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

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

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