Evaluation of farm management practices as risk factors for clinical listeriosis and fecal shedding of Listeria monocytogenes in ruminants

Objective - To assess seasonal variation in prevalence of Listeria monocytogenes on ruminant farms and identify management practices associated with ruminant listeriosis and fecal shedding of L monocytogenes. Study Design - Case-control study. Sample Population-2,056 samples of feces, feed, soil, and water from 24 case farms with listeriosis and 28 control farms without listeriosis. Procedure - Samples were collected and evaluated via bacterial culture for L monocytogenes. Univariate associations between farm management practices and listeriosis and fecal shedding of L monocytogenes were assessed. Multivariate models were developed to identify farm management practices associated with listeriosis and fecal shedding of L monocytogenes. Results - The prevalence of L monocytogenes on cattle, goat, and sheep farms was seasonal, especially in fecal samples, with peak prevalence in winter. Although the prevalence of L monocytogenes in feedstuffs from small-ruminant farms also peaked during winter, the bacterium was detected at a constant rate in cattle farm feedstuffs throughout the year. Farm management practices, animal health and hygiene, and feedstuff quality and storage were associated with ruminant listeriosis and fecal shedding of L monocytogenes. Conclusions and Clinical Relevance - Results suggest that the prevalence of L monocytogenes on ruminant farms is seasonal, management practices are associated with ruminant listeriosis and fecal shedding of L monocytogenes, and the epidemiologic features of listeriosis differ in cattle versus small ruminants. Awareness of risk factors may be used to develop control measures to reduce animal disease and introduction of L monocytogenes into the human food chain.