#19,402
In the spring of 2024 a mysterious illness spreading among Texas, Kansas, and New Mexico dairy cattle was
identified as avian H5N1, an outbreak that has now spread to at least 21 states, and has affected
> 1200 herds.
At that time cattle were believed poorly susceptible to influenza A (see
A Brief History Of Influenza A In Cattle/Ruminants), and so testing for H5N1 was delayed.
The immediate global reaction was that this was an
`American problem', caused by a new (
and presumably unique to North America) strain (
B3.13) of H5N1 (see
DEFRA Risk Assessment Of HPAI H5N1 Occurring in Cattle In the UK), and unlikely to occur in Europe.
This strain has not been detected in the UK, and none of the viruses detected in the UK over the 2020 to 2024 HPAI outbreak period have contained genetic material originating from North or South American viruses.
The risk to GB of H5N1 in livestock is assessed at very low.
That assumption was challenged in June of 2024 (see
Germany: FLI Statement On Experimental Infection Of Dairy Cows With European H5N1 Virus) when researchers demonstrated that a
German virus isolate could replicate in a cow's udder after experimental infection.
Over the summer of 2024 the USDA reassuringly suggested that
B3.13 entered dairy cattle via
a single spillover from birds - and was subsequently spread by the interstate transport of infected dairy cows. That assumption held until early 2025 when another genotype (
D1.1) turned up in dairy cattle in
two states (Nevada & Arizona).
In March of 2025, the
UK's Defra reported H5N1 Detected In Domestic Sheep with Mastitis, and over the previous year we'd seen reports of other
non-B3.13 H5N1 in goats and sheep in Pakistan, horses in Mongolia, and
pigs in Oregon.
Last April, in
Preprint: Infection of the Bovine Mammary Gland by Avian H5N1 Subclade 2.3.4.4b Influenza viruses. we saw even more evidence that
diverse HPAI H5 strains could infect dairy cattle. The authors wrote:
Our findings show that mammary tissue from common cattle breeds is permissive to clade 2.3.4.4b H5N1 infection. These results support the view that bovine mammary epithelium represents a susceptible tissue environment and suggest that IAV infection in cattle may be more widespread than previously assumed.
Four months ago, in
Eurosurveillance: Detection of antibodies against avian influenza in European dairy cattle, the Netherlands, January 2026), we saw additional evidence of HPAI spillover into dairy cattle outside of the United States.
But surveillance remains passive, and testing largely up to the discretion of the livestock owner. Something that many farmers find unappealing, fearing the quarantining of their herds and the stigma of infection.
Today we've an
EID Journal research letter which reports compelling serological evidence not only of
HPAI H5 infection in Egyptian cattle, but
LPAI H9N2 as well. The authors write:
Our findings indicate that spillover of avian influenza viruses to cattle and other livestock is not geographically restricted or caused by certain genotypes of H5N1 virus.
Testing included both hemagglutination inhibition (HI) and microneutralization (MN) assays, and positive results weren't confined to cattle.
Sheep and goats tested positive for LPAI H9N2 as well.
I've only posted some excerpts from this letter. Follow the link to read it in its entirety. I'll have a postscript after the break.
Volume 32, Number 12—December 2026
Research Letter
Serologic Evidence of Avian Influenza Virus Exposure in Livestock, Egypt, 2024–2026
Mokhtar Gomaa, Rabeh El-Shesheny, Ahmed El Taweel, Omnia Kutkat, Hager Emam, Basant Helal, Ayat Swelam, Mohamed GabAllah, Ahmed Kandeil, Pamela P. McKenzie, Richard J. Webby, Mohamed Ahmed Ali, and Ghazi Kayali
Abstract
Spillover of influenza A(H5N1) virus to cattle in the United States sparked global concern. We investigated whether endemic avian influenza viruses are potentially spilling over into domestic livestock in Egypt.
We detected influenza H9N2 antibodies in 2.5% and H5N1 antibodies in 2.9%–4.5% of tested animals. Additional surveillance will elucidate host infection dynamics.
(SNIP)
Clade 2.3.4.4b H5N1 virus and low-pathogenicity avian influenza A(H9N2) virus are widely and endemically circulating in poultry in Egypt on farms and backyards and at live bird markets (
7). Subtype H5N1 was detected in feral rats in poultry production areas (
8). In addition, reassortment events between the H5N1 and H9N2 subtypes led to the emergence of novel clade 2.3.4.4b influenza A(H5N2) viruses (
9).
To determine whether those viruses are spilling over to livestock in Egypt, particularly in mixed-species settings, we conducted a serosurveillance study in northern Egypt.
During October 2024–January 2026, we collected 444 serum samples from 33 conveniently selected small farms (≈10 cattle, no mixed species) and backyards housing cattle (1–3 cattle with mixed species) in 3 governorates (n = 155, n = 59, and n = 230) in northern Egypt, representing common practices in Egypt. Sheep and goats were also sampled if housed in the same backyards as cattle. All sampled animals were apparently healthy adults.
We tested serum samples for antibodies against a 2025 Egyptian clade 2.3.4.4b H5N1 (A/duck/Egypt/BA20361C/2022) virus using hemagglutination inhibition (HI) and microneutralization (MN) assays and against a G1-like Egypt influenza A(H9N2) (A/chicken/Egypt/RA20191OP/2022) virus by HI in accordance with World Health Organization protocols (
10). We considered an antibody
titer >1:40 as positive for both assays. Data on the number of cows, presence of other mammals (e.g., donkeys and horses), and presence of avian species (poultry and/or wild birds) were available for 271 samples. We performed statistical comparisons with χ2 or Fisher exact tests; we considered p<0.05 statistically significant.
Overall, 11 (2.5%) serum specimens tested positive for influenza A(H9N2) antibodies, 20 (4.5%) were positive for influenza A(H5N1) antibodies by HI, and 13 (2.9%) were positive for influenza A(H5N1) antibodies by MN (Figure, panel A). Positive titers were 40–160 (Figure, panel B). None of the samples tested positive for antibodies against both viruses. Of the 20 H5N1 virus specimens positive by HI, 12 tested positive by MN; 1 specimen was negative by HI and positive by MN. All influenza H9N2-positive specimens were from 3 locations in the same governorate (p = 0.005). Influenza A(H5N1) antibodies were detected in 2 governorates; the differences in detection rates by governorate were statistically significant (0%, 1.3%, and 4.8%; p = 0.049). All H5N1 virus–seropositive specimens were from cattle (Table).
We detected H9N2 antibodies in 6/374 (1.6%) of cattle specimens, 1/31 (3.2%) of goat specimens, and 4/39 (10.3%) of sheep specimens (p = 0.004). Presence of other animals did not predict seropositivity. Small farms had a significantly higher proportion of H5N1 virus–positive animals tested by MN (p = 0.039).
Our findings indicate that spillover of avian influenza viruses to cattle and other livestock is not geographically restricted or caused by certain genotypes of H5N1 virus. Clade 2.3.4.4b H5N1 virus of the EA-2021-AB genotype and G1-like H9N2 virus appear to be spilling over into livestock in Egypt; however, because our evidence is serologic, we could not ascertain whether true infection is occurring and whether the same signs seen in the United States are common in cattle in Egypt.
Even so, the evidence is a strong indicator that spillover is occurring, similar to that reported in Europe (
4,
6).
Furthermore, spillover is not restricted to cattle; some sheep and goats tested in our study were seropositive for influenza A(H9N2) virus. Surveillance for avian influenza viruses in Egypt and other countries, especially those in which avian influenza is endemic, will verify infection and provide data on frequency, routes of transmission, and factors affecting infection of and transmission to livestock.
(Continue . . . )
Despite the accrued evidence to date - for a myriad of political, societal, economic, and logistical reasons - governments around the world appear slow to respond to HPAI (
and now LPAI) spillover into mammalian livestock.
Although this
laissez faire approach may work out in the short run, it provides these viruses with ample opportunities to spread, to evolve, and to adapt.
Admittedly, most of these viruses will likely never pose a serious public health threat.
But it only takes one overachiever -
aided and abetted by inaction on our part - to plunge the world back into another pandemic crisis.
https://afludiary.blogspot.com/2026/11/eid-journal-serologic-evidence-of-avian.html
