Human–animal interactions are closely intertwined. The connection between animal, human, and environmental health is becoming increasingly complicated with globalization, industrialization, and climate change. Since the beginning of the 20th century, the number of domestic cats has increased rapidly worldwide, including in China. There are approximately 600 million domesticated cats worldwide, including 65 million cats in China, most of whom have close human contacts. These close contacts create more chances for pathogen spillover among humans and cats, which could lead to the emergence of new pathogenic strains or variants. Cats living in proximity to their owners carry a particular risk of catching pathogens, as they often share snuggles, kisses, dining, and beds. We share hundreds of pathogens with our animals, which they serve as intermediate or reservoir hosts for pathogens that affect human health. Cats, owing to their genetic similarity to humans, are more susceptible to catching diseases from their owners. Recently, it has been estimated that humans spillover far more pathogens to animals than animals transmit to humans.

The natural transmission of disease and infection from humans (reservoir hosts) to animals is usually known as reverse zoonosis. It is also called zooanthroponosis or anthroponosis and is considered the opposite of “zoonosis.” Reverse zoonotic events can form potential disease reservoirs that can reintroduce pathogens into human populations. Over the years, zoonotic events and pathogen spillover from animals to humans have been extensively studied, and reverse zoonotic events have remained understudied from animal health perspectives. Influenza viruses are genetically highly variable and remain the most significant concern for One Health. Influenza viruses now consist of four types within the family Orthomyxoviridae, including types A, B, C, and D. Type A and B influenza viruses are more abundant and are usually linked to seasonal flu outbreaks worldwide. Independent anthroponotic spillover of IAV viruses into farmed, captive, and wild animals has been reported.