Distinguishing smallpox from other infections: a primer. (Initial Lesions Resemble Chickenpox).
The incubation period for smallpox averages 10-14 days, although it can be as short as a week or as long as 17 days. Early symptoms include abrupt onset of headache and fatigue, sometimes accompanied by intense muscle pain--particularly in the lower back. The high fever occurs 2-4 days from symptom onset; some patients experience nausea, vomiting, and abdominal pain. These symptoms may be indistinguishable from influenza.
This nonspecific "preeruptive phase" lasts about 3-5 days. Unfortunately, the disease can be contagious before external lesions appear, when intraoral lesions may precede skin rash by approximately 24 hours. Although virus is detectable in the preeruptive phase, data suggest that it may not be contagious until some lesions appear in the mouth or on the skin (JAMA 281:2127-37, 1999).
Virus is shed in highest titers and is most contagious in the first week of rash. The high fever may decrease once pox appear on the skin.
Initial lesions can be confused with chickenpox; however, there are some key differences to keep in mind, Dr. Harrison says.
Varicella typically starts and dusters on the scalp within the hairline, neck, and the upper trunk, and then spreads outward to the legs, arms, hands, and feet. Smallpox goes the other way: It starts and is most dense on the face, hands, and legs, and then spreads inward to the trunk.
Smallpox lesions are harder, firmer, and more deeply embedded in the skin than varicella lesions. Both varicella and smallpox lesions evolve through similar stages, starting as flat, red macules, evolving to bumpy papules, then to vesicles, and finally becoming pustules.
With chickenpox, in any given 5-inch chunk of skin, you will see chickenpox lesions in different stages of evolution. But in smallpox, the lesions will be nearly all the same--all macules, all papules, all vesicles, or all pustules. You might see smallpox of somewhat different stages at one time in different parts of the body--the trunk and the face, for example--but in any given body part all lesions will be evolutionarily equivalent.
All chickenpox lesions are usually crusted over by 10-14 days, but smallpox lesions may take 3-4 weeks. Both viruses are contagious throughout those periods.
Smallpox is 30%-50% fatal, compared with less than 1% for chickenpox. Smallpox patients who survive the first 7-10 days will likely pull through, unless they develop a secondary bacterial infection.
If you suspect a patient has smallpox, call the health department immediately and make a list of everyone who was in the waiting room and your office that day, Dr. Harrison says. Smallpox is spread by airborne droplets, and is most contagious within 3 feet. A 17-day quarantine is recommended for anyone who is exposed.
Evidence suggests that the smallpox vaccine is protective within 3-5 days after exposure. Vaccinia immune globulin also may be offered, although data have not conclusively shown that it works.
If immunization is necessary, be prepared for side effects. Back when children were routinely vaccinated for smallpox, about 15%-20% developed fevers of more than 1020 F for up to 1 week, and 70% had a fever for at least i day Swollen regional lymph nodes arose in about one-third of recipients. Some form of encephalitis (in about 1%) and cutaneous side effects (in about 85%) also may develop.
There is no proven treatment for smallpox, but cidofovir and adefovir have shown efficacy in the test tube and in primates. A third drug, methisazone, was tested long ago against smallpox; no new data are available.
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|Publication:||OB GYN News|
|Date:||Dec 15, 2001|
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