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Home Books Fitzpatrick's Dermatology in General Medicine, 8e

Chapter 195. Poxvirus Infections

Caroline Piggott; Sheila Fallon Friedlander; Wynnis Tom

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Poxviruses at a Glance
  • Poxviruses are the largest animal viruses; they can cause disease of varying severity in humans.
  • Smallpox is the only poxvirus for which humans are the sole reservoir, which allowed its eradication.
  • The smallpox vaccine virus, vaccinia, has its own adverse effects.
  • Monkeypox is a zoonotic infection endemic in Africa, but it has recently appeared in the Western Hemisphere.
  • Milker's nodule and orf mainly cause localized cutaneous infections.
  • Molluscum contagiosum is generally a benign cutaneous disease most frequently seen in children and immunocompromised individuals.
  • Histopathologic features of poxviral cutaneous lesions include the presence of intracytoplasmic eosinophilic inclusion bodies.

Poxviruses are double-stranded DNA viruses that replicate in the cytoplasm of host cells (Table 195-1). These “brick-shaped” viruses constitute the largest known animal viruses and can be seen with light microscopy.1 The poxviruses that cause significant disease in humans are reviewed here. Their effects on the host range from systemic disease to localized infection to epithelial cell proliferation alone.

Table 195-1 Poxviruses with Humans as Hosts
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Table 195-1 Poxviruses with Humans as Hosts

Genus

Species

Hosts

Main Portal of Entry

Clinical Features

Orthopoxvirus

Variola virus

Humans

Respiratory tract

High fever and myalgias precede oropharyngeal enanthem and centrifugal exanthem.

Simultaneous progression of skin lesions from macules to papulovesicles, pustules, and crusts, resulting in significant scars.

Last reported case in 1978; concern for use in bioterrorism.

Vaccinia virus

Humans

Skin

Used as vaccine for smallpox and monkeypox.

Vaccination site progresses from papule to vesicle, pustule, and crust, leaving scar.

Adverse events occur when virus spreads locally or in a generalized manner, more severe in individuals with disruption of the skin barrier or immunocompromise.

Monkeypox virus

Rodents, humans, monkeys, anteaters

Skin

Clinical presentation similar to that of smallpox but more prominent lymphadenopathy and lower mortality.

Cowpox virus

Rodents, cats, humans, cattle

Skin

Contact with infected animal host gives rise to papule that becomes vesicular, hemorrhagic, pustular, and ulcerative; resulting eschar heals over 3–4 weeks with scarring.

Pustular stage: often umbilicated with surrounding zone of erythema and edema.

Constitutional symptoms and lymphangitis common.

Can be extensive or severe if skin barrier disrupted.

Parapoxvirus

Orf virus

Sheep, goats, humans

Skin

Contact with infected animal or fomite leads to papule(s) that forms pustules or nodules with central umbilication and surrounding gray-white or violaceous ring and outer zone of erythema; lesion usually occurs on hand.

Lesions become weepy then dry and crust.

Healing occurs over 4–8 weeks, usually without scarring.

Constitutional symptoms/lymphangitis occur less commonly.

Paravaccinia virus

Cattle, humans

Skin

Transmission by contact with infected teats/mouths of cattle.

Clinical findings and course similar to those of orf; differentiated by their different animal hosts.

Bovine papular stomatitis virus

Cattle, humans

Skin

Transmitted by contact with infected mouths of cattle.

Clinical findings and course similar to those of orf and paravaccinia.

Molluscipoxvirus

Molluscum contagiosum virus

Humans, chimpanzees (one report)

Skin

Discrete firm, ...

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