Monkeypox: A Potential Global Pathogen
Abstract & Commentary
Synopsis: High incidence of human-to-human transmission of monkeypox, a potentially fatal infection similar to smallpox, raises concern about further spread in humans.
Source: Mwamba PT, et al. Human monkeypoxKasai Oriental, Zaire, 1996-1997. MMWR Morb Mortal Wkly Rep 1997;46:304-307.
Recent evidence from zaire suggests that another poxvirus thought previously to be a curious enzootic can be spread by human-to-human transmission. Monkeypox is from the orthopoxvirus family and has been known in the rainforests of central and western Africa, after first being reported in 1958 following acquisition from cynomolgus monkeys. Human illness is nearly indistinguishable from smallpox, although occasionally, lymphadenopathy is seen in monkeypox. This infection was clinically described in Zaire and West Africa in 1970. Until 1996, only a few hundred cases had been reported, but an outbreak in 1996 that continues into 1997 has shown striking ability to be passed among humans.
In 1985, a low secondary attack rate in households offered reassurance that this virus would only appear in sporadic cases resulting from animal contact. However, in a single village in February 1996, a single family member became infected from animal contact and, subsequently, eight members of his family became infected. In fact, between February and August 1996, 71 clinical cases were found, including six deaths, occurring in 13 villages in Africa in the Katako-Kombo health zone (pop. 15,698), Sankuru Subregion, Kasai Oriental, Zaire. This outbreak was associated with a far higher (73%) secondary attack rate compared with previous reports (30%). The diagnosis was confirmed virologically in 11 cases using serum and/or crusted scab or vesicular fluid. Virologically, there is no evidence that the virus itself has changed. In fact, there is little genetic difference between the 1996-1997 virus and the monkeypox described in the decade of the ’70s. By late February, a total of 92 possible cases were identified by a village-to-village search.
Akungula is the village with the highest attack rate (11 per 100 population). The 45 cases in this village were clustered in eight of 44 housing compounds. A total of 84 cases provided vaccination data. Of these, 15 (18%) had a vaccinia vaccination scar. Of these, 13 (87%) were older than 25 years of age. Three patients (3%) died, and all of these were under the age of 3, although some deaths were not counted in the analysis because the village was not searched for cases. This was a lower case fatality rate, compared with previous reports of about 10%. Where histories were available, 73% of patients reported having been in contact with another patient 7-21 days prior to the onset of the illness. Following August 1996, the reported cases decreased, although an increase was again noted in February 1997. Given the political situation that currently exists in that country, reliability of data must be somewhat tenuous. Investigators are looking into tree squirrels (Funisciurus sp.) and sun squirrels (Heliosciurus sp.) as possible reservoirs, but data are pending.
COMMENT BY STEPHEN L. SACKS, MD
While this outbreak does not ring the world alarm for reinstitution of vaccinia vaccination, the appearance of this disease in the context of person-to-person spread does bear a very probably direct relationship to the abandonment of routine vaccination in the late 1970s. Happily, secondary transmission in this outbreak appears to have a lower fatality rate. For now, authorities have been trying to reduce infection through education concerning contact with animals and by encouraging only people with full vaccination status to provide primary care to patients.
Some limited reinstitution of vaccinia vaccination may be called for. One can only imagine how the current political crisis in this country may be affecting these attempts at assessment and control. The world abandoned vaccinia vaccine because the reservoir for infection was entirely human and had been entirely eliminated. A new gift from the animal kingdom does not represent a new disease, but it does represent a new understanding of an old disease. For now, we can only watch and wait and hope that this person-to-person transmission potential stays highly localized and controlled.
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