Smallpox (Infective Dose (ID₅₀) believed to be 10-100 organisms) follows deposition of virions in airways or oral passages. After exposure, the virus replicates in the pharynx and respiratory tract, and then travels to regional lymph nodes where it replicates and gives rise to viremia and then rash. During the prodrome, but before pox lesions are seen, the virus can be isolated from the blood. Once multiplication begins, the disease progresses rapidly.

• Malaise, fever, pharyngitis, rigors, vomiting, headache, backache and, in some, delirium
• Two to three days later, small red spots appear on the tongue and in the mouth.
• This is followed by development of rash; beginning on the face, then spreading to the arms and legs, then to the hands and feet.
• By the third day, the rash becomes raised bumps, which later become pustular and firm, like small round objects under the skin.
• In the second week, pustules form scabs with depressed, depigmented scars
• Virus can be recovered from scabs throughout convalescence
• Patients should be considered infectious until all scabs separate at 2-3 weeks

Diagnostic Samples : Pharyngeal swab, scab matter, nasal swab, serum

Differential Diagnosis : varicella, erythema multiforme, contact dermatitis

Isolation/Decon Precautions

• Victim (overt attack): Undress, soap, and shower. Use 1:10 household bleach (0.5%)diluted with water for gross or visible contamination.
• Responder: Surveillance and containment (S/A/C) (maintain minimum 17d until all scabs separate)
• Environment: 0.5% bleach
• At time of illness, environment is probably no longer contaminated from initial attack. However, virus may survive in scabs from patient for several weeks. (Note: Virons in scabs may remain viable for years, but their being bound in fibrin probably reduces their practical danger).

Therapy

• Smallpox vaccine Give immediately if previous vaccination was > 3y earlier. Otherwise, effective if given within 3d of exposure.
• Cidofovir (pediatric dosage is not established) possibly effective, at least prophylactically, based on in vitro and animal data. Not licensed for this indication.
• Supportive therapy plus antibiotics to curtail secondary infection may be indicated.

Prophylaxis

• Vaccination with vaccinia. A single dose by scarification. Guidance during the era of endemic smallpox was to boost every 10 years.