Survey on the presence of Salmonella gallinarum in Dermanyssus gallinae in intensive poultry farms

Salmonella enterica subsp. enterica ser Gallinarum is the causative agent of fowl typhoid. The disease represents a major concern among industrial poultry farms, causing heavy economic losses due to its detrimental effects on productivity and animal welfare. The pathogen is highly persistent and its eradication from an infected farm is often difficult. A possible cause of its survival may be the association with parasites, such as the poultry red mite Dermanyssus gallinae. The latter is widespread among European poultry farm, with infestation rates raising up to 90%. This study is aimed to evaluate the association among D. gallinae and S. gallinarum in the Italian intensive poultry farms. Seventy-four samples of mites were collected from 62 intensive poultry farms. Up to 100 mites per sample underwent to homogenization and DNA extraction. The extracted DNA was used as template in a seminested-PCR-based protocol, already proved to be sensitive and specific. Four samples out of 74 (5.41%) resulted positive for the presence of S. gallinarum. Three positive samples came from different laying hen farms, while the other came from a broiler parent farm. Such data confirm the association between D. gallinae and S. gallinarum, once again evidencing the potential vectorial role of the mite for the bacterial pathogen. Furthermore, they suggest that D. gallinae may act as a reservoir of S. gallinarum, as it could be hosted by the mite even during the sanitary breaks, which are carried out in order to eradicate fowl typhoid from an infected poultry farm