Search USGS⌕ Search
Home/Archive/USGS

USGS · 70137964

Testing of candidate non-lethal sampling methods for detection of Renibacterium salmoninarum in juvenile Chinook salmon Oncorhynchus tshawytscha

Diane G. Elliott·Constance L. McKibben·Carla M. Conway·Maureen K. Purcell·Dorothy M. Chase·Lynn M. Applegate
View original source ↗Export metadata ↓

Abstract

Non-lethal pathogen testing can be a useful tool for fish disease research and management. Our research objectives were to determine if (1) fin clips, gill snips, surface mucus scrapings, blood draws, or kidney biopsies could be obtained non-lethally from 3 to 15 g Chinook salmon Oncorhynchus tshawytscha , (2) non-lethal samples could accurately discriminate between fish exposed to the bacterial kidney disease agent Renibacterium salmoninarum and non-exposed fish, and (3) non-lethal samples could serve as proxies for lethal kidney samples to assess infection intensity. Blood draws and kidney biopsies caused ≥5% post-sampling mortality (Objective 1) and may be appropriate only for larger fish, but the other sample types were non-lethal. Sampling was performed over 21 wk following R. salmoninarum immersion challenge of fish from 2 stocks (Objectives 2 and 3), and nested PCR (nPCR) and real-time quantitative PCR (qPCR) results from candidate non-lethal samples were compared with kidney tissue analysis by nPCR, qPCR, bacteriological culture, enzyme-linked immunosorbent assay (ELISA), fluorescent antibody test (FAT) and histopathology/immunohistochemistry. R. salmoninarum was detected by PCR in >50% of fin, gill, and mucus samples from challenged fish. Mucus qPCR was the only non-lethal assay exhibiting both diagnostic sensitivity and specificity estimates >90% for distinguishing between R. salmoninarum -exposed and non-exposed fish and was the best candidate for use as an alternative to lethal kidney sample testing. Mucus qPCR R. salmoninarum quantity estimates reflected changes in kidney bacterial load estimates, as evidenced by significant positive correlations with kidney R. salmoninarum infection intensity scores at all sample times and in both fish stocks, and were not significantly impacted by environmental R. salmoninarum concentrations.

Explore related subjects

Diseases of Aquatic OrganismsArticle

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Diane G. Elliott, Constance L. McKibben, Carla M. Conway, Maureen K. Purcell, Dorothy M. Chase, Lynn M. Applegate. 2015. Testing of candidate non-lethal sampling methods for detection of Renibacterium salmoninarum in juvenile Chinook salmon Oncorhynchus tshawytscha. https://doi.org/10.3354/dao02846

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2025

Histological progression and bacterial load dynamics of Renibacterium salmoninarum in Chinook salmon Oncorhynchus tshawytscha

Renibacterium salmoninarum , the cause of bacterial kidney disease (BKD), severely impacts salmonid populations. Much of our understanding of the BKD pathology in salmonids comes from evaluating fatal infections in wild populations or spawning Pacific Northwest salmonids. Our study investigated the histological progression and bacterial load dynamics of R. salmoninarum infection in Chinook salmon following intraperitoneal injection to enhance understanding of the disease’s dynamics. Seventy presmolt salmon were injected with the ATCC-33209 isolate of R. salmoninarum and monitored over 10 wk. Histological signs of disease were observed in spleen and liver tissues at 1 wk post-injection and in kidney tissues at 4 wk post-injection, with signs of disease increasing over time. Additionally, histopathological analysis revealed splenic and hepatic capsulitis (coelomitis), individual hepatocyte necrosis, progressive granulomatous hepatitis, splenitis, and nephritis with necrosis. Gram staining confirmed the presence of Gram-positive bacteria within macrophages and extracellularly in infected tissues. Quantitative PCR revealed significant increases in bacterial loads in both kidney and liver tissues over the study period, with higher bacterial loads observed in the kidney tissue. Bacterial load was strongly correlated with disease stage, with peak bacterial burdens coinciding with the most severe histological changes. Our study provides a comprehensive account of R. salmoninarum infection and disease progression in Chinook salmon after intraperitoneal injection.

Diseases of Aquatic Organisms↗
USGS2024

Cytology in cnidaria using Exaiptasia as a model

A need exists for additional methods to examine cnidaria at the cellular level to aid our understanding of health, anatomy, and physiology of this important group of organisms. This need is particularly acute given that disease is emerging as a major factor in declines of ecologically important functional groups such as corals. Here we describe a simple method to process cnidarian cells for microscopic examination using the model organism Exaiptasia . We show that this organism has at least 18 cell types or structures that can be readily distinguished based on defined morphological features. Some of these cells can be related back to anatomic features of the animal both at the light microscope and ultrastructural level. The cnidome of Exaiptasia may be more complex than what is currently understood. Moreover, cnidarian cells, including some types of cnidocytes, phagocytize cells other than endosymbionts. Finally, our findings shed light on morphologic complexity of cell-associated microbial aggregates and their intimate intracellular associations. The tools described here could be useful for other cnidaria.

Diseases of Aquatic Organisms↗
USGS2024

Evaluation of in vitro treatments against the causative agent of Diadema antillarum scuticociliatosis (DaSc)

ABSTRACT: In the 1980s, a mass die-off of the long-spined sea urchin Diadema antillarum occurred on Florida and Caribbean coral reefs. D. antillarum populations largely did not recover, and in 2022, remaining populations experienced another mass mortality event. A ciliate most similar to Philaster apodigitiformis was identified as the causative agent of the 2022 event, which was named D. antillarum scuticociliatosis (DaSc). Here, we investigated possible treatments for this pathogen. We tested the efficacy of 10 compounds at final concentrations of 100, 50, 25, 12.5, 6.25, and 3.13 µM, or a 10-fold serial dilution series, against ciliates cultured from an infected D. antillarum specimen. Of the tested compounds, 8 induced 100% ciliate mortality at some dose after 24 h. The most effective (defined as those requiring the lowest dose to induce 100% ciliate mortality) were quinacrine and tomatine (both effective at 12.5 µM), followed by furaltadone and plumbagin (25 µM), bithionol sulfoxide and 2’4’ dihydroxychalcone (50 µM), and oxyclozanide and carnidazole (100 µM). Toltrazuril and a commercially available anticiliate product containing naphthoquinones were not effective at any dose tested. Shortened (15 min) time trials were performed using ciliate cultures reared in natural seawater to better reflect natural environmental conditions, and revealed that 2 of the compounds (quinacrine and tomatine) induced 100% ciliate mortality at 100 µM, with tomatine also effective at 50 µM. This study identified several treatments effective against the causative agent of DaSc in vitro , but their toxicity and utility in vivo remain unknown.

Diseases of Aquatic Organisms↗