Anthrax: Always a possibility here in the Dakotas

We’ve spent a lot of time over the past couple months learning about and tracking some animal diseases that most of us have never heard of before, let alone experienced firsthand. Cases of avian influenza continue to pop up in the area, and lately we’re becoming aware of a new strain of influenza in dogs. They serve as a reminder that viruses and bacteria are constantly changing in the ways they make our animals sick.

While these new diseases certainly catch our attention, we can’t lose sight of the ailments that have threatened our animal populations for years. For example, one of the oldest maladies of cattle is still something we deal with on an almost yearly basis here in the Dakotas: anthrax.

For decades and even centuries, veterinarians and cattle producers have recognized anthrax as a potential cause of death loss in beef cattle on pasture. The disease hit our state early this year, being diagnosed in a couple of replacement heifers in central South Dakota back in late March.

The bacteria that causes anthrax, Bacillus anthracis, can exist in a very resistant spore form in the soil, able to survive years of Dakota winters and summers. Wherever the disease has hit in the past, the spore could still be present in the soil. If the soil in these areas is disrupted by excavation or flooding, or if cattle graze droughted pastures close to the ground, the spores can be more easily taken in by cattle. We normally see anthrax cases in the summer, as hot humid conditions cause more of these spores to become active. The dry, relatively warm spring probably contributed to the cases in late March.

Once the spores are eaten by the cow, they get through the gut wall into the local lymph nodes. It’s here where the spores change into active bacteria and spread throughout the body. These bacteria produce toxic substances that result in shock and rapid death. The onset of illness is so rapid that usually the only sign of anthrax is simply cattle being found dead on the pasture.

Despite the persistence of the spore in the soil over time, it’s not always predictable where the disease will hit. Most areas of North and South Dakota have experienced cattle death losses due to anthrax at some time in the past, which makes it a possibility any time in the future. However, not all of these locations experience losses every year, and cases show up in different locations every year. Weather conditions play a role, as does the vaccination status of cattle grazing those areas. If our dry conditions continue into the summer, it’s possible that we may see an uptick in the number of anthrax cases. Pastures that have experienced flooding or standing water are also at risk. When the water recedes, those once-wet areas may be places where spores are now washed up and available to be eaten by an unsuspecting animal.

But there’s one thing we can reliably predict about anthrax in South Dakota, and that’s the fact that it will show up somewhere. In eight of the past ten years, anthrax has been diagnosed somewhere in the state. Fortunately, we have a very effective tool to prevent anthrax in cattle – the anthrax vaccine. It is inexpensive and widely available from veterinarians. One dose prior to turnout to summer pasture protects animals throughout the grazing season.

If cattle are already out on summer pasture and it’s too late to feasibly vaccinate them, producers then need to be vigilant about death losses on pasture. When producers find unexplained death losses of cows or bulls on pasture, the carcass should be left undisturbed until a veterinarian can take an appropriate sample. An animal that has died from anthrax can serve as a source for a tremendous number of new spores in the environment once the body is opened up or moved. The nature of anthrax is possibly the most important reason that sudden, unexplained death losses in cows or bulls on summer pasture should be promptly investigated by your veterinarian.

Russ Daly, DVM, is the Extension Veterinarian at South Dakota State University. He can be reached via e-mail at russell.daly@sdstate.edu or at 605-688-5171.