Human Virus Spillover

Spillover of human respiratory viruses was always a concern at sites where chimpanzees and gorillas were habituated to close human approach. However, it wasn’t until 2008 that Fabian Leendertz and colleagues at the Robert Koch institute confirmed this potential by amplifying human metapneumovirus and respiratory syncytial virus RNA from samples collected at Christoph Boesch’s Cote d’Ivoire chimpanzee study site. Coalescent analyses conducted by my Ebola collaborator Roman Biek estimated that these isolates had common ancestors with isolates circulating in Beijing and Buenos Aires as recently as two to four years earlier, implying that they had been recently carried to Cote d’Ivoire by international travelers. Hjalmar Kuhl and I added demographic analyses suggesting that undetected respiratory viruses had caused large numbers of chimpanzee deaths in outbreaks dating back two decades. We also showed how regular outbreak cycles self-organized when infant deaths synchronized the reproductive cycles of adult females, with subsequent outbreaks triggered when infants matured to high levels of play driven social connectivity. These results spurred the adoption of masks and social distancing protocols at many chimpanzee and gorilla research and tourism sites.