A study identifies host and viral traits that predict zoonotic spillover from mammals. The research shows that the proportion of zoonotic viruses in a species is influenced by phylogenetic relatedness to humans, host taxonomy, and human population within a species range. Bats are found to have a significantly higher proportion of zoonotic viruses than other mammalian orders. The study also identifies regions with the highest number of 'missing viruses' and 'missing zoonoses' for future surveillance. Phylogenetic host breadth and other viral traits are significant predictors of zoonotic potential, providing a framework to assess if a newly discovered mammalian virus could infect people. The study analyzed 2,805 mammal-virus associations, including 754 mammal species and 586 unique viral species. The results show that the number of viruses per wild host species varies by host order and viral family, with bats, primates, and rodents having a higher proportion of zoonotic viruses. The study also found that the proportion of zoonotic viruses is higher for RNA viruses than DNA viruses. The study highlights the importance of understanding factors driving viral diversity in mammals, viral host range, and cross-species transmission to humans. The findings suggest that bats are a key reservoir for zoonotic viruses, and that factors such as phylogenetic proximity to humans and human contact increase the likelihood of zoonotic transmission. The study provides a framework for predicting zoonotic potential based on viral traits and host characteristics, which can help prioritize surveillance efforts for new viruses. The study also identifies regions with high potential for discovering novel zoonotic viruses and highlights the need for further research to understand the mechanisms underlying zoonotic spillover. The study's findings have implications for public health and global security, as zoonotic diseases are a major threat to human health. The study's results can help inform strategies for preventing future pandemics by identifying high-risk species and regions for viral discovery.A study identifies host and viral traits that predict zoonotic spillover from mammals. The research shows that the proportion of zoonotic viruses in a species is influenced by phylogenetic relatedness to humans, host taxonomy, and human population within a species range. Bats are found to have a significantly higher proportion of zoonotic viruses than other mammalian orders. The study also identifies regions with the highest number of 'missing viruses' and 'missing zoonoses' for future surveillance. Phylogenetic host breadth and other viral traits are significant predictors of zoonotic potential, providing a framework to assess if a newly discovered mammalian virus could infect people. The study analyzed 2,805 mammal-virus associations, including 754 mammal species and 586 unique viral species. The results show that the number of viruses per wild host species varies by host order and viral family, with bats, primates, and rodents having a higher proportion of zoonotic viruses. The study also found that the proportion of zoonotic viruses is higher for RNA viruses than DNA viruses. The study highlights the importance of understanding factors driving viral diversity in mammals, viral host range, and cross-species transmission to humans. The findings suggest that bats are a key reservoir for zoonotic viruses, and that factors such as phylogenetic proximity to humans and human contact increase the likelihood of zoonotic transmission. The study provides a framework for predicting zoonotic potential based on viral traits and host characteristics, which can help prioritize surveillance efforts for new viruses. The study also identifies regions with high potential for discovering novel zoonotic viruses and highlights the need for further research to understand the mechanisms underlying zoonotic spillover. The study's findings have implications for public health and global security, as zoonotic diseases are a major threat to human health. The study's results can help inform strategies for preventing future pandemics by identifying high-risk species and regions for viral discovery.