Vibriosis

Overview

What is Vibriosis?

Vibriosis is a collective term for bacterial diseases caused by pathogenic species of the genus Vibrio, and in aquaculture it often also includes the closely related genus Aliivibrio. These are gram-negative, asporogenous rods that are ubiquitous inhabitants of marine and estuarine environments worldwide. The disease is also referred to as "vibriosis" generically, with species-specific names such as Vibrio anguillarum infection, "red pest" or "red disease of eels," and luminescent vibriosis (for bioluminescent species). In severe form, the systemic presentation is known as haemorrhagic septicaemia 1.

The most clinically significant species in marine aquaculture are V. anguillarum, V. ordalii, V. vulnificus, V. alginolyticus, V. harveyi, V. parahaemolyticus, and Aliivibrio salmonicida (formerly V. salmonicida). More than 130 recognized Vibrio species exist, grouped into 14 clades, including commensal, mutualistic, and pathogenic forms 1. Two fish‑pathogenic bacteria from this group are particularly important in Norwegian waters: Vibrio anguillarum, which causes "classical vibriosis", and Aliivibrio salmonicida (formerly Vibrio salmonicida), which causes "cold‑water vibriosis/Hitra disease" 15.

Vibriosis affects a broad range of commercially important marine fish species, compromising both wild an reared fish, including gilthead seabream (Sparus aurata), European seabass (Dicentrarchus labrax), Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss) Atlantic cod (Gadus morhua), turbot (Scophthalmus maximus), Asian seabass (Lates calcarifer), tilapia, and numerous flatfish species. Shellfish, crustaceans, mollusks, corals, and rotifers are also severely affected 16 All cultured marine fish may, to varying degrees, host opportunistic Vibrio species 1.

Vibriosis is one of the most widespread and devastating bacterial diseases in global aquaculture. In 1997, the World Bank estimated disease losses in aquaculture at US$3 billion per year, with Vibrio spp. playing an important role in those losses. By approximately 2017, estimates had doubled to over US$6 billion annually 1.

Vibrio infections are particularly devastating during the early, larval stages of development, where they are a common cause of high mortality rates, and outbreaks can lead to the loss of entire populations within a single aquaculture system. The ongoing rise of antibiotic resistance among Vibrio species, linked to both climate change and intensive aquaculture practices, has made vibriosis an increasingly urgent global challenge 1 2.

Clinical Signs of Vibriosis

Common Signs

• Physical Signs:

  • Haemorrhagic Septicaemia: Extensive external and internal haemorrhages, particularly at the base of fins, operculum, and ventral surface are a hallmark sign of acute vibriosis. The infection often becomes systemic, with haemorrhages in internal organs such as the pyloric caeca, abdominal fat, musculature and liver 1 16.
  • Skin Ulcers and Lesions: External skin ulcers, focal necrosis, and erosion of the tail are characteristic of advanced infection 1.
  • Dark Pigmentation: Affected fish exhibit abnormal darkening of the skin 1.
  • Exophthalmos: Protruding or "pop-eye" appearance due to fluid accumulation behind the eye 1.
  • Splenomegaly: Marked enlargement of the spleen observed at post-mortem 1.
  • Pale Kidney: Renal discoloration indicating organ compromise 1.
  • Skeletal Deformity (Lordosis): Spinal curvature reported in chronically affected fish 1.
  • Organ Necrosis: Multifocal areas of cell death commonly observed in the gill, liver, spleen and kidney, where affected foci appear pale and poorly demarcated 1 16.
  • Ascites: Accumulation of clear or bloody fluid in the abdominal cavity, often leading to a swollen abdomen 1.

• Behavioural Changes:

  • Lethargy: Reduced activity and slow, labored swimming where they tend to swim near the surface of the water 1 16.
  • Loss of Appetite: Significant reduction in feed intake and associated weight loss 1.
  • Erratic Swimming: Disoriented movement patterns in acutely affected fish 1.

Progression of Clinical Signs

• Early Stages: Subtle, non-specific signs including mild reduction in feed intake, slight lethargy, and skin discoloration 16. Fish may appear clinically normal while harboring significant bacterial loads. Disease onset is often linked to environmental stressors such as rising water temperature, handling, or deteriorating water quality 1.
• Advanced Stages: Pronounced haemorrhagic septicaemia with extensive skin lesions, complete erosion of the tail, exophthalmic eyes, and gross internal organ pathology. Acute outbreaks can cause sudden and catastrophic mortality. Regardless of host developmental stage, Vibrio infections may occur suddenly and can lead to the loss of the entire population reared in a given system 1.
• Impact on Fish Health: Vibriosis severely compromises immune function and overall vitality. Mortality rates vary widely depending on the causative species, water temperature, and host susceptibility. V. harveyi was shown to be prevalent and causing disease year-round across multiple fish species and geographic regions in long-term surveillance 3.

Causes of Vibriosis

Etiology

• Causative Agent: Vibrio spp. are Gram-negative rod-shaped and motile via one or more polar flagella. They are mesophilic, with facultative fermentative metabolism. With the exception of V. cholerae and V. mimicus, Vibrio species are halophilic, commonly occurring at 30–35 ppt salinity, though their ability to thrive in estuarine environments is well documented 1. 

• Clinically important Aliivibrio salmonicida (formerly V. salmonicida), the cause of cold‑water vibriosis in salmonids, shares these general features but is adapted to low seawater temperatures (grows best at 12-15°C) 15.

• V. anguillarum is one of the best-characterized fish pathogen, and is highly adaptable and occurs in several serotypes but O1, O2, and O3 are the serotypes most consistently associated with fish vibriosis 2.

• Key Virulence Factors: Pathogenic Vibrio spp. produce a diverse arsenal of virulence factors including enterotoxins, haemolysins, cytotoxins, proteases, lipases, phospholipases, siderophores, and adhesive factors/haemagglutinins that allow them to adhere to fish epithelial cells, breach mucosal barriers, and colonize internal organs. V. anguillarum additionally encodes Type VI Secretion System (T6SS) components (hcp-2, vipB/mglB) and RTX toxins (rtxC). The small RNA VaRyhB plays a critical role in regulating iron homeostasis and siderophore biosynthesis, and deletion of this regulatory RNA results in reduced pathogenicity, demonstrating its importance in establishing infection 4 6.

• Transmission Methods:

  • Horizontal Transmission: Water-borne transmission is the primary route. Vibrio spp. are free-living in the water column and sediment, entering fish via gill epithelium, skin abrasions, or the digestive tract during feeding. Live feed organisms such as rotifers (Brachionus spp.) and Artemia are documented carriers of V. anguillarum, V. alginolyticus, V. parahaemolyticus, V. harveyi, and other species, making larval rearing systems particularly high-risk environments 1.
  • Vertical Transmission: Not well established for Vibrio spp., though environmental contamination of eggs is possible.
  • Vector/Environmental Transmission: Vibrio species are ubiquitous in marine and estuarine environments. They thrive in association with zooplankton, shellfish, crustaceans, benthic invertebrates and tank biofilms, serving as persistent environmental reservoirs. Organic matter-enriched water in intensive aquaculture systems favors rapid Vibrio proliferation 1.

Risk Factors

• Environmental Factors: Temperature is the main environmental driver of fish vibriosis, but its effect is species-specific. Many Vibrio spp. proliferate and cause more outbreaks during warmer spring and summer conditions, and field studies often identify temperature-seasonality as the strongest epidemiologic risk factor 1. However, V. anguillarum can also cause disease in cold water aquaculture, and A. salmonicida causes cold-water vibriosis where disease usually develops when seawater is below 12°C 17. Salinity in the range of 30–35 ppt and high organic loading further support pathogen growth 1. Climate change is predicted to increase the frequency and geographic range of vibriosis outbreaks 1.
• Farm Management Practices: High stocking density, physical handling and crowding stress, suboptimal nutrition, poor water quality, and high organic matter loads from feed and excretions all increase host susceptibility. The use of live feed in larval rearing substantially elevates pathogen transmission risk 1.

Diagnosis

Diagnostic Methods

• Clinical Examination: Gross lesion examination focuses on the characteristic combination of haemorrhagic septicaemia (blood poisoning), external skin ulcers, darkened coloration, exophthalmos, splenomegaly, and pale kidney and gills (anaemia). However, clinical signs alone are not sufficient for species-level diagnosis given the broad overlap with other bacterial pathogens and vary among Vibrio species. Isolation of the causative agent from affected tissues (liver, spleen, kidney) is required for definitive diagnosis 1.

• Laboratory Tests:

  • Bacterial Culture: Vibrio spp. are routinely cultured on selective media such as thiosulfate-citrate-bile salts-sucrose (TCBS) agar. However, standard biochemical identification methods frequently fail at the species level due to the high genetic diversity and phenotypic similarity between closely related species (e.g., V. parahaemolyticus and V. alginolyticus share nearly identical 16S rRNA gene sequences) 1.
  • PCR-Based Methods: Molecular identification using species-specific target genes encoding virulence factors (toxR, toxS, haemolysin, collagenase, or genes from pathogenicity islands) offers superior species-level discrimination. A TaqMan probe-based multiplex real-time PCR assay has been validated for the simultaneous detection of V. anguillarum, V. alginolyticus, V. harveyi, and V. scophthalmi in a single reaction, with 100× greater sensitivity than conventional PCR and results within one hour 4. Real-time qPCR targeting the groEL gene effectively detects and quantifies V. alginolyticus, Listonella anguillarum (syn. V. anguillarum), and V. harveyi with detection limits as low as 48 CFU/mL 5.
  • Serological Methods: Agglutination tests and ELISA targeting Vibrio-specific antigens (e.g., LPS) are used for serovar typing (particularly O1, O2, O3 for V. anguillarum) and for monitoring immune responses in vaccination trials 9.
  • MALDI-TOF Mass Spectrometry: MALDI-TOF MS offers rapid, cost-effective, and automated identification of Vibrio isolates without the need for highly trained operators. Accuracy depends critically on database completeness; combined use of the Luvibase and Bruker databases has achieved successful identification of diverse Vibrio species. MALDI-TOF MS is increasingly used alongside molecular methods in routine aquaculture diagnostics 1.
  • Histopathology: Tissue section examination reveals focal necrosis of liver, kidney, and spleen, with bacterial aggregates in affected tissues 1. Immunohistochemistry can be applied to demonstrate Vibrio antigens in situ and support species‑level diagnosis 15.

Differential Diagnosis

• Distinguishing Vibriosis from Other Diseases: Clinical signs of vibriosis overlap significantly with other bacterial infections, such as furunculosis (Aeromonas salmonicida), pasteurellosis (Photobacterium damselae subsp. piscicida), tenacibaculosis (Tenacibaculum spp.), and yersiniosis (Yersinia ruckeri). Infectious salmon anaemia (ISA) can give similar patterns of general haemorrhages. Definitive differentiation requires bacterial culture with biochemical or molecular characterization. The multiplex PCR approach allows simultaneous exclusion of multiple Vibrio species, while MALDI-TOF MS enables broad-spectrum pathogen identification from the same sample 1 415.

Treatment and Prevention

Treatment Options

• Current Treatments:

  • Antibiotics: Oxytetracycline is historically the most widely used antibiotic in aquaculture for vibriosis, both prophylactically and therapeutically. Florfenicol is also approved for use in several major producing countries. Most Vibrio species, including Aliivibrio salmonicida, retain sensitivity to tetracycline, oxytetracycline, chloramphenicol, and florfenicol, though sensitivity profiles vary considerably across strains and geographic regions 1. There is currently no international uniformization of antibiotic use approval, with licensing determined by each country's legislation 1.
  • Treatment Challenges: Antibiotic resistance among Vibrio species is a growing and urgent concern. Resistance genes for tetracycline, quinolones, and carbapenems have been identified in V. anguillarum strains via genomic analysis 2. A meta-analysis of resistance profiles across Mediterranean aquaculture facilities shows an increasing trend in multidrug resistance among V. alginolyticus, V. harveyi, V. parahaemolyticus, and V. splendidus over time. Resistance is often carried on mobile genetic elements (resistance plasmids and horizontal gene transfer), which makes it easy for resistance traits to spread between bacteria 1. Antibiotic residue concentrations in seafood biomass frequently exceed maximum residue limits in major producing countries, underlining the need for improved surveillance 1.
  • Antimicrobial resistance in LMICs: Across low- and middle-income countries (LMICs) in Africa and Asia, antimicrobial resistance in Vibrio species poses a particularly acute dual threat to aquaculture productivity and public health. Key AMR genes found across V. parahaemolyticus, V. alginolyticus, V. vulnificus, and V. cholerae isolates from fish, shellfish, and aquatic environments. Ampicillin resistance is near-universal in many surveyed regions, with resistance to tetracycline, ciprofloxacin, and trimethoprim/sulfamethoxazole also widely reported. In African nations such as Nigeria, isolates from river environments showed resistance to doxycycline (71–89%), erythromycin (86–100%), and tetracycline (86–100%). AMR is estimated to cause US$1 billion in losses annually across LMICs from Vibrio-related disease alone 13.

• Vaccines:

  • Commercial Vaccines: Commercially available vibriosis vaccines include AquaVac™ Vibromax™ (for shrimp via Artemia nauplii bioencapsulation) and ALPHA JECT 3000 (PHARMAQ AS, Norway; intraperitoneal injection for adult fish). These products offer efficacy against the most common V. anguillarum serotypes and have been successfully deployed in salmonid aquaculture 1. In addition, multicomponent vaccines such as ALPHA JECT micro 6 (PHARMAQ AS, Norway) and AquaVac® S7 vet (MSD Animal Health, Norway) include antigens against both Aliivibrio salmonicida (cold‑water vibriosis) and Vibrio anguillarum, and are used routinely to control against these infections in Norwegian salmon farming 15.
  • Whole Cell Inactivated Vaccines: A formalin-killed V. harveyi vaccine administered intraperitoneally to marine red hybrid tilapia resulted in 87% survival post-challenge, compared to 20% in unvaccinated controls. Vaccinated fish showed significantly elevated IgM antibody titers and lysozyme activity 7.
  • Feed-Based Vaccines: A field study of an oral feed-based inactivated vibriosis vaccine in cage-cultured Asian seabass demonstrated significantly enhanced innate immune responses (lysozyme activity), elevated serum and mucosal IgM levels, and improved growth performance over 16 weeks. Survival rate was 71.3% in vaccinated vs. 67.7% in non-vaccinated groups under field conditions 8.
  • Bath Immunization: Atlantic cod bath-immunized with formalin-fixed V. anguillarum serotype O2a developed protective IgM-mediated immunity, providing full protection against O2a challenge and partial protection against O2b. Passive transfer of purified IgM from immunized donors protected naïve fish, confirming the protective role of antibody-mediated immunity even in species lacking classical CD4 T-cell help 9.
  • Vaccine Implementation: The successful implementation of vaccination programs in Norway during the late 1980s — combined with a phase-out of prophylactic antibiotic use — is regarded as a model example of how vaccination can dramatically reduce antibiotic dependence in intensive fish farming 1 10. These commercial vaccines are administered to smolts well before sea transfer and have provided near‑complete control of the bacterial diseases included in the vaccine; virtually all Atlantic salmon entering sea cages in Norway today are vaccinated against vibriosis 15.

Preventive Measures

• Biosecurity Protocols:

  • Monitoring and controlling Vibrio loads in rearing water, live feed, and broodstock using molecular surveillance tools 1.
  • Careful management of live feed (Artemia, rotifers) to minimize introduction of pathogenic Vibrio strains into larval rearing systems 1.
  • Early application of vaccination programs for juvenile and adult fish; bath immunization as a practical method for large-scale or larval fish where injection is not feasible 9 10.

• Farm Management Practices:

  • Reducing stocking density and minimizing handling stress, which increase susceptibility to opportunistic Vibrio infection 1.
  • Maintaining optimal water quality parameters including temperature, salinity, dissolved oxygen, and limiting organic matter accumulation; high organic load and warm temperatures favour Vibrio growth 16 1.
  • Probiotic supplements are increasingly used in some aquaculture systems as a supportive, antibiotic‑free way to stabilise the microbiota and compete with opportunistic pathogens like Vibrio and improve gut health and water quality. Selected strains that can compete with or inhibit Vibrio spp. (for example Bacillus velezensis and Phaeobacter spp.) have demonstrated efficacy in inhibiting Vibrio biofilm formation and growth in aquaculture‑relevant experimental systems, and are therefore considered promising probiotic candidates for future applications 1.

• Measures under development:

  • Exploring phage therapy as a pathogen-specific, environmentally targeted intervention, particularly for species or developmental stages where vaccination is not applicable 1.
  • Novel biocontrol agents such as Paratapes undulata extract have shown promise in reducing V. alginolyticus infection in tilapia, improving growth by ~284% and reducing mortality by 75% in infected groups compared to untreated infected controls, through immune modulation and direct antimicrobial activity 14.

Case Studies

Real-World Examples

• Notable Outbreaks:

  • Greece — 13-Year Aquaculture Monitoring (2010–2023): A comprehensive 13-year monitoring program tracking vibriosis in Greek marine aquaculture characterized 273 bacterial isolates from disease cases originating in eight regions and nine host species. The principal hosts were European seabass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata). Vibrio harveyi was the dominant pathogen, isolated year-round from all host species and throughout all regions, with frequent co-isolation of Photobacterium damselae subsp. damselae and V. alginolyticus during summer. During spring, other species — V. lentus, V. cyclitrophicus, and V. gigantis — were relatively more abundant. Phylogenetic analysis using the mreB gene revealed high variability within the collection 3.
  • Mediterranean Seabream Outbreaks: A meta-analysis of ten vibriosis outbreaks in both farmed and wild gilthead seabream in the Mediterranean Sea identified V. alginolyticus as the most frequently isolated species, followed by V. harveyi, V. splendidus, V. anguillarum, V. parahaemolyticus, and V. tubiashii. Vibrio isolates were most commonly recovered from liver, spleen, and kidney, followed by external lesions, gills, brain, eyes, gut, hepatopancreas, and blood. Interestingly, V. ichthyoenteri-like strains were isolated exclusively from asymptomatic individuals 1.
  • Atlantic Salmon — Novel Vibrio sp. in Canada: A novel Vibrio species (sp. J383), related to V. splendidus with 93% genomic identity, was isolated from the internal organs of vaccinated Atlantic salmon showing clinical signs of ulcer disease at cage-sites in the North Atlantic. Infection assays demonstrated low-level mortality when administered intracelomic at 10⁷–10⁸ CFU/dose. Interestingly, disease severity was greatest at 12°C but absent at 16°C, and the pathogen persisted in the bloodstream for at least 8 weeks at cold temperatures, underscoring the threat posed by cold-adapted novel Vibrio species in high-latitude aquaculture 11.

• Lessons Learned:

  • The dominance of V. harveyi in Greek aquaculture — where it replaced V. anguillarum as the primary pathogen — highlights the need for ongoing, region-specific surveillance rather than reliance on historical assumptions about causative agents 3.
  • The emergence of novel Vibrio species in vaccinated Atlantic salmon confirms that existing commercial vaccines may not protect against phylogenetically divergent strains, reinforcing the importance of regular pathogen characterization in each farming region 11.
  • Live feed represents a critical but controllable vector for Vibrio introduction into larval systems; microbiome management of Artemia and rotifers is an important preventive lever 1.

Data Insights

Disease Impact by Country

Greece

• Vibriosis Incidence:

  • Over a 13-year monitoring period, vibriosis was a persistent and widespread concern across all eight surveyed marine aquaculture regions. Vibrio harveyi was prevalent year-round and across all nine host species, indicating it is the dominant pathogen in the Greek marine aquaculture sector. Seasonal patterns showed elevated co-isolations with Photobacterium damselae subsp. damselae and V. alginolyticus during warm summer months, while spring was characterized by higher diversity of Vibrio spp. including V. lentus and V. cyclitrophicus 3.
  • Principal affected species: European seabass (D. labrax) and gilthead seabream (S. aurata) 3.

• Economic Impact:

  • While country-specific economic loss data for Greece were not quantified in the reviewed studies, the severity and frequency of outbreaks — combined with the dominance of V. harveyi as the principal agent — make vibriosis a leading constraint on aquaculture productivity in the Greek sector 3.

• Treatment & Management:

  • Antibiotic use follows Mediterranean patterns, with oxytetracycline and florfenicol as primary therapeutic agents. Increasing antibiotic resistance trends have been documented for V. alginolyticus and V. harveyi in Mediterranean facilities. Development and adoption of probiotics and vaccines as alternatives is ongoing 1 3.

Africa (Egypt, South Africa, Nigeria, Tunisia)

• Vibriosis Incidence:

  • Pathogenic Vibrio species are widely distributed in aquatic fish environments across sub-Saharan and North Africa. In Egypt, studies identified V. parahaemolyticus, V. alginolyticus, and V. cholerae from fish, with virulence genes including TL, TDH, and collagenase confirmed. In South Africa, V. parahaemolyticus isolates from fish (n=45, June–September 2023) carried blaTEM, blaOXA, aadA, sul1, tetA, tetB, and ermB resistance genes, with ampicillin resistance at 88.9%, erythromycin (84.4%), and tetracycline (75.6%). In Nigeria, 315 river isolates spanning V. parahaemolyticus, V. alginolyticus, V. vulnificus, V. mimicus, V. harveyi, and V. cholerae were characterized, with blaOXA (27%), ampC (39%), blaTEM (11%), tet39 (8%), aacC2 (24%), and aphA1 (14%) (aminoglycosides) AMR genes detected. In Tunisia, 126 fish isolates of V. alginolyticus and V. parahaemolyticus were characterized using the toxR gene 13.

• Economic Impact:

  • AMR-related vibriosis is estimated to cost LMICs approximately US$1 billion annually, with African aquaculture disproportionately affected due to limited diagnostic infrastructure, overreliance on selective culture methods, and poor antibiotic stewardship 13.

• Treatment & Management:

  • The majority of isolates in African studies demonstrated high resistance to ampicillin, with variable resistance to ciprofloxacin, nalidixic acid, and tetracycline. The emergence of multidrug-resistant strains highlights the urgent need for improved molecular surveillance tools and antibiotic stewardship programs tailored to LMIC contexts 13.

Asia (China, Bangladesh, India, Thailand)

• Vibriosis Incidence:

  • In China, 312 shrimp-derived isolates of V. alginolyticus, V. parahaemolyticus, V. harveyi, V. cholerae, and V. campbellii were identified, with virulence genes chiA, hucR, vlhh, sero, flaA, vch, VAC, and rpsS detected. AMR genes strA, QnrV, sul2, and Int4 were identified, with streptomycin (43.8%) and QnrV (11.7%) as notable resistance determinants. In Bangladesh, V. parahaemolyticus isolates from fish and water (n=51) showed high resistance to amikacin (90.9%), cefotaxime and tetracycline (37.6–64%), with widespread multidrug resistance. In India, V. parahaemolyticus, V. vulnificus, and V. harveyi from fish and shrimp showed virulence genes tdh, tlh, dlA, vhpA, and pilF, with resistance to gentamicin (33–66%). In Thailand, V. parahaemolyticus isolates (n=74) from shellfish carried virulence genes tdh, trh, vcrD1, vcrD2, vopT, and totR, with cefotaxime resistance at 100% 13.

• Economic Impact:

  • Southeast Asian countries demonstrated considerably higher species richness in Vibrio isolations compared to African nations, reflecting the greater intensity of aquaculture operations and the corresponding selection pressure for AMR traits. The concentration of AMR aquaculture effluents in river systems and coastal environments creates persistent environmental reservoirs of resistant strains that threaten both aquatic animal and human health 13.

• Treatment & Management:

  • Consistent with global trends, ampicillin resistance is near-universal across Asian isolates. Resistance to ciprofloxacin, tetracycline, trimethoprim/sulfamethoxazole, and third-generation cephalosporins is widespread and increasing. The integration of advanced molecular diagnostics (multiplex PCR, chromogenic media) is essential for surveillance in resource-limited settings across the region 13.

Mediterranean Region (Spain, Italy, Turkey, North Africa)

• Vibriosis Incidence:

  • Vibrio species are the dominant bacterial pathogens affecting gilthead seabream and sea bass throughout the Mediterranean zone. V. alginolyticus was historically the most commonly isolated species, but V. harveyi has emerged as increasingly prevalent. Multiple outbreaks have been documented in coastal aquaculture facilities throughout Spain, Turkey, Italy, and North Africa 1.
  • The chronic degradation of Mediterranean coastal waters — including sewage discharge, industrial effluents, and agricultural runoff — is correlated with elevated prevalence of pathogenic Vibrio species in both farmed and wild fish populations, increasing outbreak risk 1.

• Economic Impact:

  • Vibrio infections are a major contributor to the overall disease burden estimated at US$3–6 billion annually in global aquaculture. The Mediterranean zone represents one of the most heavily impacted regions globally due to intensive seabream and seabass production 1.

Norway

• Vibriosis Incidence:

  • Vibrio anguillarum in Norway have been identified from numerous fish species, including Atlantic salmon, lumpfish, rainbow trout, cod and European seabass. Other Vibrio spp. (including V. ordalii and V. splendidus–like strains) have been reported in various marine fish 18.
  • Classical vibriosis caused by V. anguillarum occurs at moderate temperatures, while cold‑water vibriosis caused by Aliivibrio salmonicida is associated with sea temperatures below about 10 °C and has historically been an important disease in Northern Norway. Cold‑water vibriosis was first described from Finnmark in the late 1970s in farmed salmon, and by 1979 an increasing number of outbreaks with pronounced mortality were recorded at Hitra, where the disease was originally referred to as “Hitrasyke” (Hitra disease). It reached a peak in the late 1980s with hundreds of recorded outbreaks, before the introduction of effective vaccines led to a marked decline in cases through the 1990s 15 18.
  • A notable resurgence of cold‑water vibriosis occurred in 2012– 2013, with multiple outbreaks reported from Nord‑Trøndelag to Finnmark and particularly in North‑Norway. This increase may be linked to vaccination status, and possibly an elevated infection pressure of unknown origin. Since 2013, cold‑water vibriosis has again been very rarely diagnosed in Norwegian aquaculture 15.

• Treatment & Management:

  • In the earlier years of intensive farming, substantial quantities of antibiotics such as tetracycline, trimethoprim/sulfamethoxazole and furazolidone were administered, and the pathogen subsequently became resistant to these agents. In modern practice, broad‑spectrum antibiotics are reserved for serious outbreaks and prescribed under veterinary oversight 15.
  • When disease appears in fish that are nearly at market size, emergency slaughter is often considered a better option, because low seawater temperatures prolong withdrawal times after treatment 15.
  • From the late 1980s onwards, vaccination has become the main tool for controlling vibriosis and cold‑water vibriosis. Polyvalent vaccines are administered to salmon in the hatchery phase, well before sea transfer, and have provided very high protection against the bacterial diseases they cover. The few cases that do occur today are mostly seen in slaughter‑size fish, where immunity is likely reduced because of the long time elapsed since vaccination 15.

Research and References

Latest Research Findings

Epidemiology and Ecology

1. "Vibriosis Outbreaks in Aquaculture: Addressing Environmental and Public Health Concerns and Preventive Therapies Using Gilthead Seabream Farming as a Model System"
   Authors: Sanches-Fernandes, G. M. M., Sá-Correia, I., & Costa, R.
   Reference: Frontiers in Microbiology, 2022; 13: 904815.
   Key findings: Comprehensive review of vibriosis ecology, epidemiology, molecular detection, antibiotic resistance trends, and alternative prevention strategies (vaccines, phage therapy, probiotics) using gilthead seabream as a model system. Documents increasing antibiotic resistance among Vibrionaceae in the Mediterranean and identifies probiotics as a promising sustainable alternative.
   DOI: 10.3389/fmicb.2022.904815

2. "Pathogenic and Opportunistic Vibrio spp. Associated with Vibriosis Incidences in the Greek Aquaculture: The Role of Vibrio harveyi as the Principal Cause of Vibriosis"
   Authors: Triga, A., Smyrli, M., & Katharios, P.
   Reference: Microorganisms, 2023; 11(5): 1197.
   Key findings: 13-year monitoring program characterizing 273 isolates from eight regions and nine hosts. Vibrio harveyi emerged as the principal pathogen, prevalent year-round. Seasonal patterns identified, with high diversity during spring and V. harveyi/V. alginolyticus co-isolations during summer.
   DOI: 10.3390/microorganisms11051197

Genomics and Pathogenesis

3. "Multiscale Comparative Pathogenomic Analysis of Vibrio anguillarum Linking Serotype Diversity, Genomic Plasticity and Pathogenicity"
   Authors: Shahed, K., Chakma, A., Bin Manjur, O. H., & Islam, S. I.
   Reference: Journal of Genetic Engineering & Biotechnology, 2025; 23: 100522.
   Key findings: Pan-genomic analysis of 16 V. anguillarum strains revealed an open pangenome with 2,038 core and 5,197 cloud genes. Identified 118 pathogenic genomic islands, AMR genes (tetracycline, quinolone, carbapenem), and virulence factors including T6SS components and RTX toxins. O1 serotypes show genetic homogeneity; O2 and O3 show divergence.
   DOI: 10.1016/j.jgeb.2025.100522

4. "Characterization of the Vibrio anguillarum VaRyhB Regulon and Role in Pathogenesis"
   Authors: Li, Y., Yu, X., Li, P., Li, X., & Wang, L.
   Reference: Frontiers in Cellular and Infection Microbiology, 2025; 14: 1531176.
   Key findings: VaRyhB small RNA in V. anguillarum regulates iron homeostasis, siderophore production, motility, and oxidative stress responses. Deletion of VaRyhB reduces pathogenicity, identifying this regulatory RNA as a key virulence determinant.
   DOI: 10.3389/fcimb.2024.1531176

5. "Comparative Genomic Analysis of a Novel Vibrio sp. Isolated from an Ulcer Disease Event in Atlantic Salmon (Salmo salar)"
   Authors: Ghasemieshkaftaki, M., Vasquez, I., Eshraghi, A., Gamperl, A. K., & Santander, J.
   Reference: Microorganisms, 2023; 11(7): 1736.
   Key findings: Novel Vibrio sp. J383, related to V. splendidus (93% identity), isolated from vaccinated Atlantic salmon with ulcer disease. Pathogen is cold-adapted (disease at 10–12°C, absent at 16°C) and persists in blood for ≥8 weeks, representing a novel emerging threat in high-latitude aquaculture.
   DOI: 10.3390/microorganisms11071736

Diagnostics

6. "Development of Multiple Real-Time Fluorescent Quantitative PCR for Vibrio Pathogen Detection in Aquaculture"
   Authors: Zhang, B., Qiu, Y., Shi, C., & Zhang, J.
   Reference: Veterinary Sciences, 2025; 12(4): 327.
   Key findings: TaqMan probe-based multiplex real-time PCR enables simultaneous detection of V. anguillarum, V. alginolyticus, V. harveyi, and V. scophthalmi with 100× greater sensitivity than conventional PCR. Results within one hour, high specificity, and capacity for co-infection detection.
   DOI: 10.3390/vetsci12040327

7. "Real-Time PCR Protocol for Detection and Quantification of Three Pathogenic Members of the Vibrionaceae Family"
   Authors: Costa, C., Ferreira, G. D., Simões, M., Silva, J. L., & Campos, M. J.
   Reference: Microorganisms, 2022; 10(10): 2060.
   Key findings: qPCR targeting the groEL gene detects and quantifies V. alginolyticus, Listonella anguillarum, and V. harveyi with detection limits of 48–600 CFU/mL. DNeasy Blood and Tissue kit provides the highest DNA extraction efficiency. Matrix effects must be accounted for when applying to complex samples such as algae.
   DOI: 10.3390/microorganisms10102060

Vaccine Development

8. "Efficacy of Whole Cell Inactivated Vibrio harveyi Vaccine against Vibriosis in a Marine Red Hybrid Tilapia (Oreochromis niloticus × O. mossambicus) Model"
   Authors: Abu Nor, N., Zamri-Saad, M., Md Yasin, I.-S., Salleh, A., Mustaffa-Kamal, F., Matori, M. F., & Azmai, M. N. A.
   Reference: Vaccines, 2020; 8(4): 734.
   Key findings: Intraperitoneal vaccination with formalin-killed V. harveyi achieved 87% survival post-challenge versus 20% in controls. Significantly elevated serum IgM titers and lysozyme activity confirm stimulation of both innate and adaptive immunity.
   DOI: 10.3390/vaccines8040734

9. "Field Efficacy of a Feed-Based Inactivated Vaccine against Vibriosis in Cage-Cultured Asian Seabass, Lates calcarifer, in Malaysia"
   Authors: Amir-Danial, Z., Zamri-Saad, M., Amal, M. N. A., Annas, S., Mohamad, A., Jumria, S., Manchanayake, T., Arbania, A., & Ina-Salwany, M. Y.
   Reference: Vaccines, 2023; 11(1): 9.
   Key findings: Oral feed-based inactivated vibriosis vaccine in cage-cultured Asian seabass significantly enhanced innate immune responses, elevated serum/mucosal IgM, and improved growth performance over 16 weeks under field conditions. Survival was 71.3% vaccinated vs. 67.7% unvaccinated.
   DOI: 10.3390/vaccines11010009

10. "Current Challenges of Vaccination in Fish Health Management"
    Authors: Kumar, A., Middha, S. K., Menon, S. V., Paital, B., Gokarn, S., Nelli, M., et al.
    Reference: Animals, 2024; 14(18): 2692.
    Key findings: Review of current fish vaccination approaches, including whole-killed, subunit, recombinant, DNA, and live-attenuated vaccines. Identifies key challenges including route of administration, adjuvant use, and lack of efficacy at larval stages. Biotechnological innovations (plant-derived, mucosal vaccines) are highlighted as future directions.
    DOI: 10.3390/ani14182692

Immunology

11. "Protective IgM-Mediated Immunity against Vibrio anguillarum in Atlantic Cod with Evolutionary Losses of mhc class II and cd4"
    Authors: Jonsson, A., López-Porras, A., Nørstebø, S. F., Guslund, N. C., Sørum, H., Qiao, S.-W., & Johansen, F.-E.
    Reference: Frontiers in Immunology, 2025; 16: 1579541.
    Key findings: Atlantic cod bath-immunized with formalin-fixed V. anguillarum O2a developed protective IgM-mediated immunity without classical CD4 T-cell help. Full protection against O2a challenge; partial protection against O2b. Passive IgM transfer conferred protection in naïve fish. Protective antibodies targeted a proteinase K-sensitive protein antigen rather than LPS.
    DOI: 10.3389/fimmu.2025.1579541

12. "Multi-Organ Transcriptomic Profiles and Gene-Regulation Network Underlying Vibriosis Resistance in Tongue Sole"
    Authors: Chen, Q., Ma, X., Wang, J., Shi, M., Hu, G., Chen, S., & Zhou, Q.
    Reference: Scientific Data, 2024; 11: 775.
    Key findings: RNA-seq analysis across liver, spleen, intestine, skin, and gill of vibriosis-resistant and susceptible tongue sole identified 12 organ-specific transcriptional modules and co-expression networks underlying disease resistance, providing targets for genetic breeding programs.
    DOI: 10.1038/s41597-024-03651-z

Antimicrobial Resistance in LMICs

13. "Antibiotic Resistance and Pathogenicity of Vibrio Species in Aquaculture: Implications for Fish Health and Food Safety in LMICs"
    Authors: Hobe, A., Msolo, L., Ebomah, K. E., Jaja, I. F., Oguttu, J. W., & Okoh, A. I.
    Reference: Veterinary Medicine and Science, 2026; 12: e70877.
    Key findings: Systematic review of AMR and pathogenicity in Vibrio spp. across LMICs (2016–2025 literature). Documents virulence gene profiles (tdh, trh, toxR, hlyA, ctxA, ureR) and AMR genes (blaTEM, blaOXA, sul1, tetA, tetB, qnrVC) in fish and aquaculture environments across Africa (Egypt, South Africa, Nigeria, Tunisia, Burkina Faso, Tanzania) and Asia (China, Bangladesh, India, Thailand). Ampicillin resistance is near-universal; multidrug resistance is increasing. Estimates US$1 billion in annual LMIC losses from AMR-associated vibriosis. Calls for improved molecular surveillance, targeted interventions, and antibiotic stewardship.
    DOI: 10.1002/vms3.70877

Biocontrol

14. "Innovative Vibriosis Control in Open Aquaculture: Paratapes undulata as a Sustainable Growth and Resistance Enhancer in Red Tilapia"
    Authors: Mowafy, R. E., Megahed, H. M., Abou Khadra, S. H., Bakry, M. A., Moustafa, A. H., & El-Demerdash, A. S.
    Reference: Scientific Reports, 2025; 15: Article ID not specified.
    Key findings: Paratapes undulata extract significantly improved growth (~284% in infected/treated group) and reduced mortality by 75% in V. alginolyticus-infected tilapia. Mechanistically, modulated cytokine balance toward anti-inflammation, enhanced antioxidant capacity, and directly inhibited Vibrio virulence. GC-MS and FTIR analyses identified active bioactive compounds.
    DOI: 10.1038/s41598-025-01026-x

Conclusion

Vibriosis remains one of the most economically significant and ecologically widespread bacterial diseases in global marine aquaculture. The diverse ecology of pathogenic Vibrio species — their ubiquity in marine environments, broad host range, rapid opportunistic pathogenesis at elevated temperatures, and growing antibiotic resistance — means that vibriosis poses a persistent and increasing challenge as aquaculture intensifies and global ocean temperatures rise.

The critical management strategies currently available include: (1) robust molecular surveillance using multiplex PCR and MALDI-TOF MS for early, species-level pathogen identification; (2) vaccination programs using inactivated whole-cell vaccines (IP, bath, or feed-based) that have proven efficacy in multiple commercially important species; (3) the strategic shift away from antibiotic prophylaxis toward probiotics, phage therapy, and novel biocontrol agents as sustainable long-term solutions; and (4) rigorous biosecurity with attention to live feed management, stocking density, and water quality optimization.

Future research should prioritize: (a) characterization of emerging and novel Vibrio species (e.g., cold-adapted strains in Atlantic salmon, V. harveyi dominance in Mediterranean systems) to ensure vaccines and diagnostics remain current; (b) development of multivalent vaccines or broadly protective formulations that address the genetic diversity of pathogenic Vibrio serotypes; (c) understanding of host immune mechanisms — particularly in species with atypical adaptive immune systems such as Atlantic cod — to guide rational vaccine design; (d) genomic epidemiology studies to track AMR gene dissemination (particularly blaTEM, blaOXA, sul1, tetA, qnrVC families) across aquaculture systems and into human pathogen reservoirs; (e) strengthening surveillance capacity in LMICs through deployment of advanced molecular diagnostic tools accessible in resource-limited settings 13; and (f) scaling of alternative control strategies (probiotics, phage therapy, plant bioactives) to field-applicable, commercially viable products. Addressing vibriosis effectively will require an integrated, "One Health" approach that connects aquatic animal health, environmental management, and human public health.

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Last Modified: 2026-07-18

Tags: #Vibriosis, #Vibrio, #BacterialDiseases, #Bacteria

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Citations:

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[4] Zhang, B., Qiu, Y., Shi, C., & Zhang, J. (2025). Development of multiple real-time fluorescent quantitative PCR for Vibrio pathogen detection in aquaculture. Veterinary Sciences, 12(4), 327. https://doi.org/10.3390/vetsci12040327 · Full text

[5] Costa, C., Ferreira, G. D., Simões, M., Silva, J. L., & Campos, M. J. (2022). Real-time PCR protocol for detection and quantification of three pathogenic members of the Vibrionaceae family. Microorganisms, 10(10), 2060. https://doi.org/10.3390/microorganisms10102060 · Full text

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