The One Health approach to zoonotic illnesses is predicated on the connection that exists between people, animals, and the environment. As a discipline, One Health includes specialists from multiple health sectors: human medicine and public health, veterinary medicine, and environmental health; its areas of interest cover zoonotic diseases, antimicrobial resistance, food safety and food security, vectorborne diseases, and other shared health threats at the human–animal–environment interface.
No single sector can address challenges at the human–animal–environment interface alone, but coordinated efforts to identify and manage animal or environmental sources of infection can prevent, detect, and respond to infectious disease threats. For example, programs that use a One Health approach between medical and veterinary professionals have controlled rabies in animals; annual or biannual mass dog vaccination campaigns prevent human rabies deaths.
Diseases addressed by the One Health approach are typically zoonotic. Approximately 60% of all known human infectious disease agents originate in animals, including brucellosis, anthrax, and salmonellosis. Most new or emerging infectious diseases in humans are zoonotic, such as Ebola, Middle East respiratory syndrome, and highly pathogenic avian influenza. Further, 80% of disease agents identified with bioterrorism potential are zoonotic.
International travelers may be at risk of zoonotic diseases through a variety of exposures not limited to wild or domestic animal contact or insect vectors. Contaminated environmental surfaces, freshwater sources (such as ponds and rivers), and food and beverages have also 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 employ the One Health approach. In the pretravel consultation, providers should make travelers aware of zoonotic and other infectious disease risks in the areas where they are traveling, encouraging them to take measures to reduce those risks (for example, through vaccinations or prophylactic medications). In the posttravel setting, providers should ask questions about interactions with animals (such as pets, free-roaming animals, livestock, and wildlife), including the apparent health of these animals, and animal habitats encountered during travel. Occasionally, health care providers and veterinarians may need to consult together on a patient with a suspected zoonotic disease.
Travelers must remain 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 of exposure to zoonotic pathogens; common routes of contact include petting or handling animals and being bitten or scratched (for details see Animal Bites & Stings [Zoonotic Exposures] in this chapter). Additionally, ecotourism ventures that involve riding animals such as horses, camels, or elephants pose a potential risk for injury or zoonotic diseases. However, it is difficult to know which animals could be carrying pathogenic organisms, especially since animal carriers can appear healthy. Contact with environmental surfaces where animals have been can also pose a risk of zoonotic disease transmission. Travelers should avoid contact with animals and their secretions, and if animal contact cannot be avoided, travelers should ensure they are up-to-date with recommended vaccinations and seek medical care if bitten or scratched.
Rickettsial diseases, plague (Yersinia pestis infection), and yellow fever are all 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 (for details see Mosquitoes, Ticks & Other Arthropods in this chapter).
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 (cheese, for example) made from unpasteurized milk carries the risk of Brucella, Campylobacter, Cryptosporidium, Listeria , and others. 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, fish, shellfish, eggs, and other foods, and to drink only pasteurized milk and dairy products, to reduce the risk of foodborne illness while traveling (see Chapter 2, Food & Water Precautions, for more details).
Ria R. Ghai, Casey Barton Behravesh
Perspectives sections are written as editorial discussions aiming to add depth and clinical perspective to the official recommendations contained in the book. The views and opinions expressed in this section are those of the author and do not necessarily represent the official position of CDC.