## 1 Introduction  
_Dermanyssus gallinae_ ([PERSON], 1778), the poultry red mite (PRM), is a serious concern for the poultry production system worldwide [1]. PRM infestations are associated with a wide range of repercussions, which can affect the infested animals, as well as the poultry workers [2]. Indeed, this hematophagous ectoparasite can severely impair the health, welfare, and productivity of birds, leading to restlessness, feather-pecking, cannibalism, anemia, and even death, as well as qualitative and quantitative decline in egg production [1, 3]. Furthermore, in case of heavy infestations, humans also may be attacked by \(D\). _gallinae_, showing conditions as itching, dermatitis, and erythema [4, 5, 6]. Besides the direct effects on animals and humans, the PRM is also well known for its role as a vector of infectious agents [7]. Several viruses and bacteria have been found to be associated with \(D\). _gallinae_, such as avian pathogenic _Escherichia coli_ (APEC) [8], _Chlamydia pstitaci_[9], _Pasteuella multicodia_[10], Newcastle disease virus [11], and Fowlpox virus [12]. However, mite-mediated transmission has been demonstrated only for a few pathogens, as in the case of Influenza A virus [13], _Salmonella enterica_ subsp. _ enterica_ (\(S\).) servovars Enteritidis [14] and Gallinarum [15]. The latter is the causative agent of fowl typhoid (FT), a septicaemic disease often associated with high morbidity and subacute mortality, which generally occurs in up to four days [16, 17]. Although the disease has been eradicated in many countries, outbreaks occasionally occur in commercial poultry farms, severely impairing the health and productivity of the affected flocks [18]. Considering the heavy impact of FT, the relationship between the pathogen and \(D.\)_gallinae_ has been widely investigated during the years. [PERSON] et al. [19] first reported that mites collected in a poultry farm with a history of FT were positive for the pathogen, carrying it for up to four months. The persistence of \(S.\) Gallinarum in the PRM has been better elucidated in a field study, in which the pathogen was detected in mites during a FT outbreak, in the following sanitary break, and even five months after the housing of new laying hens [20]. More recently, the mite-mediated transmission of \(S.\) Gallinarum from animals experimentally infected with the pathogen to healthy ones has been confirmed by an in vivo study in isolators [15]. Such a relationship may lead to a constant passage of bacteria from infected mites to birds and vice versa, making the eradication of the disease difficult to achieve as long as the PRM persists in the farm. In the light of those considerations, the role of \(D.\)_gallinae_ as a vector of \(S.\) Gallinarum becomes even more important in the perspective of a proper eradication of the disease in the affected poultry farms. Nevertheless, some crucial aspects of the PRM-pathogen relationship have not been yet assessed. Among these, the modality in which the mite acquires the pathogen is still not clear, as well as the possibility of the vertical transmission of \(S.\) Gallinarum across the different PRM life stages. Until recently, those questions were still hard to address, due to the lack of proper experimental techniques for the peculiar feeding and reproductive behaviour of the PRM. Great support has come from the recent development of a novel in vitro feeding system, which allows mites to suck blood through a goldbeater's skin (Baudruche membrane) [21]. These devices have been proven to be highly effective, ensuring a feeding rate of about 50% of the tested mites, and allowing putting the fed mites in the best conditions to perpetuate their biological cycle [21]. However, the small size of \(D.\)_gallinae_ impairs downstream molecular analyses, requiring a large number of mites (50-100 specimens per aliquot) to be tested to obtain an adequate amount of DNA [7]. Those large-sized aliquots may impair, among others, the retrieval of accurate data about the pathogen load within mites [7].