What is it?
Smallpox is a life-threatening infectious disease. The symptoms appear after one to two weeks after infection, and begin as those typical to the flu, such as fever, headache, and fatigue. A few days later, flat red spots appear on the face and hands, spreading from there over the rest of the body. These spots turn into the fluid-filled blisters commonly associated with smallpox. Eventually scabs form and then come off, leaving deep and pitted scars.
The earliest indications of the presence of smallpox date back to the 1500 BC India. It is believed that in the 8th century smallpox killed one third of the population of Japan. By the 16th century, the disease had become an established part of most European societies with regular epidemics that killed around 30% of those infected, and the disease was particularly fatal to the native populations of America and Australia. Smallpox was the leading cause of death in the 18th century Europe, and in Sweden, for example, 10% of all infants died of it. In all honesty, things were pretty bad.
Smallpox vaccinations were introduced to the public in the early 19th century. Many were suspicious and refused to get vaccinated, but especially after making the vaccination obligatory in some areas, the rates of disease began to fall in wealthy countries. I’m very happy to be able to say that despite the big problems that were encountered, smallpox was in 1980 declared to be the first infectious disease eradicated from the face of the planet, thanks to the efforts of the WHO.
What causes it?
Smallpox is caused by the infection of one of two virus variants. The two viruses are significantly different in terms of mortality: one of them leads to death in 30-35% of cases, the other in 1% of cases. People become infected when they inhale the virus. Usually this happens when someone is simply spending too much time too close to someone carrying the virus.
What happens during it?
Viruses have no metabolism, need other cells to reproduce, and basically, are just protein shells stuffed with genetic material. When they do reproduce, they invade a cell and release the genetic material inside it. The cell starts to produce virus proteins according to the new instructions, and eventually the cell assembles a set of new viruses, releases them to wreak further havoc, and dies.
The smallpox virus enters the body through the respiratory tract, and these are the cells it first invades. It then moves to the lymph nodes and multiplies there for a week or two. At this stage, there are rarely any symptoms. Soon, however, the viruses break out from the cells and invade the bloodstream, and a second round of multiplication occurs in the spleen, bone marrow, and lymph nodes. Now the flu-like symptoms appear, as the immune system reacts to the suddenly increased number of viruses and some cells are damaged. At this point it is also common to experience nausea, as the virus often invades the digestive tract. The fever usually starts to fall after a few days.
The virus likes to attack skin cells, and at this stage of the disease, small red patches of rash begins to appear on the skin of the infected. The tiny blood vessels in the skin are dilated, and as a result of this, the skin cells start to swell as they are filled with liquid, and may eventually rupture. The patches grow bigger, and eventually, in 90% of cases, become filled with liquid tissue derbis. The liquid slowly leaks away from them, and they dry up.
When a cell is invaded by a virus it turns into a virus factory, but it also releases molecules called interferons that warn the surrounding cells so that they can protect themselves from an attack. A few years ago researchers found that smallpox is so fatal because of its ability to block these interferons and that way cause a lot more damage in the body.
How can it be treated?
Other than trying to relieve symptoms, there is no treatment for smallpox. Vaccination, however, plays a big role in preventing it. Our bodies remember the microbes that we have once been exposed to, and if the same microbe were to try to attack us again, our bodies will response much more quickly and effectively. Vaccines take advantage of this mechanism by introducing the microbe to us in safe circumstances, so that our body can create a memory of it without being under immediate threat. Without doubt, the success of the smallpox vaccine remains one of the most inspiring and significant advances in the history of medicine.
Sources: http://www.cidrap.umn.edu/infectious-disease-topics/smallpox, http://emergency.cdc.gov/agent/smallpox/overview/disease-facts.asp, http://www.mayoclinic.org/diseases-conditions/smallpox/basics/causes/con-20022769, http://emedicine.medscape.com/article/237229-overview, http://www.emedicinehealth.com/smallpox/page2_em.htm, http://www.dnaindia.com/health/report-how-smallpox-kills-you-1326714, https://en.wikipedia.org/wiki/Smallpox#cite_note-AFIP-7, http://www.who.int/csr/disease/smallpox/en/