First U.S. Cowpox Infection: Acquired From Lab Contamination

17 February 2011 12:59 pm

A student laboratory worker at the University of Illinois, Urbana-Champaign, is the first person in the United States to come down with cowpox, a less dangerous relative of smallpox, and the culprit is lab contamination. Researchers from the U.S. Centers for Disease Control and Prevention (CDC) reported last week at the International Meeting on Emerging Diseases and Surveillance in Vienna that the unvaccinated patient was infected by a genetically modified cowpox virus strain in her research lab, one she had never even worked with, by inadvertently handling contaminated materials.

Cowpox exists in the wild in Europe and Asia, where it is carried by rats and other animals and is often reported in veterinarians and zoo workers, but isn't found in the United States except in research labs. It can severely affect immunocompromised patients, but is not normally lethal. CDC still recommends smallpox vaccination for all lab workers who come in contact with intact orthopoxviruses, a category that includes vaccinia, cowpox, and other animal viruses. The cowpox patient had declined vaccination since she had no intention of handling the virus, and the lab hadn't worked on cowpox for 5 years previous to the incident.

However, CDC investigators found cowpox DNA in many locations around the lab and in stocks of purportedly harmless virus, although no live poxvirus was found on surfaces. The student said she didn't recall an injury or needle stick prior to developing a painful lesion on her finger in July 2010, so it seemed the infection likely occurred from handling chemicals and contaminated samples. In October, a biopsy was sent to CDC, which worked with the Illinois Department of Public Health (IDPH) to identify the disease as cowpox caused by one of the modified virus strains stored in the lab's freezer.

Mary Reynolds, an epidemiologist in the CDC's Division of High-Consequence Pathogens and Pathology who worked on the study, said that CDC and IDPH have made safety recommendations to the University of Illinois's biological safety department that are now under consideration. University spokesperson Robin Kaler said that while the investigation showed that the lab had been following established campus policy for storing hazardous materials, the campus is now taking steps to ensure that all people in a lab with such materials are aware of safety procedures. The laboratory personnel worked with investigators to track the course of the infection and concluded that no data from the contaminated samples had been published.

Gigi Kwik Gronvall of the Center for Biosecurity of the University of Pittsburgh Medical Center in Baltimore, Maryland, calls the incident "one more example of many examples that speaks to the need for more vigilance" in lab practices. Infections from labs, she says, could be far more common than reported, partly because labs don't want the blame and partly because in the absence of a needle stick, patients have trouble pinning down why they are sick. Identifying the cause may be particularly difficult in the case of infection by recombinant organisms, which must be reported to the National Institutes of Health and CDC. A patient's symptoms may be different than those caused by a wild organism. Fortunately in this case the distinct pustule formed by cowpox was telling.

"We're becoming quite interested in the concept of people inadvertently being infected with recombinant organisms, not necessarily because of a high safety risk but because of the challenge it provides to state health departments in confirming diagnosis," says Reynolds. Genetic modification of viruses can confound the usual DNA sequencing methods used to identify the virus and make it even more difficult to track down the source. Reynolds says that CDC investigators are beginning to work with the National Institutes of Health Office of Biotechnology Activities and state public health agencies to discuss better ways to diagnose such infections.

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