Control of smallpox by deliberate infection with mild forms of the disease was practiced for centuries. This process, called variolation, was dangerous but decreased the disastrous effects of major epidemics, reducing the case-fatality rate from 25% to 1%. Edward Jenner introduced vaccination with live cowpox virus in 1798.

In 1967, the World Health Organization introduced a worldwide campaign to eradicate smallpox. Epidemiologic features of the disease (described later) made it feasible to attempt total eradication. At that time, there were 33 countries with endemic smallpox and 10–15 million cases per year. The last Asian case occurred in Bangladesh in 1975, and the last natural victim was diagnosed in Somalia in 1977. Smallpox was officially declared eliminated in 1980. There were several reasons for this outstanding success: There is a single serotype of virus; most infections are clinically apparent; the vaccine was easily prepared, stable, and safe; the vac cine could be given simply by personnel in the field; and mass vaccination of the world population was not necessary. Cases of smallpox were traced, and contacts of the patient and those in the immediate area were vaccinated.

Even though there has been no evidence of smallpox transmission anywhere in the world, the World Health Organization coordinated the investigation of 173 possible cases of smallpox between 1979 and 1984. All were diseases other than smallpox, most commonly chickenpox or other illnesses that produce a rash. Even so, a potential case of smallpox becomes a public health emergency and must be promptly investigated by means of clinical evaluation, collection of laboratory specimens for diagnosis, and patient isolation.

The presence of stocks of virulent smallpox virus in laboratories is of concern because of the danger of laboratory infection and subsequent spread into the community. Variola virus stocks supposedly were destroyed in all laboratories except two World Health Organization collaborating centers (one in Atlanta and the other in Moscow) that pursue diagnostic and research work on variola-related poxviruses. However, in the 1990s, it was learned that the former Soviet Union had used smallpox virus in its biologic warfare program, and it is possible that it was transferred to other countries as well. Small pox virus is considered to be a dangerous potential biothreat agent, and it is theoretically possible that virus frozen in permafrost could reinfect the human population. Because of the worldwide eradication of variola virus and subsequent discontinuation of vaccination programs, today’s human population possesses low or nonexistent smallpox immunity and thus is highly susceptible to infection with smallpox virus.

Research scientists may obtain portions of the variola virus genome from the collaborating centers but not a complete genome. The distribution, synthesis, and handling of variola virus DNA are governed by recommendations from the World Health Organization.

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المزيد

مواضيع ذات صلة

HIV Infections in Humans: Laboratory Diagnosis

HIV Infections in Humans :Clinical Findings

HIV Infections in Humans : Pathogenesis and Pathology

Animal Lentivirus Systems

Classification of Lentiviruses

Viral DNA Is Integrated into the Host-Cell Genome in Some Nonlytic Viral Growth Cycles

Lytic Viral Growth Cycles Lead to Death of Host Cells

Viral Capsids Are Regular Arrays of One or a Few Types of Protein

Structure and Composition of Lentiviruses

HERPESVIRUSES

POLYOMAVIRUSES

Human T-Lymphotropic Viruses