMs) at its N-terminus and a Bin-amphiphysin-Rvs-2 (BAR2) domain at its C-terminus. A phylogenetic analysis revealed that EhSWP1 is similar to an uncharacterized spore wall protein from Enterospora canceri. In a cohabitation bioassay using EHP-infected shrimp with naïve shrimp, the expression of EhSWP1 was detected by RT-PCR in the naïve test shrimp at 20 days after the start of cohabitation. Immunofluorescence analysis confirmed that EhSWP1 was localized in the walls of purified, mature spores. Subcellular localization by an immunoelectron assay revealed that EhSWP1 was distributed in both the endospore and exospore layers. An in vitro binding assay, a competition assay and mutagenesis studies revealed that EhSWP1 is a bona fide heparin binding protein.

Conclusions

Based on our results, we hypothesize that EhSWP1 is an important host-parasite interaction protein involved in tethering spores to host-cell-surface heparin during the process of infection.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2758-z) contains supplementary material, which is available to authorized users.

Laboratory cohabitation challenge model for shrimp hepatopancreatic microsporidiosis (HPM) caused by Enterocytozoon hepatopenaei (EHP)

BACKGROUND

Enterocytozoon hepatopenaei (EHP) causes hepatopancreatic microsporidiosis (HPM) in shrimp. It is probably endemic in Australasia and was first characterized and named from the giant or black tiger shrimp Penaeus monodon from Thailand in 2009. Later, it was also found to infect exotic Penaeus vannamei imported for cultivation in Asia. HPM is not normally associated with shrimp mortality, but information from shrimp farmers indicates that it is associated with significant growth retardation that is not clearly noticeable until 2-3 months of cultivation. In order to study modes of HPM transmission and to test possible control measures, a laboratory challenge model was needed that would mimic the mode of infection in shrimp ponds.

RESULTS

We describe successful transmission in a cohabitation model with natural E. hepatopenaei (EHP)-infected shrimp in closed, perforated plastic containers placed in aquaria together with free-swimming, uninfected shrimp. After a period of 14 days all the free-swimming shrimp tested positive by PCR (approximately 60% with heavy infections evident by 1-step PCR positive test results) and gave positive histological and in situ hybridization results for E. hepatopenaei (EHP) in the hepatopancreas.

CONCLUSIONS

A laboratory cohabitation model for studying E. hepatopenaei (EHP) has been developed and used to confirm that E. hepatopenaei (EHP) can be directly transmitted horizontally among shrimp via water. The model will facilitate studies on methods to prevent the E. hepatopenaei (EHP) transmission.

Dense populations of the microsporidian Enterocytozoon hepatopenaei (EHP) in feces of Penaeus vannamei exhibiting white feces syndrome and pathways of their transmission to healthy shrimp

White feces syndrome (WFS) is an emerging problem for penaeid shrimp farming industries in SE Asia countries, Thailand, Malaysia, Vietnam, Indonesia, China, and in India. This occurrence of this syndrome is usually first evidenced by the appearance of white fecal strings floating on surface of the shrimp ponds. The gross signs of affected shrimp include the appearance of a whitish hindgut and loose carapace, and it is associated with reduced feeding and growth retardation. To investigate the nature of the white feces syndrome, samples of white feces and shrimp hepatopancreas tissue were collected from Penaeus vannamei in affected farms in Indonesia, and these were examined histologically. Within the white feces, we found densely packed spores of the microsporidian Enterocytozoon hepatopenaei (abbreviated as EHP) and relatively fewer numbers of rod-shaped bacteria. From WFS ponds, hepatopancreas samples form 30 individual shrimp were analyzed by histology and in situ hybridization. The results showed that all of the shrimp examined were infected with EHP accompanied by septic hepatopancreatic necrosis (SHPN). Midgut epithelial cells were also infected and this increased the number of tissue types being affected by EHP. By PCR, EHP was detected in all the samples analyzed from WFS-affected ponds, but not in those sampled from healthy shrimp ponds. To determine the modes of transmission for this parasite, we performed feeding and cohabitation bioassays, the results showed that EHP can be transmitted through per os feeding of EHP-infected hepatopancreas tissue to healthy shrimp and through cohabitation ofinfected and healthy shrimp. In addition, we found the use of Fumagillin-B, an antimicrobial agent, was ineffective in either reducing or eliminating EHP in infected shrimp.

Development of in situ hybridization and PCR assays for the detection of Enterocytozoon hepatopenaei (EHP), a microsporidian parasite infecting penaeid shrimp

A microsporidian parasite, Enterocytozoon hepatopenaei (abbreviated as EHP), is an emerging pathogen for penaeid shrimp. EHP has been found in several shrimp farming countries in Asia including Vietnam, Thailand, Malaysia, Indonesia and China, and is reported to be associated with growth retardation in farmed shrimp. We examined the histological features from infected shrimp collected from Vietnam and Brunei, these include the presence of basophilic inclusions in the hepatopancreas tubule epithelial cells, in which EHP is found at various developmental stages, ranging from plasmodia to mature spores. By a PCR targeting the 18S rRNA gene, a 1.1kb 18S rRNA gene fragment of EHP was amplified, and this sequence showed a 100% identity to EHP found in Thailand and China. This fragment was cloned and labeled with digoxigenin-11-dUTP, and in situ hybridized to tissue sections of infected Penaeus vannamei (from Vietnam) and P. stylirostris (Brunei). The results of in situ hybridization were specific, the probe only reacted to the EHP within the cytoplasmic inclusions, not to a Pleistophora-like microsporidium that is associated with cotton shrimp disease. Subsequently, we developed a PCR assay from this 18S rRNA gene region, this PCR is shown to be specific to EHP, did not react to 2 other parasitic pathogens, an amoeba and the cotton shrimp disease microsporidium, nor to genomic DNA of various crustaceans including polychaetes, squids, crabs and krill. EHP was detected, through PCR, in hepatopancreatic tissue, feces and water sampled from infected shrimp tanks, and in some samples of Artemia biomass.