Salmonella dublin: What you need to know about an emerging disease threat in the calf industry

There’s a new, multi-drug resistant disease in Ontario and its affecting the province’s dairy and veal farms. Although Salmonella dublin predominantly affects cattle, it is also transmissible to humans as well as other livestock species, and can cause massive devastation in a herd with high levels of illness and death.

Dr. Dave Renaud

The disease has been present in New York State since the 1980s, Dr. Dave Renaud of the Ontario Veterinary College said in a presentation at the Building the Foundation 2016 Dairy and Veal Healthy Calf Conference, but it has entered Quebec in recent years with cases spread throughout that province.

A 2015 surveillance study of 169 dairy herds in Quebec found that almost nine per cent of herds across the province had at least one suspect or seropositive cow on the farm.

“The first case of Salmonella dublin was diagnosed in Ontario in 2012, and it’s an immediately notifiable disease in Ontario,” Renaud said, explaining this means veterinarians must report diagnosed cases of the disease to the Ontario Ministry of Agriculture, Food and Rural Affairs.

There have been 23 confirmed cases in Ontario since that first diagnosis, found on 15 farms mostly in southwestern Ontario and mostly on veal farms. The largest number of cases to date was discovered in 2015, with 2016 showing the second largest number of cases.

There is a wide variety of clinical presentation, Renaud said, but it can most often look like pneumonia or septicemia. There is no diarrhea, which is a sign of other forms of Salmonella, but it can cause abortions in mature cows.

“The key thing you see is poor response to treatment, for example you’ll treat for pneumonia but the animal is not responding,” Renaud said, adding about half of Ontario’s Salmonella dublin cases initially present as pneumonia.

Clinical signs are most prevalent in young animals around two months of age, with 60 per cent of Ontario cases affecting calves two to five months old.

Three-quarters of the strains are multi-drug resistant, which means poor response to treatment and high levels of mortality. Spread is caused by cattle movement from farm to farm, with transmission by so-called carrier animals that are infected but show no signs of the disease.

“The bacteria can survive well in the environment and produces life-long sub-clinical carrier animals that are shedding it in their feces or milk,” Renaud stated. “This spreads or maintains infection on-farm and if you introduce a carrier to a naive herd, it causes a massive outbreak.”

Spread within a farm stems from fecal-oral transmission with calves showing signs of the disease typically infected at calving. Feeding raw milk to calves is also risk, especially from hospital cows or recently fresh cows, he cautioned.

According to Renaud, diagnosis of the disease is complex and depends on the purpose (confirming the disease or identifying infected herds or carrier animals), the age of the animals and the timing of the infection, as it takes six to 12 days after infection for an animal to generate an antibody response.

Infected herds and live animals can be identified through a blood or milk test. These blood and milk tests are currently available in the United States. When a suspect animal with Salmonella dublin dies, a post-mortem must be completed for diagnosis, where samples are sent to a lab for bacterial culture.

Identifying carrier animals, by comparison, is very difficult as they show no clinical signs and more research is needed in this area, Renaud said.

Key to preventing the disease is reducing a herd’s exposure by maintaining strict biosecurity, he advised. This includes:

  • Maintaining a closed herd or buying only from low risk herds
  • Quarantining new arrivals as cattle tend to shed most when they are stressed
  • Minimizing the stress of newly arrived animals
  • Having a clean, well-sanitized maternity area
  • Avoiding adult to calf contact
  • Minimizing fecal contamination
  • Limiting bird, rodent and waterfowl exposure
  • Disinfecting and clean high risk areas – this is critical because the bacteria survives well in the environment

Although vaccines exist, they’re not available in Canada and there isn’t great evidence of their efficacy, Renaud said.

If the herd is infected, it’s important to break the fecal-oral transmission link. Quarantine newly-arrived animals, clean and disinfect anything in the livestock environment that could help spread the disease and handle all animals as though they are infected.

“Remember that Salmonella dublin is zoonotic, so it can infect you as well. Wash your hands and if you’re visiting other farms, change your coveralls and wash your boots,” Renaud advised. “And if you have animals with signs of Salmonella dublin, contact your herd veterinarian.”

More information is available from Veal Farmers of Ontario, as well as fact sheets by University of Madison and Cornell University.