Characterization of Erysipelothrix rhusiopathiae isolates from laying hens and poultry red mites (Dermanyssus gallinae) from an outbreak of erysipelas

Infection with the zoonotic bacterium Erysipelothrix rhusiopathiae causes severe disease outbreaks (erysipelas) in poultry flocks. As this bacterium has been isolated from the poultry red mite (Dermanyssus gallinae), this parasite has been suggested as a possible means of transmission of E. rhusiopathiae on and between poultry farms. To further elucidate the capacity of the mite as a reservoir, we analysed and compared 56 bacterial isolates from laying hens and nine isolates from mites by pulsed-field gel electrophoresis (PFGE), using the restriction enzyme SmaI. The isolates originated from one outbreak in a laying hen flock housed in an indoor litter-based aviary system. Except for two isolates, a homogeneous banding pattern was obtained from all isolates analysed, suggesting that a single strain was the cause of the outbreak. Another finding was that isolates from individual hens could exhibit slightly different PFGE patterns. Mites collected from the same house at the end of the production period of the following flock were negative for the presence of E. rhusiopathiae. An increasing number of erysipelas outbreaks as well as escalating problems with D. gallinae are expected in other European countries related to the forthcoming changes in housing systems for laying hens. Consequently, further studies are needed to investigate the importance of erysipelas in poultry and the importance of D. gallinae in the transmission of E. rhusiopathiae.