I always thought anthrax was man made:

Scores of bison found dead during anthrax monitoring in N.W.T.

The Canadian Press

FORT PROVIDENCE, N.W.T. The Northwest Territories government is warning people to stay away from 128 dead bison that were found during a routine flight to monitor anthrax. The animals were discovered Tuesday near Mills Lake northwest of Fort Providence. The territory says samples are being sent to the Canadian Food Inspection Agency lab in Lethbridge, Alta., for testing. Humans can develop skin, respiratory or intestinal infections if they contract anthrax from an infected animal. Anthrax can be fatal but is controllable if promptly treated with antibiotics. The disease is caused by a bacterium that, once introduced into an area, leaves spores that can remain viable in the soil for many years. Under certain conditions such as wet weather followed by a hot, dry spell, the spores become concentrated in low-lying areas. Bison usually contract the disease by inhaling contaminated soil while they are wallowing in dust baths. Anthrax is not normally spread from animal to animal. There have been two documented outbreaks of anthrax in the Northwest Territories between 1962 and 2010.

Anthrax is an acute disease caused by the bacterium Bacillus anthracis. Most forms of the disease are lethal, and it affects both humans and other animals. There are effective vaccines against anthrax, and some forms of the disease respond well to antibiotic treatment.
Like many other members of the genus Bacillus, Bacillus anthracis can form dormant endospores (often referred to as "spores" for short, but not to be confused with fungal spores) that are able to survive in harsh conditions for decades or even centuries. Such spores can be found on all continents, even Antarctica. When spores are inhaled, ingested, or come into contact with a skin lesion on a host, they may become reactivated and multiply rapidly. Anthrax commonly infects wild and domesticated herbivorous mammals that ingest or inhale the spores while grazing. Ingestion is thought to be the most common route by which herbivores contract anthrax. Carnivores living in the same environment may become infected by consuming infected animals. Diseased animals can spread anthrax to humans, either by direct contact (e.g., inoculation of infected blood to broken skin) or by consumption of a diseased animal's flesh. Anthrax spores can be produced in vitro and used as a biological weapon. Anthrax does not spread directly from one infected animal or person to another; it is spread by spores.These spores can be transported by clothing or shoes. The body of an animal that had active anthrax at the time of death can also be a source of anthrax spores.
Until the twentieth century, anthrax infections killed hundreds of thousands of animals and people each year worldwide, particularly in the concentration camps during WWII. French scientist Louis Pasteur developed the first effective vaccine for anthrax in 1881. Thanks to over a century of animal vaccination programs, sterilization of raw animal waste materials, and anthrax eradication programs in North America, Australia, New Zealand, Russia, Europe, and parts of Africa and Asia, anthrax infection is now relatively rare in domestic animals (with only a few dozen cases reported every year). Anthrax is especially rare in dogs and cats, as is evidenced by a single reported case in the USA in 2001. Anthrax typically does not cause disease in carnivores and scavengers, even when these animals consume anthrax-infected carcasses. Anthrax outbreaks do occur in some wild animal populations with some regularity. The disease is more common in developing countries without widespread veterinary or human public health programs.
Bacillus anthracis bacterial spores are soil-borne, and, because of their long lifetime, they are still present globally and at animal burial sites of anthrax-killed animals for many decades; spores have been known to have reinfected animals over 70 years after burial sites of anthrax-infected animals were disturbed.