What to know about bird flu in dairy cows and the risk to humans
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[April 26, 2024]
By Julie Steenhuysen
CHICAGO (Reuters) -U.S. officials have strengthened measures to contain
the further spread of the first known outbreak of H5N1 or bird flu in
dairy cows, which has now spread to 33 herds in eight states and bled
over into the country's milk supply.
So far, only one person - a Texas farm worker - has tested positive for
H5N1, and while health officials and scientists say the risk to people
remains low, many questions remain.
WHY IS H5N1 OR BIRD FLU A CONCERN?
The spread of bird flu among dairy cattle reflects an expansion of the
range of mammals that can be sickened by the virus that typically
infects birds.
Scientists are on alert for changes in H5N1 that could signal the virus
is adapting to spread easily among humans. The virus has caused serious
or fatal infections among people in close contact with wild birds or
poultry. It has long been on the list of viruses with pandemic
potential, and any expansion to a new mammal species is concerning.
The infections in cattle are from the same subtype of bird flu that has
been infecting wild birds and poultry flocks globally for more than two
years, also killing several mammal species that likely contracted the
virus from consuming sick or dead birds.
![](http://archives.lincolndailynews.com/2024/Apr/26/images/ads/current/graue_sda_042021.png)
HOW WIDESPREAD IS THE BIRD FLU OUTBREAK IN CATTLE?
The full extent remains unknown, but several recent developments suggest
it may be in more herds than documented.
On April 23, the U.S. Food and Drug Administration said it has detected
particles of H5N1 in the milk supply. Tests suggest they are remnants of
virus killed during the pasteurization process, and that the milk is
safe. Early testing has not detected any live virus in milk samples, and
U.S. health officials believe people cannot get sick from drinking
pasteurized milk and warn not to drink unpasteurized milk.
Officials have learned the virus can be present in cows that show no
signs of infection, and milk from those cows does not show signs of
infection such as being thicker and yellow.
To contain the outbreak, the U.S. government is requiring dairy cattle
moving between states to be tested for bird flu.
WHEN DID THIS BIRD FLU OUTBREAK START?
U.S. officials had thought the outbreak was recent, but new information
suggests it may have started late last year.
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![](../images/042624PIX/health99.jpg)
A dairy cow stops to look up while feeding at a dairy farm in
Ashland, Ohio, December 12, 2014. REUTERS/Aaron Josefczyk/File Photo
![](http://archives.lincolndailynews.com/2024/Apr/26/images/ads/current/bennet_lda_010722.png) After the U.S. Department of
Agriculture released some raw genetic data onto a public database on
April 21, a team of evolutionary biologists led by Dr. Michael
Worobey of the University of Arizona pieced together the viral
genetic codes.
The team mapped the outbreak by tracking changes in the virus as it
spread among herds. Based on their analysis, Worobey said in an
April 24 interview that the outbreak in dairy cattle occurred
through a single transmission event from a bird to a cow in late
2023, likely in December.
HOW IS H5N1 SPREADING?
It is still unclear how the virus is spreading, but there is
evidence of wild bird-to-cow, cow-to-cow, cow-to-poultry, and one
case of cow-to-human transmission. There is no evidence of
human-to-human transmission.
Because of the heavy viral load in milk and mammary glands,
scientists suspect the virus is being spread to animals during the
milking process, either through contact with infected equipment or
with virus that becomes aerosolized during cleaning procedures.
Whether the virus can spread through respiratory droplets that
infect the airway, as flu viruses typically spread in humans,
remains unclear.
IS THERE A BIRD FLU VACCINE FOR HUMANS?
The U.S. has a stockpile of bird flu vaccines matched with the
strain currently circulating, as well as antivirals that could be
used to treat human infections. For a major epidemic or a pandemic,
the U.S. would have to scale up considerably.
Flu vaccine suppliers Sanofi, GlaxoSmithKline and CSL Seqirus have
said they are monitoring avian flu and stand ready.
(Reporting by Julie Steenhuysen and Tom Polansek in Chicago; Editing
by Caroline Humer and David Gregorio)
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