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Chickenpox is an infection that causes an itchy, blistering rash and is very contagious, meaning it is spread easily from one person to another. It is caused by varicella-zoster virus (VZV), which enters the body through the mouth and nose after contact with an infected person.
A person with chickenpox can spread the disease to someone else from one day before the rash appears until all chickenpox blisters have crusted over. Once someone has had a chickenpox infection, he or she almost always develops a lifelong immunity, meaning that person usually does not get chickenpox a second time. The exception is a child who is infected at a very young age. Young children usually have milder cases and may not build up enough protection against the disease. Therefore, these children may develop the disease again later in life.
Because chickenpox is so contagious, 90 percent of a patient's family also will develop the illness if they live in the same house and are not already immune. In the past, chickenpox cases often occurred in groups (epidemics), usually during the late winter and early spring. However, the number of cases of chickenpox has dropped dramatically because of the chickenpox (varicella) vaccine, which was licensed in 1995 and is recommended for all children.
Chickenpox is an uncomfortable infection that, in most cases, goes away by itself. However, chickenpox also has been associated with serious complications, including death. About one of every 100 children infected with chickenpox will develop a severe lung infection (pneumonia), an infection of the brain (encephalitis), or a problem with the liver. Dangerous skin infections also can occur. Before the introduction of the vaccine, about 100,000 people were hospitalized and 100 people in the United States died each year of chickenpox, most of them previously healthy children. Adolescents and adults who develop chickenpox are also at high risk of developing serious complications.
After a person has chickenpox, the virus typically lives silently in the nervous system of the body for the rest of a person's life. It may reactivate (come to life again) at any time when the body's immune defenses are weakened by stress or illness (such as cancer or HIV infection) or by medications that weaken the immune system. The most common reason for the virus to reactivate is getting older. Reactivation of the virus causes a condition called shingles, a painful blistering skin rash that typically occurs on the face, chest or back, in the same area where one or two of the body's sensory nerves travel.
Smallpox is a contagious and sometimes fatal disease caused by two related viruses: variola major and variola minor. Variola major is the more common and severe form, with an overall historical fatality rate of about 30%. Variola minor is less common and causes a milder form of smallpox that is usually not fatal. Historic death rates were less than 1%. Smallpox eradication was one of the greatest successes of modern public health. Through a sophisticated global vaccination campaign, the World Health Organization officially declared in 1980 that smallpox had been eliminated worldwide. The last known case of smallpox in the United States occurred in 1949, and the last case of naturally occurring smallpox was reported in 1977 in Somalia.
Today, the smallpox virus is known to exist only in secured laboratory stockpiles in the United States and Russia. However, it is theorized that other countries may have possession of the virus as well.
For this reason, there is some concern that terrorists may have access to the virus, which could be used as a bioterrorism agent. Because smallpox has been eradicated, any human smallpox infection would be evidence of bioterrorism. For these reasons, the Centers for Disease Contol and Prevention have developed a response plan for possible smallpox outbreaks, with detailed instructions on how to mobilize appropriate personnel and vaccines.
Smallpox is usually spread through direct and fairly prolonged contact with an infected person, particularly with face-to-face contact. It is typically spread among people who share living quarters. This is probably because patients with smallpox are severely ill in the period when they are most infectious, and so they are unlikely to have contact with many people outside their homes. Smallpox also can be acquired from infected bedding and clothes. Rarely, smallpox is spread through the air of enclosed settings such as buildings, buses and trains.
Tetanus, also called lockjaw, is a life-threatening infection caused by Clostridium tetani bacteria. Although these bacteria are especially common in the soil and manure of farms, they can be found almost anywhere. They live in the dirt of suburban gardens and in the dirty waters of floods. They also contaminate dust in cities.
Tetanus bacteria usually enter the body through a dirty puncture wound, cut, scrape or some other break in the skin. Once inside the skin, they multiply and produce a toxin, or poison, that affects the body's nerves. This toxin causes severe muscle spasms, cramps and seizures. Spasms in the jaw muscles produce lockjaw. Spasms also occur in muscles of the throat, chest, abdomen and extremities. If you don't receive proper treatment, the toxin's effect on respiratory muscles can interfere with breathing. If this happens, you may die of suffocation.
A tetanus infection may develop after almost any type of skin injury, major or minor. This includes cuts, punctures, crush injuries, burns and animal bites. In rare cases, a tetanus infection also can occur after surgery, an ear infection, a dental infection or an abortion. Among drug users, tetanus infections have followed heroin injections, especially if the heroin was mixed with quinine. Tetanus also can develop after body piercing, tattooing, an insect sting or even a tiny splinter.