Present and future potential of plant-derived products to control arthropods of veterinary and medical significance

The use of synthetic pesticides and repellents to target pests of veterinary and medical significance is becoming increasingly problematic. One alternative approach employs the bioactive attributes of plant-derived products (PDPs). These are particularly attractive on the grounds of low mammalian toxicity, short environmental persistence and complex chemistries that should limit development of pest resistance against them. Several pesticides and repellents based on PDPs are already available, and in some cases widely utilised, in modern pest management. Many more have a long history of traditional use in poorer areas of the globe where access to synthetic pesticides is often limited. Preliminary studies support that PDPs could be more widely used to target numerous medical and veterinary pests, with modes of action often specific to invertebrates. Though their current and future potential appears significant, development and deployment of PDPs to target veterinary and medical pests is not without issue. Variable efficacy is widely recognised as a restraint to PDPs for pest control. Identifying and developing natural bioactive PDP components in place of chemically less-stable raw or 'whole’ products seems to be the most popular solution to this problem. A limited residual activity, often due to photosensitivity or high volatility, is a further drawback in some cases (though potentially advantageous in others). Nevertheless, encapsulation technologies and other slow-release mechanisms offer strong potential to improve residual activity where needed. The current review provides a summary of existing use and future potential of PDPs against ectoparasites of veterinary and medical significance. Four main types of PDP are considered (pyrethrum, neem, essential oils and plant extracts) for their pesticidal, growth regulating and repellent or deterrent properties. An overview of existing use and research for each is provided, with direction to more extensive reviews given in many sections. Sections to highlight potential issues, modes of action and emerging and future potential are also included

Comparison of synthetic membranes in the development of an in vitro feeding system for Dermanyssus gallinae

Although artificial feeding models for the poultry red mite (Dermanyssus gallinae) most frequently use biological membranes consisting of day-old chick skin, there are ethical considerations associated with the use of skin. The few studies reported in the literature that have investigated the use of synthetic membranes to feed D. gallinae in vitro have reported limited success. The current study describes an investigation into the use of synthetic membranes made from either Nescofilm® or rayon and silicone, used either alone or in combination with different feather or skin extracts, as well as the use of capillary tubes. In all, 12 different treatments were used, and the feeding rate of D. gallinae was compared to that of day-old chick skin. Allowing mites to feed on a membrane consisting of Nescofilm with a skin extract resulted in the highest proportion of mites feeding (32.3%), which was not significantly different to the feeding rate of mites on day-old chick skin (38.8%). This study confirms that synthetic membranes can be used to feed D. gallinae artificially. Further optimization of the membrane and mite storage conditions is still necessary, but the study demonstrates a proof of concept

Chlamydia psittaci infection in canaries heavily infested by Dermanyssus gallinae

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

The role of Cytochrome P450s towards the control of ticks and other arthropods

Introduction Ticks most notably Rhipicephalus (Boophilus) microplus are becoming increasingly resistant to acaricides .This resistance is often broken down into the 3 main mechanisms of detoxification involving 3 groups of enzymes; Cytochrome P450s (CYPs), Glutathione-S-transferases (GST) or Esterases (EST or carboxylesterases) (Foil et al., 2004) Material and Methods Acaricide resistance research to date, has focused on identifying which acaricides are becoming redundant in terms of effectiveness to kill the arthropod. Often, this research uses mortality based experimental procedures (Li et al., 2003; Miller et al., 2005), and investigations into the molecular/enzymatic basis of resistance have focused on GSTs and ESTs rather than CYPs. Another method used in our laboratory investigating the role of CYPs in resistance is employing tick cell cultures as a model system developed in partnership with the Roslin Institute (Bell-Sakyi et al., 2007). This system provides an ideal way to monitor CYP expression before, during and after various treatments such as acaricides. In Anopheles gambiae, expression levels of CYPs, GSTs and ESTs were monitored using a microarray following infection of the mosquito by Plasmodium (Felix et al., 2010). A similar micro array approach could be employed with ticks and mites as more data becomes available. Results Our group is monitoring the expression levels of different CYPs in tick cell lines as well as looking to identify novel CYPs and work on phylogenetic links for those genes between different arthropod groups. We are also investigating polymorphisms between different tick cell lines and different arthropod species. Discussion and Conclusions Among the arthropods, research strongly suggests that the CYP6 (Hemingway et al., 2004) and CYP9families are most highly associated with xenobiotic resistance and a lot of research has been carried out looking at these CYP families in various insect species. In mosquito species some resistance to pesticides is due to their CYP enzymes evolving to detoxify these chemicals at increasing concentrations (Nikou et al., 2003

Opportunities for integrated pest management to control the poultry red mite, Dermanyssus gallinae

Dermanyssus gallinae is the most economically important ectoparasite of laying hens in Europe. Control of D. gallinae is already hampered by issues of pesticide resistance and product withdrawal and, with the prohibition of conventional cages in 2012 and the resulting switch to more structurally complex housing which favours red mite, the importance of managing this pest will increase. Integrated Pest Management (IPM), as often employed in agricultural pest control, may be a way to address these issues where a combination of different novel control methods could be used with/without conventional management techniques to provide a synergistic and more efficacious effect. Work at in our laboratory has shown that essential oils including thyme and garlic may act as effective D. gallinae repellents and acaricides, whilst preliminary vaccine studies have demonstrated a significant increase in mite mortality in vitro using concealed antigens. Work elsewhere 27 has considered predators and fungi for D. gallinae control and other husbandry techniques such as manipulating temperature and lighting regimes in poultry units. This paper will review the available and emerging techniques for D. gallinae control and discuss which techniques might be suitable for inclusion in an integrated management programme (e.g. synthetic acaricides and diatomaceous earths)

Dermanyssus gallinae in layer farms in Kosovo: a high risk for salmonella prevalence

Background The poultry red mite (PRM), Dermanyssus gallinae (D.g.) is a serious ectoparasitic pest of poultry and potential pathogen vector. The prevalence of D. g. and the prevalence of Salmonella spp. within mites on infested laying poultry farms were investigated in Kosovo. Findings In total, 14 populated layer farms located in the Southern Kosovo were assessed for D. g. presence. Another two farms in this region were investigated 6 months after depopulation. Investigated flocks were all maintained in cages, a common housing system in Kosovo. A total of eight farms were found to be infested with D. g. (50%) at varying levels, including the two depopulated farms. The detection of Salmonella spp. from D. g. was carried out using PCR. Out of the eight layer farms infested with D. g., Salmonella spp. was present in mites on three farms (37.5%). Conclusions This study confirms the high prevalence of D. g. in layer flocks in Kosovo and demonstrates the link between this mite and the presence of Salmonella spp. on infested farms

Conformational flexibility influences structure–function relationships in tyrosyl protein sulfotransferase-2

Tyrosine sulfation is a very important posttranslational modification of proteins. It is catalyzed by tyrosylprotein sulfotransferase and recently became increasingly important for biomedicine and pharmacy. An important insight about structure–activity relationships of human tyrosylprotein sulfotransferase has been received by elucidating the crystal structure, but there is still no understanding about how conformational flexibility and dynamics which are fundamental protein properties influence structure–function relationships of the enzyme. In order to provide this missing but crucially important knowledge we performed a comprehensive atomistic molecular dynamics study which revealed that (i) the conformational flexibility influences sensitively key structural determinants and interactions between the enzyme, the substrate and the cofactor; (ii) a more open conformation adopted by the substrate for binding in TPST 2; (iii) the mutations of key residues related with catalysis and binding change alter the enzyme structure and influence important interactions between the enzyme, the cofactor and the substrate