Anthrax is one of the oldest killers of humans and livestock, mentioned in early recorded history several thousand years ago. It has been called by many names, including splenic fever, charbon, and woolsorter’s disease.

Anthrax is caused by a bacterium, Bacillus anthracis, and occurs sporadically in the U.S. and Canada. This disease occurs worldwide, associated with sudden death of cattle and sheep, though it can infect all warm-blooded animals. Because of human risk, anthrax is a reportable disease. Cases of anthrax in livestock must be reported to the state veterinarian or animal health agency.

Dr. Dustin Oedekoven—South Dakota state veterinarian and executive secretary, South Dakota Animal Industry Board—says there were seven cattle herds in South Dakota affected with anthrax in 2018.

“In all cases, the cattle had not been vaccinated. We remind producers that anthrax exists all across the state. It’s difficult to predict when and where we might see cases, so vaccination is the best prevention,” he says.

The vaccine is readily available and affordable. “When we see losses in a herd, there are generally multiple animals dying. The cost of annual vaccination is cheap insurance against the possibility of losing several animals to anthrax,” he says.

“We commonly see anthrax in South Dakota, North Dakota, and Minnesota and occasionally in other surrounding states. A few years ago, there were several herds affected in Colorado. There have also been cases in cattle in Montana and Wyoming.”

There were outbreaks a few years ago in bison in Montana, and there are periodic outbreaks in wildlife in Texas.

“People sometimes become complacent, especially if it’s been several decades since the disease occurred in their area, but it can crop out any time, so it’s good to include it in spring vaccinations. Annual vaccination is protective; it can be given in the fall if that’s the only time the rancher can vaccinate. Spring vaccination is probably best, however, in terms of how the vaccine is intended to be used, since summer is the most risky time for this disease,” says Oedekoven.

Risk factors

Anthrax spores can survive for many years, causing disease when conditions are right. “Some of those conditions include heat and high humidity. We often see anthrax when we have flooding or drought,” Oedekoven says.

Pastures may be contaminated by water from an area where there were infected carcasses at an earlier time. Low-lying ground or marshes are readily contaminated by flooding; stagnant water holes as the area dries again may serve as a source of infection.

“When grazing animals have exposure to alkaline soils—where the spores live quite well—either through flooding or drought, they may pick up spores while grazing,” Oedekoven continued. Hay contaminated with spores may account for outbreaks during winter, though anthrax is usually a warm weather disease. It may crop up in summer after springtime flooding.

The spores usually are picked up through the mouth. Anthrax can also be spread through skin wounds caused by blood-sucking insects, dehorning, or castration. Outbreaks have occurred because of contaminated feed, such as bone meal, meat scraps, or other animal protein products, but current regulations for manufacture and importation of these products eliminates these feeds as a source of infection in this country.

Ruminants seem to be most susceptible to this disease. The rumen seems to be a perfect environment (moisture, temperature, pH, etc.) for anthrax bacteria to incubate and start releasing toxins. Anthrax is sometimes seen in deer, elk, and other wild ruminants in certain regions from the Gulf of Mexico to the Northwest Territories of the Yukon. It probably existed long ago in the bison herds that grazed these areas.

The disease

Anthrax is generally not spread from live animal to live animal but is transmitted via spores in soil that’s been contaminated by the carcass of an animal that died from anthrax. Other animals may contract the disease by licking the carcasses of animals that died of it.

“Flies feeding on carcasses that died from anthrax can pick up blood and pass it on to the next animal they feed on,” Oedekoven says.

The spores vegetate in heat and humidity. The bacteria come to life and start reproducing in the infected animal, releasing toxins. The result is system-wide bleeding and rapid death. Most animals are not found in time to treat; they are simply found dead.

After the animal dies and the carcass is opened and the bacteria are exposed to the air, they form spores. These spores are very resistant to heat, cold, freezing, chemical disinfectants, or drying and can survive in contaminated soil a very long time—maybe 100 years or more in the right conditions. The original infected carcass may be long gone—torn apart by predators and scattered, or decomposed and disappeared many years ago, but the spores are still viable in the surrounding soil.

Carcass disposal

“We recommend that any time a producer has death loss in the herd, it’s a good idea to consult with a veterinarian—especially if multiple animals died without an obvious cause. Don’t necropsy the animal; a veterinarian can take a blood sample for testing first, if anthrax might be a possibility. Today the lab can do a rapid test to determine if it is anthrax or not. We don’t want the carcass opened because that will release more bacteria into the environment and allow more contamination and spread of the disease,” says Oedekoven.

“We want to dispose of a carcass quickly so there won’t be flies landing on it, and so there’s no chance for wildlife, dogs, etc. to drag the carcass around. In South Dakota we have a state law that requires burning and burying carcasses that are known or suspected to have died from anthrax,” he says. — Heather Smith Thomas, WLJ correspondent

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