Exposure Risk Assessment
Poxvirus Genera and Strains
A majority of occupational laboratory Orthopoxvirus infections reported in the United States are caused by Vaccinia virus. However, many other wild-type orthopoxviruses (e.g., camelpox, cowpox, monkeypox) can cause infections in humans.
Distinguishing between replication-competent and replication-deficient poxvirus strains is required to assess the risk of infection from accidental exposure:
- Replication-deficient poxvirus strains and vectors do not produce infectious virus in humans and therefore do not cause clinical infection. These include MVA, NYVAC, TROVAC, and ALVAC strains of Vaccinia virus.
- Replication-competent poxvirus strains are capable of causing clinical infection in humans as well as producing infectious virus that can be transmitted to other people. Vaccinia virus strains commonly used in laboratories include Western Reserve, Copenhagen, NYCBOH, Lister, and Temple of Heaven. Replication-competent strains may or may not have a TK gene knockout. Indeed, a majority of reported exposures to Vaccinia virus and subsequent infections involve a TK gene knockout strain. All wild-type orthopoxviruses are replication competent.
In laboratory settings, common exposures are through accidental inoculation (needle sticks) or contact with broken skin. Other exposures include contact with mucous membranes (e.g., ocular splashes) or inhalation.