05 November 2026
A new serosurveillance study conducted in northern Egypt provides evidence that avian influenza viruses are spilling over into domestic livestock outside North America and Europe. Investigating the potential transmission of endemic avian flu strains to domestic mammals, researchers screened 444 serum samples collected between October 2024 and January 2026 across small farms and mixed-species backyards in three governorates. The analysis revealed serologic evidence of exposure to both highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b and low-pathogenicity avian influenza A(H9N2).
H5N1 Exposure in Cattle: Antibodies against H5N1 were detected in 2.9% to 4.5% of tested animals (depending on the assay used), with all seropositive samples originating exclusively from cattle.
H9N2 Spread Across Species: H9N2 antibodies were identified in 2.5% of tested specimens overall, spanning cattle (1.6%), goats (3.2%), and sheep (10.3%).
Dual Exposure: None of the sampled animals tested positive for antibodies against both viruses simultaneously.
The authors note that while these serologic findings confirm exposure rather than active viral replication or clinical illness, they demonstrate that interspecies spillover is not confined to specific geographic regions or limited to North American genotypes.
Gomaa et al. (2026). Serologic evidence of avian influenza virus exposure in livestock, Egypt, 2024–2026. Emerg Infect Dis. 2026 Dec
Editorial Notes: The study relies exclusively on serological detection of antibodies, which documents past immunological exposure rather than productive viral infection, tissue tropism, or active viral replication. Positive titers ranged moderately from 40 to 160. At low cutoffs (), bovine and ovine sera are prone to nonspecific hemagglutination inhibition or potential cross-reactivity, requiring rigorous assay validation protocols specific to ruminant matrices. For H5N1, 20 cattle were positive by hemagglutination inhibition (HI), but only 12 were confirmed by microneutralization (MN), while 1 animal tested negative by HI and positive by MN. This discordance illustrates interpretive ambiguities when standard WHO avian protocols are applied to mammalian livestock without validated species-specific reference controls.
