Bacterial Kidney Disease (BKD)

Bacterial Kidney Disease (BKD) is a chronic bacterial infection affecting various fish species in aquaculture, including Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), and other freshwater and marine fish. It is caused by the bacterium Renibacterium salmoninarum, leading to significant economic losses due to high mortality rates, reduced growth performance, and increased susceptibility to secondary infections 1 2 3.

Etiology

• Causative Agent: Renibacterium salmoninarum bacterium 1 2.

• Transmission Methods:

  • Direct Contact: Spread between infected & healthy fish through close proximity 1 2.
  • Waterborne: The bacterium can spread through water, especially under conditions of poor water quality and high organic load 1 2.
  • Vertical Transmission: Infected broodstock can transmit the bacterium to their offspring through eggs 1 2.

Risk Factors

• Environmental Factors: Poor water quality, high stocking densities, and stressful conditions can increase susceptibility to BKD 1 2.
• Farm Management Practices: Ineffective biosecurity measures and lack of routine health monitoring can facilitate the spread of the bacterium 1 2.

Diagnostic Methods

• Clinical Examination: Observation of physical and behavioral symptoms indicative of BKD.

• Laboratory Tests:

  • Bacterial Culture: Isolation and identification of Renibacterium salmoninarum from tissue samples. However, R. salmoninarum is slow-growing on bacteriological media, and samples may become overgrown by faster-growing microorganisms, making culture difficult 5 7.
  • PCR (Polymerase Chain Reaction): Detects bacterial DNA in tissue samples 5 7.
  • Histopathology: Microscopic examination of kidney and other tissues to assess the extent of damage and infection 7.
  • Fluorescent Antibody Test (FAT): Used for confirmatory identification 5.
  • Enzyme-Linked Immunosorbent Assay (ELISA): Quantifies the level of soluble antigen (p57) in kidney tissue 4 8.

Differential Diagnosis

• Distinguishing BKD from Other Diseases: It is crucial to differentiate BKD from diseases with similar symptoms, such as Infectious Hematopoietic Necrosis (IHN) and other bacterial infections 8.

Treatment Options

• Current Treatments:

  • Antibiotics: Erythromycin and sulfamethazine can control the disease while administered, but mortality often resumes when treatment is withdrawn 2.
  • Supportive Care: Improving water quality and reducing stress to support recovery.

• Experimental Treatments: Research is ongoing into potential vaccines and alternative treatment methods.

Preventive Measures

• Biosecurity Protocols:

  • Implementing strict biosecurity measures to prevent the introduction and spread of _Renibacterium salmoninarum 5.
  • Regular disinfection of equipment and facilities to minimize the risk of contamination 6.
• Farm Management Practices:

  • Reducing stocking densities to decrease the risk of bacterial transmission 4.
  • Using water treatment systems to maintain optimal water quality 4.
  • Regular health monitoring and early detection programs to identify and manage outbreaks promptly 5.
  • Culling of infected broodstock and/or total hatchery depopulation followed by disinfection 5.

Real-World Examples

• Notable Outbreaks:

  • Scotland (1933): First reported in wild Atlantic salmon populations in the rivers Spey and Dee 8.
  • Japan (1970s): BKD is believed to have been introduced with imports of Coho salmon eggs certified as infection-free 5.
• Response Strategies and Outcomes:

  • Scotland: In 1997, when BKD was first diagnosed in a rainbow trout farm, the infected farm and a downstream farm were emptied, cleaned, disinfected, and restocked after a 60-day fallowing period. However, the disease reappeared the following year 5.

• Lessons Learned: The importance of early detection, robust biosecurity, and coordinated response efforts in controlling BKD outbreaks.

Recent studies on Bacterial Kidney Disease (BKD) have focused on various aspects of the disease, including its diagnosis, prevalence, and control. Here are some notable recent research findings:

1. "Prevalence and diagnosis of bacterial kidney disease (BKD) in Scotland between 1990 and 2002"
   Authors: Bruno, D. W.
   Reference: Bruno, D. W. (2004). Prevalence and diagnosis of bacterial kidney disease (BKD) in Scotland between 1990 and 2002. Diseases of Aquatic Organisms, 59(2), 125-130.
   Link to study
2. "BACTERIAL KIDNEY DISEASE"
   Authors: J.W. Warren
   Reference: Great Lakes Fishery Commission Special Publication 83-2, Chapter 21.
   Link to study
3. "Report of the Scientific Committee on Animal Health and Animal Welfare on Bacterial Kidney Disease"
   Authors: Scientific Committee on Animal Health and Animal Welfare
   Reference: European Commission, Health & Consumer Protection Directorate-General.
   Link to study

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Last Modified: 2024-07-26

Tags: #BacterialKidneyDisease, #AtlanticSalmon, #RainbowTrout, #Trout, #Salmonoids #Salmon, #Norway, #Scotland, #BacterialDiseases, #Bacteria