unwell during a smallpox epidemic amongst humans. It was concluded that human-to-orangutan transmission had taken place and not animal-to-animal. “Silent monkeypox virus infections” were observed on three separate occasions during the 1964 and 1965 outbreaks in cynomolgus colonies in the Netherlands. 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. 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. Gispen also demonstrated cross protection from monkeypox in monkeys with smallpox vaccine. Death He died on 6 December 2000 in Bilthoven, at the age of 90. Selected publications Gispen published numerous papers and has been cited on many occasions. See also Derrick Baxby References 1910 births 2000 deaths Dutch virologists Dutch medical researchers Dutch expatriates in Indonesia People from Zwolle University of Amsterdam alumni Academic staff of Utrecht University