Why is it so dangerous to step on a rusty nail? - Louise Thwaites

In the 5th century, Greek physician Hippocrates, creator of the Hippocratic Oath, was sailing with a very ill shipmaster. The captain was suffering a nasty infection that caused his jaws to press together, his teeth to lock up, and the muscles in his neck and spine to spasm. Hippocrates dutifully recorded these symptoms, but he was unable to treat the mysterious disease. And six days later, the shipmaster succumbed to his illness.

Today, we know this account to be one of the first recorded cases of tetanus, and thankfully, modern physicians are much more prepared to handle this peculiar infection. Unlike other common bacterial infections like tuberculosis and strep throat, tetanus doesn’t pass from person to person. Instead, the offending bacterium, known as Clostridium tetani, infects the body through cuts and abrasions.

These infection sites are why tetanus is so strongly associated with rusty nails and scrap metal, which can cause such wounds, but the condition's connection to rust is actually much less direct. Clostridium tetani bacteria are often found in soil, manure, and dead leaves, where they can survive for years in the form of spores, even amidst extreme heat and dryness. These piles of organic material can sit undisturbed for long periods, potentially concealing old metal, which rusts over time.

So, if someone does blunder into this environment and cuts themselves, it would likely increase their odds of infection. Especially since rusty metal can create jagged wounds with lots of deoxygenated dead tissue for them to latch on to. Once in the body, the spores begin to germinate. This process releases several toxins, including deadly tetanus toxin. Nerve endings soak up this toxin, drawing it into the brain and spinal cord where it wreaks havoc on interneurons.

Typically, these work alongside motor neurons to regulate our muscle actions, from endeavors as complex as kicking a ball to those as simple as breathing. But by blocking neurotransmitters released by interneurons, tetanus toxin causes uncontrollable muscle contractions and spasms. Typically within 7 to 10 days of infection, patients begin experiencing general aches, trouble swallowing, and lockjaw. The head and neck tend to show symptoms first.

But as the toxin spreads, stronger muscle groups become more rigid, leading to a frightening arching of the back. Left untreated, these spasms become more extreme, eventually seizing the muscles in the windpipe and chest, leading patients to suffocate within 72 hours of symptoms appearing. Without treatment, tetanus has an extremely low rate of survival.

But fortunately, medical professionals have developed a robust plan to handle a tetanus diagnosis. First, doctors clean the infected wound and administer antibiotics, killing the bacteria and preventing further toxin production. Then, they inject antitoxin to neutralize any tetanus toxin still in the body that has yet to enter the central nervous system. Finally, patients begin a several week period of supportive care, which can include muscle relaxants to stop spasms and ventilators to prevent suffocation.

In the days of Hippocrates, the only course of treatment was to wait and hope. But now we know the best time to tackle Clostridium tetani is before an infection even takes place. Tetanus vaccines—originally developed in the early 1920s—are crucial to preventing tetanus and stopping its spread. Experts recommend a series of shots and boosters beginning at two months old and ending around age 12.

Yet over 20,000 infants still die of tetanus every year, mostly in low and middle income countries where vaccine access is limited, including South Asia and sub-Saharan Africa. And newborn babies are especially at risk if their mothers are unvaccinated, as Clostridium tetani can infect a newborn's umbilical stump. Though vaccinating mothers during pregnancy can help with this problem.

The fact is tetanus remains a significant threat to human health. So people should get vaccinated and take measures to prevent infection after cutting themselves—whether it’s on a rusty nail or a 2,400-year-old ship anchor.