Human Monkeypox—Kasai Oriental, Zaire, 1996–1997*

Monkeypox is an orthopoxvirus with enzootic circulation in rainforests of central and western Africa; the virus can be transmitted to humans and cause a syndrome clinically similar to smallpox (e.g., pustular rash, fever, respiratory symptoms, and in some cases, death). From February through August 1996, a total of 71 clinical cases of monkeypox, including six deaths, occurred in 13 villages in Africa in the Katako-Kombe health zone (1996 combined population: 15,698), Sankuru subregion, Kasai Oriental, Zaire. During the initial investigation of this cluster of human cases, specimens of serum and/or crusted scab or fluid from vesicles were collected from 11 patients, and monkeypox virus infection was confirmed in all 11 patients by the World Health Organization (WHO) Collaborating Center for Smallpox and Other Poxvirus Infections at CDC. Preliminary DNA phylogenetic studies of this strain of virus indicated only minor genetic variation compared with other strains of monkeypox virus from Zaire collected during 1970-1979. Because of reports by local public health officials of ongoing disease transmission, the Zaire Ministry of Health and WHO organized a follow-up investigation in February 1997 to characterize the magnitude of the outbreak. This report summarizes the preliminary results of the ongoing multidisciplinary investigation, which suggest that person-to-person transmission accounted for most monkeypox cases investigated in 1996 and 1997; in contrast, during previous years, reports were primarily for sporadic cases that resulted from animal-to-human transmission.