[en] Human listeriosis is a severe foodborne disease caused by Listeria monocytogenes. It is a zoonosis that represents a significant concern for the food industry due to the high mortality rate it causes and the fact that the organism is capable of growing at refrigeration temperatures. Dairy products and ready-to-eat meats are among the foods most often involved in listeriosis outbreaks. Listeria is a common contaminant in the dairy environment, both on the farm and in the processing plant. The main sources of L. monocytogenes in dairy farms are manure and improperly fermented silage. If silage crops are grown on contaminated land, a new cycle of silage contamination and faecal shedding by ruminants that consume such silage may ensue. High loads of L. monocytogenes produced in farm environments may thus represent a primary source for the introduction of this pathogen into the human food supply chain; dairy cows would represent a reservoir for the bacterium, and raw milk and beef would represent the main vehicles for its transmission from dairy farms to humans. Even if contamination originates in post-processing environments, contaminated raw foods may still represent a vehicle for introducing L. monocytogenes into food processing plants.Molecular typing methods have confirmed that common strains of L. monocytogenes are present in dairy farm-associated isolates and isolates from both human epidemic and sporadic cases. Pre-harvest (on-farm) control of listeriosis should be basedmainlyon the control of manure, silage, herd health and milking practices.

[es] La listeriosis humana es una grave enfermedad transmitida por alimentos y causada por Listeria monocytogenes. Se trata de una zoonosis que supone una gran preocupaci&oacute;n para la industria alimentaria debido a su alta tasa de mortalidad y al hecho de que el microorganismo es capaz de crecer a temperaturas de refrigeraci&oacute;n. Listeria es un contaminante habitual en las granjas y plantas de productos l&aacute;cteos. En las granjas las fuentes principales de L. monocytogenes son el esti&eacute;rcol y los ensilados mal fermentados. Si la cosecha utilizada para producir ensilados procede de campos contaminados, puede comenzar un nuevo ciclo de contaminaci&oacute;n de los ensilados y liberaci&oacute;n del pat&oacute;geno en las heces de los animales. El ganado vacuno lechero representa uno de los principales reservorios de este microorganismo y la leche y la carne representar&iacute;an los principales veh&iacute;culos para su transmisi&oacute;n desde la granja de producci&oacute;n de leche al ser humano. Incluso cuando la contaminaci&oacute;n del alimento procede de etapas posteriores al procesado, los alimentos crudos contaminados tambi&eacute;n representan uno de los veh&iacute;culos de entrada de L. monocytogenes en las plantas de procesado de alimentos. Los m&eacute;todos de tipificaci&oacute;n molecular han confirmado que en las granjas de ganado vacuno lechero existen cepas de L. monocytogenes id&eacute;nticas a las cepas responsables de casos espor&aacute;dicos y epid&eacute;micos de listeriosis humana. El control de la listeriosis en las granjas de producci&oacute;n de leche ha de basarse fundamentalmente en el control del esti&eacute;rcol, los ensilados, la salud de los animales y las pr&aacute;cticas de orde&ntilde;o.