Why should dairy and beef producers look out for salmonella dublin?

Russ Daly

Do any of you remember a TV public service announcement from the 1970’s featuring an animated bacterial bad guy called “Sal Monella”? Sporting a nasty New York accent, he worked to contaminate an unsuspecting family’s food, only to be foiled by a knowledgeable housewife. 

Since my initial daytime TV introduction to salmonella as a food safety threat, I’ve lived with it as a cause of illness in my clients’ animals. Salmonella bacteria (over 2,400 different “serovars” of them) are widespread throughout animal species. Some are found in healthy animals, but others can cause severe illness.

It’s usually useful to know what serovar of salmonella is involved in cases of disease. Comparing strains among animals can help identify common infections and an ultimate source of the problem. Some salmonella serovars are more troublesome than others. Salmonella enteritidis can be a problem in poultry farms, and the reason we’re supposed to cook eggs thoroughly. Salmonella typhimurium can cause illness in many different livestock species. Most salmonella infections cause intestinal problems: diarrhea, dehydration, and fever. These illnesses are particularly harsh for young animals and can cause high mortality.

One salmonella serovar is getting more press in the cattle world lately: Salmonella dublin. Some veterinary diagnostic labs are seeing an increase in cases of salmonella dublin, and it’s also been implicated in an outbreak of human illness from contaminated ground beef. Of all the salmonella serovars that can affect cattle, dublin’s probably the nastiest. Unlike most salmonella, dublin causes pneumonia, septicemia (a devastating whole-body infection), and abortions in heifers and cows. Outbreaks can be devastating, and because it causes issues besides diarrhea, salmonella dublin problems are sometimes confused with other, more common diseases.

Salmonella dublin is considered “host-adapted” for cattle. This means the bacteria is well-suited to hang around the bovine body, instead of being noticed by and eliminated by the immune system. As such, salmonella dublin can enter a “carrier state” in cattle, where healthy-appearing animals harbor and spread the bacteria, mostly through their manure.

Antibiotics are our primary treatment tools for bacterial infections like salmonella, but a recent review of cases here at SDSU’s veterinary diagnostic lab shows that salmonella dublin strains are very resistant to antibiotics. In fact, for many recent cases, the only antibiotics deemed potentially effective were ones for which extra-label use is not legal.

A few of those SDSU salmonella dublin cases originated from beef cattle, but the vast majority came from dairy animals — especially calves. The germ’s ability to spread between animals and set up carrier states is particularly well-suited to dairy operations. Calves can become infected shortly after birth from a salmonella dublin-carrying mother. Severe pneumonia and septicemia takes hold days later and can spread between calves. As dairies “beef up” their breeding programs to create calves destined for the beef feedlot, it’s increasingly possible for salmonella dublin to find its way into beef herds.

Most salmonella dublin control measures focus on sanitation of the maternity pen, prompt removal of the calf, and extra attention paid to quality and quantity colostrum for new calves. Cleanliness of calf areas can reduce spread. Decreasing stress in transition cows and first-calf heifers helps reduce shedding and infection rates, too. The host-adapted nature of salmonella dublin makes the development of an effective vaccine difficult. Some herds resort to autogenous vaccines, with variable results.

In light of these challenges, keeping salmonella dublin out of a herd through biosecurity practices would be best. Identifying carrier animals among groups of incoming new animals is difficult, though. Isolating incoming animals will decrease stress-related shedding around the time of arrival, but it doesn’t guarantee a carrier animal won’t shed the bacteria after it’s entered the herd.

Finally, people working with livestock should recognize that they can get sick with salmonella themselves. Proper use of coveralls, boots, and gloves and washing hands is important, especially when working with sick animals.

When unusual cases of pneumonia or fevers hit calves, salmonella dublin should be on the list. As always, your first call should be to your veterinarian for diagnosis and treatment options, as well as for a plan to limit the spread of the germ to other animals.

Russ Daly

Russ Daly, DVM, is the Extension Veterinarian at South Dakota State University.