CBRNE - Smallpox Clinical Presentation

Updated: Dec 16, 2014
  • Author: Christopher J Hogan, MD; Chief Editor: Duane C Caneva, MD, MSc  more...
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Presentation

History

Incubation periods for the major types of variola infection range from 7-17 days. Prodromal features are as follows:

  • An asymptomatic viremia occurs 72-96 hours after infection
  • At the end of the incubation period, a second viremia results in the onset of clinical symptoms such as high fever (102-105° F), myalgias (particularly backache), and headache
  • Rigors and vomiting are present in more than one half of patients
  • Delirium occurs in 15% of the infected population
  • This prodrome lasts 2-4 days, and, during this time, viremia is present and patients are most infectious

A rash appears 48-72 hours after the prodrome and progresses from macules to characteristic papules. During the period of mucosal lesions (just after appearance of the rash), the virus is highly contagious because the mucosal membranes lack a keratinized layer. As these cells slough, virus particles are shed, coughed, or sneezed into the outside environment.

Virus titers in saliva are highest the first week of infection, but infectivity can last up to 3 weeks (until the scabs fall off). Live virus can be cultured from scabs.

Early in the course of the disease, the rash and macules can easily be mistaken for varicella, given the coincidence of fever and myalgias. The macules give way to papules, and, finally, the characteristic pustules form, although this can take up to 2 weeks from exposure. The distribution and character of these lesions are the sine qua non of variola. These lesions contain a high viral load and are infectious.

Next:

Physical Examination

The clinical diagnosis of smallpox is based on major and minor criteria. [5] The major criteria are as follows:

  • A febrile prodrome 1-4 days before rash onset
  • The classic smallpox lesions (ie, deep-seated, firm, round, well-circumscribed)
  • Lesions that are at the same stage of development

The minor criteria include the following:

  • Centrifugal distribution of lesions, with the first lesions on the oral mucosa or palate, face, or forearms
  • Toxic or moribund appearance
  • Slow evolution of lesions of 1-2 days per stage
  • Lesions that appear on the palms and soles

A child with lesions of the variola strain is shown in the images below.

Unvaccinated infant with centrifugally distributed Unvaccinated infant with centrifugally distributed umbilicated pustules on day 3 of ordinary form of variola major strains of smallpox. Reprinted with permission from Fenner F, Henderson DA, Arita I, et al: Smallpox and its eradication. Geneva, Switzerland: World Health Organization; 1988: 10-14, 35-36; photographs by Arita.
Unvaccinated infant with centrifugally distributed Unvaccinated infant with centrifugally distributed umbilicated pustules on day 5 of ordinary form of variola major strains of smallpox. Reprinted with permission from Fenner F, Henderson DA, Arita I, et al: Smallpox and its eradication. Geneva, Switzerland: World Health Organization; 1988: 10-14, 35-36; photographs by Arita.
Unvaccinated infant with centrifugally distributed Unvaccinated infant with centrifugally distributed umbilicated pustules on day 7 of ordinary form of variola major strains of smallpox. Reprinted with permission from Fenner F, Henderson DA, Arita I, et al: Smallpox and its eradication. Geneva, Switzerland: World Health Organization; 1988: 10-14, 35-36; photographs by Arita.

In 10% of fair-skinned patients, a fleeting, erythematous exanthem can be seen before the typical cutaneous manifestations occur.

Lesions occur first in the oral mucosa, spreading to the face, then to the forearms and hands, and, finally, to the lower limbs and trunk. This is in distinction to the rash from varicella, which progresses centrally from the limbs.

Lesions are concentrated on the hands, face, feet, and calves. Lesions favor ventral surfaces and progress through stages of macule, papule, vesicle, papules (often umbilicated, like molluscum contagiosum), and crusts. Unlike in varicella, in which lesions in different stages are present, the exanthem of variola is synchronous, with numerous monomorphic lesions.

Crusts detach after 2-4 weeks, leaving depressed, hypopigmented scars. Pustular lesions are shown in the image below.

Adult with variola major with hundreds of pustular Adult with variola major with hundreds of pustular lesions distributed centrifugally. Fitzsimmons Army Medical Center slide file.

While the description above fits ordinary cases of smallpox (variola major), other presentations may occur. Hemorrhagic smallpox, shown in the image below, accounts for 3% of infections and has an exceptionally high mortality rate (94% in unvaccinated patients). Death usually ensues before the hemorrhagic macules can progress to papules.

Hemorrhagic-type variola major lesions. Death usua Hemorrhagic-type variola major lesions. Death usually ensued before typical pustules developed. Reprinted with permission from Herrlich A, Mayr A, Munz E, et al: Die pocken; Erreger, Epidemiologic und klinisches Bild. 2nd ed. Stuttgart, Germany: Thieme; 1967. In: Fenner F, Henderson DA, Arita I, et al: Smallpox and its eradication. Geneva, Switzerland: World Health Organization; 1988: 10-14, 35-36.

Soft or velvety skin lesions are present in flat smallpox, which has a 95-100% mortality rate in unvaccinated patients.

Alastrim, or variola minor, shown in the images below, presents with lesions like those in variola major except that they are smaller and less numerous.

Ordinary form of variola minor strain of smallpox Ordinary form of variola minor strain of smallpox (alastrim) in an unvaccinated woman 12 days after onset of skin lesions. The facial lesions are sparser and evolved more rapidly than the extremity lesions. Reprinted with permission from Fenner F, Henderson DA, Arita I, et al: Smallpox and its eradication. Geneva, Switzerland: World Health Organization; 1988: 10-14, 35-36; photographs by Arita.
Ordinary form of variola minor strain of smallpox Ordinary form of variola minor strain of smallpox (alastrim) in an unvaccinated woman 12 days after onset of skin lesions. The facial lesions are sparser and evolved more rapidly than the extremity lesions. Reprinted with permission from Fenner F, Henderson DA, Arita I, et al: Smallpox and its eradication. Geneva, Switzerland: World Health Organization; 1988: 10-14, 35-36; photographs by Arita.
Ordinary form of variola minor strain of smallpox Ordinary form of variola minor strain of smallpox (alastrim) in an unvaccinated woman 12 days after onset of skin lesions. The facial lesions are sparser and evolved more rapidly than the extremity lesions. Reprinted with permission from Fenner F, Henderson DA, Arita I, et al: Smallpox and its eradication. Geneva, Switzerland: World Health Organization; 1988: 10-14, 35-36; photographs by Arita.

Variola may be seen without an eruption in 30-50% of vaccinated contacts of patients with smallpox. Patients develop a mild prodrome followed by conjunctivitis without skin changes.

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