Washington, DC – Throughout history, diseases that have afflicted humans often originated from animals. For example, the virus responsible for AIDS made the leap from chimpanzees. More recently, the virus that led to the COVID-19 pandemic is believed to have come from bats. However, a recent study reveals that the transmission of viruses between humans and animals is not one-sided.
In a comprehensive analysis of millions of viral genome sequences, researchers made a surprising discovery. Contrary to popular belief, humans actually transmit more viruses to animals than animals transmit to humans – nearly twice as many. The study identified thousands of instances where viruses jumped from one species to another, with a significant majority (79%) occurring between different animal species. The rest (21%) involved transmissions between humans and animals, with 64% being human-to-animal and 36% animal-to-human.
The range of animals affected by human-to-animal transmissions is broad and includes pets like cats and dogs, domesticated animals such as pigs, birds like chickens and ducks, primates such as chimpanzees and gorillas, and even wild animals like raccoons and marmosets. Specifically, wild animals were found to be more susceptible to human-to-animal transmissions compared to the reverse.
Cedric Tan, a doctoral student in computational biology at the University College London Genetics Institute and lead author of the study, emphasizes the significant impact humans have on the environment and surrounding animal populations. The study examined viral transmissions across all vertebrate groups, including mammals, birds, reptiles, amphibians, and fish.
Viruses can easily jump between species through various modes of transmission, such as direct contact with infected fluids or bites from other species. Tan explains that for a virus to successfully infect a new host, it must possess the biological mechanisms to enter and exploit the cells of the host species. Throughout history, pandemics resulting in millions of deaths have been caused by pathogens that originated from animals and jumped to humans. Zoonosis, the transmission of diseases from animals to humans, remains a significant concern for emerging infectious diseases.
Francois Balloux, a computational biologist and study co-author, highlights the alarming fact that the majority of pathogens circulating in humans have been acquired from animals at some point. Current threats like bird flu H5N1 and past pandemics like the Black Death, caused by a bacterium from wild rodents, underscore the dangers of zoonotic diseases.
The COVID-19 pandemic, believed to have originated from horseshoe bats, serves as a stark reminder of the risks associated with animal-to-human transmissions. Throughout the pandemic, cases of SARS-CoV-2 outbreaks in farmed minks infected by humans have been documented. While many species-to-species transmissions are harmless, some can lead to disease outbreaks, epidemics, or pandemics.
Balloux notes that while small zoonotic disease outbreaks are common, full-blown epidemics are relatively rare. The study sheds light on the intricate interplay between humans and animals in the transmission of viruses, highlighting the need for continued vigilance and research to prevent future disease outbreaks.
Washington, DC – As researchers delve deeper into the dynamics of viral transmissions between animals and humans, the study underscores the importance of understanding these interactions to mitigate the risks of future pandemics.