Anthrax facts — Select the true statement about Bacillus anthracis and the forms of anthrax in humans.

Introduction / Context:
Anthrax is a zoonotic disease of herbivores that occasionally affects humans through contact with infected animals or contaminated animal products. The etiologic agent is Bacillus anthracis, a spore-forming Gram-positive bacillus. Clinical forms include cutaneous, inhalational, gastrointestinal, and injection anthrax. Understanding transmission and infectious dose is critical for risk assessment and public health responses.

Given Data / Assumptions:

• We compare correctness of statements about causative agent, contagion, strain differences, and infectious dose.
• Human-to-human spread is rare to negligible.
• Spores are the infectious form; dose thresholds matter.

Concept / Approach:
Bacillus anthracis causes anthrax; it is not viral. Anthrax is typically not spread person to person; most cases result from environmental or occupational exposure to spores. The same species and overlapping lineages cause the various clinical forms depending on route of exposure and dose, rather than distinct specialized strains for each form. Inhalational anthrax requires exposure to a relatively large number of spores to overcome host defenses in the respiratory tract, making the statement about a large infective dose the best true choice here.

Step-by-Step Solution:

Verification / Alternative check:
Public health guidance describes inhalational anthrax onset after substantial aerosol exposure to spores, with estimates of infective dose being much higher than for many respiratory pathogens.

Why Other Options Are Wrong:

• Virus: incorrect; B. anthracis is a bacterium.
• Highly contagious: generally false; typical cases do not spread between people.
• Separate strains for forms: misleading; route and dose drive presentation.

Common Pitfalls:
Equating environmental stability of spores with ease of person-to-person transmission; the two are distinct.

Final Answer:
Inhalation Anthrax requires infection with a large number of spores