^{From left to right: Robert Kozak, Sharmistha Mishra and Darrell Tan}

March 7, 2024

By Betty Zou

A new University of Toronto study has found that mpox virus DNA can be found in different parts of the body for up to four weeks after symptom onset.

The study, led by researchers at Unity Health Toronto and Sunnybrook Research Institute, is one of several projects supported by the mpox rapid research response launched by the Emerging and Pandemic Infections Consortium and its hospital partners during the global mpox outbreak in 2022.

According to the World Health Organization, nearly 94,000 confirmed cases of mpox, including 179 deaths, have been reported from 117 countries since January 2022. As of September 2023, 1,515 cases have been confirmed in Canada, mostly in Ontario and Quebec.

“Even though we’ve known about mpox for over 70 years, it was new to us because we hadn’t seen it outside the endemic regions. There was still a lot about the virus and disease that we didn’t know,” says Robert Kozak, one of the study’s authors and an assistant professor of laboratory medicine and pathobiology at U of T’s Temerty Faculty of Medicine.

To answer key questions about viral shedding, Kozak teamed up with Darrell Tan and Sharmistha Mishra, both associate professors in the Temerty Faculty of Medicine and infectious disease physicians at Unity Health Toronto, where some of Toronto’s first patients with mpox were identified and cared for.

The researchers analyzed samples from 64 men who contracted mpox, which included participants from the Mpox Prospective Observational Cohort Study (MPOCS) led by Tan. The samples were taken from six different sites on the body — genital region, nasal cavity, semen, skin, throat and urine — and over an extended period of time.

Using a technique called quantitative polymerase chain reaction (qPCR), the researchers found that the persistence of mpox virus DNA varied depending on where the samples were taken from. On average, mpox DNA was detected in skin swabs from the genital and perianal region and from other skin sites at 30 and 22 days after symptom onset, respectively. These findings are consistent with the sexually transmitted nature of mpox during the recent global epidemic, which primarily affected gay, bisexual and men who have sex with men. Notably, mpox virus DNA was still detectable in nearly half of genital skin swabs and in one in five skin swabs from other sites a week after all symptoms had resolved.

The researchers were unable to detect viral DNA in a large proportion of semen samples and nasal cavity swabs taken when individuals first presented with symptoms whereas in urine and throat swab samples, mpox DNA persisted for roughly two weeks after symptom onset.

Interestingly, the researchers did not observe a difference in the length of viral DNA persistence between people who received the antiviral drug tecovirimat and those who did not. Tan notes that while study participants were not randomly assigned to receive the drug, these results underscore the uncertainty around tecovirimat’s effectiveness in treating mpox infections.

As a clinician, Tan thinks the study provides several key learning for his clinical colleagues. “First, we’ve documented the breadth of clinical samples in which mpox DNA can be identified and therefore can be used to confirm a diagnosis. Our findings also reinforce that it’s worthwhile for clinicians to collect such samples in individuals where an mpox diagnosis is being considered, even after symptoms of feeling unwell are gone.”

The researchers caution that just because mpox DNA can be detected up to four weeks after symptom onset, it doesn’t mean that individuals are infectious for that long.

“We don’t know for sure whether the presence of detectable viral DNA necessarily means that the virus is transmissible to other people, so more research definitely needs to be done to determine definitively the period of infectiousness,” says Tan.

To answer that question, Jacklyn Hurst, a postdoctoral fellow in Kozak’s lab, recently started work in the Toronto High Containment Facility (THCF) to look for live virus in the same samples from which mpox DNA was detected. The researchers are also using the THCF’s biobank of mpox patient samples to identify biomarkers that could predict whether a person will have a mild or severe infection.

“Without the Toronto High Containment Facility, we wouldn’t be able to do any of this. Having that facility will help us answer a lot of questions about this virus and how to stop it,” says Kozak, who is also a clinical microbiologist and scientist at Sunnybrook Research Institute.

He also acknowledges the immense contributions of the patient community to this work. “A huge thank you to all the study participants. We wouldn’t be able to do this work without their sacrifice and commitment.”