Escherichia coli O157

E coli O157 is one of many strains of the bacteria, E coli. A few of the E coli strains cause disease while many do not. For instance, some E coli cause toxic forms of mastitis while others cause scours in baby calves. E coli O157 is commonly thought of as the "hamburger" E coli because some of the initial human outbreaks were traced back to undercook hamburgers. Other sources are raw milk and juices, vegetables, drinking water, swimming ponds and sick people. The bacteria cause human disease by producing toxins. While O157 bacteria present an insignificant disease problem to cattle, it causes diarrhea, cramping, vomiting and urinary problems in people. E coli O157 currently is the most significant cause of kidney disease in children.

O157 can be found on most dairies, however; only a few animals will be shedding the bacteria in their manure at any one time. It is most easily found in weaned calves. Adult cattle are the least common shedders of all cattle types, but market cattle can shed significant amounts in their feces. On the dairy, E coli O157 is often found in water troughs and wet feeds. It is more commonly found on dairies with flush alleys, during warmer months and in improperly cured silages. Few control measures have been tested on dairies. Some measures that might reduce the amount of E coli O157 on the dairy are :

1. to frequently clean water troughs
2. chlorinate water troughs
3. insure proper silage preparation
4. compost manure to be used for bedding.

Salmonella

Salmonella bacteria can be found in many cattle as well as humans, birds and reptiles. There are over 2,300 types of salmonella, many of which are shared by humans and animals. Human food borne outbreaks have been traced to milk, beef, pork, and poultry as well as vegetables and eggs. Salmonella typhimurium DT104 has recently increased the level of concern, as it may be resistant to 5 or more of the commonly used human antibiotics.
In cattle, salmonella cause diarrhea, decreased milk production, abortions and sometimes death. Some salmonella such as Salmonella dublin affect primarily calves while others like Salmonella typhimurium attack adult animals. Carrier cows, especially during time of stress like around calving, can spread salmonella in their manure wherever they go on the dairy. Salmonella infections can be reduced by:

1. veterinary herd health programs focused on judicious drug use and preventive vaccinations
2. not allowing fresh cows to commingle with sick cows in the hospital pen
3. pasteurization of colostrum and waste milk fed to calves
4. vigilant attention to sanitation of milk feeding equipment and utensils
5. refrigeration of calf milk feeds.

Listeria

Listeria monocytogenes is one of the causes of "circling disease" in cattle. With Listeria infections, cattle often show generalized sickness with abnormal behavior and posture such as circling or head pressing. These sporadic cattle diseases are felt to originate in poorly fermented silages. In humans, this bacteria causes a flu-like illness of ten with nausea, vomiting and diarrhea. In some cases, there are neurological signs and abortions. Both carrier animals and human exist without showing signs of disease. The common sources of human infections are raw milk, cheeses or meats as well as foods contaminated during processing or food preparation. This bacteria grow readily at refrigerator temperatures therefore a small amount of contamination may become an infective dose as the food is stored in the refrigerator.

Since the disease in cattle is associated with poorly fermented silages, some measure of prevention can be gained by carefully preparing silages, checking silage pH periodically and by avoiding feeding obviously spoiled silage. Cattle with signs of neurological disease should never be shipped to slaughter.

Campylobacter

Even though Campylobacter jejuni is rarely a cause of serious illness in animals, it is the leading cause of sporadic food borne illness in humans. Campylobacter are common in the intestine of animals and birds and therefore found in their manure. As with other human food borne illnesses, the common signs are diarrhea and cramps. It often occurs in infants and young adults and is sometimes followed by chronic problems and Guillain-Barre syndrome. Human sources of campylobacter are fecal contamination of poultry skin, meat, milk and water. Asymptomatic human carriers can also contaminate foods during processing. Reduction of farm animal contamination is difficult, as the on-farm reservoirs are numerous and the mode of transmission remains unknown.

General Control Measures

While the routes of transmission of the bacteria from on-farm sources to animals are not well delineated, some general control measures may help to reduce the number of market dairy cattle going to slaughter carrying these important food borne pathogens:

1. Complete composting and deep stacking of manure may reduce bacterial numbers.
2. Minimize re-cycling of water from lagoon into cattle housing areas.
3. Irrigate forage crops with lagoon water long before they are to be harvested for cattle feed.
4. Avoid re-cycling lagoon water through the sprinkler pens.
5. Protect water troughs from manure contamination.
6. Clean and sanitize water troughs often and regularly.
7. Reduce chances of feed contamination from rodents and birds.
8. Avoid hauling dead animals or manure in front end loaders used with feeds.
9. Restrict entry to your dairy to prevent introduction of new pathogens.
10. Utilize veterinary herd health programs to control disease and minimize carriers.
11. Keep fresh cows out of hospital pens.

Increasingly, the burden of preventing contamination of human foods is being transferred closer and closer to the farms of origin. Currently the focus is on the slaughterhouses where market dairy cattle are shipped and where the raw food is processed and packaged for distribution. The slaughterhouse operators are now thinking of ways to reduce the numbers of contaminated market cows arriving at their facilities. In the future, they may ask dairymen to help them control these bacteria on their dairies though on-farm food safety programs. It is not too early to begin to consider steps you might take on your dairy.