¹Veterinary Medicine Extension, School of Veterinary Medicine
University of California Davis, Tulare, CA

²California Department of Food and Agriculture, Animal Health Branch
Disease Program, Sacramento

Anthrax is as old as antiquity. The Bible speaks of "the plague, which caused sudden death in livestock". The Animal Health Branch—Emergency Disease Programs has historical records dating from 1926 showing 34 anthrax outbreaks in 12 counties of California. During 1984, an anthrax outbreak occurred in the Carrisa Plains that affected 12 general areas, and killed 43 cattle and 135 sheep. Since 1991, there have only been 10 known cases of anthrax in California livestock, nine of which occurred in cattle.

Anthrax has recently been the topic of several news articles addressing concerns about vaccinating soldiers in the US military, bioterrorism threats and naturally occurring disease outbreaks in cattle. For instance, following sudden cattle deaths, anthrax has been diagnosed on five farms in Manitoba with about 25 deaths, on two farms in Minnesota with about 15 deaths and in 17 North Dakota herds with approximately 100 deaths. Other deaths have been recently reported in South Dakota and Nebraska. While deaths from anthrax occur sporadically ever year, these outbreaks in the Midwest are somewhat unusual. The purpose of this article will be review anthrax primarily as it occurs cattle so that livestock owners may be aware of the signs and risk factors of anthrax in cattle.

The bacteria, Bacillus anthracis, cause anthrax. The bacteria are found in two states — the vegetative state and the spore state. The vegetative state is the growing, reproducing form of the bacteria found in infected animals and people. The vegetative form is the state that causes the disease, anthrax. If untreated the disease in animals is generally fatal. After an animal dies from anthrax, if the carcass is opened by a veterinarian during a necropsy, scavengers or by decay, the vegetative state is exposed to oxygen in the air. When the vegetative state is exposed to oxygen in the air, it forms spores. The spores are highly resistant to disinfectants and remain viable for years in the soil. The spores are found naturally in the soil of California and many western states. When the spores enter another animal, usually through grazing contaminated vegetation or inhaling spores, the bacteria revert to the disease causing vegetative form.

In cattle, the most initial sign of anthrax is animals found suddenly dead. The course of the disease is usually short at 1-3 days. Once an outbreak begins, animals may be seen with fever, lack of rumination, excitement followed by depression, difficulty breathing, 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 treated very early with penicillin or tetracyclines.

In animals that die, bloody discharges from the body openings are commonly found. 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. Enlargement of the spleen is almost always present. An open, decaying carcass as well as discharges and secretions from the carcass or dying animals will contaminate the ground and protected spores will develop. Scavengers or well-meaning veterinarians seeking to the learn the cause of death may also open the carcass. Carrion-feeding animals may carry the infection to other distant locations. The vegetative form of the bacteria dies rapidly in unopened carcasses.

Most outbreaks occur in areas where animals have previous died of anthrax, as the spores remain viable for many years. Spores over 35 years old have been able to cause the disease. Often, the outbreaks occur after climatic changes such as heavy rain, flooding, or drought. Climatic changes bring spores to the ground surface and perhaps concentrates the spores in low spots. Working the land may also bring the spores up to the soil surface. Once the animals eat the spores, the vegetative develops, multiplies and is ready to cause anthrax again. In August 2000, an anthrax outbreak in Nevada killed 30 cattle. This outbreak was associated with a recent ditch cleaning, which may have disturbed spores deep in the soil.

When anthrax is suspect, dead animals should not be opened for routine examination, as the discharges and blood are highly infectious to humans and other animals. As previous state, open carcasses will deposit enormous quantities of bacteria on the ground that will sporulate to the long lasting, protected state. Your veterinarian can confirm anthrax by taking blood from a peripheral vein (ear or tail) and submitting it to the diagnostic laboratory. The bacteria can be seen in the blood when properly smeared and stained on a glass slide.

In many states, anthrax is a reportable disease meaning that your veterinarian will have to inform the state agency when cases of anthrax are suspected. Quarantine of the premises and animals may be necessary. To prevent spread of an outbreak, where possible, dead animals should be burned where they are found dead. An alternative is to bury them at a depth of 10 feet and cover the carcass with lime. The 1984 Carrisa Plains outbreak was associated with movement of an infected band of sheep and dumping the carcasses from this band in several locations. Your state animal health agency can provide helpful advise on disposal of carcasses. Proper carcass disposal is important to prevent surface soil contamination. Vaccines are available to protect animals in endemic areas or when outbreaks occur.

Always keep in mind that anthrax can cause serious disease in humans as well as animals. Three syndromes are recognized in man. The cutaneous form is usually seen in people who work with animal carcasses, wool, hides or fur. The infections are seen as large, local abscesses often on the hand or finger. These skin infections can spread to the blood stream and cause serious illness or death. Inhaling the bacteria causes the pulmonary form. Most lung infections result in rapid death. The intestinal form results from eating the bacteria and is seen as violent intestinal pain with vomiting and bloody stools. A high mortality rate is seen with the intestinal form of anthrax. For this reason, great care should be taken to protect anyone handling the carcass or live animals suspected to have anthrax. Meat obtained from animals dying of unknown causes, or suspected of having anthrax or another infectious disease, should not be consumed.

In summary, anthrax is cause by bacteria that can exist in two forms. The vegetative form causes disease in both animals and man but is rapidly killed in unopened carcasses. The spore form lives for years in the soil. When the spores surface, they revert to the vegetative form to cause further disease when eaten by animals. Carcasses of animal dying with anthrax should not be opened as the vegetative form turns to spores when exposed to air. Suspected cases of anthrax should be reported to your veterinarian first and then to state animal health agencies. Animal health officials are available 24 hours a day to assist your veterinarian in managing an outbreak and minimizing losses. Use caution when handling dead animals suspected to have anthrax. For more information, call the CDFA, Animal Branch in your area.