Preprint: Detection of Antibodies Specific to H5 Avian Influenza Virus in a Sheep in Norway, June 2024

 

#18,840

Our view of avian influenza changed abruptly 17 months ago when HPAI H5N1 was detected in goats in the United States (see Minnesota BOAH Statement On HPAI H5N1 Infected Goat Kids), followed a few days later (March 25th) by the first HPAI detection in dairy cattle (see USDA Statement on HPAI In Dairy Cattle in Texas & Kansas Herds).

As we discussed at that time in A Brief History Of Influenza A In Cattle/Ruminants, while cattle had been experimentally infected with H5N1 in 2008, there had been little prior evidence of natural infection of ruminants.

Since then at least 1,078 cattle herds across 17 states have been infected, and we've seen scattered outbreaks in Alpacas and pigs in the United States, along with recent reports of sheep in both the UK and in Norway.

While most of the emphasis has been on U.S. dairy cattle, we've also seen reports of HPAI H5 in goats and sheep in Pakistan and horses in Mongolia, while in 2023, we saw a worrying spillover into pigs in Italy (Seroconversion of a Swine Herd in a Free-Range Rural Multi-Species Farm against HPAI H5N1 2.3.4.4b Clade Virus).

Testing of livestock around the globe remains limited, passive, and largely  voluntary, and we've seen studies (see Nature: A Mathematical Model of H5N1 Influenza Transmission in US Dairy Cattle) suggesting the we may only be seeing the tip of the iceberg.

Three months ago, in  First discovery of H5N1 in sheep in Norway, we looked at report on a retrospective seroprevalence study - conducted by the Norwegian Veterinary Institute - which turned up serological evidence of prior H5N1 infection in a sheep that had grazed in an area with high HPAI activity nearly a year earlier.

While only 1 sheep (out of 220) tested positive on all 3 antibody tests (ELISA, hemagglutination inhibition (HI), and microneutralization (MN)), 6 others showed partial evidence of prior infection. 

From the preprint: 

Detection of antibodies in one out of 220 sheep corresponds to a serological prevalence of approximately 0.5%. It is possible that this number underestimates the true rate of spillover infections, as the eleven-month interval between exposure and sampling could have decreased the sensitivity of our surveillance.

Six additional sheep showed partial serological evidence of H5 exposure, based on detection of antibodies against the H5 virus in the ELISA or the MN assay, despite testing negative in the comparatively less sensitive HI assay and for antibodies against type A influenza.

These findings should be interpreted with caution, considering the gaps in knowledge of antibody response kinetics to different viral proteins following H5 avian influenza virus infection in sheep and the limited validation of serological assays in this species.

The full report - uploaded to the bioRxiv on the 14th - only runs 8 pages and is well worth reading in its entirety (link below).  I'll have a bit more when you return. 

Detection of antibodies specific to H5 avian influenza virus in a sheep in Norway, June 2024, eleven months after an outbreak of  highly pathogenic avian influenza in a nearby seabird colony

Johanna Hol Fosse 1*, Grim Rømo 1*, Francesco Bonfante 2, Ida Kristin Myhrvold1, Kristin Stangeland Soetart1, Kristin Udjus1, Ragnhild Tønnessen 1.8*   

Abstract

A 2023 outbreak of highly pathogenic avian influenza in seabirds in Norway caused substantial environmental contamination of grazing areas frequented by local sheep. Eleven months later, 220 sheep were tested for antibodies to type A influenza and H5 subtype using ELISA, haemagglutination inhibition, and microneutralisation assays. One ewe (0.5%) tested positive by all methods, consistent with prior spillover infection. This underscores the importance of restricting livestock access to outbreak areas to mitigate cross-species transmission and zoonotic risk.

(SNIP)

HPAI in ruminants constitutes a zoonotic threat, with cattle identified as the likely source of 41 human cases during the ongoing U.S. outbreak (7). Our findings add to previous reports providing direct and indirect evidence of HPAI spillover from wild birds to small ruminants (12, 17).

From a One Health perspective, our findings underscore the need to prevent livestock contact with HPAI-contaminated grassland, diseased birds, and carcasses, and to include small ruminants in HPAI outbreak investigation and surveillance. 

        (Continue . . . ) 

For nearly a year following the announced discovery of HPAI H5N1 in dairy cows in the United States the USDA maintained it was the result of a single spillover from birds of a specific genotype (B3.13), and that all subsequent spread was likely due to the shipment of infected cattle to other states. 

They believed this was a `rare', one-off event, sparked by a single rogue genotype, and unlikely to be repeated.  A hope that was widely embraced by many other countries, comforted by the lack of spread of B3.13 outside of the United States. 

The May 2024 UK HAIRS Risk Statement On Avian Influenza (H5N1) In Livestock estimated that H5N1 genotype B3.13 presents ` at most, a very low risk' to the UK, citing a low likelihood of the virus being carried across the Atlantic to Europe. 

But less than a month later, in Germany: FLI Statement On Experimental Infection Of Dairy Cows With European H5N1 Virus, researchers reported `. . . not only the US isolate but also a recent H5N1 virus from a wild bird in Germany was able to multiply very well in the udder.'

In November of 2024 a different genotype (D1.2) was detected in two pigs on a farm in Oregon, but the big news came in February of 2025, when the USDA announced The Occurrence of Another Highly Pathogenic Avian Influenza (HPAI) Spillover from Wild Birds into Dairy Cattle.

This time, it was genotype D1.1, which has emerged the previous fall in wild and migratory birds, and had sparked numerous poultry outbreaks and roughly 2 dozen human infections, some serious (1 fatal). 

 Several weeks later a 3rd spillover into cattle was announced by the USDA (see APHIS Statement On HPAI Genotype D.1 In Arizona Dairy Cattle), where they reported:

Whole genome sequencing indicates that this detection is a separate wild-bird introduction of HPAI to dairy cattle, now the third identified spillover event into dairy cattle.

This finding may indicate an increased risk of HPAI introduction into dairies through wild bird exposure.

While reported spillover events are fairly rare, they obviously occur more often than originally assumed.  And their incidence appears to be on the ascendent. 

Scientists continue to call for better surveillance, more testing, and the timely sharing of data under a coordinated `One Health' strategy (see here, here, here, here, and here).

But we appear to be frozen in a holding pattern, unwilling to take decisive action. Whether we can shake ourselves free from this lethargy - before the virus does it for us - remains to be seen.