Mapping Reported Modes of Transmission of Highly Pathogenic Avian Influenza A (H5N1) to Humans: A Scoping Review.
The study identifies multiple reported pathways for H5N1 transmission to humans, emphasizing the complexity of the virus's transmission routes.
Where it sits
this study against the rest of the mgf (mechano growth factor) corpusSummary and findings
This study mapped reported transmission pathways of Highly Pathogenic Avian Influenza A (H5N1) to humans. It included 120 sources, comprising 70 studies and 50 pieces of grey literature. The findings highlight various transmission routes without implying causation.
Abstract
<h4>Background</h4>Highly Pathogenic Avian Influenza A (subtype H5N1) poses a threat to human health, and its pandemic potential emphasizes the need to better understand detailed reported transmission pathways to humans. Existing literature is outdated or lacks detailed, comprehensive analysis of the range of transmission routes and how the virus may enter the human body.<h4>Objective</h4>To comprehensively map all reported H5N1 transmission pathways to humans, as well as viral entry routes.<h4>Methods</h4>CINAHL, Embase, MEDLINE, Scopus, PubMed, grey literature, and reference lists (of included studies) were searched up to October 29th, 2025, with no language restrictions. Observational studies and grey literature reporting H5N1 transmission evidence to humans were included. Two reviewers conducted duplicate screening independently (two of three reviewers per record). One reviewer completed data extraction, which was cross-verified for accuracy by a second. Findings were summarized narratively.<h4>Results</h4>120 sources met inclusion criteria (70 studies, 50 grey literature). Reported H5N1 transmission pathways were classified into animal-to-human (109 of 120 sources, 90.8%; including poultry-to-human in 100 sources [83.3%] and cattle-to-human in nine sources [7.5%]), environment-to-human (32 of 120 sources, 26.7%), and human-to-human (14 of 120 sources, 11.7%). Reported transmission pathways were further classified as direct or indirect contact, synthesized, and linked to suspected routes of human entry, including mucosal entry (eyes, nose, mouth), inhalation of aerosols or droplets, ingestion, and percutaneous exposure. Entry routes are biologically plausible and do not imply relative likelihood or causal attribution.<h4>Conclusions</h4>There are multiple reported pathways of H5N1 exposure, and a single pathway may involve multiple ways to infect humans. Further research is needed to determine causal mechanisms, identify specific risk factors and measures of association, and strengthen evidence-based prevention strategies.
Background
This paper addresses the clinical and biological question of how Highly Pathogenic Avian Influenza A (H5N1) transmits to humans. Previous literature has been criticized for being outdated or lacking comprehensive analysis of transmission routes. Understanding these pathways is crucial for public health and pandemic preparedness.
Methods
The study conducted a scoping review using databases such as CINAHL, Embase, MEDLINE, Scopus, and PubMed, searching up to October 29th, 2025. Inclusion criteria encompassed observational studies and grey literature reporting H5N1 transmission evidence to humans. Data extraction was performed by one reviewer and cross-verified by another.
Results
From the 120 sources included, 109 (90.8%) reported animal-to-human transmission pathways. Poultry-to-human transmission was noted in 100 sources (83.3%), while 32 sources (26.7%) reported environment-to-human pathways. Human-to-human transmission was noted in 14 sources (11.7%).
Interpretation
The findings align with existing literature that suggests multiple transmission pathways for H5N1. However, the effect sizes reported do not imply clinical significance, as they do not establish causation or relative likelihood. Limitations include reliance on observational data and grey literature, which may introduce bias.
Key findings
- 90.8% of sources reported animal-to-human transmission pathways, n=120.
- 83.3% of sources indicated poultry-to-human transmission, n=120.
- 26.7% of sources reported environment-to-human transmission, n=120.
- 11.7% of sources reported human-to-human transmission, n=120.
Limitations
- observational study design
- reliance on grey literature
- no causal attribution established
- potential bias in data sources