Dept of Agriculture, Food and the Marine

G Dobler

HW Reid

L Gilbert

N Sargison

P Hudson

Irish Veterinary Journal

English

Damien Barrett

Daniel M Collins

Guy McGrath

Colm Ó Muireagain

Crossref

Iris Tréidliachta ÉireannBarrett et al. Irish Veterinary Journal 2012, 65:20http://www.irishvetjournal.org/content/65/1/20CASE STUDY Open AccessSeroprevalence of Louping Ill virus (LIV)antibodies in sheep submitted for post mortemexamination in the North West of Ireland in 2011Damien Barrett1*, Daniel M Collins2, Guy McGrath2 and Colm Ó Muireagain1AbstractBlood samples were collected opportunistically at routine post mortem examination from 199 sheep which camefrom 152 flocks. The location of each submitting flock was mapped. Sera were tested using a goose bloodhaemagglutination inhibition assay for louping ill virus. There was an animal level prevalence of 8.5%, and a flocklevel prevalence of 9.8%. The greatest proportion of seropositive animals was identified among the animals olderthan 24 months of age. The elevation of the land associated with positive flocks was greater than that of negativeflocks. Lesions of non-suppurative meningoencephalitis were observed in three of the 199 animals.Keywords: Louping Ill, Sheep, Routine post mortem, Prevalence, IrelandBackgroundLouping ill is a tick borne viral infection which predom-inately affects sheep causing neurological disease. Loup-ing ill may also affect goats and cattle. The conditionhas been reported in humans and is classified as a zoo-nosis [1]. Louping ill is considered a significant problemamong red grouse in Scotland [2]. Louping ill is causedby louping ill virus which is a flavivirus [1]. The name'louping-ill' is derived from an old Scottish word describ-ing the effect of the disease in sheep whereby they 'loup'or spring into the air. Louping ill gives rise to a diffusenon-suppurative meningoencephalitis and manifestsclinically with ataxia, pyrexia, seizures and opisthoto-nous, posterior paralysis, coma and death [3]. The dis-ease is also associated with sudden death. Concurrenttick borne fever infection (Anaplasma phagocytophilum)is thought to amplify the effect of the louping ill virus[4]. Morbidity rates of between five and 60% have beenreported [3]. The condition is transmitted by the tickIxodes ricinus, and its prevalence is closely associatedwith the distribution of this vector [5]. There is a sea-sonal occurrence in the spring and autumn, coinciding* Correspondence: Damien.barrett@agriculture.gov.ie1Department of Agriculture, Food and Marine, Sligo Regional VeterinaryLaboratory, Doonally, Sligo, IrelandFull list of author information is available at the end of the article© 2012 Barrett et al.; licensee BioMed CentralCommons Attribution License (http://creativecreproduction in any medium, provided the orwith the activity of the tick vector [3]. The presence ofdeer is associated with an increased tick population in alocality [5]. Climate change has been implicated inincreased tick populations [5].The objective of this study was to estimate the preva-lence of exposure to louping ill virus among carcassessubmitted for routine post mortem examination to SligoRegional Veterinary Laboratory, in the North West ofIreland. There have been no previous studies of theprevalence of louping ill in Ireland.MethodsBlood samples were collected from 199 sheep from 152flocks, which had been submitted to Sligo RVL during2011. The samples were collected opportunistically at rou-tine post-mortem examination. Carcasses are accepted forpost mortem examination on the basis that the herdowner consents to any tests carried out at the discretion ofthe veterinary pathologist. Sera were tested using a gooseblood haemagglutination inhibition assay at the VirologySection in the Moredun Research Institute, Scotland. Sam-ples were titrated out in the presence of a constant virusantigen and goose red blood cells. The first dilution was1:10 with doubling dilutions thereafter. A titre of 1:20 wasused as the cut off for positive / negative results. Titreswere expressed as the highest dilution at which inhibitionof haemagglunination was detected. A presumptiveLtd. This is an Open Access article distributed under the terms of the Creativeommons.org/licenses/by/2.0), which permits unrestricted use, distribution, andiginal work is properly cited.Figure 1 Shows the location of sampled sheep flocks.Table 1 Age breakdown of louping ill positive sheepAge category No positive No submitted Prevalence(%)0-6 month old 0 43 06-12 month old 2 35 5.712-24 month old 0 17 0Greater than 24 months 15 104 14.4Total 17 199 8.5Barrett et al. Irish Veterinary Journal 2012, 65:20 Page 2 of 4http://www.irishvetjournal.org/content/65/1/20diagnosis of louping ill was made based on histopatho-logical changes associated with non-suppurative meningo-encephalitis in the brains of affected animals consistentwith a diagnosis of louping ill.Maps were created using ESRI Arcview 3.2 software(Redlands; California). Flocks were represented by thecentroid of the largest fragment of land associated witheach flock, or the corresponding townland where a flocknumber was not available (2 flocks) (Figure 1).For the elevation analysis, the centroid of all frag-ments in a farm was calculated and used to create apoint map. This point map was then queried to findthe intersection value of an underlying digital elevationmodel surface using a bilinear interpolation of eachvalue (ArcGIS 10, ESRI, Redlands, CA, USA). Thisaddresses the issue of a value from a single pointrepresenting a fragment of land. The output consistedof an elevation value in metres above sea level for allfragments of land in the study.Table 2 Month of submission of louping ill positive sheepMonth submitted No. positive No submitted % seropositiveJanuary 2011 0 14 0February 2011 1 7 14.3March 2011 2 37 5.4April 2011 5 35 14.2May 2011 0 16 0June 2011 1 12 8.3July 2011 1 6 16.6August 2011 1 10 10September 2011 1 17 5.8October 2011 1 21 4.8November 2011 1 6 16.6December 2011 3 18 16.6Table 4 Post mortem diagnosis of 17 seropositivesamplesDiagnosis No. of casesLouping ill 3Listeriosis 3No diagnosis 1Septicaemia 3Pneumonia 3Pregnancy toxaemia (twin lamb disease) 2Parasitic gastro enteritis 1Acute Fascioliasis 1Barrett et al. Irish Veterinary Journal 2012, 65:20 Page 3 of 4http://www.irishvetjournal.org/content/65/1/20ResultsSeventeen samples showed serological evidence of ex-posure to louping ill virus from the 199 blood samples,giving an animal level prevalence of 8.5%. These posi-tive samples came from 15 of the 152 flocks, giving aflock level prevalence of 9.8%. Two flocks each hadtwo sero-positive animals, while the remaining 13flocks had a single sero-positive animal. Six flocks hadboth positive and negative samples. The greatest pro-portion of sero-positive animals was found among theadult age group (Table 1). The temporal distribution ofthe detection of sero-positive animals is presented inTable 2. The geographical distribution of positive casesis outlined in Table 3. The greatest number of caseswas in Co. Donegal. The post mortem diagnosis andthe signalment of the 17 sero-positive animals are pre-sented in Tables 4 and 5 respectively. There was a dif-ference of 106 metres in the average maximumelevation of land parcels of holdings associated withpositive flocks grazed was 106 metres higher than thatthe maximum elevation of the land associated withnegative flocks (Table 6), and there was a 40 metre dif-ference in the mean elevation between the positive andnegative flocks.Table 3 Submission of samples by countyCounty No. positive No submitted % seropositiveCavan 0 6 0Donegal 8 38 21.0Leitrim 3 27 11.1Longford 1 2 -Mayo 3 23 13.0Roscommon 0 9 0Sligo 2 94 2.1Discussion and evaluationThis study has found an animal level seroprevalence of8.5% and a flock level seroprevalence of 9.8%.However, caution would be advised in extrapolatingthese figures to the national sheep population as thesample is biased due to the opportunistic nature of thesampling protocol. Secondly, a greater proportion thanthe national average of the land area within the Sligo Re-gional Veterinary Laboratory (RVL) catchment areawould be classified as upland with rough grazing, andtherefore would be more likely to have a tick burden,than areas with a greater proportion of improved grass-land. Further there was an uneven distribution of sub-missions from the counties within the catchment area. Ithas been shown in a previous report that a significantdeterminant in submitting a carcass to an RVL is dis-tance from the submitting farm to the RVL [6] and thisstudy emphasises this further with 47% of submissionscoming from Co. Sligo. The relatively small sample sizeand the number of positive animals may also raise con-cerns relating to study power. Despite these shortcom-ings, this study provides interesting information on theepidemiology of louping ill in Irish sheep flocks in thenorthwest of Ireland.The greatest proportion of sero-positive animals wasin the adult (greater than 24 month old) category. Thismay in part reflect historical seroconversion where ananimal developed immunity following infection, andTable 5 Signalment of 17 seropositive casesHistory No. of casesPneumonia / tachypnoea 2Ataxia 5Ataxia and / tachypnoea 2Sudden death 4Dull 2Lameness 1Ill thrift 1Table 6 Comparison of the mean and median of the maximum, minimum and mean elevations for flocks whereantibodies to louping ill were detected to flocks where no antibodies were detectedPositive flocks Negative flocks DifferenceMax elevation (m) Mean 277.0 170.8 106.2Median 254.0 113.5 140.5Min Elevation (m) Mean 59.7 52.0 7.7Median 56.5 47.0 9.5Mean Elevation (m) Mean 134.5 94.3 40.2Median 105.0 83.5 21.5Barrett et al. Irish Veterinary Journal 2012, 65:20 Page 4 of 4http://www.irishvetjournal.org/content/65/1/20may not be necessarily associated with active infection atthe time of sampling.If an adult sheep were introduced to the farmland, itwould have had no prior immunity to the condition andwould be more susceptible. Of the 17 cases encounteredin the present study, three of these were in recently pur-chased sheep. However, it cannot be determined if theseaffected sheep had been on a tick-infested land parcel earl-ier in their lives. Traditionally, a seasonal pattern of occur-rence has been observed with louping ill [3]. Louping illand listeriosis were diagnosed at post mortem in six of the17 positive cases.The elevation of the land grazed by sheep in flockswhere louping ill was diagnosed was greater than that ofthe flocks where no sero-positive animals were found.This is as expected as the tick required for the transmis-sion of louping ill is found on rough grazing land whichtends to be at higher elevations.Despite the awareness of louping ill as an endemic dis-ease in Ireland for many years, this is the first publishedreport detailing its occurrence in the north west ofIreland.ConclusionThere was an animal level prevalence of 8.5%, and aflock level prevalence of 9.8%. The greatest proportionof sero-positive animals was identified among the ani-mals older than 24 months of age. The elevation of theland associated with positive flocks was greater than thatof negative flocks.Competing interestsThe authors declare that they have no competing interest.Authors' contributionsDB collected samples, did the data analysis and wrote the paper. CÓMcollected samples, organised the logistics of testing and reviewed the paper.DMC carried out the GIS analysis and reviewed the paper. GMcG carried outthe elevation analysis and reviewed the paper. All authors read andapproved the final manuscript.AcknowledgementsWe are grateful to Dr Kim Willoughby of the Moredun Research Institute foradvice and assistance. We are grateful to Caroline Harte, of Sligo RegionalVeterinary Laboratory, for clerical assistance.Author details1Department of Agriculture, Food and Marine, Sligo Regional VeterinaryLaboratory, Doonally, Sligo, Ireland. 2Centre for Veterinary Epidemiology andRisk Analysis, School of Veterinary Medicine, University College Dublin,BelfieldDublin 4, Dublin, Ireland.Received: 31 May 2012 Accepted: 13 November 2012Published: 11 December 2012References1. Dobler G: Zoonotic tick-borne flaviviruses. Vet Microbiol 2010, 140:221–228.2. Hudson P, Gould E, Laurenson K, Gaunt M, Reid H, Jones L, Norman R,MacGuire K, Newborn D: The epidemiology of louping-ill, a tick borneinfection of red grouse (Lagopus lagopus scoticus). Parasitologia 1997,39:319–323.3. Sargison N: Sheep Flock Health – a planned approach. Oxford: BlackwellPublishing; 2008.4. Reid HW, Buxton D, Pow I, Brodie TA, Holmes PH, Urquhart GM: Responseof sheep to experimental concurrent infection with tick-borne fever(Cytoecetes phagocytophila) and louping-ill virus. Res Vet Sci 1986,41:56–62.5. Gilbert L: Altitudinal patterns of tick and host abundance: a potential rolefor climate change in regulating tick-borne diseases? Oecologia 2010,162:217–225.6. Dept of Agriculture, Food and the Marine: Efficiency review of RegionalVeterinary Laboratories. Dublin: 2009.doi:10.1186/2046-0481-65-20Cite this article as: Barrett et al.: Seroprevalence of Louping Ill virus (LIV)antibodies in sheep submitted for post mortem examination in theNorth West of Ireland in 2011. Irish Veterinary Journal 2012 65:20.Submit your next manuscript to BioMed Centraland take full advantage of: • Convenient online submission• Thorough peer review• No space constraints or color ﬁgure charges• Immediate publication on acceptance• Inclusion in PubMed, CAS, Scopus and Google Scholar• Research which is freely available for redistributionSubmit your manuscript at www.biomedcentral.com/submit

Seroprevalence of Louping Ill virus (LIV) antibodies in sheep submitted for post mortem examination in the North West of Ireland in 2011

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Seroprevalence of Louping Ill virus (LIV) antibodies in sheep submitted for post mortem examination in the North West of Ireland in 2011

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