Epidemiology, clinical and pathological features and outcomes of listeriosis in ruminants: a systematic review and meta-analysis

We performed a systematic review and meta-analysis of the epidemiology, clinical and pathological features, outcomes, and therapy for listeriosis in ruminants. PubMed, Web of Science, and Scopus were searched with no publication date limits. A random-effects meta-analysis model was used to calculate the pooled effect size using morbidity and case fatality rate data. 63 and 38 studies met the inclusion criteria for the systematic review and meta-analysis, respectively. 56 out of 63 studies were published before 2016 when cgMLST was developed. A comprehensive analysis of historical data shows that the association of silage as a source of contamination in ruminants should be re-evaluated. The most common clinical presentation was encephalitis (64.8% of the animals, 1839/2837), followed by abortion (21.3% of the animals, 604/2837). The mortality rate was high despite treatment. Overall, the mean morbidity, case fatality rate, and abortion rate were 12.6%, 50.6%, and 12.8%, respectively. Meta-analysis of the subgroups revealed a Hedges' g value of -4.60 for the abortive form, indicating greater morbidity than mortality in this form. In contrast, the encephalitic form was characterized by a higher case fatality rate than morbidity (Hedges' g 9.46). Literature gaps exist since most reported outbreaks are from the twentieth century and only from a few countries. There is a lack of information on the current prevalence, consequences, and effectiveness of antimicrobial treatment of listeriosis in domestic ruminants. There is also an incomplete picture of the prevalence of <i>Listeria</i> infection worldwide.