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The poultry red mite (PRM), Dermanyssus gallinae, is a major threat for the poultry industry worldwide. Chemical compounds have been extensively used for PRM control, leading to selection of resistant mites. Molecular mechanisms of resistance have been investigated in arthropods, showing the role of target-site insensitivity and enhanced detoxification. Few studies are available about those mechanisms in D. gallinae, and none have yet focused on the expression levels of detoxification enzymes and other defense-related genes through RNA-seq. We tested PRM populations from Italy for their susceptibility to the acaricidal compounds phoxim and cypermethrin. Mutations in the voltage-gated sodium channel (vgsc) and in acetylcholinesterase (AChE) were investigated, detecting mutations known to be associated with acaricide/insecticide resistance in arthropods, including M827I and M918L/T in the vgsc and G119S in the AChE. RNA-seq analysis was performed to characterize metabolic resistance in fully susceptible PRM and in cypermethrin-resistant PRM exposed and unexposed to cypermethrin as well as phoxim resistant PRM exposed and unexposed to phoxim. Detoxification enzymes (including P450 monooxygenases and glutathione-S-transferases), ABC transporters and cuticular proteins were constitutively overexpressed in phoxim and cypermethrin resistant mites. In addition, heat shock proteins were found constitutively and inductively upregulated in phoxim resistant mites, while in cypermethrin resistant mites esterases and an aryl hydrocarbon receptor were constitutively highly expressed. The findings suggest that acaricide resistance in D. gallinae is due to both target-site insensitivity and overexpression of detoxification enzymes and other xenobiotic defense-related genes, which is mostly constitutive and not induced by treatment. Understanding the molecular basis of resistance could be useful to screen or test PRM populations in order to select targeted acaricides and to avoid the abuse/misuse of the few available compounds., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Background: The poultry red mite Dermanyssus gallinae (De Geer, 1778) is a major ectoparasite of poultry. Infestations are found in most laying hen farms in Europe, and breeder flocks have also been reported to be affected. Mite infestation has detrimental effects on animal welfare, it causes significant economic losses, and, additionally, D. gallinae is often considered as a vector for pathogens. Despite suspicion of a close relationship between the poultry red mite and Salmonella enterica enterica serovar Gallinarum biovar Gallinarum (serovar Gallinarum), the causative agent of fowl typhoid disease (FT), there has been no definitive proof of mite-mediated transmission. Therefore, an investigation was conducted to determine if D. gallinae-mediated transmission of serovar Gallinarum could be demonstrated among four different hen groups., Methods: Two groups of 8 hens (A and B) were experimentally infected with serovar Gallinarum in two isolators. After 7 days, when birds showed signs of FT, about 25,000 mites were introduced. After 3 days, mites were harvested and used to infest two other hen groups of 8 (C and D), in two separate isolators. The health status of hens was constantly monitored; detection and quantification of serovar Gallinarum were performed by PCR and qPCR from mites and organs of dead hens. The maximum likelihood estimation of the infection rate and mite vectorial capacity were calculated., Results: Clinical disease was observed in groups infected with serovar Gallinarum (A and B) and in hens of groups C and D infested with mites harvested from the isolators containing groups A and B. In all four groups, serovar Gallinarum was detected from liver, spleen, ovary, and cecum of hens, thus confirming the diagnosis of FT. Mite analysis demonstrated the presence of the pathogen, with an estimated infection rate ranging between 13.72 and 55.21 infected per thousand mites. Vectorial capacity was estimated to be 73.79., Conclusions: Mites harvested from birds infected with serovar Gallinarum were shown to carry the mite, and then to transfer serovar Gallinarum to isolated groups of pathogen-free birds that subsequently showed signs of FT. Mite vectorial capacity was high, demonstrating that D. gallinae should be considered an effective vector of FT.

Avian pathogenic Escherichia coli (APEC) is a group of strains responsible for avian colibacillosis, an impactful disease for poultry farming. The spread of APEC is mainly horizontal, and insects may play a role in their dissemination. However, no data are available about the interaction of APEC with Dermanyssus gallinae, a major arthropodal parasite of poultry. Escherichia coli was detected in the microbiome of the mite, but no specific data have been published till now. Therefore, the presence of the most diffused APEC-associated serogroups has been assessed by PCR in mites collected from 30 flocks of 21 Italian commercial laying hens farms. Escherichia coli was found in 53.3% of the tested groups, corresponding to 66.7% of farms. The most frequent serogroup was O2, but O8, O78, and O109 were also detected. More detailed investigations were carried out in a laying hen farm that was experiencing colibacillosis by APEC O2. The same serogroup was found in both hens and mites, and the maximum likelihood estimation (MLE) of the infection rate (IR) resulted in 24.39 infected mites per thousand, with a pathogen load of 171.47 E. coli O2 cells per mite. The results strongly support the hypothesis of an association between PRM and APEC, confirmed by the contemporary circulation of the same serogroup in both hens and mites, suggesting the potential of D. gallinae as a reservoir or APEC., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Dermanyssus gallinae (De Geer, 1778) is a major problem for the poultry industry worldwide, as it negatively affects virtually all kinds of rearing systems. Therefore, the control of infestation has become a routine process, and its economic cost is constantly increasing. Until now, most of the control strategies have relied on the use of synthetic chemical drugs, but their efficacy is often questioned by the emergence and diffusion of resistant mite populations. With this in mind, the efficacy of λ -cyhalothrin, amitraz, and phoxim has been verified by testing them against 86 mite populations collected from the same number of poultry farms in Italy from 2008 to 2015. Assays were performed according to the filter paper method using the recommended, half, quarter, double and quadruple doses. The results showed that phoxim and amitraz were the most effective acaricides (median efficacies 80.35% and 80.83%, respectively), but amitraz exhibited a sharp fall in its efficacy during 2011 and 2012, while phoxim maintained its high effectiveness up to 2015, when it dropped. The overall median efficacy of λ -cyhalothrin was 58.33%. The data also highlighted the importance of the use of the right concentration, as an increase in dosage was not always useful against resistant populations, while its reduction also diminished efficacy, simultaneously increasing the risk for the development of resistance.

Dermanyssus gallinae (Mesostigmata: Dermanyssidae, De Geer, 1778) is an ectoparasite of poultry, suspected to play a role as a vector of Salmonella enterica subsp. enterica ser. Gallinarum. Despite an association between them being reported, the actual dynamics in field remain unclear. Therefore, the present study aimed to confirm the interactions among mites, pathogen and chickens. The study was carried out in an industrial poultry farm infested by D. gallinae, during an outbreak of fowl typhoid. The presence of S. Gallinarum in mites was assessed and quantified by a semi-nested polymerase chain reaction (PCR) and real-time PCR, respectively, in mites collected during two subsequent productive cycles and the sanitary break. The anti-group D Salmonella antibodies were quantified by an enzyme-linked immunosorbent assay. During the outbreak and the sanitary break, S. Gallinarum was constantly present in mites. In the second cycle, scattered positivity was observed, although hens did not exhibit signs of fowl typhoid, as a result of the vaccination with BIO-VAC SGP695 (Fatro, Ozzano Emilia Bo, Italy). The data strongly suggest that D. gallinae acts as reservoir of S. Gallinarum, thus allowing the pathogen to persist in farms. Furthermore, the present study has highlighted the interactions among D. gallinae, S. Gallinarum and hens with respect to enhancing the mite-mediated circulation of S. Gallinarum in an infested poultry farm., (© 2018 The Royal Entomological Society.)

Dermanyssus gallinae (Mesostigmata: Dermanyssidae) is the most harmful ectoparasite of laying hens, represents an occupational hazard for poultry workers, and a growing threat to medical science per se. There is increasing demand for alternative products, including plant-derived acaricides, with which to control the mite. The present study investigated the efficacy of neem oil against D. gallinae on a heavily infested commercial laying hen farm. A novel formulation of 20% neem oil, diluted from a 2400-p.p.m. azadirachtin-concentrated stock (RP03™), was administered by nebulization three times in 1 week. Using corrugated cardboard traps, mite density was monitored before, during and after treatment and results were statistically analysed. Mite populations in the treated block showed 94.65%, 99.64% and 99.80% reductions after the first, second and third product administrations, respectively. The rate of reduction of the mite population was significantly higher in the treated block (P < 0.001) compared with the control and buffer blocks. The results suggest the strong bioactivity of neem, and specifically of the patented neem-based formulation RP03™, against D. gallinae. The treatment was most effective in the 10 days following the first application and its effects persisted for over 2 months. Further studies will aim to overcome observed side effects of treatment represented by an oily layer on equipment and eggs., (© 2018 The Royal Entomological Society.)

Dermanyssus gallinae is a haematophagous ectoparasite responsible for anemia, weight loss, dermatitis and a decrease in egg production. Dermanyssus gallinae may play a role in the modulation of the host immune system, maybe predisposing the host to some bacterial infections such as chlamydiosis. This is an important zoonosis. Humans are exposed to Chlamydia psittaci through inhalation of the agent dispersed from the infected birds. In this study, a syndrome observed in an aviary of canaries was investigated. A heavy infestation by D. gallinae was reported. Simultaneously, a C. psittaci infection was molecularly confirmed in the canaries. Combined therapy was applied successfully. The association of C. psittaci with the examined mites has been confirmed. Therefore, we think that D. gallinae have played a role in the spreading of C. psittaci infection among the canaries. Moreover, D. gallinae could have played an important role predisposing the canaries to the development of chlamydiosis, by inducing anemia and debilitation. The control of mites in the aviaries may represent a crucial step for the prevention of important infection such as chlamydiosis in birds and humans.