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ARS Home » Northeast Area » Leetown, West Virginia » Cool and Cold Water Aquaculture Research » Research » Publications at this Location » Publication #399625

Research Project: Improving Salmonid Health through Breeding, Vaccination and Microbiome Modulation

Location: Cool and Cold Water Aquaculture Research

Title: Detection Of Lactococcus spp. in environmental samples and wild fish from Four Lakes in Southern California

Author
item ABRAHAM, TAYLOR - University Of California, Davis
item YAZDI, ZEINAB - University Of California, Davis
item LITTMAN, ERIC - University Of California, Davis
item SHAHIN, KHALID - University Of California, Davis
item HECKMAN, TAYLOR - University Of California, Davis
item QUIJANO CARDÉ, EVA MARIS - University Of California, Davis
item NGUYEN, DIEM - University Of California, Davis
item HUA, RUIXUE - University Of California, Davis
item SOTO, ESTEBAN - University Of California, Davis
item ADKISON, MARK - California Department Of Fish & Game
item VEEK, TRESA - California Department Of Fish & Game
item MUKKATIRA, KAVERY - California Department Of Fish & Game
item RICHEY, CHRISTINE - California Department Of Fish & Game
item KWAK, KEVIN - California Department Of Fish & Game
item MOHAMMED, HAITHAM - Assiut University
item ORTEGA, CESAR - Universidad Autonoma Del Estado De Hidalgo
item AVENDAÑO-HERRERA, RUBEN - Universidad Andres Bello (UNAB)
item HYATT, MICHAEL - Wildlife Conservation Society
item KELEHER, WILLIAM - Kennebec River Biosciences
item Welch, Timothy - Tim

Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Piscine lactococcosis is an emerging bacterial disease of fish that is caused by Lactococcus garvieae L. petauri, and L. formosensis. In 2020, outbreaks of Lactococcosis, caused by L. petauri, were detected in farmed rainbow trout at 3 California state fish hatcheries in southern California. In this study, we conducted surveillance for the etiological agents of piscine lactococcosis in the ecosystems near one of the California outbreak sites in order to better understand the distribution of these pathogens in the neighboring aquatic environments and hosts during this outbreak. L. garvieae was isolated from Largemouth bass from one of the four lakes near the outbreak site, however, these strains were not infectious when tested in laboratory challenges. DNA indicative of Lactococcus spp. was also detected in fish, water, or sediment samples in all 4 of the lakes sampled using a recently developed quantitative PCR assay. However, it was not possible to identify the Lactococcus species present in these samples. These studies failed to identify an environmental reservoir of pathogenic strains of Lactococcus at the California outbreak site. However, since the sampling was carried out at a time of year when the lakes were too warm to support stocked trout, we cannot discount the possibility that trout are a seasonal reservoir of this pathogen. This epidemiologic survey provides a better understanding of the environmental reservoirs of Lactococcus spp. which will aid in the development of control measures that help prevent future outbreaks.

Technical Abstract: Piscine lactococcosis is an emerging disease of salmonids in North America. While historically attributed solely to the bacteria L. garvieae, recent investigations have revealed that lactococcosis is also caused by the closely related species L. petauri and L. formosensis. These three species are indistinguishable by conventional diagnostic methods, leading to the misidentification of L. petauri or L. formosensis as L. garvieae. To gain an understanding of the presence of these bacteria in California, 359 fish and 161 environmental samples were collected from four lakes near two affected fish farms during an outbreak of piscine lactococcosis in California in 2020. Lactococcus garvieae was isolated from the brains of two largemouth bass (Micropterus salmoides) in one of the lakes by standard microbiological methods. Additionally, Lactococcus spp. were detected in 14 fish (8 bluegills and 6 largemouth bass) from 3 out of the 4 lakes using a recently developed quantitative PCR (qPCR) assay. Of the collected environmental samples, all 4 lakes tested positive for Lactococcus spp. in the soil samples, while 2 of the 4 lakes tested positive in the water samples through qPCR. The second objective of the study was to compare the virulence of the Lactococcus spp. in rainbow trout (Oncorhynchus mykiss) and largemouth bass. Treatment groups were injected with representative isolates of L. petauri (n=17), L. garvieae (n=2), or L. formosensis (n=4), and monitored for 14 days post-challenge (dpc). Challenged largemouth bass did not show any signs of infection post-injection throughout the challenge period. Rainbow trout infected with L. petauri showed clinical signs within 3 dpc and presented a significantly higher cumulative mortality (62.2%; p<0.0001) at 14 dpc when compared to L. garvieae (0%) and L. formosensis (10%) infected treatments. The current study demonstrates the potential use of the developed qPCR assay in detection of the agents of piscine lactococcosis in the environment, and its potential use as a tool for piscine lactococcosis surveillance in natural and commercial settings.