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 |Favorite Table|Download (.pdf)
Table 195-1 Poxviruses with Humans as Hosts
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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.
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.
Rodents, humans, monkeys, anteaters
Clinical presentation similar to that of smallpox but more prominent lymphadenopathy and lower mortality.
Rodents, cats, humans, cattle
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.
Sheep, goats, humans
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.
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
Transmitted by contact with infected mouths of cattle.
Clinical findings and course similar to those of orf and paravaccinia.
Molluscum contagiosum virus
Humans, chimpanzees (one report)
Discrete firm, ...