Which disease was caused by the variola virus prior to its eradication in 1975?

The disease caused by the variola virus prior to its eradication in 1975 is smallpox. Smallpox is a highly contagious and often deadly disease characterized by fever, body aches, and a distinctive rash that develops into fluid-filled blisters. The causative agent, the variola virus, led to significant morbidity and mortality throughout history, prompting extensive vaccination efforts. Its eradication is a landmark achievement in public health, underscoring the effectiveness of the vaccine developed to combat this virus.

The other diseases listed—mononucleosis, bubonic plague, and tetanus—are caused by different pathogens: mononucleosis is typically caused by the Epstein-Barr virus, bubonic plague is caused by the bacterium Yersinia pestis, and tetanus is due to the toxin of Clostridium tetani. Therefore, these options are unrelated to smallpox and the variola virus.