Final answer:
Smallpox, caused by the Variola virus, is the only infectious disease that has been completely eradicated from the earth, thanks to a worldwide vaccination effort led by the WHO. It was officially declared eradicated in 1979, with the last diagnosed case in 1977. Efforts to eradicate polio are also underway and have been largely successful.
Step-by-step explanation:
The only disease organisms ever to have been completely eradicated from the earth is smallpox. Smallpox is a contagious disease caused by two Variola viruses and was unique to humans as its only carriers. The global eradication of smallpox was achieved in 1979 following a worldwide vaccination campaign spearheaded by the World Health Organization (WHO).
This remarkable achievement marked smallpox as the only human infectious disease to have been completely eradicated from nature. Following the success with smallpox, scientists and global health organizations have turned their attention with the hope of eradicating polio, a crippling viral disease that has been nearly annihilated thanks to extensive vaccination efforts.
While no new cases of smallpox have been diagnosed since 1977, its historical impact was significant, with fatality rates in past epidemics exceeding 50% in susceptible populations. The eradication of smallpox stands as a testament to the effectiveness of vaccines and coordinated public health strategies. Eradication of diseases such as polio and rinderpest is ongoing, with smallpox being the first microbial disease to be eradicated from the general population.