Experimental studies on the potential role of the poultry red mite, Dermanyssus gallinae, as a vector of Salmonella serotype Enteritidis

Dermanyssus gallinae is the most important and common ectoparasite of laying hens in Europe and it is suspected of being a vector of pathogens. Salmonellosis is a major sanitary problem in poultry farms. We performed an in vitro experiment to evaluate the role of D. gallinae as a vector of Salmonella enterica serotype Enteritidis (SE). Two ways of infection of the mites were tested: through the blood meal by artificially engorging mites on contaminated blood, and after cuticular contact by leaving mites on a bacterial coating. The results showed that the mites could be infected via both infection routes. Bacterial multiplication within the mites has also been demonstrated, as well as the transstadial passage of Salmonella from the protonymph to the deutonymph stage, and the transovarial passage associated with a negative effect of SE on Dermanyssus oviposition. Mites have been shown to retransmit bacteria through a blood meal. In order to check whether the ingestion of previously contaminated mites by chicks led to an infection dose sufficient to contaminate birds, sets of 10 mites were orally administered to 1-day-old chicks. Each bird was found to be positive 12 days post-inoculation. Salmonella colonized the intestinal tracts and invaded liver, spleen, and caeca. Therefore, this study demonstrated experimentally that D. gallinae is a vector of SE. The mite may represent a suitable environment for the development of Salmonella and could be an additional factor for the persistence of Salmonella infection between two flocks. This underscores the importance of effective red mite control during the down time following a batch of poultry infected by Salmonella.