Smallpox (also known by the Latin names Variola or Variola vera) is a contagious disease unique to humans. Smallpox is caused by either of two virus variants named Variola major and Variola minor. The deadlier form, V. major, has a mortality rate of 30–35%, while V. minor causes a milder form of disease called alastrim and kills ~1% of its victims. Long-term side-effects for survivors include the characteristic skin scars. Occasional side effects include blindness due to corneal ulcerations and infertility in male survivors.
Smallpox (430 BC? - 1979):
Killed more than 300 million people worldwide in the 20th century alone, and most of the native inhabitants of the Americas
Smallpox killed an estimated 60 million Europeans, including five reigning European monarchs, in the 18th century alone. Up to 30% of those infected, including 80% of the children under 5 years of age, died from the disease, and one third of the survivors became blind.
As for the Americas, after the first contacts with Europeans and Africans, some believe that the death of 90 to 95 percent of the native population of the New World was caused by Old World diseases. It is suspected that smallpox was the chief culprit and responsible for killing nearly all of the native inhabitants of the Americas. In Mexico, when the Aztecs rose up in rebellion against Cortés, outnumbered, the Spanish were forced to flee. In the fighting, a Spanish soldier carrying smallpox died. After the battle, the Aztecs contracted the virus from the invaders' bodies. When Cortes returned to the capital, smallpox had devastated the Aztec population. It killed most of the Aztec army, the emperor, and 25% of the overall population. Cortés then easily defeated the Aztecs and entered Tenochtitlán, where he found that smallpox had killed more Aztecs than had the cannons.
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. After successful vaccination campaigns throughout the 19th and 20th centuries, the WHO certified the eradication of smallpox in 1979. To this day, smallpox is the only human infectious disease to have been completely eradicated from nature.
Spanish Flu (1918 - 1919):
Killed 50 to 100 million people worldwide in less than 2 years
If the flu passed the stage of being a minor inconvenience, the patient was usually doomed. There is no cure for the influenza virus, even today. All doctors could do was try to make the patients comfortable, which was a good trick since their lungs filled with fluid and they were wracked with unbearable coughing. The "bluish cast" of victims' faces eventually turned brown or purple and their feet turned black. The lucky ones simply drowned in their own lungs. The unlucky ones developed bacterial pneumonia as an agonizing secondary infection. Since antibiotics hadn't been invented yet, this too was essentially untreatable. The pandemic came and went like a flash. Between the speed of the outbreak and military censorship of the news during World War I, hardly anyone in the United States knew that a quarter of the nation's population -- and a billion people worldwide -- had been infected with the deadly disease. More than half a million died in the U.S. alone; worldwide, more than 50 million.
Black Death (1340 - 1771):
Killed 75 million people worldwide
The three forms of plague brought an array of signs and symptoms to those infected. Bubonic plague refers to the painful lymph node swellings called buboes, mostly found around the base of the neck, and in the armpits and groin. The septicaemic plague is a form of blood poisoning, and pneumonic plague is an airborne plague that attacks the lungs before the rest of the body. The classic sign of bubonic plague was the appearance of buboes in the groin, the neck and armpits, which oozed pus and bled. Victims underwent damage to the skin and underlying tissue, until they were covered in dark blotches. Most victims died within four to seven days after infection. When the plague reached Europe, it first struck port cities and then followed the trade routes, both by sea and land. The bubonic plague was the most commonly seen form during the Black Death, with a mortality rate of thirty to seventy-five percent and symptoms including fever of 38 - 41 °C (101-105 °F), headaches, painful aching joints, nausea and vomiting, and a general feeling of malaise. Of those who contracted the bubonic plague, 4 out of 5 died within eight days. Pneumonic plague was the second most commonly seen form during the Black Death, with a mortality rate of ninety to ninety-five percent.
The same disease is thought to have returned to Europe every generation with varying virulence and mortalities until the 1700s. During this period, more than 100 plague epidemics swept across Europe. On its return in 1603, the plague killed 38,000 Londoners. Other notable 17th century outbreaks were the Italian Plague of 1629-1631, the Great Plague of Seville (1647-1652), the Great Plague of London (1665–1666), the Great Plague of Vienna (1679). There is some controversy over the identity of the disease, but in its virulent form, after the Great Plague of Marseille in 1720–1722 and the 1771 plague in Moscow it seems to have disappeared from Europe in the 18th century. The fourteenth-century eruption of the Black Death had a drastic effect on Europe's population, irrevocably changing Europe's social structure. It was a serious blow to the Roman Catholic Church and resulted in widespread persecution of minorities such as Jews, foreigners, beggars and lepers. The uncertainty of daily survival created a general mood of morbidity influencing people to "live for the moment", as illustrated by Giovanni Boccaccio in The Decameron (1353).
Malaria (1600 - today):
Kills about 2 million people per year
Malaria is one of the most common infectious diseases and an enormous public-health problem. It's parasites are transmitted by female Anopheles mosquitoes. The parasites multiply within red blood cells, causing symptoms that include symptoms of anemia (light headedness, shortness of breath, tachycardia etc.), as well as other general symptoms such as fever, chills, nausea, flu-like illness, and in severe cases, coma and death. The disease is caused by protozoan parasites of the genus Plasmodium. It is widespread in tropical and subtropical regions, including parts of the Americas, Asia, and Africa.
AIDS (1981 - today):
Killed 25 million people worldwide
The pandemic is not homogeneous within regions with some countries more afflicted than others. Even at the country level there are wide variations in infection levels between different areas. The number of people living with HIV continues to rise in most parts of the world, despite strenuous prevention strategies. Sub-Saharan Africa remains by far the worst-affected region, with 23.8 million to 28.9 million people living with HIV at the end of 2005, 1 million more than in 2003. Sixty-four percent of all people living with HIV are in sub-Saharan Africa, as are more than 77% of all women living with HIV. South & South East Asia are second most affected with 15%.
The key facts surrounding this origin of AIDS are currently unknown, particularly where and when the pandemic began, though it is said that it originated from the apes in Africa.
Cholera (1817 - today):
8 pandemics; hundreds of thousands killed worldwide
The major cholera pandemics are generally listed as: First: 1817-1823, Second: 1829-1851, Third: 1852-1859, Fourth: 1863-1879, Fifth: 1881-1896, Sixth: 1899-1923: Seventh: 1961- 1970, and some would argue that we are in the Eighth: 1991 to the present. Each pandemic, save the last, was accompanied by many thousands of deaths. As recently as 1947, 20,500 of 30,000 people infected in Egypt died. Despite modern medicine, cholera remains an efficient killer.
Typhus (430 BC? - today):
Killed 3 million people between 1918 and 1922 alone, and most of Napoleon's soldiers on Russia
The first description of typhus was probably given in 1083 at a convent near Salerno, Italy. Before a vaccine was developed in World War II, typhus was a devastating disease for humans and has been responsible for a number of epidemics throughout history. During the second year of the Peloponnesian War (430 BC), the city-state of Athens in ancient Greece was hit by a devastating epidemic, known as the Plague of Athens, which killed, among others, Pericles and his two elder sons. The plague returned twice more, in 429 BC and in the winter of 427/6 BC. Epidemic typhus is one of the strongest candidates for the cause of this disease outbreak, supported by both medical and scholarly opinions. Epidemics occurred throughout Europe from the 16th to the 19th centuries, and occurred during the English Civil War, the Thirty Years' War and the Napoleonic Wars. During Napoleon's retreat from Moscow in 1812, more French soldiers died of typhus than were killed by the Russians. A major epidemic occurred in Ireland between 1816-19, and again in the late 1830s, and yet another major typhus epidemic occurred during the Great Irish Famine between 1846 and 1849.
In America, a typhus epidemic killed the son of Franklin Pierce in Concord, New Hampshire in 1843 and struck in Philadelphia in 1837. Several epidemics occurred in Baltimore, Memphis and Washington DC between 1865 and 1873. During World War I typhus caused three million deaths in Russia and more in Poland and Romania. De-lousing stations were established for troops on the Western front but the disease ravaged the armies of the Eastern front, with over 150,000 dying in Serbia alone. Fatalities were generally between 10 to 40 percent of those infected, and the disease was a major cause of death for those nursing the sick. Following the development of a vaccine during World War II epidemics occur only in Eastern Europe, the Middle East and parts of Africa.