Author(s): Ria Ghai, Casey Barton Behravesh

The One Health approach recognizes that the health of people is closely connected to the health of animals and our shared environment. This concept is not new but has been increasingly recognized in recent years as an effective way to address health issues at the human–animal–environment interface. One Health issues include zoonotic diseases, emerging infectious diseases like coronavirus disease 2019 (COVID-19), antimicrobial resistance, food safety and food security, and other shared health threats at the human–animal–environment interface.

Because no single person, organization, or sector can address challenges at the human–animal–environment interface, successful public health interventions require the cooperation of many partners. Professionals in human health (epidemiologists, nurses, physicians, public health practitioners), animal health (agricultural workers, paraprofessionals, veterinarians), environment (climate scientists, ecologists, wildlife experts), and other areas of expertise need to communicate, collaborate on, and coordinate activities based on a common, overarching goal: to achieve optimal health outcomes for people, animals, plants, and our shared environment.

Numerous benefits of One Health collaboration have been documented. For example, rabies is fatal in >99% of human cases and causes ≈59,000 human deaths annually around the world. Most (>99%) deaths are associated with exposure to rabid dogs. Preventing rabies in canines through annual or biannual mass dog vaccination campaigns has effectively prevented human-associated mortality. To be most successful, this strategy requires a One Health approach that includes partnership between human, animal, and environmental health professions at the programmatic and policy levels.

Zoonotic Diseases

Zoonotic diseases are diseases that can be transmitted between animals. Zoonotic diseases require a One Health approach for effective prevention, detection, and response. Approximately 60% of all known human infectious disease agents originate in animals, including Brucella, HIV, Salmonella, and rabies virus. Most new or emerging infectious diseases in humans are zoonotic (e.g., COVID-19, Ebola, and highly pathogenic avian influenza). Furthermore, 80% of diseases with bioterrorism potential are zoonotic (e.g., anthrax, plague).

One Health & Travel Medicine

International travelers can be at risk for zoonotic diseases through various types of exposures, not just direct or indirect contact with wild or domestic animals or arthropod vectors. Contaminated environmental surfaces, freshwater sources (e.g., ponds, rivers), and food and beverages have been implicated as sources of zoonotic illness in humans. Failure to identify sources of exposure associated with a traveler’s destination, itinerary, and activities can delay correct diagnosis and treatment and potentially increase the risk for further transmission of disease.

Patients benefit when health care providers use a One Health approach. In pretravel consultations, ensure travelers are aware of zoonotic and other infectious disease risks in areas where they are traveling, and encourage them to take measures to prevent or reduce those risks. For example, advise travelers to avoid settings with elevated zoonotic disease transmission risks like wildlife markets and farms. Consider administering rabies vaccine or offer prophylactic medications (e.g., antibiotics), as appropriate, to travelers for whom visiting high-risk zoonotic transmission settings is unavoidable.

In the posttravel setting, ask questions about interactions with animals, including domestic animals like companion and production animals and wildlife, both free-ranging and captive. Inquire about the apparent health of these animals and about animal habitats encountered during travel. Occasionally, health care providers and other zoonotic disease experts (e.g., veterinarians) might need to consult on a patient with a suspected zoonotic disease.

Direct & Indirect Animal Contact

Travelers should be aware of the risks associated with animal contact. Direct contact with the saliva, blood, urine, mucus, feces, or other body fluids of an infected animal increases the risk for exposure to zoonotic pathogens; common routes of contact include petting or handling animals and being bitten or scratched (see Sec. 4, Ch. 7, Zoonotic Exposures: Bites, Stings, Scratches & Other Hazards). Additionally, visits to locations that pose a heightened risk of contact with animals that can carry diseases, such as wet markets where animals and their products are sold, or caves inhabited by bats, are best avoided when possible.

Because knowing which animals could be carrying pathogenic organisms can be difficult, especially because animal carriers often appear healthy, recommend that travelers avoid contact with unfamiliar animals and their products, including gifts or souvenirs made of animal products that might not have been treated to ensure their safety. If contact with live animals or animal products cannot be avoided, travelers should ensure they seek medical care immediately if they are bitten, scratched, or develop signs of illness following animal interactions, and report their animal interactions to the health care provider.

Zoonotic Disease Vectors

Plague (Yersinia pestis infection), rickettsial diseases, and yellow fever are examples of zoonotic diseases transmitted by insect vectors. Travelers can minimize exposure to vectors by adhering to insect precautions and regularly performing tick checks on people and any traveling pets (see Sec. 4, Ch. 6, Mosquitoes, Ticks & Other Arthropods).

Zoonotic Foodborne Exposures

Because many foodborne pathogens have an animal reservoir, consuming raw or undercooked animal parts or products exposes travelers to zoonotic pathogens. In many developing countries, for example, unpasteurized milk, or dairy products made from unpasteurized milk, such as cheese, could put travelers at risk for Brucella, Campylobacter, Cryptosporidium, Listeria, and other pathogens. Travelers should avoid eating bushmeat—raw, smoked, or partially processed meat from bats, nonhuman primates, rodents, or other wild animals. Advise travelers to eat only fully cooked meat, eggs, fish, shellfish, and other foods, and to drink only pasteurized milk and dairy products, to reduce the risk for foodborne illness while traveling (see Sec. 2, Ch. 8, Food & Water Precautions, for more details).