Infectious Agents

Infectious agents comprise a diverse array of organisms and particles—bacteria, viruses, fungi, protozoa, helminths and prions—capable of breaching host defences, replicating within tissues and provoking disease. Bacteria employ surface adhesins, invasins and secreted toxins to colonise, invade and damage cells, while viruses hijack cellular machinery through receptor‐mediated entry, uncoating, replication and egress, often triggering cell death. Fungi may form biofilms or acquire invasive hyphal forms that penetrate epithelia, protozoa exploit intracellular or extracellular niches, and helminths traverse tissues with specialised enzymes. Prions, composed solely of misfolded protein, induce templated conformational changes in host proteins, leading to neurodegeneration. Host susceptibility reflects anatomical barriers, innate phagocytic and inflammatory programmes, adaptive immunity and genetic factors shaping pathogen recognition and response. Emerging and re-emerging infections are driven by antibiotic and antifungal resistance, environmental change, population mobility and zoonotic transmission at human–animal interfaces. Antimicrobial resistance arises through mutational escape, horizontal gene transfer of resistance elements—such as integrons and conjugative plasmids—and gene amplification. Zoonoses, including malaria species and novel coronaviruses, underscore the need for One Health surveillance. Understanding the interplay between pathogen virulence strategies, host defence mechanisms and environmental drivers is essential to develop targeted diagnostics, vaccines, antimicrobial stewardship and ecological interventions that can interrupt transmission and mitigate disease burden.

Research from Nature Portfolio

Large-scale surveillance of clinical samples in the Southwest Amazon region has mapped the molecular epidemiology of carbapenem-resistant bacteria, identifying multiple species carrying class A, B and D carbapenemase genes and revealing diverse genetic contexts, including plasmid and chromosomal reservoirs. These data have informed regional state laboratory networks and emphasised the need for coordinated public-health responses. In southern Malaysia, spatiotemporal modelling of human case data has demonstrated that individual reproductive numbers for the zoonotic malaria parasite remain below unity, confirming that sustained nonzoonotic transmission is unlikely and that human cases primarily reflect spillover from macaque reservoirs. In a multidrug-resistant Klebsiella pneumoniae isolate, three concurrent mechanisms—tandem chromosomal amplifications, elevated plasmid copy number and transposition of resistance cassettes onto cryptic plasmids—were shown to confer transient heteroresistance to multiple antibiotic classes. These amplifications incurred fitness costs and reverted rapidly when antibiotic pressure was removed, yet caused in vivo treatment failure in murine gut colonisation models, highlighting gene dosage as a dynamic driver of resistance.

Research from all publishers

Integrons have been shown to underpin the rapid dissemination of β-lactamase genes across clinical and environmental reservoirs. A global survey of nearly two thousand class 1 integrons revealed 159 distinct β-lactamase cassettes spanning all Ambler classes, frequently co-mobilised alongside aminoglycoside and sulphonamide genes in wastewater and hospital settings, signalling complex integron architectures as key hotspots for co-resistance. In Acinetobacter baumannii, genome-wide functional profiling identified the BfmRS two-component regulator as a master modulator of capsule production, which in turn dictates bacteriophage adsorption, replication and bacterial killing. Disruption of BfmRS reduced capsule levels and blocked phage infection, while hyperactivation increased phage susceptibility, uncovering regulatory strategies that bacteria can deploy to evade or enhance phage therapy. In Plasmodium vivax endemic settings, modelling of a novel serological test-and-treat approach demonstrated that targeted screening for hypnozoite carriers, combined with high-efficacy radical cure, could reduce point prevalence by around 25 percent with fewer treatments than mass drug administration, guiding cost-effective elimination strategies.

Infectious Agents publication trend

The graph below shows the total number of articles in infectious agents across all publications each year (not limited to Nature Index journals).

Technical terms

Integron: A genetic platform containing an integrase and recombination site that captures and expresses resistance gene cassettes.

Heteroresistance: A phenomenon in which a minor subpopulation displays significantly higher antimicrobial resistance than the main bacterial population.

Capsular polysaccharide (CPS): A surface layer of repeating sugar units that shields bacteria from host immunity and environmental stresses.

Reproductive number (Rc): The average number of secondary cases generated by an index case in a partially immune population, indicating transmission potential.

Spillover: Transmission of a pathogen from its primary reservoir species (often wildlife) to an incidental host, such as humans.

Radical cure: Antimalarial therapy aimed at eliminating both blood-stage parasites and dormant liver-stage hypnozoites.

One Health: An integrated approach recognising that human, animal and environmental health are closely interconnected.

References

1. Infectious Agents: From the Red Queen Paradigm to Some of Their Genuine Traits.
2. Biodiversity of carbapenem-resistant bacteria in clinical samples from the Southwest Amazon region (Rondônia/Brazil). Scientific Reports (2024).
3. No evidence of sustained nonzoonotic Plasmodium knowlesi transmission in Malaysia from modelling malaria case data. Nature Communications (2023).
4. Three concurrent mechanisms generate gene copy number variation and transient antibiotic heteroresistance. Nature Communications (2024).
5. Integrons are key players in the spread of beta-lactamase-encoding genes. International Journal of Antimicrobial Agents (2024).
6. Genome-wide phage susceptibility analysis in Acinetobacter baumannii reveals capsule modulation strategies that determine phage infectivity. PLOS Pathogens (2023).
7. Accelerating towards P. vivax elimination with a novel serological test-and-treat strategy: a modelling case study in Brazil. The Lancet Regional Health - Americas (2023).