People handling certain historical materials should consider the possibility of residual contamination with viruses and bacteria that could potentially still be viable. This includes orthopoxviruses such as Variola virus, the cause of smallpox, a serious but eradicated disease. Historical materials include, but not limited to, biological specimens (particularly human and zoological), artifacts, and library archives.
What are orthopoxviruses?
Orthopoxvirus is a genus of viruses (e.g., camelpox, cowpox, monkeypox, and smallpox viruses) that generally cause skin lesions in humans and other vertebrates, most notably cats, rodents, and ungulates (e.g., camels, cows, sheep).
The most concerning Orthopoxvirus species is Variolavirus, which causes smallpox. A serious disease that only affects humans, smallpox was eradicated worldwide in 1980 using vaccination with live Vaccinia virus, another Orthopoxvirus.
What are the symptoms of Orthopoxvirus infections?
Symptoms of smallpox include skin lesions such as vesicles and scabs. Vaccination with Vacciniavirus produces a localized lesion at the vaccination site. Infections with other orthopoxviruses in humans can produce similar skin lesions to smallpox but with milder symptoms.
How could orthopoxviruses be transmitted from historical specimens?
Transmission of Variolavirus, Vacciniavirus, and other orthopoxviruses can occur through direct contact with skin lesions (vesicles or scabs), or through objects contaminated by them.
The viability of orthopoxviruses in well-preserved human samples (skin lesions and scabs) has not been fully determined. Environmental conditions are likely to influence the longevity of the virus. For example, lesion materials stored in dry, dark, and cool conditions can remain infectious for years. Under experimental conditions, viable Variolavirus was isolated from human skin scabs stored in envelopes at room temperature for at least 13 years (researchers did not examine longer durations). Conversely, high humidity and direct sunlight will rapidly inactivate Variola virus.
Have live orthopoxviruses ever been recovered from historical specimens?
There are no published reports of residual live orthopoxviruses in historical specimens, or of human cases acquired from handling such specimens. In the United States, the CDC Poxvirus Laboratory has tested several cadavers and human skin scabs associated with smallpox infection and vaccinia vaccines. None of these yielded live Orthopoxvirus capable of infecting people.
The risk of human infection from historical specimens is low. However, the scarcity of data makes the risk difficult to assess and the possibility of live orthopoxviruses in well-preserved tissues or other materials cannot be excluded.
What historical specimens might carry orthopoxviruses?
Historical specimens include exhumed cadavers (particularly when preserved in crypts or permafrost) and artifacts contaminated by skin lesions. These might include scabs contained within envelopes, clothing, blankets, medical memorabilia (e.g., vaccination kits), or zoological specimens (e.g., hides and mounted animals).
Natural history museums or other mammalogical research collections may contain specimens that were collected from areas afflicted with Orthopoxvirus enzootics. Rodent specimens are of particular concern as certain species are putative reservoirs of members of the genus Orthopoxvirus.
When evaluating risk, collections authorities may recognize the presence of lesions consistent with orthopoxviruses or vaccine use in human or animal tissue. However, not all human or animal tissues with Orthopoxvirus infection will necessarily display visible lesions.
Managers should also consider whether specimens or artifacts originated from historical periods and areas with known Orthopoxvirus epidemics (monkeypox and smallpox).
Historical records indicate that smallpox outbreaks might have occurred since 1122 BCE. The last known outbreak in the United States was in 1949, and in 1980 the World Health Organization declared the disease eradicated worldwide.
What should you do if you suspect artifacts or human remains contain Orthopoxvirus?
Although smallpox has been eradicated, the possibility that it could re-emerge remains. This would have severe public health implications as routine vaccination is no longer practiced and therefore most people do not have immunity against it. If you suspect an Orthopoxvirus risk in historical materials, immediately contact your local or state public health department. State/local public health departments should call CDC at 770-488-7100 for consultation.
Because each historical object and associated account is unique and the circumstances of preservation differ, it is difficult to assess whether a material poses a risk just by looking at it. Suspicious items should be tested at state or federal public health laboratories for viable Variolavirus or other orthopoxviruses before any additional work is done with the specimens.
How can you mitigate the risk of unearthing live orthopoxviruses from historical materials?
People who work with potentially contaminated historical materials, such as archeologists, museum curators, collections managers, archivists, and construction workers, should be aware of the risk of Orthopoxvirus infection and wear gloves, gown, eye protection, and a fitted respirator when handling suspect material.
Routine smallpox vaccination is no longer practiced in the United States and is reserved for military personnel, and select laboratory and healthcare personnel.