28 July 2026
The dramatic expansion of global poultry production in recent decades has not only reshaped avian ecology but has also created a "pathogen sponge" that accelerates the evolution and cross-species transmission of major zoonotic bacteria. A comprehensive genomic study published in the Proceedings of the National Academy of Sciences (PNAS) investigated the evolutionary dynamics of Campylobacter jejuni, the leading bacterial cause of gastroenteritis in humans worldwide. Human infections occur primarily through contaminated food, with an estimated 60% to 80% of cases originating from poultry reservoirs.
Analyzing 2,747 whole-genome sequences of C. jejuni isolates from farmed chickens and wild birds, the researchers demonstrated that poultry intensification, which has resulted in chickens accounting for approximately 70% of the global avian biomass, has eroded historic host-strain associations and created an expanding ecological niche.
Main research findings:
Following the rapid intensification of poultry farming after the 1960s, the inferred rate of Campylobacter host transitions between chickens and wild birds increased by more than 100-fold compared with pre-domestication levels.
Epidemiological model simulations revealed that dense, high-volume chicken populations act as an ecological sponge, absorbing diverse wild bird lineages, sustaining high coinfection rates, and allowing even poorly adapted strains to proliferate.
Genome-wide association analyses (GWAS) identified key genetic features enriched in chicken-adapted strains, including antimicrobial resistance genes, enhanced survival in the poultry gut, and genetic traits that promote bacterial persistence throughout the food supply chain.
The authors conclude that modern livestock production systems are fundamentally altering pathogen ecology. By generating vast, interconnected host networks, agricultural intensification creates evolutionary feedback loops that transform local avian microbes into rapidly evolving, globally disseminated public health threats.
Kyne, O. J., Penman, B. S., Kelly, D. J., & Sheppard, S. K. (2026). Accelerating Campylobacter zoonosis in the Anthropocene. Proceedings of the National Academy of Sciences (PNAS), 123(32), e2609969123.
