Anthrax and Livestock
Revised by John Wenzel
College of Agricultural, Consumer and Environmental Sciences, New Mexico State University
Author: Extension Veterinarian, Department of Extension Animal Sciences and Natural Resources, New Mexico State University. (Print Friendly PDF)
What Is Anthrax?
Anthrax is a disease of warm-blooded animals, including humans, most livestock, and some wildlife species. It is caused by the spore-forming bacteria Bacillus anthracis. Herbivorous animals are highly susceptible to anthrax, while carnivores are more resistant. The incubation period is not known, but it probably ranges from one to 14 days (Coetzer and Tustin, 2004). In livestock, the disease is usually peracute to acute, resulting in death in one to three days. By the time an animal displays signs of disease, including staggering, trembling, convulsions, or bleeding from body openings, death usually follows quickly. Body temperatures may reach as high as 107°F. The disease occurs in cattle, sheep, goats, horses, and mules. In swine and dogs, anthrax generally occurs as a less acute form. They are more resistant than herbivores and become infected by ingesting heavily contaminated meat of animals that have died of the disease.
The anthrax bacteria are found in two forms, the vegetative state and the spore state. The vegetative state, which is the growing, reproducing form found in infected animals, actually causes the disease. If the carcass of an animal that has died from anthrax is opened during necropsy, or by scavengers or decay, the vegetative state is exposed to oxygen. This allows the vegetative state to form spores. The spores are highly resistant to disinfectants and the weather and may remain viable in the soil for as many as 50 years. When the spores enter an animal, usually by grazing contaminated vegetation or inhalation, the bacteria revert to the disease-causing vegetative state.
Photo courtesy of John Wenzel.
How Common Is Anthrax?
Anthrax is a naturally occurring disease. Although there has been a progressive global reduction in livestock cases in response to national control programs, anthrax still occurs worldwide. It is considered uncommon in most of western Europe, Canada, the U.S., and Australia, and relatively common in southern and eastern Europe, several former U.S.S.R. countries in Central Asia, southern and central America, and Africa (Coetzer and Tustin, 2004). In New Mexico, cases occur infrequently every few years. It has occurred recently in deer and cattle in southwestern Texas counties along the Rio Grande. One theory is that many areas of the country were “seeded” with anthrax spores during the great cattle drives of the 1800s. Sporadic cases still occur in the U.S. when favorable climatic conditions result in susceptible livestock becoming exposed to the spores.
Anthrax primarily occurs in alkaline soils with high nitrogen levels caused by decaying vegetation, alternating periods of rain and drought, and temperatures in excess of 60°F. Such areas are referred to as “incubator areas,” where the spores apparently revert to the vegetative form and multiply to infectious levels when optimal environmental conditions occur. Obviously, spores will be found in soils in areas where it has been diagnosed previously.
Anthrax is much like blackleg (Clostridium chauvoei), another cattle disease. Blackleg, also a spore former, is found in most soils. Both diseases are unique in that the spores can lie dormant in the soil for many years, and then suddenly the disease reoccurs in grazing animals. Even in endemic areas, anthrax occurs irregularly, often with many years between outbreaks. It is not well understood why the disease suddenly reappears, but it probably occurs in response to environmental changes. In the case of blackleg, cattle grazing short vegetation during a drought consume more soil and, therefore, more organisms. In the case of anthrax, increased periods of rainfall and flooding followed by drought seem to be ideal conditions for reoccurrence. Also, any disturbance of the soil can result in the release of spores.
What Are the Symptoms in Cattle?
In the peracute form of the disease, death can occur in less than two hours (Coetzer and Tustin, 2004). In cattle, the most common course of anthrax is the acute form of the disease, which is usually short (one to three days). Generally, the initial sign of anthrax is sudden death. Once an outbreak begins, animals may exhibit fever, lack of rumination, excitement followed by depression, difficult breathing due to pulmonary edema (fluid accumulation in the lung tissue), uncoordinated movements, convulsions, and death. Bloody discharges from the natural body openings, as well as edema in different parts of the body, are sometimes observed. Some animals may be saved if antibiotic treatment starts early.
In animals that die, bloody discharges from body openings are common. Decomposition is more rapid than in other conditions, and the carcasses become bloated with gases. Rigor mortis or stiffening is not complete. When necropsied, hemorrhages are found in the internal organs. The spleen is almost always enlarged.
What to Do if Anthrax Is Suspected
Never open the carcass of an animal suspected of dying from anthrax. The discharges and blood are highly infectious to humans and other animals. Opened carcasses will deposit enormous quantities of bacteria on the ground that will sporulate to the long-lasting, protective form. A veterinarian can confirm anthrax by taking blood from a peripheral vein and submitting it to a diagnostic laboratory.
Inhaling bacteria can cause the pulmonary form of the disease in humans. So, great care should be taken to protect anyone who handles carcasses or live animals suspected of having anthrax. All livestock producers should keep a supply of shoulder-length disposable gloves for handling animals that show symptoms of infectious disease. Meat obtained from animals dying of unknown causes or suspected of having anthrax should not be consumed.
In New Mexico, anthrax is one of 26 reportable diseases affecting livestock that have considerable economic impact. When a reportable disease is suspected or diagnosed, the attending veterinarian must, by law, report it to the New Mexico Livestock Board’s State Veterinarian (https://www.nmlbonline.com/animalhealth). This ensures that the proper authorities are notified and a containment system can be put into place. The authorities will assist ranchers in proper disposal of carcasses, either by burning or burial.
Carcasses should be isolated from other livestock and pets and protected from scavengers as much as possible, but remember that minimal handling of the carcass is essential.
Treatment of Livestock with Anthrax (Coetzer and Tustin, 2004)
In domestic animals, specific treatment is indicated in all clinical cases. Treatment is recommended even in advanced cases that may terminate in death because treatment will greatly reduce, if not terminate, the infecting load of bacteria, thereby reducing possible subsequent contamination of the environment. In advanced cases, antibiotic treatment delays, but does not prevent, death. It is vitally important to quarantine the area where an outbreak is occurring to prevent the spread of the disease.
Can Humans Be Infected from Soil Spores?
Yes. However, spores in the soil generally are not ingested or inhaled by humans. They do not “float in the air” in abundance like the “germ warfare” types.
What Are the Symptoms of Anthrax in Humans?
Symptoms of the disease vary depending on how the disease was contracted. Symptoms usually occur within seven days.
Cutaneous: Most anthrax infections occur when the bacteria enter a cut or abrasion on the skin, such as when handling contaminated wool, hides, leather, or hair products of infected animals. The disease is often referred to as “woolsorters’ disease.” Skin infection begins as a raised, itchy bump that resembles an insect bite, but within one to two days it develops into a vesicle (a small blister) and then a painless ulcer. Ulcers are usually 1/2 to 1 1/2 inches in diameter, with a characteristic black area in the center. Other symptoms, such as swollen glands, fever, and malaise, often develop after several days if left untreated. About 20% of untreated cases of cutaneous anthrax result in death, but deaths are rare with appropriate antibiotic treatments.
Inhalation: Initial symptoms may resemble a common cold and include a cough, chills, and aches. After several days, however, the symptoms may progress to severe breathing problems and shock. If left untreated, inhalation anthrax is usually fatal.
Intestinal: The intestinal form of anthrax may follow consumption of undercooked, contaminated meat. It is characterized by an acute inflammation of the intestinal tract. Initial signs of nausea, loss of appetite, vomiting, and fever are followed by abdominal pain, vomiting of blood, and severe diarrhea. Intestinal anthrax can result in death in 25–60% of cases. However, the chances of anthrax contaminating our food supplies are very small. The relatively short incubation time, coupled with the rapid onset of the disease and quick death, all work to make it unlikely that meat from diseased animals will enter the food chain in any form. Under no circumstances should meat from infected animals be consumed. Spores can resist steaming or boiling for five minutes, but are killed by autoclaving at 248°F for 20 minutes.
Can Infected Livestock Infect Humans?
This probably is an ineffective way of spreading anthrax to humans. Animal-to-animal is not a primary method of transmission. The general method is by inhaling or ingesting spores. However, caution should be exercised when handling carcasses of animals that have died of the disease because they contain large reservoirs of spores. The disease can also be transmitted by consuming undercooked meat. Should an outbreak be diagnosed in an area, great caution will be taken by the proper health authorities to ensure that affected animals are isolated, a vaccination program is put in place, and carcasses are disposed of properly.
For Further Reading
B-121: Biosecurity on the Beef and Dairy Operation
B-229: Immunity and Serum Neutralization Titers for Cattle
B-230: Trichomoniasis in Beef Cattle
B-230: Tricomoniasis en el ganado de carne
John C. Wenzel is the Extension veterinarian in the Extension Animal Sciences and Natural Resources department at NMSU. He earned his B.S. from NMSU and his DVM from Kansas State University College of Veterinary Medicine. His work focuses on cow/calf medicine and preventative health programs for livestock producers in southwestern New Mexico.
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Revised September 2019 Las Cruces, NM