Egyptian livestock carry avian-flu antibodies, hinting at wider spillover beyond US cattle

When highly pathogenic H5N1 avian influenza jumped into dairy cattle in the United States in early 2024, it marked the first sustained transmission of the virus in a mammalian livestock species — and raised an obvious question about whether the same thing was happening elsewhere, unnoticed [s1]. A new serosurvey in Egypt, published in the CDC journal Emerging Infectious Diseases, offers early evidence that it may be [s1].

Researchers set out to test whether endemic avian influenza viruses are spilling over into domestic livestock in Egypt, a country where avian influenza circulates widely in poultry [s1]. They looked for antibodies — immunological evidence of past exposure — rather than active virus, and found signals of both of the viruses they screened for [s1].

What the testing found

Across the animals tested, 11 serum specimens — 2.5% — were positive for influenza A(H9N2) antibodies, and H5N1 antibodies turned up in 2.9% to 4.5% depending on the assay [s1]. By haemagglutination inhibition, 20 specimens (4.5%) were positive for H5N1; by the more specific microneutralization test, 13 (2.9%) were positive, with positive titres ranging from 40 to 160 [s1]. Of the 20 specimens positive by haemagglutination inhibition, 12 were also positive by microneutralization, and one specimen negative by the first test was positive by the second [s1]. No sample tested positive for antibodies against both viruses [s1].

The positives were not randomly scattered. All of the H9N2-positive specimens came from three locations within a single governorate, a clustering unlikely to be chance (p = 0.005), while H5N1 antibodies were detected in two governorates, with statistically significant differences in detection rates between areas [s1]. Spillover, the data suggest, was concentrated rather than uniform.

Crucially, the signal was not limited to cattle. Some sheep and goats in the study were seropositive for influenza A(H9N2), broadening the picture of which species on an Egyptian farm may be exposed [s1]. In mixed smallholder settings, where poultry, cattle, sheep and goats are often kept in close quarters, that mix of hosts is exactly the kind of interface at which an avian virus has repeated chances to cross into mammals.

Why serology is a signal, not a verdict

The viruses behind the antibodies matter for how the finding is read. The H5N1 detected belongs to clade 2.3.4.4b — the same clade circulating globally — of the EA-2021-AB genotype, distinct from the B3.13 genotype that spread through US dairy herds, while the H9N2 was a G1-like virus [s1]. Egypt is not a bystander in avian influenza: H5N1 and H9N2 have circulated in its poultry for years, so the country is precisely where one would expect endemic bird viruses to press repeatedly against the species barrier into the mammals kept alongside the birds. That the spillover in Egypt involves different genotypes than the American outbreak is itself the authors' central point: it indicates the phenomenon is not geographically restricted or tied to one particular strain [s1].

The authors are careful about the limits of serologic evidence. Antibodies show that an animal's immune system encountered a virus; they cannot, on their own, confirm that true infection occurred, or establish whether the clinical signs seen in US cattle — the marked tropism for the mammary gland, the high viral loads in milk — are also present in Egyptian herds [s1]. Even so, the researchers judge the evidence a strong indicator that spillover is occurring, echoing reports from Europe [s1].

What the study calls for is more watching. Surveillance for avian influenza viruses in Egypt and other countries where the disease is endemic, the authors write, will be needed to verify infection and to map how often it happens, by what routes, and what lets these viruses move into and between livestock [s1]. The broader context gives the question weight: every additional mammalian host in which an avian virus circulates is another setting in which it can adapt, and an endemic-poultry country with livestock already showing antibody evidence of exposure is exactly where that watching should be close. The US cattle outbreak was a reminder of how quickly an unexpected host can rewrite assumptions about a virus; this serosurvey is a nudge to check, systematically, how many other such hosts are already quietly exposed [s1].

This article is informational and is not medical advice.