January 9, 2024


California heaviest affected by avian influenza as disease rages across US




Farms across California, the United States, have had to euthanise several million chickens and ducks in recent weeks, as a wave of avian influenza threatens to upend US poultry and egg supplies.


While cases of the disease have been cropping up throughout the United States, agricultural hubs in Northern California have endured the greatest losses over the past month.


As of midday January 5, about 10.62 million birds in 63 flocks nationwide had been affected by highly pathogenic avian influenza (HPAI) outbreaks over the past 30 days, according to the US Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS).


Of these flocks, 37 were commercial and 26 were backyard, and a total of 3.8 million birds were concentrated in California.


The current spike in HPAI — on the rise since mid-fall — is the latest escalation in a nationwide outbreak that has ebbed and flowed since 2022.


A previous surge in the disease rattled the US' poultry industry last year, leading to national egg shortages and record-high price tags. The country could be headed in that direction again. While egg prices are still half of what they were about a year ago, they have risen 12% over last month, according to The Wall Street Journal.


Cal-Maine Foods, the US' biggest egg producer, cited a 91% loss in profits in its fiscal 2024 second quarter earnings, generating US$17 million in quarterly net income, as opposed to US$198.6 million during the same period last year.


Maurice Pitesky, an avian disease specialist at the University of California Davis (UC Davis) School of Veterinary Medicin, described migratory birds as "the primary reservoir" for HPAI, noting that ducks and geese often travel thousands of miles, meeting during fall in the Arctic, before heading south.


"When all those different flyways interface with each other, that's where you get all these exchange[s] of viruses," he said.


While wild waterfowl often carry the virus without developing symptoms, spreading to domestic poultry can result in what institute researcher Michael Payne described in a statement as "catastrophic mortality."


"It doesn't take much," Payne warned. "A drop of manure from an infected bird weighing only a gram, about the same as a dime, contains enough virus to infect one million birds."



California's Central Valley hosts about 500 to 600 commercial poultry farms, as well as robust habitats for both non-migratory and migratory waterfowl, according to Pitesky. This domestic-wild combination, he explained, has created a "spatial interface" for disease transmission.


Exacerbating that clash, Pitesky said, are the dual threats of human development and climate change — which have collectively caused shifts in the proximity of waterfowl to these farms.


The five California counties that currently have active infections of HPAI include Sonoma, Marin, Merced, Fresno and San Joaquin, the California Department of Food and Agriculture determined in a recent investigation.


Last December, Sonoma County declared a state of emergency following the detection of HPAI at two commercial poultry farms in the southern portion of the county. To protect other flocks in the region, those locations were put under quarantine and about 250,000 birds were euthanised.


Such action served to prevent further disease spread, but also came at the expense of the local agricultural economy, Sonoma County supervisor David Rabbitt said in a statement at the time.


Southern Sonoma County poultry farms supply "hundreds of thousands of eggs each and every day," which in turn bolsters the "food chain for the entire West Coast if not beyond," he added.


More recently in Sonoma County, about 494,200 birds were affected by HPAI at a commercial table egg layer farm, according to APHIS.


A similar fate befell 54,000 and 37,300 birds located at two such farms on December 28, per the APHIS data. On the same day, the disease was also detected in Marin County, impacting 151,000 birds at a table egg pullet farm — a farm that houses immature laying hens.   


More than 2.3 million birds residing at multiple Merced County table egg layer farms were affected by the disease during December, the data determined.


Also impacted throughout these counties have been broiler chickens, ducks and turkeys.


Other states with reported outbreaks include South Dakota, Minnesota, Wisconsin, Kansas, Arkansas, Minnesota, Ohio and Pennsylvania.


While four HPAI vaccines are licensed in the US, none have been approved for the most virulent strain, according to the American Veterinary Medical Association. Meanwhile, the USDA has completed initial testing on five HPAI vaccine candidates but is still evaluating their efficacy.


- The Hill

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