Abstract
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.
Highlights
Foodborne diseases cause a significant burden on public health and the economy
Zoonoses include many diseases transmitted to humans by routes other than food, and are reported to affect over 380,000 European Union (EU) citizens each year (EFSA, 2011; Lahuerta et al, 2011)
Dairy cows represent a suitable reservoir for L. monocytogenes; a reduction of the intestinal carriage rate in livestock herds would contribute to reducing the contamination risk at the slaughterhouse (Esteban et al, 2009; Adam & Brülisauer, 2010)
Summary
Foodborne diseases cause a significant burden on public health and the economy. The World Health Organization estimates that unsafe food sickens one in three people every year worldwide, but the actual incidence of foodborne illness is probably much higher (Buckley & Reid, 2010). Pasteurisation has significantly reduced the zoonotic risks from contaminated dairy products, outbreaks of illness continue to result from post-processing contamination and consumption of raw milk products (Van Kessel et al, 2011). Transmission of these strains to both humans (Lopez et al, 2006) and animals (Bundrant et al, 2011) may occur through various routes, mainly through food or feed, and directly from other infected humans or animals, as well as a consequence of the greater dissemination in the environment due to the spread of organic wastes/effluents from dairy farms (Swaminathan et al, 2007; Van Kessel et al, 2011) (Fig. 1).
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