Louis Pasteur once said that “it is within the power of man to eradicate infection from the earth”. Yet more than a century later, we have eradicated only smallpox in humans. Even the World Health Organization has limited its eradication ambitions to a few diseases, such as polio, measles, rubella, Guinea worm disease, and yaws, currently. Most other diseases are approached with the more cautious goal of elimination, rather than eradication. Pasteur’s statement, in hindsight, underestimated the complexity of biology. While some diseases are subject to human control, many coexist with us in ways that make their permanent disappearance impossible.
Eradication vs elimination
In public health, eradication refers to the permanent elimination of a disease, resulting in zero cases worldwide, with no further interventions required. Once achieved, routine vaccination and surveillance can safely stop. Smallpox is the only human disease (and rinderpest in animals) to have been eradicated. Elimination refers to reducing a disease to zero cases in a defined geographical area or to a number that is so low that it no longer poses a significant threat to public health, while continued efforts are necessary to prevent reintroduction. A country/region may eliminate a disease, but the disease may still exist elsewhere.
Eradication criteria
For a disease to be eradicated, it must be infectious, and certain conditions must be met. The causative organism must be clearly identifiable and biologically stable without mutations. There must be an effective intervention capable of preventing the disease, such as a vaccine or medication. Once medicated or vaccinated, there should ideally be lifelong immunity. The disease should be easily diagnosable so that surveillance can detect every case. Crucially, the mode of transmission must be completely understood, and the organism should not be able to survive outside of humans.
Checklist with tetanus
Smallpox fulfilled all these criteria perfectly. At first glance, tetanus seems to fit many of these same conditions. The bacterium responsible, Clostridium tetani, is well understood and biologically stable. A highly effective vaccine is available, and treatment with immunoglobulins, along with supportive care, is well established. The disease is clinically distinctive, and its mode of transmission is completely understood. There are no hidden carriers, no asymptomatic spread, and no person-to-person transmission. Every case arises through a clearly defined mechanism. Paradoxically, this complete understanding is precisely why tetanus can never be eradicated.
Unlike smallpox, Clostridium tetani does not depend on humans to survive. It exists freely in soil and dust, and persists in the intestines of animals as spores, causing no disease in them. Through animal faeces and environmental contamination, its spores are continuously replenished in nature. These spores are extraordinarily resilient, surviving extreme temperatures and harsh conditions for years. Vaccinating humans does not interrupt this cycle. There is no transmission chain to break, because humans are not the bacterium’s natural reservoir. The organism is embedded in the environment itself.
A second exception lies in immunity. Natural tetanus infection does not produce protective immunity. The toxin responsible for the disease is so potent that even tiny quantities can cause severe illness. Yet, those quantities are insufficient to stimulate lasting immune memory. Survivors remain fully susceptible to reinfection. Vaccine-induced immunity is effective but temporary, which is why booster doses are required throughout life.
Thus, environmental persistence and the absence of durable immunity place tetanus permanently outside the ambit of eradication.
How tetanus develops
Tetanus is a toxin-mediated disease rather than a classical invasive infection. When spores enter a wound through a penetrating injury caused by a contaminated object and encounter an oxygen-poor environment, they germinate and release tetanospasmin, a potent toxin. This interferes with normal nerve signalling, leading to sustained muscle contractions. Clinically, the disease begins with stiffness in the jaw and neck, progressing to painful, generalised spasms. Breathing may become compromised as chest muscles lock into rigidity. Consciousness is preserved, making the illness particularly distressing. Even with modern intensive care, tetanus carries a 10% mortality rate. Without treatment and vaccination, the death rate is higher.
Tetanus is unique among microbial diseases because despite being caused by a bacterium, it is not transmitted from person to person. It does not spread and does not produce outbreaks in the conventional sense. Each case occurs independently when environmental spores enter a wound. Tetanus behaves more like a non-communicable disease triggered by exposure rather than a communicable disease driven by transmission. This unusual epidemiology explains why eradication is impossible.
Burden of tetanus
Each year, an estimated 30,000 to 40,000 deaths occur worldwide, the majority in low- and middle-income countries. These deaths (though declining from previous decades) highlight the persistence of risk where vaccination coverage and healthcare access remain uneven. In India, the number of tetanus cases has fallen sharply due to the success of childhood immunisation and maternal vaccination programmes. Neonatal tetanus has been eliminated since 2015. However, adult tetanus persists, particularly among older adults and those who have missed booster doses.
Tetanus illustrates the difference between what can be eliminated and what cannot be eradicated. Neonatal tetanus is eliminated through clean delivery practices and immunisation of women. Tetanus incidence can be driven to zero in defined settings. More broadly, elimination requires sustained high vaccination coverage across the life course, regular booster doses, safe wound care, and robust health systems. These measures prevent disease without removing the bacterium from nature.
Limits of science
Pasteur’s vision remains inspiring, but tetanus reminds us that not all microbial battles are fought on human terms. Eradication would require eliminating tetanus spores from the soil itself, which is an ecological impossibility. Complete understanding of transmission, immunity, and ecology does not always lead to eradication. Sometimes, it leads to a deeper realisation of limits. Tetanus may disappear only in a world without soil, animals, or anaerobic niches, a world unlike our own. Until then, success lies not in erasing the disease from existence, but in ensuring that it no longer claims lives.
(Dr. C. Aravinda is an academic and public health physician. The views expressed are personal. aravindaaiimsjr10@hotmail.com)
Published – January 03, 2026 12:35 pm IST
