High fever, prostration, headache, & backache with the rash appearing on day 3; Rash is maculopapular, then vesicular, then pustular; Rash begins on face/forearms & spreads to trunk and legs; [Cecil, p. 86] Chickenpox rash 1st on trunk; [Wallach, p. 1019]
The last case of smallpox was reported in 1978. The illness began with malaise, fever, vomiting, backache, and headache. A rash appeared two to four days later with rapid progression from macules to papules to deep pustular vesicles. Lesions were more abundant on the extremities and face and appeared in the same stage of maturity in a given area (unlike chickenpox in which the lesions are superficial vesicles in various stages of maturity more abundant on the covered parts of the body). The fatality rate for variola major was about 30% in unvaccinated populations. Transmission was by inhalation of droplets or inoculation of skin or conjunctiva. Less than 3% of variola major cases followed a hemorrhagic, rapidly fatal course. [CCDM, p. 561-4] Patients are not contagious until the rash appears, and at that stage, most patients are bedridden. Therefore, most secondary cases would occur in households and hospitals. Laundry and waste from patients are potential sources of infection. Encephalitis, similar to that observed in cases of measles and varicella, may occur. Petechiae and bleeding from the skin and mucous membranes may occur in the 10% of smallpox cases that are termed "malignant" or "hemorrhagic." Smallpox can be rapidly confirmed in the laboratory by electron microscopy of fluid from vesicles or pustules. "Vaccination administered within 4 days of first exposure has been shown to offer some protection against acquiring infection and significant protection against a fatal outcome." [Henderson DA, et al. Smallpox as a biological weapon.JAMA.1999;281:1735-45.] Hemorrhagic shock is one of the causes of death. [PPID 7th Ed., p. 3955] Cough and bronchitis were occasionally reported, but pneumonia was an unusual complication. Orchitis in 0.1% of cases; [Guerrant, p. 371, 372]
For updated text and symptoms of infectious diseases, see iddx.com.
Clinical; Culture; Electron microscopy (EM); PCR; [CCDM] EM cannot distinguish smallpox from monkeypox, vaccinia, or cowpox; [Guerrant, p. 373] See http://www.bt.cdc.gov/agent/smallpox/diagnosis/riskalgorithm/