Chapter 17: Viral Diseases

DNA VIRUSES

1. Pox viruses

2. Papillomaviruses

3. Herpes viruses

4. Parvoviruses

5. Hepadnavirus

Pox Viruses

• Large, enveloped, double-stranded, linear DNA viruses

• Belong to the Poxviridae family

• Replicate in the cytoplasm, except for the adenovirus

• Poxviruses of clinical importance include smallpox, vaccinia, monkeypox, molluscum contagiosum, orf, and milkers' nodules

MOLLUSCIPOX (MOLLUSCUM CONTAGIOSUM; MCV)

• Common, benign, self-limiting skin disease

• Generally affects pediatric age group

• Virus commonly acquired by skin-to-skin contact (nonsexual)

• Incubation period is from 2 weeks to 6 months

• Four different strains have been identified (based on restriction endonuclease digestion pattern). Two main subtypes: MCV I, responsible for the majority of infections in the United States, and MCV II (more prevalent in HIV patients); both are genital/nongenital

• Clinical

  • 3- to 6-mm erythematous or skin-colored, dome-shaped, umbilical papules distributed over the trunk and face. The lesions may persist for 6 to 8 weeks or more (Fig. 17-1)

  • In immunocompromised patients, especially HIV-infected individuals, thousands of papules distributed on the body and face. High risk of bacterial infection and treatment resistance

  • Genital papules: usually sexually transmitted, most common in adults (Fig. 17-2)

  • Positive Koebner reaction

  • Free virus cores found in all layers of epidermis

• Diagnosis

  • Clinical

  • Confirmatory biopsy in some cases. Henderson-Paterson bodies (molluscum bodies) = viral particles in infected keratinocytes, eosinophils

• Treatment

  • Resolution is often preceded by inflammation, uncomplicated lesions heal without scaring

  • Physical destruction (salicylic acid, liquid nitrogen, cantharidin, lactic acid, CO₂, trichloroacetic acid)

  • Immune modulation: imiquimod

  • Manual extrusion (curettage) of the lesions

  • Cidofovir in immunocompromised patients

SMALLPOX

• Caused by variola virus; variola minor also known as alastrim

• Serious, contagious, and sometimes fatal infectious disease

• Eradicated after a successful worldwide vaccination program

• Face-to-face contact is not required to be infected, direct contact with infected body fluids or contaminated objects

• Humans are the only natural host

• Clinical

  • Incubation 12 to 13 days, fever, malaise, backache, body aches, and exanthem that appears after 2 to 4 days

  • Two clinical forms: Variola major, most common and severe form with a 30% incidence of mortality (secondary to pulmonary edema from heart failure), 4 clinical types: ordinary, modified (by previous vaccination), flat, and hemorrhagic; and Variola minor, less severe and 1% mortality

  • Early rash appears as small red spots in the mouth; macules → papules → vesicles → pustules; all lesions exist in the same stage

  • Complications: corneal ulceration, laryngeal lesions, encephalitis, hemorrhage

  • Progressive vaccinia related to immunosuppression, malignancy, radiation therapy, or AIDS

• Vaccination: rare postvaccinal encephalitis and progressive vaccinia; high level immunity ...