The One Health Concept

**Background:** The One Health concept is an approach to investigating infectious diseases that acknowledges the close interlinkages between humans, animals, plants, and the environment. Originating from Calvin Schwabe's 'One Medicine' idea in the mid-20th century, it evolved through the 2004 Manhattan Principles and gained prominence after the 2002-2004 SARS-CoV-1 outbreak. The term 'One Health' was coined around this time. The United Nations Sustainable Development Goals are relevant, and four global organizations (WHO, WOAH, FAO, UNEP) now form the One Health Quadripartite, focusing on six areas: laboratory services, zoonotic disease control, neglected tropical diseases, antimicrobial resistance, food safety, and environmental health.

**Methods:** This is a narrative review that synthesizes information from published literature, reports from global health organizations, and case studies to illustrate the application of the One Health approach across multiple domains. The authors discuss each of the six focus areas identified by the Quadripartite, providing examples of how cross-disciplinary collaboration can enhance disease surveillance, diagnosis, and control.

**Key Results:** The review presents numerous examples demonstrating the value of the One Health approach. For laboratory services, collaboration between medical and veterinary scientists has improved diagnostic protocols for pathogens like Leishmania spp., where PCR provides acceptable sensitivity and specificity. Surveillance systems for notifiable diseases in humans (e.g., UK Health Security Agency) and animals (e.g., DEFRA) rely on laboratory support. The review also highlights the environmental impact of laboratory waste and the need for diagnostic stewardship.

For zoonotic diseases, the review discusses rabies elimination in Europe leading to increased fox populations and subsequent Echinococcus multilocularis infections. The emergence of Plasmodium knowlesi as a cause of human malaria in Southeast Asia was clarified through molecular methods, with deforestation driving macaques and mosquitoes into human settlements. The 2022 Mpox outbreak illustrated the global interconnectedness of zoonotic threats, with case fatality rates of 2-10% and a 61% increase in cases in DRC between 2018 and 2020.

Neglected tropical diseases (NTDs) such as Chagas disease, dengue, chikungunya, and trachoma are discussed. For Chagas disease, the WHO recommends using two separate serological assays due to insufficient sensitivity/specificity of individual tests. Dengue incidence is rising, partly due to climate change, with point-of-care test sensitivities for IgM ranging from 13.8% to 90%. Trachoma control relies on the WHO's SAFE strategy (Surgery, Antibiotics, Facial hygiene, Environmental improvement).

Antimicrobial resistance (AMR) is highlighted as a major threat, with agriculture accounting for up to 80% of antibiotic consumption in some countries. The ban on colistin as a growth promoter in China led to a decline in mcr-1 E. coli in pigs from 45% to 19% within two years. Microplastics in soil are linked to AMR spread through biofilm formation.

Food safety concerns include Cryptosporidium outbreaks from contaminated water, with oocysts surviving in seawater. Bushmeat trade poses risks of zoonotic infections, with 1,149 kg seized at UK airports in 2018/19. The review notes that most food poisoning results from incorrect handling, cooking, or storage.

Environmental health is affected by climate change, which influences infectious disease transmission through temperature increases and flooding. For example, hookworm larvae can withstand temperatures up to 40°C and develop three times faster. The impact on malaria transmission is complex, with local factors like deforestation and societal conditions playing key roles.

**Clinical Implications:** The One Health approach is essential for understanding and controlling infectious diseases in an interconnected world. It requires collaboration among healthcare professionals, veterinarians, social workers, and ecologists. The Quadripartite's aims include promoting cross-sectorial approaches and producing policy guidelines. Funding for multidisciplinary research and robust evaluation is necessary. The review concludes that while schemes should focus on specific challenges, they must also be global in scope, encouraging everyone to 'think global, act local.'