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CASE NOTES

What lice?

Narelle Sales, Microbiological Diseases and Diagnostics Research, Elizabeth Macarthur Agricultural Institute

Posted Flock & Herd March 2015

Abstract

The problem with lice infestations on sheep is that by the time you can see them it may have already cost the producer money and will certainly cost more before they are cleared up. Having a test that can detect 1 or 2 lice in a flock of 400 sheep would be very handy. We can do this in the lab, now we need to be able to do it in the shearing shed. Why? If testing finds lice at subclinical levels they can be eradicated before any economic loss occurs. If testing doesn't find lice, "insurance" treatments can be eliminated saving the wool producer money. This also reduces chemical residues in the fleece capable of selecting insecticide resistant lice as well as blowflies. A study on the economic value of wool attributes (2008-2013) indicated that characteristics like unscourable fleece colour, which is often associated with lice and blowfly treatments, affected the national clip value. (1) Decreased chemical use also benefits the wool processors who save money through decreased chemical contamination in scour effluent.

We propose to convert a laboratory based lice detection ELISA to an assay carried out in the shearing shed while sheep are going across the board.

Introduction

Sheep lice cost sheep graziers an estimated $123 million per year nationally (2). This can be broken down to $84 million associated with increased costs for treatment and labour while reduced wool quality and quantity account for a $39 million reduction in income(3). Comparative figures estimate a lousy fleece will realise between $3-10 less while greasy weight will be reduced by 0.2-1.1kg(4)

In 2009 producers estimated up to 80% of flocks were lousy during national consultation with Australian Wool Innovations (AWI)(5). Lousy sheep are identified through a combination of behavioural observations like sheep rubbing and visual inspection. From July 2009 to June 2011 a highly sensitive alternative was offered by our laboratory at EMAI. This was an ELISA performed on comb and cutter washings (CCWs), which detected a unique lice protein.

A study in NSW(6) found that 16.5% of flocks assessed by visual inspection were lousy. This figure increased to 30% when a subsample of the flocks, which had been declared negative, were tested off shears using their CCW in the laboratory lice ELISA (LLE) developed by NSW DPI, CSIRO & AWI.

In general, flocks are treated for lice without knowing their true lice status. As a result, a substantial proportion of the estimated 74.3 million sheep shorn in Australia in 2014/15(7) will receive unnecessary lice treatments adding to residue levels in the 334 million kilograms of greasy wool produced. This undoubtedly increases production costs and the risk of resistance developing to lice treatments.

Discussion

A collaborative project between CSIRO and NSW DPI (EMAI) to develop an immunology-based lice detection test was funded by AWI. CSIRO produced a range of monoclonal antibodies (Mab's) and NSW DPI developed a plate based ELISA. Initially, using wool grease spiked with ground lice, this ELISA easily detected 3/100ths of a louse in 250mg of wool grease. The ELISA was then converted to a magnetic bead based assay and the sensitivity increased 30 fold, to less than 1/1000th of a louse.

Sensitivity was increased further through research on preparation and processing of positive and negative CCW samples from the field. Non-specific binding was virtually eliminated making the slightest colouration due to the presence of lice. A negative control was also added using a Mab raised against an unrelated plant protein. A collection kit and user friendly instructions were produced and the LLE was offered commercially by EMAI from 2009-2011. During this 2 year period, 657 individual flock assays requests were received from NSW, QLD, Vic, SA, WA and Tasmania.

The commercial LLE proved to be a reliable, robust and sensitive tool that producers used in a variety of ways. For example a grazier saved $6000 when the test proved his split shorn mobs were negative having been treated the previous year. When tested the following year both groups were still lice free and the grazier intended to make the LLE part of his management plan. Other graziers used the LLE on newly purchased mobs, those returning from agistment, mobs suspect due to biosecurity breaches or to allow stock movement between jointly owned properties. The LLE allowed producers to detect lice and respond quickly with chemical treatments. More importantly it also identified good management practices. One grazier used the LLE to prove his flock, which had been lice free for 22 years, rubbed because of grass seed not lice. These sheep remained untreated and reinforced the grazier's successful lice management practices.

The LLE used comb and cutter wash collected at shearing. As most lice treatments are applied during a narrow window off-shears, the delay of posting samples to a laboratory was less than ideal. This was always known to be the case however by offering the LLE the value of lice testing was proven to producers. The current focus on point-of-care diagnostics has created a new opportunity to adapt the LLE to a format that can provide rapid lice status diagnosis on-farm.

Prior to the test being converted to an on-farm assay, the LLE target lice protein needs to be characterised. This will allow comparison of the LLE target lice protein with a patented louse antigen which is responsible for the pelt defect 'cockle' in New Zealand (8). This will determine if the development of an on farm lice detection test can continue in isolation or if a patent agreement is required.

Adaption of the LLE to an on-farm format requires conversion of the ELISA to a one-step format. Considerable advances on a one-step LLE had been made prior to its termination in 2011. Despite these advances, major challenges exist. These include handling and processing the CCW without the aid of lab equipment, production of biologically active reagents in a usable field-format and developing the hardware required to carry out the physical and immunological processes of the test.

Conclusion

A robust and sensitive on-farm test to detect lice on sheep would benefit producers through increased profits. These would be achieved by reduced input costs, reduced production losses, increased sheep productivity, increased wool yield and quality, reduced insecticide residues, reduced wool processing costs, increased clip price and decreased WHS risks. It would also increase wool market opportunities and be an invaluable tool to eradicate lice from Australian sheep.

Acknowledgements

The original collaborative project between CSIRO Livestock Industries (formerly CSIRO Animal Health) and NSW DPI (formerly NSW Agriculture) was funded by Australian Wool Innovations, AWI, (formerly the Woolmark Company) in 1996. The subsequent funding of NSW DPI based projects by AWI is gratefully acknowledged. The author acknowledges the contribution of a large number people throughout this process, including Irene Bate and especially Paul Young.

References

  1. Nolan E (2015) The economic value of wool attributes phase 2 www.wool.com Published: January 2015, Accessed: February 2015
  2. Joshua E, Junk G and Levot G (2010) Sheep lice www.dpi.nsw.gov.au Published: January 2010, Accessed: February 2015
  3. Sackett D and Holmes P (2006) Assessing the economic cost of endemic disease on the profitability of Australian beef cattle and sheep producers www.mla.com.au Published: April 2006 Accessed: February 2015
  4. James P (2013) Why control sheep lice? Economic effects of lice on production www.liceboss.com.au Published: March 2013. Accessed: February 2015
  5. Littlejohn J and Schroder J (2009) Australian Wool Innovation investments and activities in sheep lice control In: Proceedings of the Annual Conference of NSW District Veterinarians (Port Macquarie) pp 23-27 www.flockandherd.net.au
  6. Popp S, Eppleston J, Watt BR, Mansfield BS and Bush RD (2012) The prevalence of lice (Bovicola ovis) in sheep flocks on the central and southern Tablelands of New South Wales Animal Production Science 52::659-664
  7. Australian Wool Production Forecasting Committee (AWPFC) (2014) Australian Wool Production Forecast Report December 2014 www.wool.com Published: December 2014. Accessed: Feb 2015
  8. Pfeffer A, Shoemaker CB, Shaw RJ, Green RS and Shu D (2010) Identification of an abundant allergen from the sheep louse, Bovicola ovis. International Journal of Parasitology 40(8):911-919

 

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