30/10/2024
First case of Avusn influenza in pigs in the USA:
From Promed this morning - AVIAN INFLUENZA (123): USA (OREGON) HPAI H5N1, PIG (FIRST REPORT),
POULTRY
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A ProMED-mail post
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International Society for Infectious Diseases
http://www.isid.org
Date: Wed 30 Oct 2024
Source: CNN [edited]
https://www.cnn.com/2024/10/30/health/bird-flu-pig-oregon
H5N1 bird flu has been identified in a pig in the United States for
the first time, the US Department of Agriculture said Wednesday [30
Oct 2024].
The USDA and Oregon veterinary officials are investigating bird flu
cases in a backyard farming operation that had a mix of poultry and
livestock, including pigs, the agency said.
"The livestock and poultry on this farm shared water sources, housing,
and equipment; in other states, this combination has enabled
transmission between species," it said in a news release.
After H5N1 was identified in other animals on the farm, 5 swine were
euthanized for testing; 2 tested negative, and results are still
pending for 2 others. The farm has been quarantined, and other animals
are under surveillance. However, it was not a commercial farm, and
"there is no concern about the safety of the nation's pork supply as a
result of this finding," USDA's Animal and Plant Health Inspection
Service said.
H5N1 is a type of influenza that's rare in humans but is highly
contagious and deadly in several species of animals, including poultry
and dairy cattle, raising fears that it could mutate and become a
virus that preys on people too.
Scientists have been concerned that H5N1 might spread to pigs, which
are considered "mixing bowl" species for flu viruses because they
carry the same kind of receptors on cells in their lungs as humans and
birds. Some previous flu infections in pigs have allowed influenza
viruses to change rapidly and develop new capabilities. The 2009 H1N1
flu pandemic is believed to have been sparked by a virus that mutated
in pigs in Mexico before it jumped to people.
Across the United States, more than 2 dozen people have tested
positive for H5N1 flu this year [2024], and nearly all of them have
reported exposure to infected dairy cows or chickens, according to the
US Centers for Disease Control and Prevention.
Some infectious disease experts said they wanted more clarity about
the nature of the swine case in Oregon. Dr. Michael Osterholm said he
was wondering whether the virus was picked up on swab of the pig's
nose or if there was evidence of deeper infection in the lungs.
"I think they use the word 'infection' too prematurely, because it
very well may be just an environmental contamination of the nose. And
so we need to get that, those data from that," said Osterholm, an
infectious disease expert who directs the Center for Infectious
Disease Research and Policy at the University of Minnesota.
He noted that a study published in 2023
(https://pmc.ncbi.nlm.nih.gov/articles/PMC10310384/), in which
researchers tried to infect pigs with H5N1 by swabbing their noses
with the virus and feeding them contaminated food, was largely
unsuccessful. Only one of 8 pigs that were experimentally dosed with
the virus later showed evidence of the infection in their blood,
demonstrating that the pigs had "high resistance" to the infection,
the study authors wrote.
Osterholm said he was glad that scientists were conducting additional
studies on the animals in the latest case to learn more.
Veterinarians who track infections that spread between animals and
people said it's not too surprising that pigs would be infected on the
same farm as infected birds.
"Sequencing of the virus will be important but it's likely the
circulating bird strain," said Dr. Scott Weese, a veterinarian and
chief of infection control at the University of Guelph in Ontario, in
an email to CNN. "I'd be more concerned if this was dairy
cow-associated because mammal-to-mammal spread would be more
concerning.
"I assume this is a dead-end spillover, but it highlights the
potential issues" for cross-contamination of different species on
farms, Weese said.
"Those issues would be greater with larger commercial farms, with more
chance for pig-to-pig transmission" and greater chances of other flu
viruses being present and swapping genes, he added.
[Byline: Jamie Gumbrecht and Brenda Goodman]
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Communicated by:
ProMED
[It should come as no surprise to anyone that H5N1 finally spilled
over into a pig, as the question has always been when, not if, it
would occur. As noted above, the sharing of the test results is
paramount to learn if infection of the pig has actually been proven
via positive samples from lung or other respiratory tissue, or if this
could be a false positive nasal swab via environmental contamination
similar to that seen in several workers conducting depopulation
operations at infected poultry farms? It will also be important to
learn if any clinical signs were observed in the pigs.
Hopefully the source of the virus can be determined as in addition to
the dairy and poultry sources mentioned, wildlife could have also been
the source given the backyard nature of the farm and likely open
access to birds in particular. Small and/or "backyard" farms with
multiple species in close contact often provide the ideal environment
for viruses to cross species and potentially spill over into people.
With pigs known to be excellent vehicles to transmit variant swine
viruses to humans, we shouldn't doubt their ability to effectively
multiply and disseminate H5N1 as well despite studies that may have
said otherwise in the past. As we've seen with H5N1 previously, when
we start to assume it's going to follow the rules and do what studies
said, it does something completely different like showing up in dairy
cattle, or not having a high mortality rate in people (at least not
yet). - Mod.JH
We found that nasal and alimentary experimental exposure of pigs to highly pathogenic avian influenza virus H5N1 clade 2.3.4.4b was associated with marginal viral replication, without inducing any clinical manifestation or pathological changes. Only ...
