May 17, 2016
2 min read

African monkeypox outbreak suggests frequent community, familial transmission

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Data from a 2013 outbreak of monkeypox virus in the Democratic Republic of the Congo indicated more frequent community and familial transmission than previously reported.

Monkeypox virus (MPXV), which belongs to the Orthopoxvirus genus, is zoonotic and endemic to western and central Africa,” Leisha Diane Nolen, MD, PhD, of the CDC’s Epidemic Intelligence Service, and colleagues wrote. “No targeted medications are licensed to treat this infection. Although smallpox vaccination can provide some protection against infection, this vaccination is not used in MPXV-endemic areas because of cost considerations and safety concerns about using a vaccine that contains live vaccinia virus.”

Reports of an approximately sixfold increase in suspected MPXV cases within one health zone of the Democratic Republic of the Congo (DRC) prompted a public health investigation of a potential outbreak, Nolen and colleagues wrote. They examined all cases of MPXV reported to the DRC’s regional surveillance system from July 1, 2013 to Dec. 8, 2013, with those displaying clinical symptoms and positive PCR results classified as confirmed cases. The researchers also defined patients’ incubation periods, and analyzed potential transmission chains within families and villages.

Nolen and colleagues identified 104 suspected cases of MPXV infection and 10 reported deaths during the study period, a marked increase over the 17 cases reported in 2011 and 13 cases observed in 2012. Of the 60 cases (57.7%) with active lesions collected for testing, 83.3% were positive for MPXV, and 8.3% were positive for varicella zoster virus. The researchers conducted household interviews for 63 case-patients in 16 households, finding a median household attack rate of 50%. The median age of these case-patients was 10 years (range, 4 months to 68 years), and nearly one-fifth were aged younger than 5 years.

Among 16 patients with well-defined incubation periods, the researchers found a mean incubation period of 9.6 days. In a secondary analysis in which additional incubation periods were calculated by using the difference in time of onset between the first and second cases within 12 households, the mean incubation period was 8.3 days, and a third analysis using a previously reported methodology found a mean of 9.7 days. Using a 5- to 13-day incubation range, the researchers also constructed transmission chains revealing at least one transmission event in 16 households, as well as longer chains of transmission in the DRC village of Bokungu, where seven or more events resulted in 42 apparent cases.

The number of positive cases and the observed household attack rate in 2013 greatly exceeded those of previous reports, the researchers wrote. Furthermore, these new data suggested incubation periods were shorter than those observed among animals, as well as widespread transmission throughout families and communities.

“Measures to decrease this attack rate should be implemented, including family-based education related to hygiene and isolation of patients,” they wrote. “The transmission patterns observed in this outbreak also suggest transmission at the community level; therefore, communitywide education should begin as soon as the first monkeypox case is identified in an area.” – by Dave Muoio

Disclosure: The researchers report no relevant financial disclosures.