Commonground
Senior Moderator
1. Background
High pathogenicity avian influenza viruses (HPAIVs) of the A(H5) Goose/Guangdong (Gs/Gd) lineage1 continue to pose a major threat to animal and
human health worldwide [1–3]. Previously largely restricted to avian hosts, these viruses have recently been involved in numerous interspecies
transmission events affecting an expanding range [1–3]. In early 2024, the first confirmed transmission of A(H5N1) virus to dairy cattle in the United
States (US) was reported, involving clade 2.3.4.4b, US genotype (as defined by the ‘GenoFlu’ [4]) B3.13 [5–7]. Since then, cattle have shown their capacity
to sustain the circulation of the B3.13 virus lineage, and the detection of at least two additional US genotype D1.1 viruses in dairy herds in early 2025
suggests multiple independent interspecies transmission events [7,8]. Experimental infections further confirm cattle’s susceptibility to other A(H5N1) [9–
11]. As of September 2025, sustained spread in cattle appears geographically limited to the US. However, the repeated occurrence of these viruses in
an atypical host raises urgent concerns about zoonotic risk, animal health, and the potential for similar incursions in other regions and species. Given its
animal and public health impact, HPAIV in cattle meets the WOAH Terrestrial Code definition of an “emerging disease,” requiring Member Countries to
notify its occurrence, and underscores the need for timely, evidence-based risk mitigation strategies.
This OFFLU Applied Epidemiology Technical Activity document provides practical, evidence-based risk mitigation measures to support countries
in making informed decisions to curb the spread of HPAIVs into and within cattle populations, and offers a flexible framework that can be adapted to
diverse regional contexts. Using the 2024- onwards A(H5N1) clade 2.3.4.4b outbreak in US dairy cattle as a case study, we first outlined putative risk
pathways for virus introduction into farms, transmission within and between herds, and onward spread to other species, including humans. These
pathways were then assessed through an extensive literature review to propose intervention strategies, proportionate to the identified risks, and
grounded in current scientific evidence. It is evident that high rates of virus transmission have occurred both within and between US dairy farms, likely
influenced by local structural characteristics of the production system, including intensive management practices, large herd sizes, spatial clustering of
farms, and substantial inter-farm movement of cattle, workers, and vehicles. However, the mechanisms of transmission to and within cattle herds are
not fully elucidated, representing a key constraint in the development of risk mitigation measures [5,12–14]. While experimental infections show multiple
possible routes, the dominant pathways under field conditions remain unresolved [11,12,15–17].
2. Risk Mitigation Measures
The recommendations presented in this document should be adapted to local contexts, considering the characteristics of the relevant production
systems (Fig. 1, Appendix). These systems plausibly vary in their likelihood of acquiring and transmitting infection, and they present different
opportunities and constraints regarding the feasibility and sustainability of risk mitigation measures. Although current evidence links infection primarily
to dairy cattle, limited investigations in beef and non-lactating cattle mean that the susceptibility of these populations, and their potential role in onward transmission remains uncertain [5,12]. For surveillance planning, we refer to the ‘FAO Recommendations for the surveillance of influenza A(H5N1) in
cattle (2024)’ 2 as a framework for adapting strategies to local capacities, production systems, and epidemiological conditions.
Continued: https://offlu.org/publications/offl...an-influenza-virus-risk-mitigation-in-cattle/
High pathogenicity avian influenza viruses (HPAIVs) of the A(H5) Goose/Guangdong (Gs/Gd) lineage1 continue to pose a major threat to animal and
human health worldwide [1–3]. Previously largely restricted to avian hosts, these viruses have recently been involved in numerous interspecies
transmission events affecting an expanding range [1–3]. In early 2024, the first confirmed transmission of A(H5N1) virus to dairy cattle in the United
States (US) was reported, involving clade 2.3.4.4b, US genotype (as defined by the ‘GenoFlu’ [4]) B3.13 [5–7]. Since then, cattle have shown their capacity
to sustain the circulation of the B3.13 virus lineage, and the detection of at least two additional US genotype D1.1 viruses in dairy herds in early 2025
suggests multiple independent interspecies transmission events [7,8]. Experimental infections further confirm cattle’s susceptibility to other A(H5N1) [9–
11]. As of September 2025, sustained spread in cattle appears geographically limited to the US. However, the repeated occurrence of these viruses in
an atypical host raises urgent concerns about zoonotic risk, animal health, and the potential for similar incursions in other regions and species. Given its
animal and public health impact, HPAIV in cattle meets the WOAH Terrestrial Code definition of an “emerging disease,” requiring Member Countries to
notify its occurrence, and underscores the need for timely, evidence-based risk mitigation strategies.
This OFFLU Applied Epidemiology Technical Activity document provides practical, evidence-based risk mitigation measures to support countries
in making informed decisions to curb the spread of HPAIVs into and within cattle populations, and offers a flexible framework that can be adapted to
diverse regional contexts. Using the 2024- onwards A(H5N1) clade 2.3.4.4b outbreak in US dairy cattle as a case study, we first outlined putative risk
pathways for virus introduction into farms, transmission within and between herds, and onward spread to other species, including humans. These
pathways were then assessed through an extensive literature review to propose intervention strategies, proportionate to the identified risks, and
grounded in current scientific evidence. It is evident that high rates of virus transmission have occurred both within and between US dairy farms, likely
influenced by local structural characteristics of the production system, including intensive management practices, large herd sizes, spatial clustering of
farms, and substantial inter-farm movement of cattle, workers, and vehicles. However, the mechanisms of transmission to and within cattle herds are
not fully elucidated, representing a key constraint in the development of risk mitigation measures [5,12–14]. While experimental infections show multiple
possible routes, the dominant pathways under field conditions remain unresolved [11,12,15–17].
2. Risk Mitigation Measures
The recommendations presented in this document should be adapted to local contexts, considering the characteristics of the relevant production
systems (Fig. 1, Appendix). These systems plausibly vary in their likelihood of acquiring and transmitting infection, and they present different
opportunities and constraints regarding the feasibility and sustainability of risk mitigation measures. Although current evidence links infection primarily
to dairy cattle, limited investigations in beef and non-lactating cattle mean that the susceptibility of these populations, and their potential role in onward transmission remains uncertain [5,12]. For surveillance planning, we refer to the ‘FAO Recommendations for the surveillance of influenza A(H5N1) in
cattle (2024)’ 2 as a framework for adapting strategies to local capacities, production systems, and epidemiological conditions.
Continued: https://offlu.org/publications/offl...an-influenza-virus-risk-mitigation-in-cattle/