Smallpox

Smallpox (also known by the Latin names Variola or Variola vera) is a highly contagious disease unique to humans. It is caused by two virus variants called Variola major and Variola minor. V. major is the more deadly form, with a typical mortality of 20-40 percent of those infected. The other type, V. minor, only kills 1% of its victims. Many survivors are left blind in one or both eyes from corneal ulcerations, and persistent skin scarring - pockmarks - is nearly universal. Smallpox was responsible for an estimated 300-500 million deaths in the 20th century. As recently as 1967, the World Health Organization (WHO) estimated that 15 million people contracted the disease and that two million died in that year.

Infection

Transmission is by droplets, and infection in the natural disease will be via the lungs. The incubation period to obvious disease is around 12 days. In the initial growth phase the virus seems to move from cell to cell, but around the 12th day, lysis of many infected cells occurs and the virus will be found in the bloodstream in large numbers. The initial or prodromal symptoms are essentially similar to other viral diseases such as influenza and the common cold - fevers, muscle pain and stomach aches etc. The digestive tract is commonly involved, leading to vomiting. Most cases will be prostrated.

Related Topics:
Lung - Lysis - Blood - Influenza - Common cold - Fever - Muscle - Stomach - Vomit

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Smallpox virus preferentially attacks skin cells and by days 14-15, smallpox infection becomes obvious. The attack on skin cells causes the characteristic pimples associated with the disease. The pimples tend to erupt first in the mouth, then the arms and the hands, and later the rest of the body. At that point the pimples, called macules, should still be fairly small. This is the stage at which the victim is most contagious.

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By days 15-16 the condition worsens - at this point the disease can take two vastly different courses. The first form is of classical ordinary smallpox, in which the pimples grow into papules, and then fill up with pus (turning them into pustules). Ordinary smallpox generally takes one of two basic courses. In discrete ordinary smallpox, the pustules stand out on the skin separately - there is a greater chance of surviving this form. In confluent ordinary smallpox, the blisters merge together into sheets which begin to detach the outer layers of skin from the underlying flesh - this form is usually fatal. If a victim of ordinary smallpox survives for the course of the disease, the pustules will deflate in time (the duration is variable), and will start to dry up, usually beginning on day 28. Eventually the pustules will completely dry and start to flake off. Once all of the pustules flake off, the patient is considered cured.

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In the other form of smallpox, known as haemorrhagic smallpox, an entirely different set of symptoms starts to develop. The skin does not blister, but remains smooth. Instead, bleeding will occur under the skin, making the skin look charred and black (this is known as black pox). The eyes will also haemorrhage, making the whites of the eyes turn deep red (and, if the victim lives long enough, eventually black). At the same time, bleeding begins in the organs. Death may occur from bleeding (fatal loss of blood or by other causes such as brain haemorrhage), or from loss of fluid. The entry of other infectious organisms, since the skin and intestine are no longer a barrier, can also lead to multi-organ failure. This form of smallpox occurs in anywhere from 3-25% of fatal cases (depending on the virulence of the smallpox strain).

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