Salmonella Dublin: A big deal

Salmonella has reared its ugly head in our area in late summer and early fall.  Particularly, our clinic has experienced more cases of Salmonella Dublin in dairy calves. While we see it on farms year round, there always seems to be an increase of cases as summer comes to an end. I’m not sure why, though I suspect it is related to heat and humidity. It also appears that S. Dublin is on the rise in the Midwest. In a 2022 summary of salmonella isolates at the Wisconsin Veterinary Diagnostic Laboratory, there were more cases of S. Dublin in cattle than any other type, a trend observed at other labs.

So what does S. Dublin look like and why is it a big deal? S. Dublin is host adapted, meaning it can hide in carrier animals that appear normal for long periods of time. In my experience, there are two “typical” presentations of S. Dublin infections in dairy herds.  The first is in pregnant heifers and cows, causing late term abortions. The second is in pre-weaned and weaned calves, where the disease presents as pneumonia with high fevers and the calves do not respond well to treatment. Occasionally calves will also have joint infections. In some instances, the mortality rates can be high despite treatment. Also, S. Dublin is nearly always multi-drug resistant, leaving few options for antibiotic treatment.

There are some specific challenges when dealing with S. Dublin outbreaks. First, the disease is zoonotic, meaning people can get infected. Second, diagnostic testing requires good sample and test selection. Third, control of S. Dublin relies on several management factors, not just on vaccination or treatment. Though I won’t touch on it in this article, adequate calf nutrition is also very important in preventing and controlling S. Dublin outbreaks.

S. Dublin can be shed in manure, milk, saliva, urine, semen and vaginal secretions of infected and carrier animals. Therefore, hygiene and sanitation are key to reduce new infections.  Though I have not experienced human infections with S. Dublin in the herds I work with, I always caution farm staff to take extra care with wearing gloves and handwashing when working with sick calves or suspected abortions.

Additionally, cleanliness of people, clothing and equipment are important to reduce spread across the farm. I would encourage producers to think about how they might “walk” salmonella around the farm or even to their homes. Can employees change into street clothes and wash work clothing at the farm? Is anyone consuming raw milk or other raw dairy products on farm? Do all employees wash their boots or change their gloves before entering maternity or calf areas after working in cow pens? Is there unnecessary foot traffic in calf areas that increases calf exposure to manure? Is machinery or equipment shared between cow pens and calves? Are cows and calves hauled in the same trailers without cleaning in between?

Diagnosis is usually made through a combination of sick calf presentation and necropsies of calves that have died. Though we believe it is shed in feces, it can be hard for diagnostic laboratories to detect in fecal samples therefore fecal testing can be unreliable. I would highly recommend necropsying calves that die of unknown causes, especially if there is an increase in pneumonia cases or calf deaths on the farm. I recommend the same strategy if abortions have increased. There are other testing methods for blood, bulk tank milk and environmental samples, but I have had the most success with testing tissues from necropsies. Work with your veterinarian or diagnostic lab to create a testing strategy that works best for your farm.

Control factors that should be considered include pasteurization of colostrum and waste milk (if used), regular cleaning and disinfection of maternity pens, newborn calf areas, calf pens and other calf feeding or moving equipment. Rinsing with water is not the same as disinfection. Use proper cleaning methods that include hot water and soap followed by a disinfectant. The University of Wisconsin Veterinary Diagnostic Lab website has specific salmonellosis disinfection protocols that are feasible to implement for on farm use and could be used to control any disease. Finally, colostrum management for passive transfer in calves is paramount in controlling disease. Holes in the farm’s colostrum program will inevitably lead to further disease despite other control methods. Our clinic has used vaccination of dry cows with commercial and autogenous vaccines to aid in the control of disease in calves, in which we rely on colostrum and passive transfer to help protect the calf until she is old enough to be safely vaccinated.

With good calf husbandry, cleaning protocols, proper nutrition, and a solid colostrum program, you can help mitigate the risks of a S. Dublin outbreak on your farm.

Megan Weisenbeck is one of six veterinarians at Northern Valley Livestock Services in Plainview, Minnesota. She practices primarily dairy production medicine in Minnesota and Wisconsin. Megan can be reached at [email protected].