title: Comparative evaluation of administration methods for a vaccine protecting rainbow trout against Yersinia ruckeri O1 biotype 2 infections.
abstract: Numerous outbreaks of enteric red mouth disease (ERM) caused by Yersinia ruckeri O1 biotype 2 in rainbow trout farms are currently being recorded despite established vaccination procedures against this disease. This could indicate that the currently used application of single immersion vaccination (using a commercial vaccine AquaVac(®) RELERA™) does not provide full protection. We elucidated by a controlled duplicated experiment if different vaccine administration methods can improve level and extent of protection. Rainbow trout, Oncorhynchus mykiss were vaccinated by: (1) a single immersion in bacterin diluted 1:10 for 30s (only primary vaccination); (2) two times 30s immersion (primary immersion vaccination followed by booster immersion vaccination 1 month later); (3) a single i.p. injection (only primary vaccination); (4) immersion vaccination followed by injection booster 1 month later; (5) a single 1h bath in bacterin diluted 1:2000; and (6) immersion (30s, 1:10) plus booster (1h in diluted 1:2000 vaccine) 5 months later). Injection challenge experiments were performed 3, 5 and 7 months post primary vaccination with 8.5×10(6) CFU/fish, 10.6×10(6) CFU/fish and 1×10(8) CFU/fish, respectively. In the first challenge trial, control fish exhibited a mortality of 76%, one time immersion vaccination had a mortality of 37%, two times immersion vaccinated fish had a 4% mortality, the one-time injection vaccinated group showed a mortality of 2% and the immersion plus injection boostered fish showed no mortality at all. When rainbow trout were challenged 5 months post primary vaccination, 26% mortality occurred in control fish, 21% in one time immersion group, 12% in two times immersion group, 5% in the one-time injection vaccinated group whereas immersion plus injection boostered fish again showed no mortality at all. When challenged 7 months post vaccination, one-time immersion vaccinated were not protected at all compared to the control group whereas injection vaccinated fish showed lower mortality (17%) compared to booster immersed fish (32% mortality) which was still better than un-vaccinated controls (44% mortality). It was noteworthy that a diluted bacterin (1:2000 for 1h after 5 months post primary vaccination) booster showed the same effect as a booster with 1:10 bacterin dilution for 30s applied 1 month after primary vaccination. Antibody levels showing significant elevations 28 days post challenge in vaccinated fish point to this immune parameter as a protective element. The superior and extended protection offered by booster vaccination or simply injection is noteworthy and may be applied in future vaccination strategies at farm level.
authors.affiliation: Laboratory of Aquatic Pathobiology, Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark. jkc@sund.ku.dk
authors.forename: Jiwan Kumar
authors.initials: JK
authors.lastname: Chettri
authors.forename: Sidhartha
authors.initials: S
authors.lastname: Deshmukh
authors.forename: Lars
authors.initials: L
authors.lastname: Holten-Andersen
authors.forename: Rzgar M
authors.initials: RM
authors.lastname: Jafaar
authors.forename: Inger
authors.initials: I
authors.lastname: Dalsgaard
authors.forename: Kurt
authors.initials: K
authors.lastname: Buchmann
mesh_terms: D000818:Animals; D001428:Bacterial Vaccines / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D005393:Fish Diseases / Q000382:microbiology / Q000517:prevention & control*; D017686:Oncorhynchus mykiss; D015009:Yersinia Infections / Q000517:prevention & control / Q000662:veterinary*; D044124:Yersinia ruckeri / Q000145:classification* / Q000276:immunology
chemical_list: D001428:Bacterial Vaccines