’Tis the season for anthrax vaccine

News
Apr 22, 2011

A wet spring can be a mixed blessing. While it gives crops and forage a head start, it can also pave the way for a silent killer—anthrax. Anthrax spores can lie dormant in the soil for years, causing no problems for the animals that graze there. It can lie in wait for 70 years or more, impervious to heat and cold. A wet spring can provide the conditions that make anthrax spores available for exposure to grazing livestock.

"The conditions this spring are definitely favorable for anthrax," said Jeff Ehrenfried, a veterinarian with Oahe Vet Clinic in Fort Pierre, SD.

While a wet spring can create positive conditions for anthrax, a drought can have the same effect. Ehrenfried said the spores are sometimes churned up by wind and the cows’ feet when conditions are dry. Some speculate that in dry years when there’s less grass, the cattle graze closer to the ground, consuming more dust and increasing their exposure to anthrax spores. Whatever the conditions that bring it into contact with cattle, veterinarians agree that it’s easier to avoid than predict or treat.

Anthrax is caused by spore-forming bacteria and affects herbivores most severely. Cattle can get the disease by ingesting the spores from the soil while grazing. Flies are also suspected of carrying the spores from one animal to another. Early symptoms of anthrax infection include fever, staggering and difficulty breathing. Often, the disease progresses so quickly producers don’t know they have a problem until they see sudden death of multiple animals, says South Dakota state veterinarian Dustin Oedekoven.

"The most effective way to manage the disease is through annual preventive vaccination, as unvaccinated animals tend to die suddenly after exposure, with no opportunity for treatment," Oedekoven said. If the disease is caught in the early stages, animals respond well to antibiotics, but producers rarely see the symptoms in time to treat it.

Producers in the area potentially affected by anthrax, which includes the Midwest and western states and reaches into Texas, should plan to vaccinate for anthrax every year, Oedekoven said. Producers in South Dakota, North Dakota, and Minnesota should be especially vigilant about vaccinating for the disease, Oedekoven said, because those states tend to see higher incidences of anthrax.

Oedekoven encourages producers to make sure an anthrax vaccine is part of their spring shot regimen and says that now isn’t too early to start. "Texas has already had their first case of anthrax," he said. The vaccine for anthrax is a stand-alone, modified live vaccine, and should be used according to local veterinary guidance.

Ehrenfried, who has dealt with more than 20 cases of anthrax, agrees, saying he encourages all of his clients to vaccinate their cows when they get the cows in for branding or pre-breeding shots. He says that in the outbreaks he’s seen, the disease hasn’t affected the calves, so advises his clients that vaccinating calves still on the cow isn’t necessary. He recommends vaccinating the cows yearly, and vaccinating yearlings in the spring. "It’s one of the cheapest vaccines on the market, at less than a dollar a head, and it’s very effective. There’s no reason for anyone not to vaccinate for anthrax," he said. He estimates that about 80 percent of his clients take that advice. "Even on places that have never had a case of anthrax, it’s best to vaccinate to be on the safe side. You never know when the conditions are going to be just right for anthrax to make an appearance," he said.

Definitive diagnosis of anthrax must be done in a laboratory, as bovine symptoms alone can result in anthrax being confused with clostridial infections, bloat, lightning strike, acute leptospirosis, bacillary hemoglobinuria, anaplasmosis, and acute poisonings by bracken fern or sweet clover, lead poisoning, and other conditions.

Once a loss is attributed to anthrax, the exposed herd must be quarantined for 30 days after the last carcass is disposed of, according to South Dakota rule. The dead animals and any contaminated bedding, feed and manure must be promptly disposed of by burning and deep burial, as the disease can spread to carnivores that will feed on the carcasses. Sick animals must be isolated and well animals must be removed from the affected area and treated with a long-acting antibiotic to kill any incubating disease. The people who are carrying out these tasks must observe special sanitary measures to avoid exposure to the spores. Ehrenfreid recommends that the people who are handling the disposal and treatment of animals wear protective clothing that they remove and isolate before they leave the area.When a herd contracts anthrax, the effects are devastating. The numbers reported—55 cases, two cases, three cases, can be misleading because those numbers are herds that are affected, not numbers of animals. Ehrenfreid said in the cases he’s seen, the numbers of cattle affected have varied from one to more than 40 per herd. While one or two cases of anthrax doesn’t carry much of a sense of urgency or tragedy, for those one or two producers, it means thousands of dollars in animal loss, disposal and other indirect costs.

Beyond beef

Virtually no species of animal is unaffected by anthrax. Sheep that have ingested anthrax exhibit many of the same symptoms as cattle. Horses that have been exposed to anthrax spores have symptoms that may include fever, chills, severe colic, anorexia, depression, weakness, bloody diarrhea, and swelling of the neck, sternum, lower abdomen, and external genitalia. Death usually follows within two to three days. Pigs are relatively resistant, but may still die from exposure to the spores. Wildlife are also affected.

Profitability is not the only thing at stake in the fight against anthrax. Since the disease can also be transmitted to humans, it becomes a human health issue. Humans can contract anthrax by breathing the spores, absorbing spores through open wounds, or eating raw or undercooked meat from animals carrying the disease. Many of the anthrax cases among humans were historically the result of exposure to spores that were carried on wool or cow hides. In South Dakota, skin infections, which happen when a cut or scrape is exposed to the anthrax spores, are the most common concern to humans dealing with anthrax infected livestock. The conditions are successfully treated with antibiotics if given early attention, Oedekoven said.

A vaccine is available for people who deal with anthrax regularly, or are in danger of coming into contact with it in cases of biological warfare, like soldiers. In general, humans are not as susceptible to the effects of the spores as animals, so accidental exposure is usually not as serious for humans, as long as they have access to medical care.

Ehrenfreid said he recommends everyone who comes into contact with the animals affected by anthrax talk to their physician about steps they should take. When he was frequently exposed to the disease, his physician did some research, but established that they didn’t need to do anything but stay alert for any signs of the disease.

Since the meat industry in the U.S. is so well-regulated, there is little concern of exposing humans to anthrax through meat. In Africa, however, because of cultural, economic and epidemiologic reasons, as many as 10 people may be infected by each infected cow.

History

For decades in South Dakota, anthrax was of little concern. Occasional cases arose and were dealt with. In 2005, northeastern South Dakota was dealing with flooding and the rest of the state was trying to cope with yet another year of drought. When the floodwaters receded and the grass came up in creekbeds, stock dams and the shores of Lake Oahe that had been under water for years, anthrax was thriving.

Between July 21 and mid-November of 2005, losses attributed to anthrax were reported in 55 herds across the state. The state Animal Industry Board set in motion a producer-awareness campaign using the media, producer meetings and contact with local veterinarians to educate producers and encourage them to immediately administer anthrax vaccine to their herds.

The following year, South Dakotans reported two cases, thanks to the increased use of vaccine. Since then, the highest number of cases reported was three in 2008, and 2010 saw no losses from anthrax. Oedekoven says as anthrax cases diminish and it is no longer a newsworthy subject, producers will eventually stop vaccinating for it, which leads to the conditions for another outbreak. "Complacency is common among generations that have not seen anthrax or do not recall their parents or grandparents having to deal with it," Oedekoven said.

Nationally, anthrax made the news in 2001 when it was used as a tool of bioterrorism. It was mailed to several members of Congress, killing five people who came into contact with it. Agricultural exposure in the U.S. rarely results in human fatalities. — Maria E. Tussing, WLJ Correspondent

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