For the first time in decades, China reported a human outbreak of vaccinia virus (VACV), according to a study yesterday in Emerging Infectious Diseases.
VACV is an orthopoxvirusvirus that is used in the live-virus vaccine against smallpox. It is related to cowpox and monkeypox viruses and can cause severe illness in humans.
Exposure from inoculated lab rabbits
The study details how five Chinese powder processing workers contracted VACV in 2017, after pulverizing a batch of frozen rabbit skins. The animals had been inoculated with VACV in a pharmaceutical lab 5 days previously, and their pulverized skin was being studied for analgesic properties.
All five case-patients handled the pulverized skin in an enclosed workspace over the course of 1 hour, and none wore personal protective equipment. Three other employees who were also in the workplace—but wore masks and did not handle the pulverized skin directly—did not contract the virus.
All five case-patients developed pulmonary infections marked by high fevers within 5 days of the exposure, and three of them went on to develop vesicular-pustular lesions on their hands, the authors said. One patients was hospitalized, and the others were treated at home with anti-inflammatory medications and instructed to avoid close contact with friends or family members until they were without fever and their lesions had healed.
Molecular data collected from patient samples tested positive for VACV.
Three of the patients had received prior smallpox vaccination and had less severe clinical manifestations than the others, the authors said. This indicated that vaccination may have reduced illness severity.
Common exposure route could lead to bigger outbreak
The authors conclude, "The likely transmission route was contact with infected rabbit skins. However, we cannot exclude transmission through aerosolized or suspended infectious particles, considering all 5 patients had pulmonary infection and only 3 cases had characteristic VACV skin lesions."
They note that transmission in this outbreak differs from outbreaks in Brazil and Europe, where cases were connected to contact with infected dairy cattle or to lab accidents.
"VACV is commonly used in research settings and the biopharmaceutical industry. Functional studies on extracts from rabbit skins inoculated with VACV are common in China," the authors wrote.
"Besides using standard contact protections, those who handle animals vaccinated with VACV, or their products, should use proper respiratory protection."
The authors also said the inadvertent exposure of VACV into local animal populations could lead to a wider zoonotic outbreak, as seen in recent years in Brazil.
Apr 23 Emerg Infect Dis study