It is not known whether the latest outbreak in France stems from the virus surviving in wild animals, such as deer, or being reintroduced from elsewhere.
A good number of species only exist in captivity and still more only exist in the wild because they have been reintroduced from zoos, or the wild populations have been boosted by captive bred animals.
The virus no longer exists in the wild, and, unless it is reintroduced from caches of smallpox virus held in laboratories in the United States and Russia, smallpox will no longer occur in humans.
However, it was reintroduced from Sweden and is doing well.... and losers The Wall Brown Picture credit: Alamy (Lasiommata megera): this used to be common along road verges, woodland rides and rough grassland but started to disappear mysteriously in the mid-1980s.
Scores of animals were painted in sheltered spots on the floor, or etched in charcoal on the soaring walls: bison, stags, ibex, aurochs, and, what is rarer, fish (salmon), and Niaux's famous "bearded horses" — a shaggy, short-legged species that, Clottes writes in his new book, has been reintroduced from their native habitat, in Central Asia, to French wildlife parks.
Closer to home, conservationists point to their success in saving the large blue butterfly in Britain, where it became extinct in 1979 but which has been reintroduced from reserves in the rest of Europe and is now established in parts of south-west England.
At some point the musk ox became extinct on the Taimyr, but was reintroduced from populations in Alaska and Canada in the 1970s.
The rare black-faced impala has been reintroduced from Kaokoland into private farms in Namibia and the Etosha National Park.
44 Two dengue virus serotypes were reintroduced from the Americas to the Pacific Islands in 1964 (DENV-3) and in 1971 (DENV-2), following a 25 year absence.
