Oral and Anal Vaccination Confers Full Protection against Enteric Redmouth Disease (ERM) in Rainbow Trout

Abstract

The effect of oral vaccines against bacterial fish diseases has been a topic for debate for decades. Recently both M-like cells and dendritic cells have been discovered in the intestine of rainbow trout. It is therefore likely that antigens reaching the intestine can be taken up and thereby induce immunity in orally vaccinated fish. The objective of this project was to investigate whether oral and anal vaccination of rainbow trout induces protection against an experimental waterborne infection with the pathogenic enterobacteria Yersinia ruckeri O1 biotype 1 the causative agent of enteric redmouth disease (ERM). Rainbow trout were orally vaccinated with AquaVac ERM Oral (MERCK Animal Health) or an experimental vaccine bacterin of Y. ruckeri O1. Both vaccines were tested with and without a booster vaccination four months post the primary vaccination. Furthermore, two groups of positive controls were included, one group receiving the experimental oral vaccine in a 50 times higher dose, and the other group receiving a single dose administered anally in order to bypass the stomach. Each group was bath challenged with 6.3×108 CFU/ml Y. ruckeri, six months post the primary vaccination. The challenge induced significant mortality in all the infected groups except for the groups vaccinated anally with a single dose or orally with the high dose of bacterin. Both of these groups had 100% survival. These results show that a low dose of Y. ruckeri bacterin induces full protection when the bacterin is administered anally. Oral vaccination also induces full protection, however, at a dose 50 times higher than if the fish were to be vaccinated anally. This indicates that much of the orally fed antigen is digested in the stomach before it reaches the second segment of the intestine where it can be taken up as immunogenic antigens and presented to lymphocytes.

B cells and their role in the teleost gut

“…Immersion vaccines have been tested with positive results showing protection against a posterior challenge and IgM specific antibodies in serum against the bacteria (Raida et al, 2011). Similarly, oral and anal vaccination against ERM with inactivated Y. ruckeri protects the animal against a subsequent infection with the pathogen (Gravningen et al, 1998; Villumsen et al, 2014). Strikingly, no specific IgM responsewas detected in serum of infected, or survivor fish after the infection, indicating the possibility that protection was not induced by antibodies, or alternatively, that IgT was involved in protective responses, as IgT responses were not measured.…”

Analysis of Yersinia ruckeri strains isolated from trout farms in northwest Germany

“…Hence Y. ruckeri can easily spread from one trout population to another and from one farm to another. In order to prevent devastating disease outbreaks and massive antibiotic treatment, appropriate vaccination and good husbandry is essential (Villumsen et al 2014). For vaccination, ERM vaccines are mainly applied by the immersion method, which allows vaccinating large numbers of juveniles in a fast and reliable manner (Chettri et al 2012).…”

The repeat structure of two paralogous genes, Yersinia ruckeri invasin (yrInv) and a “Y. ruckeri invasin-like molecule”, (yrIlm) sheds light on the evolution of adhesive capacities of a fish pathogen

“…The following antigen delivery systems have been applied for ERM: oral (Ghosh et al, 2016;Jaafar et al, 2017), anal (Villumsen et al, 2014), immersion (Ghosh et al, 2016;Buchmann, 2008) nasal (LaPatra et al, 2015;Salinas et al, 2015), and an interperitoneal injection (Chetri et al, 2013). Immersion is the preferred method of antigen delivery because it allows for massive and quick fish vaccination in the freshwater stage, when the fish are too small to receive an injection (Villumsen et al, 2014). Immersion vaccines decrease the number of Y. ruckeri outbreaks and substantially reduce the use of antibiotics in salmon farming (Chetri et al, 2013).…”