Bovine keratoconjunctivitis: a review of the bovine ocular surface microbiome and related epidemiological risk factors.

Bovine keratoconjunctivitis (BK) is a common inflammatory condition of the ocular surface (OS) of cattle, with a complex epidemiology. This review summarises current knowledge about the bovine ocular surface microbiota (OSMt) and discusses how it integrates with agent, host and environmental factors involved in BK epidemiology. A comprehensive literature review, from 1950 to 2026, was conducted to identify known constituents of the OSMt and symbionts with pathogenic potential within this community. Information about key epidemiological factors associated with BK was simultaneously collected. After applying a structured literature search and selection criteria, 321 papers remained. A directed acyclic graph was used to construct a conceptual framework that visualised the role of the bovine OSMt in BK within the epidemiological web. The graph indicated that cattle are exposed to six injurious environmental factors acting from outside the ocular surface microbiome (OSMe)-(i) ultraviolet B, (ii) lachryphagous insects, (iii) desiccation stress, (iv) nutritional deficiencies, (v) large particulate matter, and (vi) small particulate matter-and two factors acting from within the microbiome-(vii) pathogenic stages of Thelazia spp. and (viii) pathogenic viruses. Metagenomic analyses revealed marked diversity within the bovine OSMt and symbionts of both high (e.g., Moraxella bovis) and low pathogenic potential (e.g., Mesomycoplasma bovoculi). The symbiotic relationship is influenced by damaging or disruptive environmental influences impacting on barrier integrity. Integrating the OSMe within a network of agent, host, and environmental factors provides a new perspective on BK that may inform future control strategies.