The fact that smallpox is a man’s illness with no animal reservoirs played a crucial role in its effective eradication. Edward Jenner successfully established in the late 1700s that the cowpox virus might serve as a smallpox vaccine (Simonsen & Snowden, 2017). Although genetically different from cowpox, the roots of the vaccinia virus are unknown; it subsequently supplanted cowpox as a viral agent utilized for smallpox immunization. Before the elimination, there were more than 300 million deaths worldwide in the 20th century (Simonsen & Snowden, 2017). The average case mortality rate was around 30%, although survivors typically experienced significant morbidities such as blindness and skin damage. Smallpox was last observed spontaneously occurring in Somalia in 1977 (Simonsen & Snowden, 2017). Smallpox transmission occurs through direct contact with lesions, infected fomites, airborne respiratory droplet secretions, or both. The sloughing of oropharyngeal tumors and subsequent airborne contaminants of viral particles releases infectious viral particles. Transmission is possible from when lesions first appear until all shells have shed. Smallpox calls for increased infection prevention and isolation precautions and has been known to transmit airborne in hospital and lab settings.
Following the oropharyngeal or nasal viral entrance, the virus moves to nearby lymph nodes and replicates there. On days 3 to 4 following infection, there is an initial viremia, and the virus then spreads to the stem cells, spleen, and other lymph node chains (Simonsen & Snowden, 2017). Between days 8 and 12 following infection, a secondary viremia develops along with a fever and other symptoms of sickness (Simonsen & Snowden, 2017). This stage sees the appearance of a rash and clinically infectiousness as the virus localizes in the oropharynx mucosa and tiny blood vessels of a dermis.
Direct engagement with respiratory secretions from coughs and sneezes, fluids, or skin infections of an infected individual can result in the transmission of the variola virus from one person to another. Contact with infected bedding or clothing can potentially spread it. Animals or insects are not known to transmit the variola virus (Smallpox, n.d.). As soon as the first rash such as little red spots inside the mouth) develops, an individual with smallpox is infectious (Smallpox, n.d.). Until the final smallpox scab comes off, the afflicted individual is infectious.
References
Simonsen, K. A., & Snowden, J. (2017). Smallpox. StatPearls Publishing.
Smallpox. (n.d.). Virginia Department of Health. Web.