Anthrax in Animals
Livestock Update, December 2001
W. Dee Whittier, Extension Veterinarian, Cattle, VA-MD Regional College of Vet. Med.
Anthrax has historically been an important disease in cattle and sheep in the US. Effective control methods have decreased significantly the number of cases of anthrax in domestic animals so that it has become a rare disease in most areas of the US. Currently South Dakota, Arkansas, Louisiana, Texas and California have the highest incidence of the disease in livestock.
Cattle and sheep are the most susceptible to anthrax. Horses and goats also get the disease but are more resistant and dogs and cats are apparently quite resistant.
A 1955 survey of anthrax losses in livestock in 1955 showed nearly 20,000 US cases in the prior 10 years. However, by the 1960's one hundred cases or less a year were reported. The reasons for the decrease are believed to include better quarantine and hygiene when outbreaks do occur, use of antibiotics and vaccination.
Anthrax has sometimes been called "wool sorters disease". This because there have been historical outbreaks of the disease in people working in woolen mills in the US. These were generally associated with imported wools. Experts now believe that these infected wools may have been harvested from animals that had died of anthrax and hence were highly contaminated with the organisms.
Outbreaks of anthrax in livestock are thought to usually be associated with spores that came from other animals dying of the disease. Because these spores do not form until some time after the animal dies the disease is not contagious. These spores, tiny encapsulated forms of the organism, may survive in the environment for many years (37 years in one case). Flooding of areas where carcasses from anthrax infected animals decomposed carries spores to low-lying pastures where many severe outbreaks of the disease have occurred.
The anthrax organisms can enter the body through a cut in the skin, by being inhaled or by being eaten or drunk. In studies, much smaller doses of the anthrax will cause infection if the organism is airborne and then inhaled. In actuality, however, the most common route of infection for livestock occurs by ingesting the spores when they contaminate feeds. Thus it is easier for livestock to get the disease by inhaling it rather than consuming it, but since having airborne spores is rare most livestock actually get the disease by eating the spores.
Sudden death is the most common observation when livestock become infected with anthrax. Following an incubation of 1-14 days (usually 3-7 days) animals develop high fevers and become very ill. Most die with hours of developing the disease. Bloody discharges from the mouth, nose, anus and other body openings are common. Bodies of animals dying from anthrax contain huge numbers of the anthrax organism at death.
Veterinary personnel should examine any animal dying suddenly. Preventing predation of the carcasses will limit the number of spores that enter the environment. If anthrax is suspected samples are typically examined before an entire autopsy is performed since this will also limit the number of spores that are formed to contaminate the area.
In summary, anthrax is a disease that has become relatively rare in US livestock. Its major manifestation is sudden death. Any case of sudden death in domestic animals should be investigated.