Zoonotic risks of pathogens from sheep and their milk borne transmission

Graphical abstract Sheep and goats were domesticated around 9000 BC in the Middle East. Milk from sheep is very popular in many populations and areas. Taste and high fat content of cheeses from sheep milk make them popular. In many countries, dairy products from sheep and goats are consumed by children and people with allergies to cow milk. Other regions of the world, are not suitable for cows and goats, and sheep milk is an essential part of local daily diet. Consumption of raw milk and raw milk products have a zoonotic risk. The main pathogens associated with sheep milk are: Brucella melitensis, Campylobacter spp., Coxiella burnetii, Leptospira spp. Listeria spp., Salmonella spp., Shiga-toxin producing Escherichia coli, tick borne encephalitis, Toxoplasma gondii, and Rift Valley fever. This risk of these pathogens can be reduced by proper flock health management, prevention of contamination during milking and adequate milk processing, transport and storage. In small scale production systems there is a higher risk, compared to industrialized production systems because of a less protocolled and controlled production process. Especially s, young children, elderly people, pregnant women and immunocompromised (YOPI) persons, and those suffering from disease should be aware of the risk of consuming raw milk and raw milk products. Therefore, strict hygiene practices throughout the production process and supply chain in combination with stringent periodic control of these products should be applied. Although pasteurization influences the taste of milk, it sufficiently reduces zoonotic risks while not negatively influencing the nutritional value. This manuscript describes major and minor pathogens that might be transmitted in milk from sheep. Also, unintended contamination and multiplication and prevention thereof are described. We summarize some major human outbreaks caused by consumption of milk from sheep and finally discuss the implications.
Sheep were domesticated around 9000 BC in the Middle East, and since then milk from sheep gradually became very popular, not only for drinking but also for making cheeses and other dairy products. Nowadays, these dairy products are also important for people with an allergy to cow milk, and these products are an essential part of the local daily diet in regions of the world that are not suitable for cows and goats. Consumption of raw milk and raw milk products has a zoonotic risk, and with regard to sheep, the main pathogens associated with such dairy products are: Brucella melitensis, Campylobacter spp., Listeria spp., Salmonella spp., Shiga-toxin producing Escherichia coli, Staphylococcus aureus, tick borne encephalitis virus, and Toxoplasma gondii. Especially, young children, elderly people, pregnant women and immunocompromised (YOPI) persons, and those suffering from disease should be aware of the risk of consuming raw milk and raw milk products. This latter risk can be reduced by proper flock health management, prevention of contamination during milking, adequate milk processing, transport, and refrigerated storage. Only processes equaling pasteurization sufficiently reduce zoonotic risks from milk and milk products, but proper cooling is essential and recontamination must be prevented. Therefore, strict hygiene practices throughout the production process and supply chain especially for raw milk and raw dairy products, should be applied. Small scale production systems pose a greater risk compared to industrialized production systems because of a less protocolized and controlled production process. This manuscript describes zoonotic risks of pathogens from sheep and their milk borne transmission. Additionally, routes of contamination, possibilities for multiplication, and prevention measures thereof are described. We summarize some major human outbreaks caused by consumption of sheep milk and products made thereof, and finally discuss their implications.