Smallpox is the only human disease to have been eradicated. Smallpox was certified as eradicated in 1980. The last case of smallpox in the United States was in 1949. Eradication of disease is eliminating a particular disease worldwide due to public health efforts to eliminate the disease - basically through vaccination. Extinction is another concept related to disease control. Disease extinction is when the infectious agent (virus, bacteria, protozoa, etcetera) no longer exists, not even in a laboratory or nature. To date, there are no human diseases that have become extinct. Smallpox virus is kept in two laboratories worldwide (for research purposes, one in Russia at a government laboratory and one at the C.D.C.). For disease eradication to be possible certain conditions need to be met. Humans need to be the only reservoir. The disease cannot have an animal or insect reservoir or be found in the soil or water. Also, there needs to be a way of eliminating the disease, such as a vaccine. And surveillance of the disease needs to be possible. There needs to be a sensitive laboratory test to detect the disease if cases occur. To support disease eradication efforts, there needs to be a public health system to make it happen, and available funding for the costs of doing so. And there needs to be a desire in society and among political systems worldwide to eradicate the disease. Suppose countries are uninterested in eliminating the disease and do not participate in disease eradication efforts. In that case, eradicating that disease will not be possible. Smallpox eradication required massive vaccination campaigns globally, with most people becoming vaccinated. Ring vaccination was used, which is vaccinating the contacts of smallpox cases. Additionally, disease monitoring/ surveillance was needed to eradicate smallpox, as was contact tracing to identify more cases that could be vaccinated to prevent the further spread of smallpox. Contact tracing makes ring vaccination possible. And containment of smallpox cases with isolation was utilized and necessary. The variola virus causes smallpox, a D.N.A. virus also known as the smallpox virus. Smallpox is spread from person to person primarily by respiratory droplets but is also transmitted by direct contact with fluid or blood from skin lesions. Smallpox causes fever and a unique skin rash consisting of many small bumps on the skin. Red spots on the tongue and mouth appear before the onset of the rash. The rash starts on the face and then quickly spreads to the trunk and extremities, covering the entire body. The smallpox rash can be terrible. When the rash starts out, there is often a dent in the center of the pox lesion. Later the pox bumps become firm pustules and then crust and scab over as the rash ends. People remain contagious with smallpox until all scabs fall off, which usually takes four weeks. After the scabs fall off, the person is often left with marks on the skin where the rash was. Smallpox has a 30% case fatality rate, with death most likely caused by sequelae related to an overwhelming viremia. Persons with Smallpox exposure should receive post-exposure prophylaxis consisting of smallpox vaccination within four days of exposure to prevent disease transmission. Smallpox is a category A biologic agent. Category A biologic agents are classified as Category A because they:

• Can be easily spread from person to person (disseminated or transmitted).
• Cause many deaths (have a high case fatality rate) and are a significant public health threat.
• May cause public panic and disturb society's well-being.
• Require public health prepared action planning.

References:

Dowdle WR, Cochi SL. The principles and feasibility of disease eradication. Vaccine. 2011;29 Suppl 4:D70-D73. doi:10.1016/j.vaccine.2011.04.006

Dowdle WR. The Principles of Disease Elimination and Eradication. MMWR. December 31, 1999 / 48(SU01);23-7

Fenimore VL, Orenstein WA. Principles of Disease Elimination and Eradication. In: Boulton ML, Wallace RB. eds. Maxcy-Rosenau-Last Public Health & Preventive Medicine, 16e. McGraw Hill; 2022. Accessed January 02, 2022.

CDC | Bioterrorism Agents/Diseases (by category) | Emergency Preparedness & Response