Disease History

Smallpox has been noted as one of the most deadly human diseases. It has killed more people than certain wars and, in a 100 year period, was responsible for a death toll bigger than the populations of Canada, Mexico, and the United States combined.

Evidence of smallpox has been discovered in Egyptian mummies as far back as 1350 BCE. This ancient disease is caused by the Variola virus. “Smallpox” is derived from the Anglo-Saxon word “pocca” meaning “bag” or “pouch.” The disease was originally called “pockets” until around the 1500’s when it was officially recorded as “smallpox” in order to distinguish between it and the “Great” Pox aka syphilis. The virus name, “Variola,” comes from the Latin words “varius” which means “spotted” and “varus” meaning “pimple.”

Variations of the Variola Virus

There are two types of the smallpox virus—these include Variola major and Variola minor. Variola major is around 90% of smallpox infections. This type gives the infected persons severe symptoms and a high fatality rate. There is also a few different subsets of Variola major that determine the type of smallpox. These types are: Ordinary (this is the majority of cases), Flat / Severe (this is less than 7% of cases but has a 97% fatality rate), Hemorrhagic / Severe (this is less than 3% of cases but if contracted is 99% fatal), and Modified (less than 2% of cases and only occurs in individuals who have been vaccinated but is rarely fatal). Variola minor is a lesser version of the two. This type has less severe symptoms and a much lower death rate (around 12%).

Breakdown and Transmission

When broken down, smallpox is caused by a double stranded DNA virus genus called Orthopoxvirus. This genus includes: Variola virus, Vaccinia virus, Cow Pox virus, and Monkey Pox Virus. Contrary to popular thought, this disease is actually unrelated to Chicken Pox (varicella zoster virus) because it belongs to a strain of the herpes virus.

Smallpox is transmitted by means of air particles and through direct contact. There is no animal vector or reservoir species. This means that for as long as smallpox has been around, there has been a direct, unbroken chain of person to person transmission and infection. When a person becomes infected, they are estimated to further infect between two and five other people. The infected particles that are in the air enter the respiratory tract and invade mucous membranes and lymph nodes.


For the first seven to seventeen days after infection, the virus begins to replicate silently while producing no symptoms. The infection then enters the “Prodromal Phase” which lasts for about two to three days. The symptoms at this point in the infection process are severe headaches, backaches, and fever. Next, a rash of small bumps form on the tongue, mouth, and throat. The day after this rash emerges, the rash breaks out over the entire body and for the first few days it resembles chicken pox. The rash starts out as macules (flat discoloration spots) and then transitions to papules (raised bumps) and then finally to vesicles (large raised bumps). Once present, the vesicles turn into large, tough pustules that fill with puss (this is actually a sign that the immune system is making an attempt at fighting off the infection).

If the infected person survives, the pustules begin to crust and scab and after about a week, the scabs fall off. If the case is a more severe type, scarring follows in about 60 – 85% of cases. Additionally, 2 – 5% of individuals will then develop blindness or have a limb deformity.


A successful smallpox vaccine was not developed until the late 1700’s. Up until that point, the popular treatments of the disease was inoculation and variolation. These methods used scabs and puss particles from infected persons and applied them to healthy individuals. Since survival of smallpox guarantees lifelong immunity, this became a popular way of attempting to prevent a full blown onset of the disease (it was used greatly in royal families). People would attempt to infect themselves with Variola minor particles and give themselves just enough of a sickness to have their bodies produce antibodies. While these processes did have some success rate, many also died as a result of getting sicker than was intended.

This is a illustration of how smallpox would originally spread (left) and how the effects of inoculation (right) would give a sample spread.