According to Dr. Simon Peek from the University of Wisconsin – Madison School of Veterinary Medicine, Salmonella Dublin is showing up more often than any other strain of salmonella bacteria in the samples that come to the Wisconsin Veterinary Diagnostics Laboratory as well as the National Veterinary Services Laboratory. He confirms, “It’s clear Dublin is becoming the most common serotype that’s isolated and identified.”
Dublin is one of the sneakier serotypes of salmonella bacteria because it does not show itself with the clinical signs displayed by other strains. While diarrhea in calves or late-term abortions in cows are often the symptoms that lead to a diagnosis of Newport or Typhimurium strains, Dublin does not necessarily follow suit.
“More subtle manifestations, particularly in calves, make it difficult to pinpoint and diagnose when it first appears on the farm,” Peek says.
He explains S. Dublin can still present itself as a devastating outbreak with diarrhea and reproductive and production losses, but it can also emerge as respiratory disease in post-weaned calves, swollen joints and general unthriftiness.
“It loves to get in the bloodstream and go other places, and one of the other places it thrives is in the joints,” Peek adds.
In other instances, it can cause persistent fevers that, even after treatment, never quite truly develop into full-blown pneumonia or scours. Here within lies one of the dangers of this salmonella serotype: Animals that survive the infection will go on to be carriers and never actually clear it from their systems. Even if they don’t have diarrhea or clinical symptoms, they will continue to shed it in milk, colostrum, manure and sperm. There is little evidence, however, of contraction in utero.
“Perhaps one in five or one in 20 of Salmonella Dublin-infected cattle will become carriers for life if they don’t die from the infection,” Peek says. “That’s the difference between S. Dublin and other serotypes.”
Peek says the current definition of an S. Dublin carrier is an animal that has shown three strong positive ELISA blood test results over an eight- to nine-month period, but he warns producers to allow time for multiple test results because a maternally derived antibody can interfere with test results. “Don’t jump the gun and assume a positive test indicates a carrier,” he urges. Ideally, testing should be done three times, three months apart, between 3 months and 1 year old for the most accurate diagnosis of carrier status.
Other testing methods include a combination of fecal sampling and a polymerase chain reaction (PCR) test using manure, milk or colostrum, depending upon what the specific lab offers.
To control S. Dublin and reduce the risk of disease transmission, dairy producers can follow specific protocols for cows and calves that promote hygiene and sanitation and reduce the transmission of bodily fluids:
Control key points for calves:
- Remove newborn calves promptly after birth.
- Only feed pasteurized colostrum and waste milk.
- Dedicate personnel to maintaining strict hygiene with calves.
- Recognize the weaning period is a high-risk time for disease transmission.
- Discuss protocols and testing with calf or heifer raisers.
- Discuss the pros and cons of using a specific S. Dublin vaccine with the herd veterinarian.
- Do not power wash enclosed calf facilities.
Follow these protocols for disinfecting and cleaning: Wisconsin Veterinary diagnostic laboratroy - Proper cleaning and disinfection post confirmation of Salmonellosis.
Control key points for cows:
- Maintain a closed herd or purchase only animals with a negative ELISA status.
- House sick cows separate from transition cows.
- Minimize overcrowding.
- Avoid common use of equipment for manure and feed handling.
- Periodically test animals 2 years old and older, and identify carriers.
- Separate carriers by pen.
- Do a quarterly bulk tank test for negative-status groups or herds.
Dr. Simon Peek presented during the 2018 Vita Plus Dairy Summit, Dec. 4-6, 2018 in Red Wing, Minnesota.
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Peggy Coffeen
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