Histamine release factor from Dermanyssus gallinae (De Geer): characterization and in vitro assessment as a protective antigen

Characterization of a lipocalin-like molecule from Dermanyssus gallinae as a potential vaccine antigen

Poultry red mites (PRMs, Dermanyssus gallinae) are hematophagous ectoparasites of chickens that pose a significant threat to the egg-laying industry. The emergence of acaricide-resistant PRMs raises the demand for alternative control approaches such as vaccination. However, several vaccine antigens have failed to suppress the growth of PRM populations in field trials due to difficulties in maintaining antibody levels. In ticks, the molecules exposed to the host, such as lipocalins, can facilitate antibody production, and are therefore considered advantageous as vaccine antigens. Therefore, we focused on a lipocalin-like molecule (Dg-Lipocalin) identified from an RNA-seq analysis reported by Fujisawa et al. (2020) and analyzed its exposure to the host and potential as a vaccine antigen. Western blotting using 500-fold diluted plasma of chickens from PRM-contaminated farms revealed the presence of antibodies against Dg-Lipocalin, suggesting its exposure to the host. To evaluate its potential as a vaccine antigen, PRMs were artificially fed immune plasma with 32,000- to 64,000-fold antibody titers or plasma from PBS-inoculated control chickens, and their mortality was observed for 7 days. In experiment 1, the immune plasma significantly increased PRM mortality compared to the control plasma. However, these effects were not observed in experiment 2, although the total mortality was significantly increased in immune plasma-fed PRMs. Thus, the efficacy of Dg-Lipocalin appears to be limited; however, its exposure to the host may result in sustained antibody titers. Further investigation is required to evaluate its feasibility.

Growth kinetics and population density of a laboratory colony of the poultry red mite (Dermanyssus gallinae) established in Japan

The poultry red mite (PRM), Dermanyssus gallinae, is a hematophagous ectoparasite that significantly threatens the poultry industry, not only through blood-feeding but also as a vector for deadly pathogens. With the growing challenge of acaricidal resistance, the demand for alternative control measures is urgent. However, effective PRM research, particularly in acaricidal efficacy and new drug discovery, hinges on the availability of reliable laboratory colonies. In this study, we successfully established a stable PRM laboratory colony, originally isolated from the field in 2021 and maintained under controlled conditions at the Research Institute for Animal Science in Biochemistry and Toxicology (RIAS). We investigated the growth kinetics and population dynamics of the laboratory colony within a Styrofoam-based maintenance box (SBMB) containing chicks. PRM propagation was tracked over 28 days, with mites collected every seven days. The average bulk weight of the mites in the trap increased from 4.3 ± 1.2 mg on day 7 to 201.4 ± 56.5 mg on day 28, despite seasonal variations, indicating optimal conditions for population growth. The collected mites spanned various blood-feeding developmental stages such as protonymph, deutonymph, and adult stages, enabling comprehensive assessments of molting and egg-laying efficiency. Our findings confirm that the laboratory colony of PRM can be stably maintained, providing a reliable source of PRMs for further experimental research aimed at advancing control strategies against this pervasive pest.

Potential of histamine release factor for the utilization as a universal vaccine antigen against poultry red mites, tropical fowl mites, and northern fowl mites

Poultry red mites (PRMs, Dermanyssus gallinae), tropical fowl mites (TFMs, Ornithonyssus bursa), and northern fowl mites (NFMs, Ornithonyssus sylviarum) are hematophagous mites that are distributed worldwide which pose a serious challenge to the poultry industry and negatively impact poultry production and welfare. Vaccines represent a promising approach for controlling avian mites, and the identification of antigens with broad efficacy against multiple avian mite species is advantageous for vaccine control. This study aimed to identify histamine release factor (HRF), which was previously reported as a candidate vaccine antigen against PRMs, from TFMs and NFMs and to analyze its cross-reactivity and acaricidal effects on different avian mite species. The deduced amino acid sequences of the HRFs identified in the TFMs and NFMs were highly homologous to those of the PRMs. We generated recombinant HRF (rHRF) of TFMs, NFMs, and PRMs, and immune plasma against each rHRF was produced by immunization with each antigen. The immune plasma contained antibodies specific to each antigen and showed cross-reactivity with rHRFs from different avian mites. Moreover, PRM nymphs (protonymphs) artificially fed each immune plasma showed higher mortality rates than those fed the control plasma. These results suggest that HRFs can be used as candidate antigens for a universal vaccine with broad efficacy across avian mites.

In Vivo Characterization of the Anti-Glutathione S-Transferase Antibody Using an In Vitro Mite Feeding Model

Poultry red mites (Dermanyssus gallinae, PRMs), tropical fowl mites (Ornithonyssus bursa, TFMs), and northern fowl mites (O. sylviarum, NFMs) are blood-feeding pests that debilitate poultry worldwide. Glutathione S-transferase (GST) plays an important role in the detoxification and drug metabolism of mites. However, research on avian mite GSTs as vaccine antigens is still lacking. Therefore, we aimed to evaluate the potential of avian mite GSTs for vaccine development. We identified GST genes from TFMs and NFMs. We prepared recombinant GST (rGST) from TFMs, NFMs, and PRMs, and assessed their protein functions. Moreover, we evaluated the cross-reactivity and acaricidal effect of immune plasma against each rGST on TFMs, NFMs, and PRMs. The deduced amino acid sequences of GSTs from TFMs and NFMs were 80% similar to those of the PRMs. The rGSTs exhibited catalytic activity in conjugating glutathione to the 1-chloro-2,4-dinitrobenzene substrate. Immune plasma against each rGST showed cross-reactivity with rGST from different mite species. Moreover, the survival rate of PRMs fed with immune plasma against the rGST of TFMs and NFMs was significantly lower than that of the control plasma. These results demonstrate the potential application of GST as an antigen for the development of a broad-spectrum vaccine against avian mites.

Vaccination Against Poultry Parasites

The complexity of parasites and their life cycles makes vaccination against parasitic diseases challenging. This review highlights this by discussing vaccination against four relevant parasites of poultry. Coccidia, i.e., Eimeria spp., are the most important parasites in poultry production, causing multiple billions of dollars of damage worldwide. Due to the trend of antibiotic-free broiler production, use of anticoccidia vaccines in broilers is becoming much more important. As of now, only live vaccines are on the market, almost all of which must be produced in birds. In addition, these live vaccines require extra care in the management of flocks to provide adequate protection and prevent the vaccines from causing damage. Considerable efforts to develop recombinant vaccines and related work to understand the immune response against coccidia have not yet resulted in an alternative. Leucozytozoon caulleryi is a blood parasite that is prevalent in East and South Asia. It is the only poultry parasite for which a recombinant vaccine has been developed and brought to market. Histomonas meleagridis causes typhlohepatitis in chickens and turkeys. The systemic immune response after intramuscular vaccination with inactivated parasites is not protective. The parasite can be grown and attenuated in vitro, but only together with bacteria. This and the necessary intracloacal application make the use of live vaccines difficult. So far, there have been no attempts to develop a recombinant vaccine against H. meleagridis. Inactivated vaccines inducing antibodies against the poultry red mite Dermanyssus gallinae have the potential to control infestations with this parasite. Potential antigens for recombinant vaccines have been identified, but the use of whole-mite extracts yields superior results. In conclusion, while every parasite is unique, development of vaccines against them shares common problems, namely the difficulties of propagating them in vitro and the identification of protective antigens that might be used in recombinant vaccines.

Management of the poultry red mite Dermanyssus gallinae with physical control methods by inorganic material and future perspectives

Poultry red mite (PRM), the ectoparasitic mite Dermanyssus gallinae found in laying hen farms, is a significant threat to poultry production and human health worldwide. It is a suspected disease vector and attacks hosts' other than chickens, including humans, and its economic importance has increased greatly. Different strategies to control PRM have been widely tested and investigated. In principle, several synthetic pesticides have been applied to control PRM. However, recent alternative control methods to avoid the side effects of pesticides have been introduced, although many remain in the early stage of commercialization. In particular, advances in material science have made various materials more affordable as alternatives for controlling PRM through physical interactions between PRM. This review provides a summary of PRM infestation, and then includes a discussion and comparison of different conventional approaches: 1) organic substances, 2) biological approaches, and 3) physical inorganic material treatment. The advantages of inorganic materials are discussed in detail, including the classification of materials, as well as the physical mechanism-induced effect on PRM. In this review, we also consider the perspective of using several synthetic inorganic materials to suggest novel strategies for improved monitoring and better information regarding treatment interventions.

Two ferritins from Dermanyssus gallinae: characterization and in vivo assessment as protective antigens

BACKGROUND

The poultry red mite, Dermanyssus gallinae is recognized worldwide as the most important bloodsucking ectoparasite in layer and breeder flocks. In bloodsucking ectoparasites, ferritins (FERs), the iron-storage proteins, play a pivotal role in dealing with the challenge of large amounts of released iron during the digestion of blood meal. However, no information is available concerning FERs of D. gallinae. The aim of the present study was to investigate the characteristics, functions and the vaccine efficacy of FERs in D. gallinae.

RESULTS

Two heavy-chain FERs of D. gallinae were identified and characterized. Phylogenetic analysis indicated that Dg-FER1 may be a secretory FER and Dg-FER2 an intracellular one. RNAi results demonstrated that Dg-fers play key roles in mite survival, successful reproduction and blood digestion. Immunization with rDg-FER1 or rDg-FER2 successfully induced chickens to produce high levels of antigen-specific IgY, resulting in a significant increase in mite mortality (by 58.67% on Day 5) and decreases in oviposition (by 42.15%) and fecundity (by 68.97%) in the rDg-FER1 group, and a 13.73% increase in mite mortality and a 20.89% decrease in fecundity in the rDg-FER1 group. The overall immunization efficacy of rDg-FER1 was 93.51%.

CONCLUSION

Two Dg-FERs are crucial to the survival, reproduction and blood digestion of D. gallinae. This study has provided preliminary evidence demonstrating the potential of rDg-FER1 as a vaccine antigen for D. gallinae. © 2021 Society of Chemical Industry.

In vitro evaluation of a cysteine protease from poultry red mites, Demanyssus gallinae, as a vaccine antigen for chickens

Poultry red mites (PRMs, Dermanyssus gallinae) are hematophagous ectoparasites that negatively affect egg production, which causes serious economic losses to the poultry industry worldwide. Currently, the emergence of acaricide-resistant PRMs has impeded PRM control in poultry farms. Several alternatives for acaricide use have been described for managing PRM-caused problems. Vaccination is among the methods for controlling PRMs in poultry houses. Currently, several candidates for vaccine antigens have been identified. This study identified a cysteine protease, Deg-CPR-2, which differs from 2 other previously reported cysteine proteases in PRMs, from previously obtained data from RNA-sequencing (RNA-seq) analysis. We investigated the characteristics of Deg-CPR-2 and assessed its efficacy as a vaccine antigen in vitro. Phylogenetic analysis revealed that Deg-CPR-2 belonged to a different cluster from those of other cysteine proteases in PRMs. This cluster also included cathepsin L-like proteases, enzymes thought to be involved in hemoglobin digestion in ticks. Expression analysis revealed Deg-CPR-2 expression in midguts and all the life-stages; however, there were differences in the expression levels across the life-stages. The enzyme activity of recombinant Deg-CPR-2 was inhibited in the presence of a cysteine protease inhibitor, which suggests that Deg-CPR-2 functions as a cysteine protease in PRMs. Finally, there was an in vitro increase in the mortality of PRMs, mainly protonymphs that were artificially fed with plasma from chickens immunized with Deg-CPR-2. These findings suggest that Deg-CPR-2 may contribute to protein digestion in the midgut of PRMs and is crucially involved in physiological processes in PRMs. Additionally, immunization with Deg-CPR-2 may reduce the number of protonymphs, and Deg-CPR-2 should be considered as a candidate antigen for anti-PRM vaccine development.

Brown spider venom toxins: what are the functions of astacins, serine proteases, hyaluronidases, allergens, TCTP, serpins and knottins?

Accidents caused by the bites of brown spiders (Loxosceles) generate a clinical condition that often includes a threatening necrotic skin lesion near the bite site along with a remarkable inflammatory response. Systemic disorders such as hemolysis, thrombocytopenia, and acute renal failure may occur, but are much less frequent than the local damage. It is already known that phospholipases D, highly expressed toxins in Loxosceles venom, can induce most of these injuries. However, this spider venom has a great range of toxins that probably act synergistically to enhance toxicity. The other protein classes remain poorly explored due to the difficulty in obtaining sufficient amounts of them for a thorough investigation. They include astacins (metalloproteases), serine proteases, knottins, translationally controlled tumor proteins (TCTP), hyaluronidases, allergens and serpins. It has already been shown that some of them, according to their characteristics, may participate to some extent in the development of loxoscelism. In addition, all of these toxins present potential application in several areas. The present review article summarizes information regarding some functional aspects of the protein classes listed above, discusses the directions that could be taken to materialize a comprehensive investigation on each of these toxins as well as highlights the importance of exploring the full venom repertoire.

Molecular and biochemical characterization of enolase from Dermanyssus gallinae

Enolase, a multifunctional glycolytic enzyme, is known to act as a plasminogen receptor in many species, involved in the pivotal processes such as motility, adhesion, invasion, growth, and differentiation of the parasites. Knowledge on the function of enolase from Dermanyssus gallinae is very limited. Here we report on the molecular cloning, enzymatic activity, tissue distribution and plasminogen binding activity of enolase from D. gallinae (DgENO). The full-length of cDNA was 1305 bp, specifying a peptide of 434 amino acids. Bioinformatics analysis showed that DgENO was highly conserved compared with a range of organisms, indicating the potentially similar functions in D. gallinae. A recombinant DgENO (rDgENO) protein was produced and characterized, it catalyzed the dehydration of 2-phospho-D-glycerate to phosphoenolpyruvate, the optimal pH was 7.5. Polyclonal antibodies were generated in mice and western blotting indicated that antiserum specifically recognized the native enolase in the somatic extracts from D. gallinae. Immunohistochemical staining of mite sections revealed that the distribution of DgENO was ubiquitous with high level in salivary gland, mite digestive tissues and fat bodies in D. gallinae. Expression level of DgENO was observed mostly in engorged adult mites. Moreover, ELISA binding assay showed that rDgENO could bind plasminogen, and lysine analog ε-aminocaproic acid significantly inhibited this binding activity, indicating that D. gallinae enolase is a receptor of plasminogen. The present study provided foundation for understanding of the biological functions of DgENO and its application in development of vaccines against D. gallinae.

A vaccinology Approach to the Identification and Characterization of Dermanyssus Gallinae Candidate Protective Antigens for the Control of Poultry Red Mite Infestations

The poultry red mite (PRM), Dermanyssus gallinae, is a hematophagous ectoparasite considered as the major pest in the egg-laying industry. Its pesticide-based control is only partially successful and requires the development of new control interventions such as vaccines. In this study, we follow a vaccinology approach to identify PRM candidate protective antigens. Based on proteomic data from fed and unfed nymph and adult mites, we selected a novel PRM protein, calumenin (Deg-CALU), which is tested as a vaccine candidate on an on-hen trial. Rhipicephalus microplus Subolesin (Rhm-SUB) was chosen as a positive control. Deg-CALU and Rhm-SUB reduced the mite oviposition by 35 and 44%, respectively. These results support Deg-CALU and Rhm-SUB as candidate protective antigens for the PRM control.

Reduction in Oviposition of Poultry Red Mite (Dermanyssus gallinae) in Hens Vaccinated with Recombinant Akirin

The poultry red mite (PRM), Dermanyssus gallinae, is a hematophagous ectoparasite of birds with worldwide distribution that causes economic losses in the egg-production sector of the poultry industry. Traditional control methods, mainly based on acaricides, have been only partially successful, and new vaccine-based interventions are required for the control of PRM. Vaccination with insect Akirin (AKR) and its homolog in ticks, Subolesin (SUB), have shown protective efficacy for the control of ectoparasite infestations and pathogen infection/transmission. The aim of this study was the identification of the akr gene from D. gallinae (Deg-akr), the production of the recombinant Deg-AKR protein, and evaluation of its efficacy as a vaccine candidate for the control of PRM. The anti-Deg-AKR serum IgY antibodies in hen sera and egg yolk were higher in vaccinated than control animals throughout the experiment. The results demonstrated the efficacy of the vaccination with Deg-AKR for the control of PRM by reducing mite oviposition by 42% following feeding on vaccinated hens. A negative correlation between the levels of serum anti-Deg-AKR IgY and mite oviposition was obtained. These results support Deg-AKR as a candidate protective antigen for the control of PRM population growth.

Evaluation of vaccine delivery systems for inducing long-lived antibody responses to Dermanyssus gallinae antigen in laying hens

Dermanyssus gallinae, the poultry red mite, is a global threat to the commercial egg-laying industry. Control of D. gallinae is difficult, with only a limited number of effective pesticides and non-chemical treatments available. Here, we characterize the candidate vaccine antigen D. gallinae cathepsin D-1 (Dg-CatD-1) and demonstrate that purified refolded recombinant Dg-Cat-D1 (rDg-CatD-1) is an active aspartyl proteinase which digests haemoglobin with a pH optimum of pH 4. Soluble protein extracts from D. gallinae also have haemoglobinase activity, with a pH optimum comparable to the recombinant protein, and both proteinase activities were inhibited by the aspartyl proteinase inhibitor Pepstatin A. Enzyme activity and the ubiquitous localization of Dg-CatD-1 protein in sections of adult female mites is consistent with Dg-CatD-1 being a lysosomal proteinase. Using Dg-CatD-1 as a model vaccine antigen, we compared vaccine delivery methods in laying hens via vaccination with: (i) purified rDg-CatD-1 with Montanide™ ISA 71 VG adjuvant; (ii) recombinant DNA vaccines for expression of rDg-CatD-1 and (iii) transgenic coccidial parasite Eimeria tenella expressing rDg-CatD-1. In two independent trials, only birds vaccinated with rDg-CatD-1 with Montanide™ ISA 71 VG produced a strong and long-lasting serum anti-rDg-Cat-D1 IgY response, which was significantly higher than that in control birds vaccinated with adjuvant only. Furthermore, we showed that egg-laying rates of D. gallinae mites fed on birds vaccinated with rDg-CatD-1 in Montanide™ ISA 71 VG was reduced significantly compared with mites fed on unvaccinated birds. RESEARCH HIGHLIGHTS Dermanyssus gallinae cathepsin D-1 (Dg-CatD-1) digests haemoglobin Vaccination of hens with rDg-CatD-1 in Montanide™ ISA 71 VG results in long-lasting IgY levels Serum anti-rDg-CatD-1 antibodies reduce egg laying in D. gallinae after a single blood meal.

A review of the biology, ecology, and control of the northern fowl mite, Ornithonyssus sylviarum (Acari: Macronyssidae)

The northern fowl mite, Ornithonyssus sylviarum (Canestrini & Fanzago, 1877), is found on several continents and has been a major pest of poultry in the United States for nearly a century. Lack of earlier USA reports in the United States suggests an introduction or change to pest status in domestic poultry systems occurred in the early 1900s. Though predominantly a nest-parasite of wild birds, this obligate hematophagous mite is a permanent ectoparasite on domestic birds, especially egg-laying chickens. Economic damage is incurred by direct blood feeding and activation of the of host's immune responses. This in turn causes decreased egg production and feed conversion efficiency, and severe infestations can cause anemia or death to birds. Here we review the biology, ecology, and recent control measures for the northern fowl mite. Photomicrographs are included of adult males and females, protonymphs, and larvae with key characters indicated. Special emphasis is placed on current knowledge gaps of basic and applied science importance.

Field evaluation of poultry red mite (Dermanyssus gallinae) native and recombinant prototype vaccines

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Field trial testing of a native and recombinant poultry red mite vaccines.

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Vaccination with a soluble mite extract (SME) resulted in a 78% reduction in mite numbers.

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Poor antibody persistence may relate to lack of effect of a recombinant cocktail vaccine.

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A semi-protective naturally acquired immunity may develop.

Vaccination is a desirable emerging strategy to combat poultry red mite (PRM), Dermanyssus gallinae. We performed trials, in laying hens in a commercial-style cage facility, to test the vaccine efficacy of a native preparation of soluble mite extract (SME) and of a recombinant antigen cocktail vaccine containing bacterially-expressed versions of the immunogenic SME proteins Deg-SRP-1, Deg-VIT-1 and Deg-PUF-1. Hens (n = 384 per group) were injected with either vaccine or adjuvant only (control group) at 12 and 17 weeks of age and then challenged with PRM 10 days later. PRM counts were monitored and, at the termination of the challenge period (17 weeks post challenge), average PRM counts in cages containing birds vaccinated with SME were reduced by 78% (p < 0.001), compared with those in the adjuvant-only control group. When the trial was repeated using the recombinant antigen cocktail vaccine, no statistically significant differences in mean PRM numbers were observed in cages containing vaccinated or adjuvant-only immunised birds. The roles of antigen-specific antibody levels and duration in providing vaccine-induced and exposure-related protective immunity are discussed.

Characterisation of tropomyosin and paramyosin as vaccine candidate molecules for the poultry red mite, Dermanyssus gallinae

Background

Dermanyssus gallinae is the most economically important haematophagous ectoparasite in commercial egg laying flocks worldwide. It infests the hens during the night where it causes irritation leading to restlessness, pecking and in extreme cases anaemia and increased cannibalism. Due to an increase in the occurrence of acaricide-resistant D. gallinae populations, new control strategies are required and vaccination may offer a sustainable alternative to acaricides. In this study, recombinant forms of D. gallinae tropomyosin (Der g 10) and paramyosin (Der g 11) were produced, characterised and tested as vaccine candidate molecules.

Methods

The D. gallinae paramyosin (Der g 11) coding sequence was characterised and recombinant versions of Der g 11 and D. gallinae tropomyosin (Der g 10) were produced. Hens were immunised with the recombinant proteins and the resulting antibodies were fed to D. gallinae and mite mortality evaluated. Sections of mites were probed with anti- Der g 11 and Der g 10 antibodies to identify the tissue distribution of these protein in D. gallinae.

Results

The entire coding sequence of Der g 11 was 2,622 bp encoding 874 amino acid residues. Immunohistochemical staining of mite sections revealed that Der g 10 and Der g 11 were located throughout D. gallinae tissues. In phylogenetic analyses of these proteins both clustered with orthologues from tick species rather than with orthologues from astigmatid mites. Antibodies raised in hens against recombinant forms of these proteins significantly increased D. gallinae mortality, by 19 % for Der g 10 (P < 0.001) and by 23 % for Der g 11 (P = 0.009) when fed to the mites using an in vitro feeding device.

Conclusions

This study has shown that Der g 10 and Der g 11 were located ubiquitously throughout D. gallinae and that antibodies raised against recombinant versions of these proteins can be used to significantly increase D. gallinae mortality in an in vitro feeding assay. When comparing archived data for all recombinant and native proteins assessed as vaccines using this in vitro feeding assay, Der g 10 and Der g 11 ranked highly and performed better than some of the pools of native proteins.

Understanding the biology and control of the poultry red mite Dermanyssus gallinae: a review

Dermanyssus gallinae, the poultry red mite (PRM), is a blood-feeding ectoparasite capable of causing pathology in birds, amongst other animals. It is an increasingly important pathogen in egg layers and is responsible for substantial economic losses to the poultry industry worldwide. Even though PRM poses a serious problem, very little is known about the basic biology of the mite. Here we review the current body of literature describing red mite biology and discuss how this has been, or could be, used to develop methods to control PRM infestations. We focus primarily on the PRM digestive system, salivary glands, nervous system and exoskeleton and also explore areas of PRM biology which have to date received little or no study but have the potential to offer new control targets.

Identification and evaluation of vaccine candidate antigens from the poultry red mite (Dermanyssus gallinae)

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Ten poultry red mite vaccine candidate antigens were identified and recombinant versions produced.

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Mite mortality was monitored after feeding on the blood from vaccinated hens.

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A ⩾1.6-fold increased risk of mite death was observed with four of the vaccine candidates (P < 0.001).

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Best candidates include: a serpin, vitellogenin, hemelipoglycoprotein and a novel protein.

An aqueous extract of the haematophagous poultry ectoparasite, Dermanyssus gallinae, was subfractionated using anion exchange chromatography. Six of these subfractions were used to immunise hens and the blood from these hens was fed, in vitro, to poultry red mites. Mite mortality following these feeds was indicative of protective antigens in two of the subfractions, with the risks of mites dying being 3.1 and 3.7 times higher than in the control group (P < 0.001). A combination of two-dimensional immunoblotting and immunoaffinity chromatography, using IgY from hens immunised with these subfractions, was used in concert with proteomic analyses to identify the strongest immunogenic proteins in each of these subfractions. Ten of the immunoreactive proteins were selected for assessment as vaccine candidates using the following criteria: intensity of immune recognition; likelihood of exposure of the antigen to the antibodies in a blood meal; proposed function and known vaccine potential of orthologous molecules. Recombinant versions of each of these 10 proteins were produced in Escherichia coli and were used to immunise hens. Subsequent in vitro feeding of mites on blood from these birds indicated that immunisation with Deg-SRP-1 (serpin), Deg-VIT-1 (vitellogenin), Deg-HGP-1 (hemelipoglycoprotein) or Deg-PUF-1 (a protein of unknown function) resulted in significantly increased risk of mite death (1.7–2.8 times higher than in mites fed blood from control hens immunised with adjuvant only, P < 0.001). The potential for using these antigens in a recombinant vaccine is discussed.

Immunization of mice with Plasmodium TCTP delays establishment of Plasmodium infection

Translationally controlled tumour protein (TCTP) may play an important role in the establishment or maintenance of parasitemia in a malarial infection. In this study, the potential of TCTP as a malaria vaccine was investigated in two trials. In the initial vaccine trial, Plasmodium falciparum TCTP (PfTCTP) was expressed in Saccharomyces cerevisiae and used to immunize BALB/c mice. Following challenge with Plasmodium yoelii YM, parasitemia was significantly reduced during the early stages of infection. In the second vaccine trial, the TCTP from P. yoelii and P. berghei was expressed in Escherichia coli and used in several mouse malaria models. A significant reduction in parasitemia in the early stages of infection was observed in BALB/c mice challenged with P. yoelii YM. A significantly reduced parasitemia at each day leading up to a delayed and reduced peak parasitemia was also observed in BALB/c mice challenged with the nonlethal Plasmodium chabaudi (P.c.) chabaudi AS. These results suggest that TCTP has an important role for parasite establishment and may be important for pathogenesis.

Significance and control of the poultry red mite, Dermanyssus gallinae

The poultry red mite, Dermanyssus gallinae, poses a significant threat to poultry production and hen health in many parts of the world. With D. gallinae increasingly suspected of being a disease vector, and reports indicating that attacks on alternative hosts, including humans, are becoming more common, the economic importance of this pest has increased greatly. As poultry production moves away from conventional cage systems in many parts of the world, D. gallinae is likely to become more abundant and difficult to control. Control remains dominated by the use of synthetic acaricides, although resistance and treatment failure are widely reported. Alternative control measures are emerging from research devoted to D. gallinae and its management. These alternative control measures are beginning to penetrate the market, although many remain at the precommercial stage. This review compiles the expanding body of research on D. gallinae and assesses options for its current and future control. We conclude that significant advances in D. gallinae control are most likely to come through an integrated approach adopting recent research into existing and novel control strategies; this is being combined with improved monitoring and modeling to better inform treatment interventions.

Assessment of cathepsin D and L-like proteinases of poultry red mite, Dermanyssus gallinae (De Geer), as potential vaccine antigens

Vaccination is a feasible strategy for controlling the haematophagous poultry red mite Dermanyssus gallinae. A cDNA library enriched for genes upregulated after feeding was created to identify potential vaccine antigens. From this library, a gene (Dg-CatD-1) encoding a 383 amino acid protein (Dg-CatD-1) with homology to cathepsin D lysosomal aspartyl proteinases was identified as a potential vaccine candidate. A second gene (Dg-CatL-1) encoding a 341 amino acid protein (Dg-CatL-1) with homology to cathepsin L cysteine proteinases was also selected for further study. IgY obtained from naturally infested hens failed to detect Dg-CatD-1 suggesting that it is a concealed antigen. Conversely, Dg-CatL-1 was detected by IgY derived from natural-infestation, indicating that infested hens are exposed to Dg-CatL-1. Mortality rates 120 h after mites had been fed anti-Dg-CatD-1 were significantly higher than those fed control IgY (PF<0·01). In a survival analysis, fitting a proportional hazards model to the time of death of mites, anti-Dg-CatD-1 and anti-Dg-CatL-1 IgY had 4·42 and 2·13 times higher risks of dying compared with controls (PF<0·05). Dg-CatD-1 and L-1 both have potential as vaccine antigens as part of a multi-component vaccine and have the potential to be improved as vaccine antigens using alternative expression systems.

Tick histamine release factor is critical for Ixodes scapularis engorgement and transmission of the lyme disease agent

Ticks are distributed worldwide and affect human and animal health by transmitting diverse infectious agents. Effective vaccines against most tick-borne pathogens are not currently available. In this study, we characterized a tick histamine release factor (tHRF) from Ixodes scapularis and addressed the vaccine potential of this antigen in the context of tick engorgement and B. burgdorferi transmission. Results from western blotting and quantitative Reverse Transcription-PCR showed that tHRF is secreted in tick saliva, and upregulated in Borrelia burgdorferi-infected ticks. Further, the expression of tHRF was coincident with the rapid feeding phase of the tick, suggesting a role for tHRF in tick engorgement and concomitantly, for efficient B. burgdorferi transmission. Silencing tHRF by RNA interference (RNAi) significantly impaired tick feeding and decreased B. burgdorferi burden in mice. Interfering with tHRF by actively immunizing mice with recombinant tHRF, or passively transferring tHRF antiserum, also markedly reduced the efficiency of tick feeding and B. burgdorferi burden in mice. Recombinant tHRF was able to bind to host basophils and stimulate histamine release. Therefore, we speculate that tHRF might function in vivo to modulate vascular permeability and increase blood flow to the tick bite-site, facilitating tick engorgement. These findings suggest that blocking tHRF might offer a viable strategy to complement ongoing efforts to develop vaccines to block tick feeding and transmission of tick-borne pathogens.

The testing of antibodies raised against poultry red mite antigens in an in vitro feeding assay; preliminary screen for vaccine candidates

Dermanyssus gallinae (De Geer), the poultry red mite, is a blood-feeding ectoparasite that infests many bird species. We have used an in vitro feeding assay to allow the identification of protective D. gallinae antigens that may have potential as vaccine candidates. Homogenised mites were extracted sequentially with PBS, Tween 20, Triton X100 and urea giving four protein fractions. Five experimental groups of Lohmann Brown hens were used to generate antibodies; four groups were injected with one of each of the protein fractions in QuilA adjuvant and a control group was injected with adjuvant only. Booster injections were administered 2 and 4 weeks after initial immunisation. Eggs were collected throughout the experiment and soluble IgY antibodies were extracted from a pool of egg yolks collected at week six post-injection. Western blots, performed using post vaccination antibodies from test and control groups, revealed a strong antibody response against a range of injected proteins. Fresh chicken blood, supplemented with antibodies raised against these protein fractions, was fed to mites in an in vitro feeding assay in order to determine whether the antibodies had an anti-mite effect. Although there was variability in the numbers of feeding mites, it was found that the strongest anti-mite effect was seen with the PBS protein fraction, which had a cumulative average mortality of 34.8% 14 days after feeding compared with 27.3% for the control group (P = 0.043).