A technique to test novel methods of controlling poultry red mite in hens without performing field-scale trials
Lead Research Organisation:
Moredun Research Institute
Department Name: Vaccines and Diagnostics
Abstract
Infestation of hen houses with poultry red mites (PRM) is a major animal welfare and economic problem for the egg industry worldwide, irrespective of the type of laying systems employed. The two main impacts of PRM on laying hens are direct effects of the mites biting the birds and feeding on their blood which causes irritation and anaemia, and indirect effects caused by the mites transmitting diseases to the hens. Traditional methods of controlling PRM with chemical sprays in hen houses are now failing as the mites become resistant to the chemicals. Demand for novel methods of controlling PRM is therefore high and several research groups around the world are working on these new methods of control. Typically, the testing of novel control methods uses mites in laboratory-based tests initially, followed by field testing using large numbers of hens. For example, the development of vaccines to control PRM routinely uses initial laboratory-screening tests to identify potential vaccines before moving into field trials which can use up to 800 hens in each trial and last for several months. This strategy has 2 major drawbacks:
1) Results from the laboratory-based analyses are highly variable and may not accurately predict what happens in field trials;
2) Field trials involve large numbers of birds continually exposed to parasites for prolonged periods.
To address these issues we have developed an 'on-hen' mite feeding device, as an alternative to the laboratory-based tests, which will allow much more accurate assessment of vaccines and other mite control methods on small numbers of hens before field studies are conducted. This strategy addresses the "Reduction" aspect of the 3Rs principles by greatly reducing the number of hens used, as it would accurately identify poorly performing vaccines or other control methods (e.g. new pesticides) before they were progressed to field trials. This on-hen system can also be used to test the effectiveness of mite control methods across prolonged periods on small numbers of hens (4 per treatment group, as opposed to 400 per treatment group in field trials) without continually exposing birds to the parasites. This therefore addresses a second 3Rs principle - "Refinement" as it allows the birds to remain free from the parasites for the vast majority of the experimental period, with parasites only accessing the birds for short (3 hour) periods every 3 weeks instead of the continual exposure encountered in field trials.
During a field infestation of PRM each of 3 developmental stages of the mites feeds on the host; 2 juvenile stages and the adult stage. So far we have designed the on-hen device to allow adult mites to feed on the hen but any vaccine or novel acaricide should have effects on each of the three blood-feeding stages of the mite for maximum efficacy and any testing strategy which uses an on-hen feeding device as a proxy for infestation models should be able to determine these effects.
The specific aim of the proposed work is therefore to further develop the on-hen feeding device into a highly reliable tool for monitoring the effectiveness of novel mite control methods on parasite survival and ability to transmit disease and therefore reduce the reliance on large scale, prolonged field trials. This aim will be achieved through a series of experiments, as follows:
1) Optimise design of the device to allow feeding by all stages of the parasite.
2) Determine effects of hen age on the ability to use the feeding devices
3) Employ the optimised feeding devices in an extended vaccine efficacy study
4) Employ the optimised feeding devices in a disease transmission study
1) Results from the laboratory-based analyses are highly variable and may not accurately predict what happens in field trials;
2) Field trials involve large numbers of birds continually exposed to parasites for prolonged periods.
To address these issues we have developed an 'on-hen' mite feeding device, as an alternative to the laboratory-based tests, which will allow much more accurate assessment of vaccines and other mite control methods on small numbers of hens before field studies are conducted. This strategy addresses the "Reduction" aspect of the 3Rs principles by greatly reducing the number of hens used, as it would accurately identify poorly performing vaccines or other control methods (e.g. new pesticides) before they were progressed to field trials. This on-hen system can also be used to test the effectiveness of mite control methods across prolonged periods on small numbers of hens (4 per treatment group, as opposed to 400 per treatment group in field trials) without continually exposing birds to the parasites. This therefore addresses a second 3Rs principle - "Refinement" as it allows the birds to remain free from the parasites for the vast majority of the experimental period, with parasites only accessing the birds for short (3 hour) periods every 3 weeks instead of the continual exposure encountered in field trials.
During a field infestation of PRM each of 3 developmental stages of the mites feeds on the host; 2 juvenile stages and the adult stage. So far we have designed the on-hen device to allow adult mites to feed on the hen but any vaccine or novel acaricide should have effects on each of the three blood-feeding stages of the mite for maximum efficacy and any testing strategy which uses an on-hen feeding device as a proxy for infestation models should be able to determine these effects.
The specific aim of the proposed work is therefore to further develop the on-hen feeding device into a highly reliable tool for monitoring the effectiveness of novel mite control methods on parasite survival and ability to transmit disease and therefore reduce the reliance on large scale, prolonged field trials. This aim will be achieved through a series of experiments, as follows:
1) Optimise design of the device to allow feeding by all stages of the parasite.
2) Determine effects of hen age on the ability to use the feeding devices
3) Employ the optimised feeding devices in an extended vaccine efficacy study
4) Employ the optimised feeding devices in a disease transmission study
Technical Summary
Infestation of hen houses with poultry red mites (PRM) is a major animal welfare and economic problem for the egg industry worldwide. Demand for novel methods of controlling PRM is high and, typically, the testing of novel control methods uses mites in in vitro efficacy assays initially, followed by field testing using large numbers of hens.
We are developing vaccines to control D. gallinae and routinely use in vitro feeding devices to feed antibodies from immunised hens to small numbers of mites to identify effective vaccine antigens before moving into field trials which use up to 800 hens in each trial. This strategy has 2 major drawbacks:
1) Data from the in vitro feeding devices are highly variable and may not accurately reflect field trials;
2) Field trials involve large numbers of birds continually exposed to parasites for prolonged periods.
To address these issues we developed an 'on-hen' in vivo mite feeding device as an alternative to both the in vitro feeding assays and field studies. This system can be used to test vaccine efficacy in longitudinal studies across prolonged experimental periods on small numbers of hens (4 per treatment group, as opposed to 400 per treatment group in field trials) without continuous exposure of the birds to the parasites. The specific aim of the proposed work is to further develop the in vivo feeding device into a highly reliable tool for monitoring vaccine- or acaricide-induced effects on parasite mortality and therefore reduce the reliance on large scale, prolonged field trials.
This aim will be achieved through a series of experiments, as follows:
1) Optimise design of the device to allow feeding by all haematophagous stages of the parasite.
2) Determine effects of hen age on the ability to use the feeding devices
3) Employ the optimised feeding devices in a longitudinal vaccine efficacy study
We are developing vaccines to control D. gallinae and routinely use in vitro feeding devices to feed antibodies from immunised hens to small numbers of mites to identify effective vaccine antigens before moving into field trials which use up to 800 hens in each trial. This strategy has 2 major drawbacks:
1) Data from the in vitro feeding devices are highly variable and may not accurately reflect field trials;
2) Field trials involve large numbers of birds continually exposed to parasites for prolonged periods.
To address these issues we developed an 'on-hen' in vivo mite feeding device as an alternative to both the in vitro feeding assays and field studies. This system can be used to test vaccine efficacy in longitudinal studies across prolonged experimental periods on small numbers of hens (4 per treatment group, as opposed to 400 per treatment group in field trials) without continuous exposure of the birds to the parasites. The specific aim of the proposed work is to further develop the in vivo feeding device into a highly reliable tool for monitoring vaccine- or acaricide-induced effects on parasite mortality and therefore reduce the reliance on large scale, prolonged field trials.
This aim will be achieved through a series of experiments, as follows:
1) Optimise design of the device to allow feeding by all haematophagous stages of the parasite.
2) Determine effects of hen age on the ability to use the feeding devices
3) Employ the optimised feeding devices in a longitudinal vaccine efficacy study
Planned Impact
The outcomes of the proposed work programme will demonstrate impact through the reduction in use of hens in field trials and refinement of experimental procedures on hens leading to greatly increased welfare.
Specifically, we will have immediate impacts in studies which assess novel interventions for poultry red mite control. This is an expanding research area, with 47 research papers published (in PubMed-listed journals) in the last 10 years on the subject whereas only 17 papers on the topic were published in the 40 years prior to 2007. The two largest areas of growth in the development of novel interventions for poultry red mite control have been in the development of vaccines (10 papers since 2007) and novel acaricides/novel uses for existing acaricides (33 papers since 2007). Novel interventions are typically tested first in in vitro assays prior to escalation to field trials. Field trials for novel acaricides have employed ~300 hens whereas those for vaccines employ ~800 hens. During these trials hens are continually exposed to the parasites and the in vitro efficacy of the vaccines or novel acaricides are not always directly translated to efficacy in the field. We will develop a novel on-hen mite feeding system for pre-screening in vivo efficacy of products before they are advanced to field trial.
Once established, two research labs (in addition to our own) will use this system to pre-screen vaccine formulations for poor in vivo performance before embarking on field trials. This could reduce the numbers of hens used in field trials by ~800 per vaccine formulation (see attached letters of support from Prof Fiona Tomley and Dr. Oivind Oines). We recently published a list of 22 different preparations/proteins which had shown some degree of efficacy in in vitro feeding assays and a further 9 vaccine candidates have been identified by a separate academic group. To progress any of these vaccine candidates to commercial use, their efficacy in vivo will need to be demonstrated. If our optimised on-hen in vivo feeding device was able to indicate poor in vivo efficacy for 50% of these candidates, this would lead to a reduction in the number of field trials performed and the use of ~12,000 hens in those field trials.
We will promote the use of the device through several pathways: direct discussion with poultry veterinarians and scientists involved in this research; a full description (including video link) of the device and it's use on the red mite researchers' COREMI COST action website; a practical workshop for parasitologists on the use of the device; attendance of national and international conferences to highlight the 3Rs and scientific impact of the device; public engagement activities including Moredun roadshows, attendance at the Royal Highland show; engagement with the farming press at Moredun's annual Press day.
Further 3Rs and scientific impact will be delivered through the use of the device to understand vector competency of poultry red mites and scientists working on arthropod-vectored diseases will benefit as the device may be easily altered to other biting arthropod systems.
Economic impact will be delivered through the reduced use (and expense) of unproductive field trials and through the accelerated development of novel interventions for a parasite of huge economic importance.
Specifically, we will have immediate impacts in studies which assess novel interventions for poultry red mite control. This is an expanding research area, with 47 research papers published (in PubMed-listed journals) in the last 10 years on the subject whereas only 17 papers on the topic were published in the 40 years prior to 2007. The two largest areas of growth in the development of novel interventions for poultry red mite control have been in the development of vaccines (10 papers since 2007) and novel acaricides/novel uses for existing acaricides (33 papers since 2007). Novel interventions are typically tested first in in vitro assays prior to escalation to field trials. Field trials for novel acaricides have employed ~300 hens whereas those for vaccines employ ~800 hens. During these trials hens are continually exposed to the parasites and the in vitro efficacy of the vaccines or novel acaricides are not always directly translated to efficacy in the field. We will develop a novel on-hen mite feeding system for pre-screening in vivo efficacy of products before they are advanced to field trial.
Once established, two research labs (in addition to our own) will use this system to pre-screen vaccine formulations for poor in vivo performance before embarking on field trials. This could reduce the numbers of hens used in field trials by ~800 per vaccine formulation (see attached letters of support from Prof Fiona Tomley and Dr. Oivind Oines). We recently published a list of 22 different preparations/proteins which had shown some degree of efficacy in in vitro feeding assays and a further 9 vaccine candidates have been identified by a separate academic group. To progress any of these vaccine candidates to commercial use, their efficacy in vivo will need to be demonstrated. If our optimised on-hen in vivo feeding device was able to indicate poor in vivo efficacy for 50% of these candidates, this would lead to a reduction in the number of field trials performed and the use of ~12,000 hens in those field trials.
We will promote the use of the device through several pathways: direct discussion with poultry veterinarians and scientists involved in this research; a full description (including video link) of the device and it's use on the red mite researchers' COREMI COST action website; a practical workshop for parasitologists on the use of the device; attendance of national and international conferences to highlight the 3Rs and scientific impact of the device; public engagement activities including Moredun roadshows, attendance at the Royal Highland show; engagement with the farming press at Moredun's annual Press day.
Further 3Rs and scientific impact will be delivered through the use of the device to understand vector competency of poultry red mites and scientists working on arthropod-vectored diseases will benefit as the device may be easily altered to other biting arthropod systems.
Economic impact will be delivered through the reduced use (and expense) of unproductive field trials and through the accelerated development of novel interventions for a parasite of huge economic importance.
