Propionigenium and Vibrio species identified as possible component causes of shrimp white feces syndrome (WFS) associated with the microsporidian Enterocytozoon hepatopenaei

Screening of intestinal protein signatures in pacific white-leg shrimp (Litopenaeus vannamei) with white feces syndrome by proteome

White feces syndrome (WFS) has been one of the emerging diseases causing instructive economic losses in the penaeid shrimp aquaculture industry, though the etiology of WFS remains unclear. In this research, we have collected intestinal samples from normal and diseased shrimp (Litopenaeus vannamei) from the natural shrimp cultivation farm for histological and proteomic analysis. The preliminary pathogen detection confirmed that WFS in this study was (Enterocytozoon hepatopenaei) EHP-WFS that was related to Vibrio spp. Moreover, the destructive damage of the intestine in WFS-diseased shrimp revealed by histological observation indicated a deficiency in digestive capacity, which might be closely related to WFS. Furthermore, we have characterized 86 and 165 differentially expressed proteins (DEPs) through a non-directional integrative analysis, which were significantly up-regulated and down-regulated, respectively. The down-regulation of various digestive enzymes in the WFS-diseased shrimp was consistent with the results of intestinal histology. DEPs were enriched in the lysosome and sphingolipid metabolism pathway, indicating that they were strongly associated with the occurrence of WFS (P < 0.05). Of this, the expression of down-regulated proteins in the lysosomal pathway was further validated by real-time quantitative polymerase chain reaction (RT-qPCR). Ultimately, crustin, lipase, and glucosylceramidase (GBA), which were significantly decreased in WFS-diseased shrimp, were screened as the predictive protein signatures for the diagnosis and prevention of WFS. Consequently, our results will provide a theoretical reference for the diagnosis of EHP-WFS by the protein aspect and crustin, lipase, and GBA may be predictive signatures that are suitable for EHP-WFS.

Tissue and cell types infected by Ecytonucleospora hepatopenaei (EHP)

Ecytonucleospora hepatopenaei (EHP) is a microsporidian pathogen causing significant losses in shrimp aquaculture worldwide. The hepatopancreas is recognized as the primary target tissue, but the broader tissue and cell tropism of EHP and its ability to infect other components of the digestive system or non-digestive tissues remain unclear, especially when infections are intense and the host physiology is compromised. This study aimed to comprehensively investigate the histopathology of EHP infections in severely infected Penaeus vannamei to determine its tissue and cell tropism and assess the potential for systemic infection. The severity of infection was graded based on hepatopancreatic lesions. Histopathology showed that EHP spores were distributed in the digestive system of heavily infected shrimp, but not in non-digestive tissues such as gills, heart, gonad, nerves or skeletal muscle. EHP only infected the epithelial cells of the hepatopancreas, midgut, and midgut caeca, which lack the protective chitin layers. While the epithelial cells of the esophagus, stomach and hindgut were unaffected due to the protection of the inner chitinous layer, despite the presence of large numbers of EHP spores in these regions. Histopathology and ultrastructural pathology demonstrated that the R (reserve), F (fibrillar), B (blister), E (embryonic) and M (small midget) cells of the hepatopancreas were infected. These findings indicate that EHP does not cause systemic infection and has a strict cell tropism for the epithelium in the shrimp host.

Characterization of Enterocytozoon hepatopenaei infection stages in shrimp using machine learning and gene network analysis

Enterocytozoon hepatopenaei (EHP), causing hepatopancreatic microsporidiosis (HPM), significantly impacts Litopenaeus vannamei, leading to economic losses. Using bioinformatics and machine learning, this study characterized EHP infection stages and host-pathogen interactions. Consensus clustering of 2,613 metabolism-related genes from 36 shrimp samples identified four subclasses: healthy (HG), heavily (HEG), moderately (MEG), and lightly infected groups (LEG). Gene Set Variation Analysis (GSVA) revealed subclass-specific metabolic and immune patterns, with HEG showing impaired carbohydrate metabolism and upregulated amino acid degradation, MEG indicating recovery, and LEG demonstrating metabolic normalization. Weighted Gene Co-expression Network Analysis (WGCNA) linked infection subclasses to pathways like Hippo, JAK-STAT, steroid biosynthesis, and calcium signaling. Machine learning identified 52 characteristic genes involved in EHP proliferation (e.g., RAPTOR), host invasion (e.g., cell surface glycoprotein 1), and host defense (e.g., mucin-5AC). A stacked classifier model predicted infection severity with high accuracy. EHP severely impacts immunity, autophagy, and oxidative stress in early infection, with host responses evolving from detoxification to metabolic recovery and adaptation. Key pathways and genes, including polar tube protein (PTP) and mucin-5AC, were identified as critical to host-pathogen interactions, offering insights into EHP infection dynamics and potential intervention strategies.

Development of a Real-Time Enzymatic Recombinase Amplification Assay (RT-ERA) and an ERA Combined with a Lateral Flow Dipstick (LFD) Assay (ERA-LFD) for Enteric Microsporidian (Enterospora epinepheli) in Grouper Fishes

Enterospora epinepheli poses a severe threat to grouper aquaculture due to the absence of effective prevention and treatment strategies. To address this challenge, we developed and validated two isothermal diagnostic tools, the real-time enzymatic recombinase amplification (RT-ERA) assay and the enzymatic recombinase amplification combined with a lateral flow dipstick (ERA-LFD) assay, targeting the 18S rDNA gene of the parasite. These assays operate under isothermal conditions at ≤40 °C and offer rapid detection, with RT-ERA yielding results in 14~20 min and ERA-LFD in approximately 10 min. The RT-ERA assay demonstrated a strong linear relationship between plasmid copy numbers and cycle threshold (Ct) values (y = -2.1226x + 19.562, R2 = 0.9915), enabling accurate quantification. Both methods displayed a detection limit of 2 × 100 copies/μL and no cross-reactivity with other aquaculture pathogens. Validation using grouper tissue and water samples from Hainan, China, demonstrated 100% concordance rates with basic ERA and outperformed compared to conventional PCR. These assays provide sensitive, specific, and rapid detection tools for effective monitoring and pathogen load assessment of E. epinepheli, with broad applicability to pathogen detection in aquaculture systems.

Gut microbiota and functional metabolic predictions in white feces disease-infected Pacific white shrimp, Penaeus vannamei, from Indonesian farms

The etiological agent of white feces disease (WFD) infecting Pacific white shrimp Penaeus vannamei in Indonesia farms remains obscure. The present study aimed to identify possible causative agents of WFD infection in Pacific white shrimps cultured in Indonesian farms. WFD-infected and healthy samples (shrimp gut and rearing water) were collected from 8 commercial shrimp farms in East Java, Indonesia followed by bacterial community profiling using HiSeq sequencing of 16S rRNA gene amplicons. The results showed that the microbiota composition in the guts of WFD-infected shrimps was significantly different (p < 0.05) from the guts of healthy shrimps in term of genus and bacterial species. The intestinal bacterial communities of WFS-infected shrimps were overrepresented by Vibrio coralliilyticus, whereas Paracoccus was underrepresented. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States functional predictions indicated that relative abundances of 12 genes associated with the pathogenicity of bacteria including amino acid metabolisms, carbohydrate metabolisms, glycan biosynthesis, and xenobiotic biodegradation and metabolism were significantly (p < 0.05) higher in the gut microbiota of WFD-infected shrimps. These findings provide insights into the microbiome domination and their metabolic activities in the digestive tract of WFD-infected shrimps and suggest that V. coralliilyticus is a possible causative agent of WFD in cultured Indonesia Pacific white shrimp.

Advanced Pathogen Monitoring in Penaeus vannamei from Three Latin American Regions: Passive Surveillance Part 2

This study presents the second phase of a year-long investigation comparing multiple PCR analyses and histological examinations to confirm the presence of characteristic lesions of each pathogen in three different regions of Latin America. More than 20 agents, including DNA and RNA viruses, bacteria and microsporidia, have been targeted. In addition to wild Penaeus vannamei, which was studied previously, samples of wild P. stylirostris and P. monodon were included. Notably, a positive PCR test result alone does not confirm the presence of a viable pathogen or a disease state. Similarly, positive PCR results do not necessarily correlate with the presence of histological lesions characteristic of the targeted pathogen. Wenzhou shrimp virus 8 (WzSV8) was found to be widespread among shrimp in all regions, including both farm-raised and wild populations. Histopathological analysis indicated that shrimp typically presented coinfections, such as WzSV8, Decapod hepanhamaparvovirus (DHPV), chronic midgut inflammation, and tubule distension/epithelial atrophy, consistent with the toxicity of Pir A/B or another bacterial toxin. Bacterial muscle necrosis was also found in some regions. In general, bacterial infection was the dominant pathology in all three regions during the year. We also postulate that both WzSV8 and DHPV can infect not only hepatopancreatic cells but also cells in the ceca and intestine.

VP28 interacts with PmRab7 irrespective of its nucleotide state

In shrimp aquaculture, white spot syndrome virus (WSSV) infections severely impact production. Previous research highlighted the crucial role of the Penaeus monodon Rab7 (PmRab7) protein in WSSV entry, specifically its interaction with the viral envelope protein VP28. PmRab7 exists in two conformations: GDP-bound (inactive) and GTP-bound (active). This study, using ELISA and isothermal titration calorimetry (ITC), reveals that the PmRab7-VP28 interaction occurs irrespective of the nucleotide binding state of PmRab7. Comparing the binding affinity between VP28 and different PmRab7 conformations, including wild-type (WT, 22.5 nM), a fast nucleotide exchange (L129F, 128 nM), a GDP-bound form (T22N, 334 nM), and a favorably GTP-bound form (Q67L, 1990 nM), PmRab7-WT exhibits the strongest binding affinity, especially at a lower temperature (25 °C). The binding of PmRab7-WT and VP28 in the presence of excess nucleotide (WT with excess GDP, 924 nM, and WT with excess GTP, 826 nM) shows a 2-fold higher binding affinity than in the absence (WT, 1920 nM) indicating that the addition of excess nucleotide for PmRab7-WT enhanced the affinity for VP28. Together, these findings support the potential of PmRab7-WT as a promising therapeutic candidate for WSSV control in shrimp. Furthermore, from an industrial point of view, the ITC platform developed to study the VP28-PmRab7 interactions provides a high-throughput method for screening additives for shrimp feed that can inhibit this interaction.

Interactions between microsporidia and other members of the microbiome

The microbiome is the collection of microbes that are associated with a host. Microsporidia are intracellular eukaryotic parasites that can infect most types of animals. In the last decade, there has been much progress to define the relationship between microsporidia and the microbiome. In this review, we cover an increasing number of reports suggesting that microsporidia are common components of the microbiome in both invertebrates and vertebrates. These microsporidia infections can range from mutualistic to pathogenic, causing several physiological phenotypes, including death. Infection with microsporidia often causes a disruption in the normal microbiome, with both increases and decreases of bacterial, fungal, viral, and protozoan species being observed. This impact on the microbiome can occur through upregulation and downregulation of innate immunity as well as morphological changes to tissues that impact interactions with these microbes. Other microbes, particularly bacteria, can inhibit microsporidia and have been exploited to control microsporidia infections. These bacteria can function through regulating immunity, secreting anti-microsporidia compounds, and, in engineered versions, expressing double-stranded RNA targeting microsporidia genes. We end this review by discussing potential future directions to further understand the complex interactions between microsporidia and the other members of the microbiome.

White feces syndrome in shrimp: Comprehensive understanding of immune system responses

White feces syndrome (WFS) is a multifactorial disease that affects global shrimp production. The diagnostic approach to identify WFS involves traditional and molecular scientific methods by examining histopathology, bioassays, PCR (polymerase chain reaction), and calorimetric estimation. The pathogenesis of WFS is closely associated with Vibrio spp., intestinal microbiota (IM) dysbiosis, and Enterocytozoon hepatopenaei (EHP). It also has caused over 10-15 % loss in the aquaculture industry and is also known to cause retardation, lethargy and slowly leading to high mortality in shrimp farms. Therefore, it is necessary to understand the molecular mechanisms processed under the association of IM dysbiosis, Vibrio spp., and EHP to analyze the impact of disease on the innate immune system of shrimp. However, only very few reviews have described the molecular pathways involved in WFS. Hence, this review aims to elucidate an in-depth analysis of molecular pathways involved in the innate immune system of shrimp and their response to pathogens. The analysis and understanding of the impact of shrimp's innate immune system on WFS would help in developing treatments to prevent the spread of disease, thereby improving the economic condition of shrimp farms worldwide.

Enterocytozoon hepatopenaei (EHP) Infection Alters the Metabolic Processes and Induces Oxidative Stress in Penaeus vannamei

Enterocytozoon hepatopenaei (EHP) is highly contagious and can cause hepatopancreatic microsporidiosis (HPM), which is typically characterized by the slow growth of shrimp. In this study, the differences in histology, metabolism, oxidative stress and growth between healthy and EHP-infected Penaeus vannamei were analyzed using an EHP challenge experiment. Histology showed that EHP caused lesions in the hepatic tubules of P. vannamei, such as hepatic tubular atrophy and epithelial cell shedding, with mature spores. Meanwhile, white feces may appear when the infection is severe. Furthermore, the content of total protein, glycogen, ATP and glucose in the EHP challenge group was significantly reduced. The qPCR results showed that EHP infection changed the expression of key genes in glucose metabolism, among which hexokinase (HK), phosphofructokinase (PFK), pyruvatekinase (PK), citrate synthase (CS) and isocitric dehydrogenase (IDH) were significantly down-regulated, while phosphoenolpyruvate carboxykinase (PEPCK), fructose bisphosphatase (FBP) and glucose-6-phosphatase (G6P) were significantly up-regulated. Obviously, the expression of growth-related genes was disordered. Simultaneously, the antioxidant genes manganese superoxide dismutase (MnSOD), catalase (CAT), glutathione peroxidase (GPX), glutathione-S-transferases (GST) and nuclear factor E2-related factor2 (Nrf2) were up-regulated to varying degrees in the EHP challenge group, and EHP infection induced significant increases in the oxidative damage products lipid peroxide (LPO) and malondialdehyde (MDA). Ultimately, the shrimp weight of the challenge group was 6.85 ± 0.86 g, which was significantly lower than that of the control group (8.95 ± 0.75 g). Taken together, we speculate that EHP changes the substance metabolism and growth process by causing oxidative damage to the hepatopancreas, which may lead to the growth retardation of P. vannamei.

Transcriptome analysis of the hepatopancreas from the Litopenaeus vannamei infected with different flagellum types of Vibrio alginolyticus strains

Vibrio alginolyticus, one of the prevalently harmful Vibrio species found in the ocean, causes significant economic damage in the shrimp farming industry. Its flagellum serves as a crucial virulence factor in the invasion of host organisms. However, the processes of bacteria flagella recognition and activation of the downstream immune system in shrimp remain unclear. To enhance comprehension of this, a ΔflhG strain was created by in-frame deletion of the flhG gene in V. alginolyticus strain HN08155. Then we utilized the transcriptome analysis to examine the different immune responses in Litopenaeus vannamei hepatopancreas after being infected with the wild type and the mutant strains. The results showed that the ΔflhG strain, unlike the wild type, lost its ability to regulate flagella numbers negatively and displayed multiple flagella. When infected with the hyperflagella-type strain, the RNA-seq revealed the upregulation of several immune-related genes in the shrimp hepatopancreas. Notably, two C-type lectins (CTLs), namely galactose-specific lectin nattectin and macrophage mannose receptor 1, and the TNF receptor-associated factor (TRAF) 6 gene were upregulated significantly. These findings suggested that C-type lectins were potentially involved in flagella recognition in shrimp and the immune system was activated through the TRAF6 pathway after flagella detection by CTLs.

White feces syndrome in Penaeus vannamei is potentially an Enterocytozoon hepatopenaei (EHP) associated pathobiome origin of Vibrio spp

White feces syndrome (WFS) is a commercially important disease in Penaeus vannamei (whiteleg shrimp) farming. The aetiology beyond the white or golden white midgut with mediocre growth performance producing a floating mass of white fecal strings in WFS-affected shrimp farms remains uncharted. To give WFS a perception of pathobiome, healthy P. vannamei shrimps were subjected to an enteric microsporidian Enterocytozoon hepatopenaei (EHP) infection along with Vibrio harveyi and V. alginolyticus in different combinations. Immune responses in haemolymph (total haemocyte count (THC), prophenoloxidase activity (proPO), respiratory burst activity (RBA), superoxide dismutase activity (SOD) and catalase activity (CAT)), plasma biochemical changes (aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP)) and digestive enzymes activity (alpha-amylase (AMY), lipase (LIP) and protease (PRO)) were assessed in the challenged shrimps at 5, 10 and 15 days post-infection (dpi). The microbial interactions between the EHP and Vibrio spp. have led to the formation of WFS in the challenged shrimps. The histological sections of the hepatopancreas revealed the presence of EHP along with colonized bacterial masses, leading to the formation of aggregated transformed microvilli (ATM) structures and increased sloughing of lipid vacuoles into the tubule lumen. A significantly decreased THC and increased proPO levels, dysregulated antioxidant system, prominent hepatic damage, reduced energy metabolism and higher lipid production were the key records supporting that EHP-associated WFS in P. vannamei is due to the pathobiome.

Shell disease syndromes of decapod crustaceans

The term shell disease subsumes a number of debilitating conditions affecting the outer integument (the carapace) of decapod crustaceans, such as lobsters and crabs. Herein, we seek to find commonality in the aetiology and pathology of such conditions, and those cases that result in the progressive erosion of the cuticle through to the visceral tissues by a cocktail of microbial-derived enzymes including lipases, proteases and chitinases. Aquimarina spp. are involved in shell disease in many different crustaceans across a wide geographical area, but the overall view is that the condition is polymicrobial in nature leading to dysbiosis within the microbial consortium of the damaged cuticle. The role of environment, decapod behaviour and physiology in triggering this disease is also reviewed. Finally, we provide a conceptual model for disease aetiology and suggest several avenues for future research that could improve our understanding of how such factors trigger, or exacerbate, this condition.

Comparative study of the impact of dietary supplementation with different types of CpG oligodeoxynucleotides (CpG ODNs) on enhancing intestinal microbiota diversity, antioxidant capacity, and immune-related gene expression profiles in Pacific white shrimp (Litopenaeus vannamei)

The CpG oligodeoxynucleotides (CpG ODNs) reportedly possess the capacity to strengthen immunity in mammals. This experiment was conducted to evaluate the impact of dietary supplementation with 17 types of CpG ODNs on intestinal microbiota diversity, antioxidant capacity, and immune-related gene expression profiles of the shrimp Litopenaeus vannamei. Diets including 50 mg kg^-1 CpG ODNs wrapped in egg whites were prepared and divided into 17 different groups, with 2 control groups (normal feed and feed with egg whites). These CpG ODNs supplemented diets and the control diets were fed to L. vannamei (5.15 ± 0.54 g) three times daily at 5%-8% shrimp body weight for three weeks. The results of consecutive detection of intestinal microbiota by 16S rDNA sequencing indicated that 11 of the 17 types of CpG ODNs significantly enhanced intestinal microbiota diversity, increased the populations of several probiotic bacteria, and activated possible mechanisms relevant to diseases. The immune-related genes expression and antioxidant capacity in hepatopancreas further demonstrated that the 11 types of CpG ODNs effectively improved the innate immunity of shrimp. Additionally, histology results showed that the CpG ODNs in the experiment did not damage the tissue structure of hepatopancreas. The results suggest that CpG ODNs could be used as a trace supplement to improve the intestinal health and immunity of shrimp.