Extended Human-to-Human Transmission during a Monkeypox Outbreak in the Democratic Republic of the Congo

Monkeypox virus (MPXV), which belongs to the genus Orthopoxvirus, is zoonotic and endemic to western and central Africa. MPXV is a close relative of the variola virus, and monkeypox illness resembles a smallpox-like infection but is less severe than smallpox. Most patients initially develop a fever, followed by rash a few days later. Lymphadenopathy is a common sign and occurs just before or concomitant with the rash (1,2). Up to 11% of unvaccinated affected persons die (3). 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. MPXV transmission among close contacts within households is well documented; previous reports have shown up to 6 intrafamily transmission events (4). Transmission is thought to occur by means of salivary or respiratory droplets or contact with lesion exudate (5,6); however, evidence suggests that infection can occur by direct inoculation (7). Previous household attack rates (i.e., rates of persons living with an infected person and developing symptoms of MPXV infection) of 3%–11% have been reported (6,8). Although some reports show a high incidence of households with single isolated cases (8), other reports have documented frequent transmission events within households (6,9). Attack rates have been found to be much higher among persons living in households with an MPXV patient and among persons with no evidence of prior smallpox vaccination (6,8). Monkeypox is a reportable disease in the Democratic Republic of the Congo (DRC), and cases are reported from 26 health districts (containing 512 health zones). During 2013, a substantial increase in the number of suspected human monkeypox cases was noted in the Bokungu Health Zone within Tshuapa District of DRC’s Equateur province (Figure 1). In December 2013, we conducted an investigation of monkeypox for this health zone and focused on cases reported during July 1–December 8, 2013. Figure 1 Region affected by monkeypox illness. A) The Democratic Republic of the Congo is outlined; Tshuapa District is highlighted in yellow and Bokungu Health Zone in red. B) Health zones within Tshuapa District; Bokungu Health Zone is highlighted in red. The ...