Anthrax is a serious zoonotic disease that can affect most mammals and several species of birds, but is particularly important in herbivores.

Etiology

Anthrax results from infection by Bacillus anthracis, a spore forming, Gram positive, aerobic rod in the family Bacillaceae.

Transmission

In animals, transmission occurs by ingestion and possibly inhalation of spores, although entry through skin lesions has not been ruled out. Herbivores usually become infected when they ingest sufficient numbers of spores in soil or on plants in pastures. Outbreaks are often associated with heavy rainfall, flooding, or drought. Contaminated bone meal and other feed can also spread this disease. Carnivores usually become infected after eating contaminated meat. Vultures and flies may disseminate anthrax mechanically after feeding on infected carcasses.

Clinical Signs

In animals, anthrax can be a peracute, acute, subacute, or chronic disease.
In ruminants, peracute systemic disease is common, and sudden death may be the only sign. Staggering, trembling, and dyspnea may be seen in some animals, followed by rapid collapse, terminal convulsions, and death. In the acute form, clinical signs may be apparent for up to 2 days before death. In this form, fever and excitement may be followed by depression, stupor, disorientation, muscle tremors, dyspnea, and congested mucous membranes. Pregnant cows may abort, and milk production can drop severely. Bloody discharges from the nose, mouth, and anus are sometimes seen.

Prevention

In endemic areas, modified live vaccines can prevent anthrax in livestock. Livestock are vaccinated annually, before the season when outbreaks generally occur. Livestock vaccines have also been used to protect cheetahs and endangered ruminants, including black rhinoceros.