One Health

One-Sentence Definition

One Health is the recognition that human, animal, and environmental health are a single interconnected system, and that infectious disease problems must be addressed across all three.

Simple Explanation

You cannot fix resistance or emerging infections in hospitals alone when the reservoirs are in farms, wildlife, and water.

Detailed Scientific Explanation

Two flagship problems

1. Zoonoses and emergence. The majority of emerging human infectious diseases originate in animals. Drivers: land-use change, intensive livestock production, wildlife trade, and climate-driven vector range shifts. Examples span influenza reassortment in birds and swine, coronaviruses, Ebola, and vector-borne disease expansion.

2. Antimicrobial resistance. Antimicrobials used in food animals — historically for growth promotion — select for resistant organisms and mobile resistance genes that reach humans through food, direct contact, and the environment. Colistin resistance via the plasmid-borne mcr-1 gene is the textbook case: detected in livestock first, then in human isolates worldwide.

Environmental dimension: wastewater and pharmaceutical manufacturing effluent create selection pressure outside any clinic; the environmental resistome is the reservoir from which clinical resistance genes are recruited (Horizontal Gene Transfer).

Practical implementation: integrated surveillance across sectors, shared genomic databases (Public Sequence Databases), restrictions on veterinary use of critically important antimicrobials, wastewater monitoring, and joint outbreak response between veterinary and public health authorities.

Barriers: separate ministries, separate budgets, separate data systems, and unequal capacity between countries (FAIR Data and Genomic Surveillance).

Clinical Importance

• Exposure history — animal contact, travel, food, occupation — changes the differential diagnosis

Research Importance

• Cross-sector genomic surveillance to trace resistance and pathogen flow between compartments

AMR Relevance

Any national AMR strategy that covers only hospitals is incomplete — see Antimicrobial Resistance.

Related MOCs

• MOC - Public Health & Epidemiology · MOC - Antimicrobial Resistance (AMR) · MOC - Bioinformatics in Microbiology

Active Recall Questions

1. Why is mcr-1 the classic One Health example?
2. Name three drivers of zoonotic emergence.
3. What is the environmental resistome and why does it matter?

Connections

• Epidemiology · Metagenomics · Human Microbiome · Viral Genomics and Surveillance