A study of 2,510 contacts of 214 patients with human monkeypox was conducted in Zaire from 1980 to 1984. Among the contacts of 130 primary cases of human monkeypox, a further 22 co-primary and 62 secondary cases were detected, and an additional fourteen people who had no evidence of clinical disease had positive serological results. A majority of the clinical and subclinical cases of monkeypox occurred in children less than 10 years of age. Immunity in vaccinated persons now appears to be waning because 16 overt cases occurred in contacts who had been vaccinated. The overall attack rate for contacts without a vaccination scar (7.2%) differed significantly from the attack rate for those who had been vaccinated in the past (0.9%). The attack rate for household contacts was significantly higher than that for other contacts, among both unvaccinated (four times higher) and vaccinated (seven times higher) household contacts. Many unvaccinated contacts living in the same household as the index case under conditions of maximum exposure, however, escaped not only the disease but also infection.

This paper examines an outbreak of five cases of human monkeypox which occurred in children belonging to two families living in the West Kasai region of Zaire during May-July 1983. Epidemiologic investigations suggest that the first case was infected from an animal source, possibly a monkey, and that each of the other four cases was infected from a previous human case. Three of these cases of presumed person-to-person transmission occurred in close household contacts. The other case infection occurred either by casual contact within the hospital compound, or possibly because of infection due to use of the same syringe for injections. Human monkeypox is the most important orthopoxvirus infection in the post-smallpox eradication period. The disease is a zoonosis and person-to-person transmission is rather difficult. Thus, this episode is a rare event and special analysis of the circumstances is discussed. However, it supports the necessity to carry out surveillance and research on this disease as recently reported by Arita et al.

SUMMARYPoliovirus isolates of serotypes 2 and 3 from patients whose paralytic poliomyelitis cases were classified as oral vaccine-associated were analysed by oligonucleotide mapping of the virus genomes and by polyacrylamide gel electrophoresis of the virus proteins. Oligonucleotide maps of all isolates were similar to the maps of the ~ corresponding oral vaccine strain. No two isolates gave identical maps. Most maps differed from that of the vaccine strain by at least one oligonucleotide spot. Maps of some isolates revealed numerous differences, indicating that multiple (> 100) genetic changes had occurred in the vaccine virus genomes during replication in one or two individuals. In contrast, maps of some neural tissue isolates showed minimal differences from the reference vaccine maps, raising the possibility that neurovirulence may be restored by a small number of genetic changes. For many isolates, changes were also detected in the mobilities and processing rates of the virus proteins.

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A poxvirus was isolated from a wild gerbil (Tatera kempii) caught in northern Dahomey, Africa at the time of an epidemic of human smallpox. Electron microscopic appearance and serologic reactions placed it in the vaccinia subgroup of poxviruses. The isolate differed from ectromelia, rabbitpox, vaccinia, monkeypox, and cowpox viruses in pock morphology on chorioallantoic membrane, ceiling temperature, relative innocuity for mice, and cytopathic effect in tissue culture. Like variola minor virus, it had a ceiling temperature of 38 C, produced small hypertrophic foci in tissue culture, and failed to grow in rabbit skin. Inoculated into a rhesus monkey, it caused fever but no skin eruption and produced seroconversion and protection from subsequent challenge with monkeypox virus. The growing list of animal viruses that differ only slightly from smallpox virus suggests the hypothesis that long-term survival of variola virus may be based on inapparent infection in animals as well as virulent spread among humans.