Smallpox (variola) is a contagious, disfiguring and sometimes deadly disease caused by the variola virus. It's believed to have first appeared in northeastern Africa or the Indus Valley of south-central Asia nearly 12,000 years ago. Since then, few other illnesses have had such a profound effect on human health and history. There is evidence that a major smallpox epidemic occurred toward the end of the 18th Egyptian dynasty. Studies of the mummy of Pharaoh Ramses V (d. 1157 BC) indicate that he likely died of smallpox infection. From ancient Egypt, it appears that traders spread the disease to India. Smallpox was brought to the Americas with the arrival of Spanish colonists in the fifteenth and sixteenth centuries. Many historians argue that smallpox infection killed more Aztec and Inca people than the Spanish Conquistadors did. A smallpox epidemic in 1837-38 killed an estimated 20,000 Native Americans, and it is believed by many that an early attempt at biological warfare was made when smallpox-infected blankets were deliberately provided to Native Americans by British General Jeffrey Amherst during the French-Indian War (1754-1763).

The smallpox virus occurs in humans and in some circumstances in monkeys. Particles containing the virus are released into the air when an infected person coughs, sneezes or simply talks. They also may spread through direct contact such as kissing or through contaminated bed linen and clothing. Inhaling a single particle may be enough to cause infection. Because it's contagious, smallpox has the potential to spread rapidly. Unlike anthrax, which is not transmitted from person to person, a smallpox epidemic could conceivably start with a single infected individual. There's no known cure, but a vaccine can help protect against the disease. In fact, an aggressive vaccination program resulted in the complete eradication of the disease from the global population in the mid-1970's. (The last reported case of smallpox occurred on October 26, 1977 in Somalia.)

So, enough about the history of the disease, you want to know all the gory little details, don't you?

The first symptoms of smallpox usually appear 12 to14 days after you're infected, although the incubation period can range from 7 to 17 days. During this time, you look and feel healthy and can't infect others.

Following the incubation period a sudden onset of flu-like symptoms occurs. These symptoms include:

Fever
A feeling of bodily discomfort (malaise)
Headache
Severe fatigue (prostration)
Severe back pain

A few days later, the characteristic smallpox rash appears as flat, red spots (lesions). Within a day or two, these lesions become filled with fluid (vesicles) and then with pus (pustules). The lesions appear first on your face, hands and forearms and later on the trunk of your body. They're especially prominent on the palms of your hands and the soles of your feet. Lesions also develop in the mucous membranes of your nose and mouth. The way the lesions are distributed is a hallmark of smallpox and a primary way of diagnosing the disease.

When the pustules erupt, the skin doesn't break, but actually tears away from its underlying layers. The pain can be excruciating. Scabs begin to form 8 to 9 days later and eventually fall off, leaving deep, pitted scars. All lesions in a given area progress at the same rate through these stages. People who don't recover usually die during the second week of illness.

Of course, simply receiving a smallpox vaccination would not guarantee immunity to the disease, as the vaccination reactions could be most nasty indeed! Here are just a smattering of the reaction images on the CDC website:

Bet you young people are happy to have been born after 1972, eh? (Old people like me probably still have an indented smallpox vaccination scar on their arm - if not worse!) It's worth reflecting on that scar and imagining a time when that one little pockmark would have been one of hundreds scarring your entire body... if you even survived.

The miracles of science, indeed!