Which biological agent is known for its high mortality rate and ability to disseminate easily?

The variola virus, responsible for smallpox, is known for its high mortality rate and its ability to spread easily among populations. Historically, smallpox has had a mortality rate of about 30% in those infected, making it one of the deadliest infectious diseases. Its transmission can occur through direct contact with infected individuals and contaminated materials, as well as through respiratory droplets, which enhances its potential for rapid dissemination.

In the context of bioterrorism and biological warfare, smallpox is particularly concerning because there is no natural immunity in populations where vaccination has ceased, following the disease's eradication in the late 20th century. The availability of smallpox vaccination in some populations does not negate the fact that a large outbreak could occur quickly in an unvaccinated populace, leading to significant fatalities.

Other biological agents mentioned, such as botulinum toxin and Clostridium difficile, pose serious health risks but do not have the same level of mortality rate or potential for rapid spread. Salmonella is primarily a foodborne illness that, while significant, does not have the same implications for high mortality or ease of dissemination as variola virus does. Thus, the characteristics of the variola virus clearly identify it as the agent of choice in this context