Smallpox epidemiology and demographics

After 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. For more than two hundred years, this disease affected all new world populations, mostly without intentional European transmission (Excluding the British Settlements), from contact in the early 1500s to until possibly as early as the French and Indian Wars (1754-1767).

Eurasia
It is important to note that, while historical epidemics and pandemics are believed by some historians to have been early outbreaks of smallpox, contemporary records are not detailed enough to make a definite diagnosis at this distance.

The Plague of Athens devastated the city of Athens in 430 BC, killing around a third of the population, according to Thucydides. Historians have long considered this an example of bubonic plague, but more recent examination of the reported symptoms led some scholars to believe the cause may have been measles, smallpox, typhus, or a viral hemorrhagic fever (like Ebola).

The Antonine Plague that swept through the Roman Empire and Italy in 165–180 is also thought to be either smallpox or measles. A second major outbreak of disease in the Empire, known as the Plague of Cyprian (251–266), was also either smallpox or measles.

The next major epidemic believed to be smallpox occurred in India]. The exact date is unknown. Around A.D. 400, an Indian medical book recorded a disease marked by pustules, saying "the pustules are red, yellow, and white and they are accompanied by burning pain … the skin seems studded with grains of rice." The Indian epidemic was thought to be punishment from a god, and the survivors created a goddess, Sitala, as the anthropomorphic personification of the disease. Smallpox was thus regarded as possession by Sitala. In Hinduism the goddess Sitala both causes and cures high fever, rashes, hot flashes and pustules. All of these are symptoms of smallpox.

Smallpox did not definitively enter Western Europe until about 581 when Bishop Gregory of Tours provided an eyewitness account that describes the characteristic findings of smallpox. Most of the details about the epidemic that followed are lost, probably due to the scarcity of surviving written records of early medieval society.

The Americas
After 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. For more than two hundred years, this disease affected all new world populations, mostly without intentional European transmission (Excluding the British Settlements), from contact in the early 1500s to until possibly as early as the French and Indian Wars (1754-1767).

In 1519 Hernán Cortés landed on the shores of what is now Mexico and was then the Aztec empire. In 1520 another group of Spanish came from Cuba and landed in Mexico. Among them was an African slave who had smallpox. When Cortés heard about the other group, he went and defeated them. In this contact, one of Cortés's men contracted the disease. When Cortés returned to Tenochtitlan, he brought the disease with him.

Soon, the Aztecs rose up in rebellion against Cortés. Outnumbered, the Spanish were forced to flee. In the fighting, the Spanish soldier carrying smallpox died. After the battle, the Aztecs contracted the virus from the invaders' bodies. Cortes would not return to the capital until August 1521. In the meantime smallpox devastated the Aztec population. It killed most of the Aztec army, the emperor, and 25% of the overall population. A Spanish priest left this description: "As the Indians did not know the remedy of the disease…they died in heaps, like bedbugs. In many places it happened that everyone in a house died and, as it was impossible to bury the great number of dead, they pulled down the houses over them so that their homes become their tombs." On Cortés's return, he found the Aztec army’s chain of command in ruins. The soldiers who lived were still weak from the disease. Cortés then easily defeated the Aztecs and entered Tenochtitlán, where he found that smallpox had killed more Aztecs than had the cannons. The Spaniards said that they could not walk through the streets without stepping on the bodies of smallpox victims.

The effects of smallpox on Tahuantinsuyu (or the Inca empire) were even more devastating. Beginning in Colombia, smallpox spread rapidly before the Spanish invaders first arrived in the empire. The spread was probably aided by the efficient Inca road system. Within months, the disease had killed the Sapa Inca Huayna Capac, his successor, and most of the other leaders. Two of his surviving sons warred for power and, after a bloody and costly war, Atahualpa become the new Sapa Inca. As Atahualpa was returning to the capital Cuzco, Francisco Pizarro arrived and through a series of deceits captured the young leader and his best general. Within a few years smallpox claimed between 60% and 90% of the Inca population, with other waves of European disease weakening them further. However, some historians think a serious native disease called Bartonellosis may have been responsible for some outbreaks of illness. The effects of smallpox were dipicted in the ceramics of the Moche people of ancient Peru.

Even after the two mighty empires of the Americas were defeated by the virus, smallpox continued its march of death. In 1633 in Plymouth, Massachusetts, the Native Americans were struck by the virus. As it had done elsewhere, the virus wiped out entire population groups of Native Americans. It reached Lake Ontario in 1636, and the lands of the Iroquois by 1679, killing millions. The worst sequence of smallpox attacks took place in Boston, Massachusetts. From 1636 to 1698, Boston endured six epidemics. In 1721, the most severe epidemic occurred. The entire population fled the city, bringing the virus to the rest of the Thirteen Colonies. In the late 1770s, during the American Revolutionary War, smallpox returned once more and killed an estimated 125,000 people. Peter Kalm in his “Travels in North America”, described how in that period, the dying Indian villages became overrun with wolves feasting on the corpses and weakened survivors.

Overview
The eradication of smallpox required a global effort. Every country was susceptible to the devastating disease. Eradicating this infection would take many years a significant sum of money, but with a worldwide commitment, it would be possible. Success was achieved in the 1970s and smallpox was officially eradicated.

Eradication process
Since Jenner demonstrated the effectiveness of cowpox to protect humans from smallpox in 1796, various attempts were made to eliminate smallpox on a regional scale. As early as 1803, the Spanish Crown organized a mission (the Balmis Expedition) to transport the vaccine to the Spanish colonies in the Americas and the Philippines, and establish mass vaccination programs there. The US Congress passed the Vaccine Act of 1813 to ensure that safe smallpox vaccine would be available to the American public. By about 1817, a very solid state vaccination program existed in the Dutch East Indies. In British India a program was launched to propagate smallpox vaccination, through Indian vaccinators, under the supervision of European officials. Nevertheless, British vaccination efforts in India, and in Burma in particular, were hampered by stubborn indigenous preference for inoculation and distrust of vaccination, despite tough legislation, improvements in the local efficacy of the vaccine and vaccine preservative, and education efforts. By 1832, the federal government of the United States established a smallpox vaccination program for Native Americans. In 1842, the United Kingdom banned inoculation, later progressing to mandatory vaccination. The British government introduced compulsory smallpox vaccination by an Act of Parliament in 1853. In the United States, from 1843 to 1855 first Massachusetts, and then other states required smallpox vaccination. Although some disliked these measures, coordinated efforts against smallpox went on, and the disease continued to diminish in the wealthy countries. By 1897, smallpox had largely been eliminated from the United States. In Northern Europe a number of countries had eliminated smallpox by 1900, and by 1914, the incidence in most industrialized countries had decreased to comparatively low levels. Vaccination continued in industrialized countries, until the mid to late 1970s as protection against reintroduction. Australia and New Zealand are two notable exceptions; neither experienced endemic smallpox and never vaccinated widely, relying instead on protection by distance and strict quarantines.

The first hemisphere-wide effort to eradicate smallpox was made in 1950 by the Pan American Health Organization. The campaign was successful in eliminating smallpox from all American countries except Argentina, Brazil, Colombia, and Ecuador. In 1958 Professor Viktor Zhdanov, Deputy Minister of Health for the USSR, called on the World Health Assembly to undertake a global initiative to eradicate smallpox. The proposal (Resolution WHA11.54) was accepted in 1959. At this point, 2 million people were dying from smallpox every year. Overall, however, the progress towards eradication was disappointing, especially in Africa and in the Indian subcontinent. In 1966 an international team, the Smallpox Eradication Unit, was formed under the leadership of an American, Donald Henderson. In 1967, the World Health Organization intensified the global smallpox eradication by contributing $2.4 million annually to the effort.

In the early 1950s an estimated 50 million cases of smallpox occurred in the world each year. To eradicate smallpox, each outbreak had to be stopped from spreading, by isolation of cases and vaccination of everyone who lived close by. This process is known as "ring vaccination". The key to this strategy was monitoring of cases in a community (known as surveillance) and containment. The initial problem the WHO team faced was inadequate reporting of smallpox cases, as many cases did not come to the attention of the authorities. The fact that humans are the only reservoir for smallpox infection, and that carriers did not exist, played a significant role in the eradication of smallpox. The WHO established a network of consultants who assisted countries in setting up surveillance and containment activities. Early on donations of vaccine were provided primarily by the Soviet Union and the United States, but by 1973, more than 80% of all vaccine was produced in developing countries.

The last major European outbreak of smallpox was in 1972 in Yugoslavia, after a pilgrim from Kosovo returned from the Middle East, where he had contracted the virus. The epidemic infected 175 people, causing 35 deaths. Authorities declared martial law, enforced quarantine, and undertook widespread re-vaccination of the population, enlisting the help of the WHO. In two months, the outbreak was over. Prior to this, there had been a smallpox outbreak in May–July 1963 in Stockholm Sweden, brought from the Far East by a Swedish sailor; this had been dealt with by quarantine measures and vaccination of the local population.

By the end of 1975, smallpox persisted only in the Horn of Africa. Conditions were very difficult in Ethiopia and Somalia, where there were few roads. Civil war, famine, and refugees made the task even more difficult. An intensive surveillance and containment and vaccination program was undertaken in these countries in early and mid-1977, under the direction of Australian microbiologist Frank Fenner. As the campaign neared its goal, Fenner and his team played an important role in verifying eradication. The last naturally occurring case of indigenous smallpox (Variola minor) was diagnosed in Ali Maow Maalin, a hospital cook in Merca, Somalia, on 26 October 1977. The last naturally occurring case of the more deadly Variola major had been detected in October 1975 in a two-year-old Bangladeshi girl, Rahima Banu.

Post-Eradication
In 1978, there was evidently an escape of smallpox from containment in a research laboratory in Birmingham, England. A medical photographer, Janet Parker, died from the disease itself, after which the Professor responsible for the unit, Professor Henry Bedson, committed suicide. In light of this accident, all known stocks of smallpox were destroyed, except the stocks at the United States Centers for Disease Control and Prevention (CDC) and the Russian State Research Center of Virology and Biotechnology VECTOR in Koltsovo, where a regiment of troops guards it. Under such tight control, smallpox would, it was thought, never be let out again. Even though the destruction of virus stocks was ordered in 1993, 1994, 1995, and 1996, they have not yet been destroyed, since a number of researchers still wish to retain the stocks for scientific purposes.

In March 2003 smallpox scabs were found tucked inside an envelope in a book on Civil War medicine in Santa Fe, New Mexico. The envelope was labeled as containing the scabs and listed the names of the patients they came from. Assuming the contents could be dangerous, the librarian who found them did not open the envelope. The scabs ended up with employees from the CDC who responded quickly once informed of the discovery. The discovery raised concerns that smallpox DNA could be extracted from these and other scabs and used for a biological attack. Even with Variola sequenced, assembling a virus from scratch remains challenging.