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SMALLPOX

Smallpox (variola) is an acute, viral illness that is highly contagious in unvaccinated populations. Because of an aggressive, successful worldwide effort toward eradication of smallpox, vaccination for this disease was discontinued (along with booster injections) in the US in 1972, and in the remainder of much of the world by the 1980s. Samples of the virus were retained in government labs in the US and Russia. The factors of high contagion in unvaccinated populations, worldwide discontinued vaccination, lack of effective drug therapy, and capability of aerosolization and distribution make smallpox a serious public health concern and an attractive tool of bioterrorism.

The smallpox virus is a large DNA virus that, when existing free in human populations, infects essentially everyone, with death following in approximately 30% of those infected. The virus is usually spread by inhalation via droplets from coughing of infected individuals. The virus is also present in high concentrations in the skin lesions, so spread also occurs via hand contact and contact with dressings, clothing, bed linens, etc. This was the case in the apparent first use of smallpox as a tool of bioterrorism in the French and Indian War (1754-1767). British soldiers introduced blankets used by smallpox victims to the American Indians; an epidemic followed, with an approximate 50% mortality rate.

After exposure to the virus, an incubation period of 7-17 days occurs (average of 12 days), after which the patient experiences nonspecific flu-like symptoms of fever, headache, and muscle aches for 2-4 days. A rash then appears most prominently on the face and extremities (including soles and palms), the skin lesions progressing together (synchronous) through the stages of papules (flat, red spots), macules (raised, red spots), vesicles (blisters), and deep pustules. The patient is contagious from the onset of the rash until the scabs of the pustules are gone, usually about 3 weeks. In rare circumstances, smallpox will present as "malignant" or "hemorrhagic" variants in which the patient dies within a day or two of onset of symptoms. Because the pustules extend well beneath the skin, healing eventually leaves scars. Clinically, smallpox is confused with chickenpox (varicella), but in chickenpox (which is contagious before the rash appears) the rash is predominately on the trunk and appears in "crops", presenting a rash in a few days with a simultaneous representation of all of the above stages.

At present, there is no approved antiviral drug for smallpox. In prior years, effective vaccination (90-95%) was accomplished using a live virus (vaccinia) related to smallpox. Protection was thought to last 10-20 years, after which a booster was recommended, though data from historical smallpox outbreaks and studies of immunologic memory suggest that protection may extend for at least 50 years after vaccination or experiencing the disease itself. It is probable that those who were even remotely vaccinated for smallpox will carry immunologic memory and be able to mount a defense. In these individuals, exposure to the smallpox virus may well function as would a booster. Current protocols suggest vaccination with the vaccinia virus if exposure occurred within 3 days; vaccination plus vaccinia immune-globulin (VIG) if greater than a 3-day exposure. There are contraindications for receiving each of the above medications.

Laboratory identification of the smallpox virus is important and is initiated by obtaining liquid material on a swab from a vesicle/pustule, placing it in a vacutainer, sealing tightly, then placing the vacutainer in a strong, sealed, water-tight container for transport to the state laboratory or CDC. The material collected, as mentioned above, is extremely infectious, and should be handled further only by a high security (Biosafety Level 4) laboratory. Gloves and universal precaution procedures for highly infectious diseases should be used, along with a dilute hypochlorite (bleach) solution for decontamination. Further information and protocols will be sent to our clients from time to time and will be available on our website (www.prlnet.com). Additional information will also be available from the Centers for Disease Control and Prevention (CDC) website (www.cdc.gov).

If smallpox is suspected, and certainly after it has been identified, patient isolation and associated procedures apply in order to limit its spread. Medical support including hydration and medications for fever, itching and secondary infections are helpful.

Kenneth C. Cummings, MD
Chief, Clinical Pathology
October, 2001