Case Report: Two Cases of Ocular form of Listeriosis in Cattle Herds

Nowadays, the widespread use of silage has led to an increased frequency of bacterial contamination of Listeria spp in ruminants. The infection of ruminants is essentially linked to the consumption of silage of poor quality or of milk products. The disease is frequent and severe in ruminants and can be present in various forms: nervous, septicaemic, genital, mastitis and ocular. The ocular form of Listeriosis can serve as a sentinel for the disease at the herd level. In this case report, 2 herds were investigated for calves and adult mortalities. In the first case, a large majority of the calves presented with hypopion but neurological examination of the calves revealed no abnormalities. The majority of the dairy cows also presented with ocular disorders but neurological examination did not reveal any abnormalities. Calves received whole milk from the dairy herd. The dairy herd diet comprised maize and grass silage, and cereals. Listeria monocytogenes was found in milk and grass silage in significant amounts. In the second case, weight loss, abortions and mortalities in adult cattle were reported. Fifty percent of animals examined presented with hypopion, and/or keratoconjunctivitis, and/or uveitis. No neurological abnormality was found. The animals’ ration of was comprised grass and maize silages. The grass silage had poor macroscopical aspect. Analysis revealed the presence of Schizophyllum commune (fungus) and L. monocytogenes in significant amounts. Furthermore, analysis of aborted foetuses also showed L. monocytogenes. Listeria infection in cattle can occur through ingestion of contaminated silage but calves can also be infected throughout the dams’milk. Ocular lesions are not pathognomonic for Listeriosis but, accompanied with abortions and poor quality silage, this can be a major indication for ancillary exams for Listeria monocytogenes at a herd level.