On the basis of reported monkeypox onset dates in a largely retrospective study complicated by a concurrent outbreak of chickenpox, about 250 serosubstantiated cases of monkeypox occurred among 0.5 million people in 78 villages, from February 1996 to October 1997. About three-fourths of the cases appeared to result from human-to-human transmission; however, the secondary attack rate of 8% among unvaccinated contacts within households appeared to be about the same as in the 1981–86 surveillance.128,131
It is not known whether the monkeypox virus has ever been weaponized. However, the process would probably be similar to the method used to weaponize the smallpox virus. If a stable, infectious monkeypox biological aerosol was produced and delivered as a fine particle aerosol under ideal atmospheric conditions over a targeted population, one would expect to see large numbers of casualties presenting at about the same time to local hospitals and doctor’s offices with signs and symptoms as described here. Studies using aerosolized monkeypox virus suspensions have shown that it is a hardy virus that could potentially remain infectious for a long time, given the ideal environment.11 One primate study discussed different exposure results; how a lethal aerosolized dose would lead to severe respiratory disease with or without skin reactions, but a lethal intravenous exposure would result in systemic reactions causing death.12 Of course, these studies have evaluated nonhuman subjects and cannot predict the outcomes of monkeypox as a biological weapon used on humans.