Biological Warfare

Smallpox

The World Health Organization (WHO) declared smallpox eradicated in the wild in 1980. Smallpox is caused by variola virus. The incubation period is about 12 days (range: 7 to 17 days) following exposure. Initial symptoms include high fever, fatigue, and headache and back pain. A characteristic rash, most prominent on the mouth, face, and forearms, spreading to the trunk and legs, follows in 2-3 days. The rash starts with flat red lesions that evolve at the same rate. Lesions become pus-filled and begin to crust early in the second week. Scabs develop and then separate and fall off after about 3-4 weeks, leaving scars on the face. The majority of patients with smallpox recover, but death occurs in up to 30% of cases.

Smallpox is spread from one person to another by infected saliva droplets that expose a susceptible person having face-to-face contact with the ill person. Persons with smallpox are most infectious during the first week of illness, because that is when the largest amount of virus is present in saliva. However, some risk of transmission lasts until all scabs have fallen off. Bedding or clothing from an infected person can also transmit viruses.

Routine vaccination of civilians against smallpox ended when the variola virus was eradicated except for small samples kept for scientific research. The level of immunity, if any, among persons who were vaccinated is uncertain. Therefore, these persons are assumed to be susceptible.

Vaccination against smallpox is not recommended to prevent the disease in the general public and therefore is not available.

In people exposed to smallpox, the vaccine can lessen the severity of or even prevent illness if given within 4 days after exposure. Vaccine against smallpox contains another live virus called vaccinia. The vaccine does not contain smallpox virus.

The United States currently has an emergency supply of smallpox vaccine.

There is no proven treatment for smallpox but research to evaluate new antiviral agents is ongoing. Patients with smallpox can benefit from supportive therapy (intravenous fluids, medicine to control fever or pain, etc.) and antibiotics for any secondary bacterial infections that occur.

Related Links

Small Pox Vaccine Information Sheet

Cidofovir in the Therapy and Short-Term Prophylaxis of Poxvirus Infections