Exportation of Monkeypox Virus From the African Continent.

BACKGROUND: The largest West African monkeypox outbreak began September 2017, in Nigeria. Four individuals traveling from Nigeria to the United Kingdom (n = 2), Israel (n = 1), and Singapore (n = 1) became the first human monkeypox cases exported from Africa, and a related nosocomial transmission event in the United Kingdom became the first confirmed human-to-human monkeypox transmission event outside of Africa. METHODS: Epidemiological and molecular data for exported and Nigerian cases were analyzed jointly to better understand the exportations in the temporal and geographic context of the outbreak. RESULTS: Isolates from all travelers and a Bayelsa case shared a most recent common ancestor and traveled to Bayelsa, Delta, or Rivers states. Genetic variation for this cluster was lower than would be expected from a random sampling of genomes from this outbreak, but data did not support direct links between travelers. CONCLUSIONS: Monophyly of exportation cases and the Bayelsa sample, along with the intermediate levels of genetic variation, suggest a small pool of related isolates is the likely source for the exported infections. This may be the result of the level of genetic variation present in monkeypox isolates circulating within the contiguous region of Bayelsa, Delta, and Rivers states, or another more restricted, yet unidentified source pool.

Tail scarification with Vaccinia virus Lister as a model for evaluation of smallpox vaccine potency in mice.

Since smallpox eradication by the WHO during the 1980s, potency of new vaccines is compared to vaccines that were used during the eradication campaign. In this work we characterize the tail scarification technique in mice as a model for scarification in humans. Similar to humans, mice develop "clinical take" which is dependent on the vaccination dose. Appearance of anti-Vaccinia IgM is followed by IgG antibodies 10 days post scarification and lasting more then 1(1/2) years. Mice with "clinical take" are 100% protected against lethal respiratory challenge (100LD(50)) of Vaccinia WR indicating that the "clinical take" can serve as a correlate of protective immunity. Reducing the vaccination dose and using Cowpox virus as a more virulent strain, enabled us to draw the limit of the vaccine potency in mice. Similar to humans, in revaccinated mice the development of "clinical take" was inversely correlated to the level of pre-existing antibodies. These results indicate that tail scarification of mice can be used as a model for evaluation of smallpox vaccines. High correlation between "clinical take" and protective immunity allows the use of visual inspection to evaluate vaccine potency.