DESCRIPTIVE EPIDEMIOLOGY OF LISTERIAL MENINGOENCEPHALITIS IN HOUSED LAMBS

During a prospective study of diseases of 4413 lambs in three housed early lambing (December and January) flocks, listerial meningoencephalitis was observed in dead lambs from two flocks (A and C) and was suspected in 1.1-1.3% (exact 95% confidence intervals (ECI), 0.3-6.7%) of live lambs from flock A. Listerial meningoencephalitis was confirmed at post-mortem in 0.5-1.6% of housed lambs which either died or were euthanased. Lambs were affected during a 2-4 week calendar period during February or March when 6-12 weeks of age. There was no age, breed or sex association with the condition. All lambs in the study were exposed to several possible risk factors but only a small proportion of lambs developed clinical signs of the disease. Previous reports of listerial meningoencephalitis in young lambs come from individual flock outbreaks or retrospective analysis of Veterinary Investigation Centre data, whereas these findings come from lambs under individual surveillance from birth to slaughter.