What causes tetanus?

The correct answer is based on the understanding of tetanus as a serious bacterial infection caused primarily by the bacterium Clostridium tetani. This bacterium is commonly found in soil, dust, and animal feces, and it usually enters the body through wounds, especially deep puncture wounds that create a low-oxygen environment where the bacteria can thrive. Once inside the body, the bacterium produces a toxin that affects the nervous system, leading to severe muscle stiffness and spasms.

In contrast, the other options represent different causes of illness. A virus transmitted through air generally refers to respiratory infections, where airborne viruses spread through respiratory droplets. A fungal infection involves pathogens like molds and yeasts, which typically differ in mode of infection and the symptoms they cause. A genetic disorder is an inherited condition that results from abnormal genes or chromosomes and is unrelated to environmental pathogens like bacteria. Understanding these distinctions helps clarify why the presence of the bacterium through wounds is specifically responsible for tetanus and why the other causes do not apply in this context.