Smallpox

I

Introduction

Smallpox, highly contagious viral disease that is often fatal. The disease is chiefly characterized by a skin rash that develops on the face, chest, back, and limbs. Over the course of a week the rash develops into pustular (pus-filled) pimples resembling boils. In extreme cases the pustular pimples run together—usually an indication of a fatal infection. Death may result from a secondary bacterial infection of the pustules, from cell damage caused by the viral infection, or from heart attack or shock. In the latter stages of nonfatal cases, smallpox pustules become crusted, often leaving the survivor with permanent, pitted scars.

Smallpox is caused by a virus. An infected person spreads virus particles into the air in the form of tiny droplets emitted from the mouth by speaking, coughing, or simply breathing. The virus can then infect anyone who inhales the droplets. By this means, smallpox can spread extremely rapidly from person to person.

Smallpox has afflicted humanity for thousands of years, causing epidemics from ancient times through the 20th century. No one is certain where the smallpox virus came from, but scientists speculate that several thousand years ago the virus made a trans-species jump into humans from an animal—likely a rodent species such as a mouse. The disease probably did not become established among humans until the beginnings of agriculture gave rise to the first large settlements in the Nile valley (northeastern Africa) and Mesopotamia (now eastern Syria, southeastern Turkey, and Iraq) more than 10,000 years ago.

Over the next several centuries smallpox established itself as a widespread disease in Europe, Asia, and across Africa. During the 16th and 17th centuries, a time when Europeans made journeys of exploration and conquest to the Americas and other continents, smallpox went with them. By 1518 the disease reached the Americas aboard a Spanish ship that landed at the island of Hispaniola (now the Dominican Republic and Haiti) in the West Indies. Before long smallpox had killed half of the Taíno people, the native population of the island. The disease followed the Spanish conquistadors into Mexico and Central America in 1520. With fewer than 500 men, the Spanish explorer Hernán Cortés was able to conquer the great Aztec Empire under the emperor Montezuma in what is now Mexico. One of Cortés's men was infected with smallpox, triggering an epidemic that ultimately killed an estimated 3 million Aztecs, one-third of the population. A similar path of devastation was left among the people of the Inca Empire of South America. Smallpox killed the Inca emperor Huayna Capac in 1525, along with an estimated 100,000 Incas in the capital city of Cuzco. The Incas and Aztecs are only two of many examples of smallpox cutting a swath through a native population in the Americas, easing the way for Europeans to conquer and colonize new territory. It can truly be said that smallpox changed history.

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Yet the story of smallpox is also the story of great biomedical advancement and of ultimate victory. As the result of a worldwide effort of vaccination and containment, the last naturally occurring infection of smallpox occurred in 1977. Stockpiles of the virus now exist only in secured laboratories. Some experts, however, are concerned about the potential use of smallpox as a weapon of bioterrorism. Thus, despite being deliberately and successfully eradicated, smallpox may still pose a threat to humanity.

II

Cause

The scientific name for smallpox is variola, from a Latin word meaning 'spotted.” Scientists recognize two main forms of smallpox caused by related subspecies of viruses. Variola major is the more serious form of the disease, believed to kill anywhere from 20 to 40 percent of those infected. Variola minor, on the other hand, produces milder symptoms and is fatal in around 1 percent of cases. In between the major and minor forms are a variety of intermediate strains. All forms of the disease, when not fatal, can leave survivors with permanent, disfiguring scars on the face and other areas. Smallpox can also cause blindness and, in the case of males, sterility.

The variola viruses belong to a virus group known collectively as orthopoxviruses, also referred to more simply as pox viruses—the largest viruses known. Smallpox viruses are shaped somewhat like bricks, measuring in size from 250 to 300 nanometers across—almost big enough to be visible with an ordinary light microscope. Inside a variola virus, within an outer shell made up of scores of proteins, lies a coiled strand of deoxyribonucleic acid (DNA), the virus’s genetic material.

Smallpox is primarily spread via airborne, virus-laden droplets exhaled by an infected person. Prolonged contact is not required. In one recorded case, for example, an infected person in a shop passed the virus to two visitors who had made a brief stop in the shop. In a laboratory accident in 1978 in the United Kingdom, a bit of mistakenly released virus traveled via an air duct from one floor of the lab to another, fatally infecting a medical photographer. The virus can also survive for extended periods in dust, clothing, bedding, and other objects, providing still more opportunities for infection.

The smallpox virus typically enters the body through the mouth or nose, ultimately invading the cells of the lymph nodes and the lungs. Once inside a cell, the smallpox virus employs the same stealthy act of hijacking employed by all viruses, commandeering the infected cell's own genetic machinery to make as many as 100,000 copies of itself. Some of these viruses instruct the host cell to send out finger-like tendrils that make contact with other cells. It is through these extensions that new cells become infected with virus particles and the viral replication process repeats. After the virus has used a cell to replicate, it abandons the cell, leaving it to die.

Eventually smallpox virus particles circulate in the bloodstream—a condition known as viremia. The virus may then invade the liver, spleen, and other internal organs, but it shows a preference for the mucous membranes of the mouth and especially the epithelial cells of the skin. This viral invasion of the skin, in turn, leads to the painful, pus-filled lesions that are the hallmark of the disease. Meanwhile, throughout the body, infected and dying cells release toxins of their own that also contribute to illness.

In nonfatal cases, the body's immune system finally succeeds in defeating the infection by developing specialized antibodies that neutralize the smallpox virus. These antibodies continue to circulate in the bloodstream and provide the disease's one compensation: long-term immunity against further smallpox infection (see Immunization).

III

Symptoms, Diagnosis, and Treatment

After a person is infected with the smallpox virus, about 12 days pass before the person begins to feel sick, a time known as the incubation period. During the incubation period, while the infected person still feels healthy, the smallpox virus multiplies in the lymph nodes, lungs, and other tissues. By the 12th day the virus moves into the bloodstream, producing sudden and dramatic symptoms that include high fever of 39º to 41ºC (102º to 106ºF), headache, muscular and abdominal pain, and vomiting. Within two to three days the virus spreads to the skin and the rash appears. At first the rash takes the form of skin spots known as macules. By the second day of the rash, as infection worsens within the skin cells, the spots become raised lesions called papules; by the seventh day these papules fill with pus and are referred to as pustules. Smallpox patients become most infectious during the week following the appearance of the rash.

In the most extreme forms of smallpox, the virus causes bleeding underneath the skin, giving the skin a charred appearance, as if burned. In these cases the virus causes massive tissue damage to skin and to internal organs, and victims bleed heavily from the mouth and other body openings. Such cases are referred to as black pox and they are almost invariably fatal.

The exact cause of death in smallpox cases is not entirely understood, but it can include shock, cardiovascular complications, and bacterial toxins from secondary infections. In those who survive the illness, the infection runs its course in about two weeks; the pustules form scabs and finally drop off within roughly a month.

Physicians diagnose smallpox by removing fluid from skin lesions and preparing slides on which the virus can be detected through an electron microscope. Laboratory tests can also check blood samples for antibodies to the smallpox virus—a sure sign that the virus is present. However, during the smallpox epidemics of the 20th century, medical workers in the developing nations of Africa and Asia did not always have such sophisticated diagnostic methods available. Medical personnel generally identified cases by the appearance of the skin rash. The texture of the lesions themselves—described as feeling like pellets when rolled between the fingers—provided another sure sign of smallpox.

There is no cure, or even a specific treatment, for a smallpox infection. In modern outbreaks, medical care usually consisted of bed rest and the treatment of symptoms: the use of intravenous fluids to prevent dehydration, sedatives to keep patients calm, and aspirin or codeine to relieve pain in the head and muscles. Antibiotic drugs such as penicillin or tetracycline were also administered to treat secondary bacteria infections. In an effort to minimize scarring of the skin, smallpox lesions were kept clean with warm antiseptic baths and dusting powders.

IV

Early Efforts Against Smallpox

Early attempts to prevent smallpox originated in China several thousand years ago. In the ancient process known as variolation, dried smallpox scabs were blown up the nose of the patient. Later, the procedure took the form of scratching the arm with a needle containing pus from a smallpox lesion. Used before scientists fully understood infectious diseases and immunology, variolation was dangerous and resulted in full-blown smallpox in 2 to 3 percent of cases. But in skilled hands variolation induced a mild infection that stimulated the production of antibodies, creating effective immunity against smallpox for several years. The practice gained popularity in both Europe and North America during the 18th century.

A more effective medical blow against smallpox, and one of history’s landmark biomedical achievements, took place in 1796 with an experiment performed by the British physician Edward Jenner. He had observed that young women who milked cows for a living often contracted a minor skin infection known as cowpox—and that these milkmaids subsequently seemed to be protected from smallpox. Jenner arranged to perform an experiment on eight-year-old James Phipps, scratching his arm with pus taken from the cowpox lesion of a milkmaid. Six weeks later, when Jenner scratched Phipps's arm with pus from a smallpox lesion, the boy failed to show any reaction or illness. The cowpox virus had created natural immunity against smallpox while carrying none of the risk posed by variolation with actual smallpox virus. Jenner was apparently not the first to attempt this procedure, but he was the first to approach it scientifically and to document and publish the results. Thus, with this new procedure, which was later dubbed vaccination (from the Latin word vacca for 'cow'), Jenner set the course that ultimately led to victory over smallpox.

The practice of vaccination did not catch on quickly, however. Some people refused the smallpox vaccine, offended by the idea of introducing matter from an animal into their bloodstreams. Others believed that a vaccine would interfere with God's will. Vaccination gradually gained acceptance and became more widely practiced.

Even after smallpox vaccination had become standard in the developed world, epidemics continued in some regions. Between 1900 and 1920 in India, for example, smallpox killed an average of 370 out of every 100,000 people in the population every year. In all, smallpox killed an estimated 300 million people in the 20th century.

In the battle against smallpox in the 20th century, two weapons were key: (1) an effective vaccine and (2) the fact that the smallpox virus exists only in humans. Unlike strains of the influenza virus, for example, which can exist in domestic fowl or pigs before jumping to humans and causing flu outbreaks, smallpox requires a chain of human hosts to keep its life cycle going. Following infection, a host falls sick and will either recover or die, but by then the virus will have moved on, renewing itself by being spread to other human hosts who have contact with the infected person. Ultimately, the strategy against smallpox was to break this chain of infection forever.

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