How is it spread?
Most times salmonella bacteria's "route of entry" into a "host ( human or animal)" is "oral", i.e., the host ingests salmonella bacteria directly ("fecal-oral") or indirectly ("fecal-fomite/food-oral"). For example it is possible to come into direct contact with manure if dirty hands are used to wipe your face/mouth/eyes, when smoking, or even to get splashed with manure in the face from a cow's tail. It is also possible to indirectly come into oral contact with Salmonella on a fomite (inanimate object) that has been contaminated with salmonella bacteria, such as a soiled cigarette, a cup, a pen placed into the mouth, and
especially when eating food or drinking fluids contaminated with fecal matter. For a cow, most often they ingest salmonellae in their water or feed, or they come into oral contact with the barn environment (various surfaces, freestall floor, etc.).
Conditions under which salmonella survive in the environment?
Salmonella bacteria love wet environments shielded from the sun.
They have the remarkable ability to survive under adverse conditions. They survive between the pH's of 4 to 8+, and can grow between 8 and 45 C. Salmonella are facultative anaerobic bacteria that can survive under low oxygen tension such as in manure slurry pits. Salmonella are known to survive for long periods in soil and in water. Salmonellae spread onto fields in the form of manure may survive for long periods; it is best to spread the manure onto flat land (to prevent runoff problems) where it is exposed to the drying effects of wind, and to the bactericidal effect of UV irradiation from the sun; manure should be spread onto cropland rather than onto pastures for grazing. There has been much recent investigation into the advantages of different manure disposal methods; composting has many advantages from the standpoint of controlling disease. Salmonellae are no more or less sensitive to the effects of commonly used disinfectants than are other fecal bacteria. Chlorine solutions, iodines, quaternary ammoniums, phenolics, etc., are very good at killing salmonellae on surfaces; however, efficient scraping/dry cleaning is important to get rid of organic matter and bedding, followed by wet cleaning with high pressure hot water/steam and then disinfection. The interval between wet cleaning and disinfection must not be too long or salmonellae can "bloom" in the wet environment. Many strains are relatively resistant to the effects of drying, salting, and smoking of foods. However, salmonellae are very sensitive to beta and gamma irradiation.