Zoonoses are infectious diseases that are naturally transmissible between vertebrate animals and humans. These infections can persist in animal reservoir populations and spill over into people through direct contact, ingestion of contaminated food or water, bites, scratches, or exposure to arthropod vectors. The spectrum of zoonotic agents spans viruses, bacteria, fungi, parasites, and prions.
Transmission routes and types
Zoonotic pathogens may be directly transmitted through handling, consumption, or bites from infected animals, or indirectly via contaminated environments. Vector-borne zoonoses involve arthropods such as mosquitoes, ticks, or fleas; examples include malaria, Lyme disease, and plague. Foodborne and waterborne zoonoses, such as salmonellosis and listeriosis, arise from ingestion of animal products contaminated during production or processing. Airborne transmission can occur through inhalation of aerosolized particles, as seen with Hantavirus pulmonary syndrome. Some zoonoses are classified as anthropozoonoses (animal to human), zooanthroponoses (human to animal), or amphixenoses (bidirectional). Control measures often require managing reservoir hosts, vectors, and environmental sources.
Examples and public health significance
Zoonoses account for a large proportion of emerging infectious diseases. Rabies is a fatal viral zoonosis transmitted via saliva from infected mammals, preventable by vaccination of pets and post-exposure prophylaxis. Yersinia pestis causes plague, historically devastating populations, and persists in rodent-flea cycles. Bacillus anthracis spores in soil can infect grazing animals and humans, leading to cutaneous, inhalational, or gastrointestinal anthrax. Influenza A viruses circulate in birds and swine and occasionally adapt to humans, causing pandemics. The 2019 emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) underscores the impact of wildlife spillover events. Factors such as habitat encroachment, wildlife trade, intensive farming, and global travel facilitate these spillovers. Effective prevention and control rely on a One Health approach that integrates veterinary, medical, and environmental disciplines.
Zoonotic diseases illustrate the interconnectedness of human and animal health. Monitoring animal reservoirs, minimizing risky contacts, and strengthening surveillance systems are essential strategies to reduce the burden of zoonoses and mitigate future outbreaks.
Related Terms: Reservoir, Vector-borne disease, One Health, Emerging infectious disease, Spillover