Abstract
Erysipelas, a disease caused by Erysipelothrix rhusiopathiae (ER), is an increasing problem in laying hens housed in cage-free systems. This study aimed to monitor immune responses during ER infection of naïve chickens and chickens vaccinated intra muscularly with a commercial inactivated ER vaccine. Chickens were infected intra muscularly with ER at 30 days of age and blood leukocyte counts, serum levels of mannose binding lectin (MBL) and ER-specific IgY were monitored until the experiment was terminated at day 15 after infection. ER was detected in blood from more chickens and at higher bacterial counts in the naïve group (day 1: 1 of 7 chickens; day 3: 6 of 6 chickens) than in the vaccinated group (day 1: 0 of 7 chickens; day 3: 1 of 6 chickens). During the acute phase of infection transient increases in circulating heterophil numbers and serum MBL levels were detected in all ER infected chickens but these responses were prolonged in chickens from the naïve group compared to vaccinated chickens. Before infection IgY titers to ER in vaccinated chickens did not differ significantly from those of naïve chickens but vaccinated chickens showed significantly increased IgY titers to ER earlier after infection compared to chickens in the naïve group. In conclusion, the ER infection elicited prompt acute innate responses in all chickens. Vaccinated chickens did not have high IgY titers to ER prior to infection but did however show lower levels of bacteraemia and their acute immune responses were of shorter duration.
Highlights
Poultry products, including eggs, are increasingly important protein food sources worldwide [1, 2] and egg production is forecasted to double globally between 2015 and 2035 [3]
We have shown that when Erysipelothrix rhusiopathiae (ER) was incubated in chicken blood in vitro ER DNA was primarily detected in a leukocyte preparation of blood cultures and not free in plasma and that a significant amount of the bacteria recovered in chicken blood during the acute phase of ER infection were intracellular in leukocytes [20]
It has been shown that chickens with low base line serum levels of mannose binding lectin (MBL) shedded higher numbers of S. enterica [32, 33] and were more prone to systemic Pasteurella multocida infection [34] upon experimental infection with respective bacterium compared to chickens with high base line MBL levels
Summary
Poultry products, including eggs, are increasingly important protein food sources worldwide [1, 2] and egg production is forecasted to double globally between 2015 and 2035 [3]. The disease caused by ER has been known since the late nineteenth century but many aspects of this infectious agent still remain unclear This includes basic knowledge on immune responses and development of protective immunity to ER. On previously affected farms pullets are vaccinated at placement with a single dose of an inactivated vaccine against erysipelas licensed for turkeys as prophylactic measure to prevent further outbreaks [10] This vaccination strategy is solely based on clinical experience and seems to be effective in many cases outbreaks in vaccinated flocks have been reported [10]. The ER strain used for infection was isolated from a field outbreak of erysipelas in a laying hen flock and is representative of current outbreaks in Swedish laying hen flocks. This strain contains all putative virulence factors as identified by bioinformatic analysis (unpublished data)
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