#18,397
A week after the first reports of H5N1 being detected in a pig in the United States (see USDA: APHIS Reports 1st Detection of HPAI H5N1 in Swine (Oregon)) the USDA has confirmed that a second pig on the premises has tested positive for the HPAI H5 virus.
While this appears to be a limited outbreak on a small, non-commercial farm, this is also the 4th livestock species - joining goats, alpacas, and dairy cattle - to be infected in the United States in the past 7 months.
This outbreak - like the large poultry outbreak in neighboring Washington state (with > 1 dozen associated human infections) - comes from the introduction of a new genotype of the virus (D1.1 in Washington State and D1.2 in Oregon) this fall.
Since its arrival in late 2021, more than 100 genotypes have been detected in the United States alone. The ability to continually reinvent itself via reassortment makes H5N1 particularly difficult to address, and raises the potential for better adaptation to mammals.
First the statement from the USDA, after which I'll have a bit more.
WASHINGTON, Nov. 6, 2024 - Today, the U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) is sharing key updates regarding the detection of HPAI H5N1 in a backyard farm operation in Crook County, Ore., as well as additional information about the agency’s proactive efforts to protect livestock, farms and communities from avian influenza.
On Wed., Oct. 30, USDA APHIS announced that H5N1 avian influenza was detected in one of the pigs at this backyard farm, that two pigs tested negative, and tests were pending for two additional pigs. The USDA National Veterinary Services Laboratories (NVSL) has completed testing on the two remaining pigs and has confirmed that one tested positive and met the clinical case definition for HPAI H5N1. Sequencing from this positive sample, while incomplete due to the low level of the virus, indicates infection from the D1.2 genotype of H5N1.
Because the amount of virus from the infected pigs was very low, only partial genomic sequences could be extracted from one of the two samples and these sequences indicate infection with the D1.2 genotype of H5N1. APHIS and the Oregon Department of Agriculture had previously also shared that H5N1 had been detected in poultry on the same farm; the samples from the poultry were also found to have the D1.2 genotype.
Genomic sequencing of samples from migratory birds in the area showed very similar sequences, which increases the probability that the pigs and poultry on this farm became infected after coming into contact with infected migratory birds, not dairy cattle or other livestock.
This farm is a non-commercial operation, and the animals were not intended for the commercial food supply. There is no concern about the safety of the nation’s pork supply as a result of this finding.
Additionally, over the past week APHIS has approved field safety trials for two additional vaccine candidates for H5N1 in cattle, bringing the total number of candidates approved for field trials to four. USDA continues to support the rapid development and timely approval of an H5N1 vaccine for dairy cows, in addition to other species.
While we've seen scattered reports of H5N1 in swine (see here, here, and here), between extremely limited testing, and the fact that H5N1 tends to be asymptomatic (or mildly symptomatic) in pigs, it is probably more common than we realize.
For years we've been warned about the dangers of H5N1 getting into the pig population, since pigs are considered excellent `mixing vessels' for influenza viruses.
- In March of 2023, the ECDC/EFSA Avian Influenza Overview December 2022 – March 2023 warned on the spread of H5N1 to mammals:
The additional reports of transmission events to and potentially between mammals, e.g. mink, sea lion, seals, foxes and other carnivores as well as seroepidemiological evidence of transmission to wild boar and domestic pigs, associated with evolutionary processes including mammalian adaptation are of concern and need to be closely followed up.
- In May of 2023, in Netherlands: Zoonoses Experts Council (DB-Z) Risk Assessment & Warning of Swine As `Mixing Vessels' For Avian Flu, we looked at concerns that avian H5N1 could increase its pandemic threat by spreading (and evolving) in farmed swine.
- That announcement was followed a week later by a report (see Study: Seroconversion of a Swine Herd in a Free-Range Rural Multi-Species Farm against HPAI H5N1 2.3.4.4b Clade Virus) at a `mixed species' farm (poultry & swine) in Italy.
- Last March, in EID Journal: Divergent Pathogenesis and Transmission of Highly Pathogenic Avian Influenza A(H5N1) in Swine, we looked at a study on the pathogenesis and transmissibility of 4 North American H5N1 viruses (2 with known mammalian adaptations) in swine.
