Dynamics of the natural transmission of bovine spongiform encephalopathy within an intensively managed sheep flock.

Martin Jeffrey,Janey P Witz,Stuart Martin,Glenda E Dexter,Steve A C Hawkins,Lisa Thurston,Lorenzo González,Sue J Bellworthy

doi:10.1186/s13567-015-0269-x

Martin Jeffrey, Janey P Witz + Show 6 more

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https://doi.org/10.1186/s13567-015-0269-x

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Abstract

Sheep are susceptible to the bovine spongiform encephalopathy (BSE) agent and in the UK they may have been exposed to BSE via contaminated meat and bone meal. An experimental sheep flock was established to determine whether ovine BSE could be naturally transmitted under conditions of intensive husbandry. The flock consisted of 113 sheep of different breeds and susceptible PRNP genotypes orally dosed with BSE, 159 sheep subsequently born to them and 125 unchallenged sentinel controls. BSE was confirmed in 104 (92%) orally dosed sheep and natural transmission was recorded for 14 of 79 (18%) lambs born to BSE infected dams, with rates varying according to PRNP genotype. The likelihood of natural BSE transmission was linked to stage of incubation period of the dam: the attack rate for lambs born within 100 days of the death of BSE infected dams was significantly higher (9/22, 41%) than for the rest (5/57, 9%). Within the group of ewes lambing close to death, those rearing infected progeny (n = 8, for 9/12 infected lambs) showed a significantly greater involvement of lymphoid tissues than those rearing non-infected offspring (n = 8, for 0/10 infected lambs). Horizontal transmission to the progeny of non-infected mothers was recorded only once (1/205, 0.5%). This low rate of lateral transmission was attributed, at least partly, to an almost complete absence of infected placentas. We conclude that, although BSE can be naturally transmitted through dam-lamb close contact, the infection in this study flock would not have persisted due to low-efficiency maternal and lateral transmissions.

Highlights

The transmissible spongiform encephalopathies (TSEs) or prion diseases comprise a group of fatal neurological disorders affecting man, domestic ruminants, farmed and free-living cervid species, domestic and captive felids and, rarely, farmed mustellids
Sheep orally challenged with cattle bovine spongiform encephalopathy (BSE) brain homogenates Attack rates were 100% for M112M ARQ Suffolk sheep (23/23), for AHQ Cheviot sheep (28/28) and for VRQ Cheviot sheep left to develop clinical disease (4/4)
14 lambs born to BSE infected dams and another born to a non-infected dam either developed clinical BSE

Summary

Introduction

The transmissible spongiform encephalopathies (TSEs) or prion diseases comprise a group of fatal neurological disorders affecting man, domestic ruminants, farmed and free-living cervid species, domestic and captive felids and, rarely, farmed mustellids. The bovine spongiform encephalopathy (BSE) epidemic of cattle in the UK and Europe was initiated and largely maintained by the inclusion of BSE contaminated meat and bone meal in concentrate feedstuffs [1, 2]. It is likely that at least some sheep and goats in the UK received concentrate feedstuffs that were at significant risk of containing the BSE agent. No natural cases of BSE in sheep have yet been confirmed, though cases of caprine BSE have been identified in Europe [4, 5]. Any infection of sheep that may have occurred in the 1980s, when cattle BSE was first identified, would potentially have undergone many serial passages over generations with potential

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