Rijk Gispen

Subsequent to experiences with the measures to control yellow fever and malaria, it became apparent that the eradication of smallpox relied upon the knowledge that no animal reservoir existed. Hence, the search for a reservoir continued. Up until 1968, seven suspected smallpox cases in monkeys were reported, but Gispen's case was the only one that confirmed the disease by isolating the virus in 1949. Two orangutans in a Djakarta zoo became unwell during a smallpox epidemic amongst humans. It was concluded that human-to-orangutan transmission had taken place and not animal-to-animal.[5]

“Silent monkeypox virus infections” were observed on three separate occasions during the 1964 and 1965 outbreaks in cynomolgus colonies in the Netherlands.[5] In 1964, Gispen isolated two viruses from the kidneys of laboratory monkeys that were not unwell. The monkeys remained without symptoms. These viruses appeared identical to smallpox. A number of further discoveries of the smallpox-like virus were later isolated from chimpanzees in West Africa and in well sun-squirrels. These incidents gave cause for concern and provided the impetus to continue WHO field research into the potential existence of a smallpox reservoir.[5][6][7] A personal correspondence from Gispen's colleague, J. G. Kapsenberg in the early 1980s, revealed that the cases of silent monkeypox were probably a result of contamination from monkeypox virus isolated in the same laboratory that tested samples from cases at an outbreak at Rotterdam Zoo.[8][9] Gispen also demonstrated cross protection from monkeypox in monkeys with smallpox vaccine.[10]