Which one of the following viruses used to be responsible for highly infectious disease Smallpox ?

Smallpox is a highly infectious and serious disease caused by the Variola virus, a member of the Poxviridae family and Orthopoxvirus genus [1][3][5]. The virus exists in two primary forms: Variola major, which is more lethal, and Variola minor, which is less severe. Smallpox is characterized by fever and a distinctive progressive skin rash that leaves permanent scars [1][3]. It is historically significant as the first human infectious disease to be successfully eradicated worldwide, a feat certified by the World Health Assembly in 1980 following a global vaccination campaign [3][5]. While other viruses like Adenovirus cause respiratory infections and Coxsackie virus causes hand-foot-and-mouth disease, only the Variola virus is the causative agent of smallpox [2]. The virus is an obligate human pathogen with no natural animal carriers, making its eradication possible through human vaccination [1].

Sources

1. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 8: Natural Hazards and Disaster Management > Smallpox > p. 80
2. [3] https://www.ncbi.nlm.nih.gov/books/NBK470418/
3. [5] https://www.sciencedirect.com/topics/neuroscience/poxviruses
4. [2] https://www.cdc.gov/smallpox/about/index.html