Flavobacterium psychrophilum: Response of Vaccinated Large Rainbow Trout to Different Strains

Moonika H Marana; Inger Dalsgaard; Per Walter Kania; Abdu Mohamed; Jens Hannibal; Kurt Buchmann

doi:10.3390/biology11121701

Flavobacterium psychrophilum: Response of Vaccinated Large Rainbow Trout to Different Strains

Biology (Basel). 2022 Nov 24;11(12):1701. doi: 10.3390/biology11121701.

Authors

Moonika H Marana¹, Inger Dalsgaard², Per Walter Kania¹, Abdu Mohamed^{1

3}, Jens Hannibal³, Kurt Buchmann¹

Affiliations

¹ Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, DK-1870 Frederiksberg, Denmark.
² Unit for Fish and Shellfish Diseases, National Institute of Aquatic Resources, Technical University of Denmark, DK-2800 Lyngby, Denmark.
³ Department of Clinical Chemistry, Bispebjerg Hospital, DK-2400 Copenhagen, Denmark.

Abstract

Background: Although Flavobacterium psychrophilum is recognized as the causative pathogen of rainbow trout fry syndrome (RTFS), often resulting in high fry mortality, it is also responsible for bacterial cold water disease (BCWD) in large and older rainbow trout (Oncorhynchus mykiss). These older fish do not experience high mortality, but sustain, through the shedding of bacteria, a constant infection pressure at farm level, which exposes fry to an unnecessary infection risk. We have produced and assessed the immunogenicity of an experimental injection BCWD vaccine, which may be used to decrease the shedding of bacteria from older fish.

Methods: A total of 800 fish were i.p.-injected: 200 fish received the bacterin with adjuvant, 200 fish received the bacterin alone, 200 fish received adjuvant alone and 200 fish were injected with physiological saline. Blood samples were taken at day 0 and at three different time points (4, 8 and 14 weeks) post-vaccination. Plasma antibody levels were measured by ELISA for reactivity against both the homologous F. psychrophilum vaccine strain (serotype Fd) and heterologous strains (serotype Th).

Results: Significantly elevated antibody titers were found against all serotypes in vaccinated fish. Welfare parameters associated with the vaccination process were evaluated by analyzing trout plasma samples for six different biochemical parameters, but no adverse effects associated with injection were indicated.

Conclusions: The study suggests that an injection vaccine containing formalin-inactivated whole cells of F. psychrophilum (serotype Fd), adjuvanted with FIA, may also induce protection against heterologous strains. We advocate for, as the next step, the performance of field trials evaluating if the vaccination of older rainbow trout will (1) reduce the infection pressure in farms, (2) elevate the general health level in all groups and (3) minimize F. psychrophilum infection in fry at farm level. This may reduce the need for the administration of antibiotics in all age classes.

Keywords: Flavobacterium psychrophilum; aquaculture; bacterial cold water disease; injection vaccination; rainbow trout fry syndrome.

Grants and funding

This work was supported by a grant under the GUDP initiative conducted by the Ministry of Environment and Food of Denmark (VaxFisk, Grant No. 34009-15-0960).