Smallpox is a serious, contagious, and sometimes fatal infectious disease caused by the variola virus. The pox part of smallpox is derived from the Latin word for “spotted” and refers to the raised bumps that appear on the face and body of an infected person.
Smallpox used to be both a common disease and a common cause of death worldwide, and outbreaks have occurred from time to time for thousands of years, but the disease is now eradicated after a successful worldwide vaccination program and smallpox was declared eradicated from the world in 1980. The last case caught in the community was in Africa in 1977. There are no animal reservoirs for the infection. After the disease was eliminated from the world, routine vaccination against smallpox among the general public was stopped because it was no longer necessary for prevention.
Attempts have been made in the past to weaponise smallpox, which focused on the airborne dispersal route (which would lead to inhalation of the organism). While the risk of a deliberate release of smallpox virus is very low, there are several factors which contribute to the bioterrorism potential of this virus; high case-fatality rate, ready transmission from person-to-person, lack of effective treatment, and declining numbers of vaccinated people
Incubation period
The incubation period for smallpox is usually 10-16 days but varies from 7-17 days. A rash starts to appear about 2 days after the first symptoms (taken as the onset of fever).
Transmission
Generally, direct and fairly prolonged face-to-face contact is required to spread smallpox from one person to another as smallpox is most often spread by inhaling virus particles through close contact with an infected person. However, smallpox also can be spread through direct contact with infected bodily fluids or contaminated objects such as bedding or clothing. Humans are the only natural hosts of variola and neither animals nor insects are involved in transmission. Rarely, smallpox has been spread by virus carried in the air in enclosed settings such as buildings, buses, and trains and, in fact, the initial infecting event during a deliberate release is likely to be airborne.
Patients are not infectious until the onset of symptoms. A person with smallpox is sometimes contagious with onset of fever (prodrome phase), but the person becomes most contagious with the onset of rash and when the lesions in their mouth ulcerate and produce a lot of airborne virus. At this stage the infected person is usually very sick and not able to move around in the community. Patients become less infectious later in the illness but the infected person is contagious until the last smallpox scab falls off.
Symptoms
There are two clinical forms of smallpox:
Variola major is the severe and most common form of smallpox, with a more extensive rash and higher fever. There are four types of variola major smallpox: ordinary (the most frequent type, accounting for 90% or more of cases); modified (mild and occurring in previously vaccinated persons); flat; and hemorrhagic (both rare and very severe). Historically, variola major has an overall fatality rate of about 30%; however, flat and hemorrhagic smallpox usually are fatal.
Variola minor is a less common presentation of smallpox, and a much less severe disease, with death rates historically of 1% or less.
Symptoms tend to begin suddenly with fever, headache, malaise and an aching head and back; patients are usually bedridden. This is called the prodrome phase and may last for 2 to 4 days.
A rash emerges first as small red spots on the tongue and in the mouth.
These spots develop into sores that break open and spread large amounts of the virus into the mouth and throat. At this time, the person becomes most contagious.
Around the time the sores in the mouth break down, a rash appears on the skin, starting on the face and spreading to the arms and legs and then to the hands and feet. Usually the rash spreads to all parts of the body within 24 hours. As the rash appears, the fever usually falls and the person may start to feel better. By the third day of the rash, the rash becomes raised bumps and by the fourth day, the bumps fill with a thick, opaque fluid (vesicles) and often have a depression in the centre that looks like a bellybutton. (This is a major distinguishing characteristic of smallpox.) Fever often will rise again at this time and remain high until scabs form over the bumps.
By about 7 days after onset of symptoms the bumps then become pustules—sharply raised, usually round and firm to the touch as if there’s a small round object under the skin. The pustules begin to form a crust and then scab and by the end of the second week after the rash appears most of the sores have scabbed over.
The scabs then begin to fall off; leaving marks on the skin that eventually become pitted scars. Most scabs will have fallen off three weeks after the rash appears.
The person is contagious to others until all of the scabs have fallen off.
When smallpox occurs in a non-immune person or population it is a particularly serious illness, and is fatal in up to 30% of cases. Many smallpox survivors have permanent scars over large areas of their body, especially their face. Some are left blind.
If a person had smallpox before and survived, he/she is immune to the disease.
Around the time the sores in the mouth break down, a rash appears on the skin, starting on the face and spreading to the arms and legs and then to the hands and feet. Usually the rash spreads to all parts of the body within 24 hours. As the rash appears, the fever usually falls and the person may start to feel better. By the third day of the rash, the rash becomes raised bumps and by the fourth day, the bumps fill with a thick, opaque fluid (vesicles) and often have a depression in the centre that looks like a bellybutton. (This is a major distinguishing characteristic of smallpox.) Fever often will rise again at this time and remain high until scabs form over the bumps.
By about 7 days after onset of symptoms the bumps then become pustules—sharply raised, usually round and firm to the touch as if there’s a small round object under the skin. The pustules begin to form a crust and then scab and by the end of the second week after the rash appears most of the sores have scabbed over.
The scabs then begin to fall off; leaving marks on the skin that eventually become pitted scars. Most scabs will have fallen off three weeks after the rash appears.
The person is contagious to others until all of the scabs have fallen off.
When smallpox occurs in a non-immune person or population it is a particularly serious illness, and is fatal in up to 30% of cases. Many smallpox survivors have permanent scars over large areas of their body, especially their face. Some are left blind.
If a person had smallpox before and survived, he/she is immune to the disease.
Treatment
There is no specific treatment for the disease and caring for patients essentially involves treating their symptoms. However, antiviral drugs have recently been developed and have been shown to be effective against other poxviruses and may therefore have a role in cases of smallpox. Cases must be isolated to prevent transmission of the disease.
Patients with smallpox can benefit from supportive therapy (e.g., intravenous fluids, medicine to control fever or pain) and antibiotics for any secondary bacterial infections that may occur.
Prevention
There is an effective vaccine against smallpox, worldwide use of which was the basis of smallpox being eradicated. Because there is no longer any possibility of naturally acquiring the disease, smallpox vaccine has not been given to the general public. Vaccination can cause serious side effects and it should not be given to pregnant women, those with impaired immunity or those with eczema. However, vaccination given up to 4 days after exposure can modify the course of the disease and reduce mortality by about 50%.