Highly Pathogenic Avian Influenza in Dairy Herds

Highly Pathogenic Avian Influenza in Dairy Herds

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May 7, 2024
Highly Pathogenic Avian Influenza in Dairy Herds
The U.S. Department of Agriculture (USDA), the Centers
dairy herds four months (i.e., since late 2023) prior to the
for Disease Control and Prevention (CDC), and the Food
USDA announcement.
and Drug Administration (FDA) confirmed a strain (H5N1)
of highly pathogenic avian Influenza A virus (HPAI) in
APHIS Federal Order
dairy herds in Texas and Kansas on March 25, 2024. To
On April 24, 2024, APHIS issued a federal order under
date, cases in dairy herds in Colorado, Idaho, Ohio,
Section 8305 of the AHPA, which allows USDA to restrict
Michigan, New Mexico, North Carolina, and South Dakota
or prohibit the movement of animals in interstate commerce
also have been confirmed.
to protect animal health. The federal order requires testing
of dairy cattle and negative results before they are moved
The Animal Health Protection Act (AHPA; 7 U.S.C. §8301
interstate. The order went into effect on April 29, 2024, and
et seq.) provides USDA’s Animal and Plant Health
requires
Inspection Service (APHIS) authorities to manage animal
health. As of May 6, 2024, APHIS had reported that 34
• dairy cattle to be tested for Influenza A by an approved
dairy herds had been infected with HPAI. APHIS reports
National Animal Health Laboratory Network (NAHLN)
the number of infected dairy herds only, as all cows in a
laboratory;
herd may not be tested once positives are confirmed. To
date, HPAI has not been confirmed in beef cattle herds.
• owners of herds with positive tests to provide
epidemiological information, including movement
HPAI
tracing;
The H5N1 strain of HPAI has a high mortality rate for
domestic birds. The latest domestic outbreak of the H5N1
• dairy cattle moving interstate to follow APHIS
strain in wild birds was first detected in late 2021 and since
conditions (see “APHIS Guidance”); and
has been found in most states. Infected wild birds shed the
virus through mucus, saliva, and feces, leading to HPAI
• immediate adoption of the movement conditions for
infection outbreaks in domestic commercial and backyard
lactating dairy cows. Conditions for other classes of
poultry flocks, as well as infections in other wildlife and
dairy cattle will be determined based on scientific
marine mammals. According to CDC, 23 countries since
factors and evolving risk profile.
1997 have reported H5N1 infections in humans, mostly due
to close exposure to infected poultry; only a small number
The federal order also requires laboratories and state
of human cases have been reported since 2022. In 2022, one
veterinarians to report positive Influenza A nucleic acid
person involved in culling HPAI infected poultry tested
detection (e.g., polymerase chain reaction [PCR] or genetic
positive for HPAI. On April 1, 2024, CDC confirmed that
sequencing) and serology diagnostic results to APHIS. The
one person exposed to dairy cattle tested positive for HPAI.
PCR test detects the presence of HPAI genetic material in
CDC considers the human health risk of HPAI to be low.
samples but does not indicate whether the detected virus is
However, the ability for Influenza A viruses to adapt and
active. Other tests can show the presence of active or live
transmit to other species is cause for concern among both
virus.
animal health and public health officials.
USDA clarified that the federal order applies to lactating
Dairy Cattle Symptoms
dairy cows moving interstate only and not to other cows
Unlike the high mortality caused by HPAI in domesticated
moving intrastate. Cows from various farms are often
poultry flocks, infected cows have been recovering in 10-20
collected at sale barns or auctions and then moved to
days. HPAI in poultry flocks is controlled through culling
slaughter. If these cows are lactating and being moved
of exposed flocks to eradicate the HPAI outbreak. Infected
interstate directly to a slaughter facility, the cows need only
dairy cows are not culled to control the outbreak.
a Certificate of Veterinary Inspection confirming they are
clinically healthy.
HPAI in dairy cattle initially showed up as an unexplained
illness in dairy herds in Texas, then in Kansas and New
APHIS Guidance
Mexico, in February and March of 2024, respectively. The
On April 26, 2024, APHIS issued testing requirements for
symptoms—drop in feed consumption, sudden decline in
interstate movement and recommendations for state animal
milk production, thick and discolored milk, tacky feces or
health officials, veterinarians, and producers.
diarrhea, and fever—were similar across herds. The illness
primarily affected older dairy cows, not dry cows or heifers
Lactating dairy cattle must receive a negative Influenza A
(i.e., cows not producing milk). Recently released research
virus test result from an approved NAHLN laboratory using
indicates that the HPAI virus may have been circulating in
an approved test before they are moved interstate. Such
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Highly Pathogenic Avian Influenza in Dairy Herds
testing includes milk samples and nasal swabs collected by
herds. FDA found no live virus in follow-up testing, leading
and supervised by an accredited veterinarian, state licensed
it to conclude that pasteurization effectively deactivates
veterinarian, or sample collector approved by state animal
HPAI virus. FDA also tested infant and toddler formula and
health officials. Milk samples are to be from each quarter of
found no viral fragments. FDA expanded testing to other
the udder. For groups of lactating dairy cows of fewer than
retail dairy products (cottage cheese and sour cream), as
30 being moved, each cow must be tested. For larger
well as fluid milk, and found no live HPAI virus.
groups, 30 of the cows must be tested. Tests must be done
no more than 7 days prior to interstate movement.
H5N1 virus can be transferred to young calves through raw
milk. FDA recommends that milk from cows showing signs
The tests are completed by a NAHLN laboratory using an
of HPAI be discarded. The discarded milk should be heat
approved PCR test that detects the HPAI pathogen in fluids.
treated to kill the virus before being dumped in a lagoon or
Producers or those that submit samples to the laboratories
spread as waste solid to prevent infection of other animals.
do not pay for the testing; APHIS reimburses the
If used to feed calves or other farm animals, such as farm
laboratories for tests but does not pay for sample collection
cats, it should also be heat treated similarly to the
or shipping.
commercial pasteurization process to kill the virus.
Lactating dairy cows are not eligible for interstate
FDA is testing raw milk sent to processors to understand
movement for 30 days from the most recent collection of
the H5N1 virus load in milk. At this time, FDA has limited
any positive testing sample from any individual animal in
information about the transmission of HPAI in raw milk.
the herd. After the 30-day period, animals must be tested
FDA has a long-standing recommendation that raw milk
again before movement. If an HPAI-positive lactating dairy
and raw milk dairy products not be sold or distributed for
cow needs to be moved to a premises in another state, the
human consumption because of the transmission of
state animal health officials and APHIS must agree to the
pathogens in raw milk.
specific circumstances.
USDA Beef Studies
APHIS recommends that cattle movement be minimized;
At the end of April, USDA reportedly started sampling
not be moved if there are any signs of HPAI; and once
ground beef from retail stores in the states with confirmed
moved, be isolated for 30 days to minimize the spread of
HPAI dairy cattle. Dairy cow beef is a key input into the
infection. APHIS also states that cattle producers need to
U.S. ground beef supply because it is lean and combined
follow any additional state cattle movement requirements.
with fed cattle beef with higher fat content to create the lean
In addition, producers are encouraged to follow biosecurity
ground beef demanded by U.S. consumers. USDA’s Food
procedures to reduce the potential spread of the virus.
Safety and Inspection Service (FSIS) announced on May 1,
2024, that all 30 of its retail ground beef samples tested
USDA Testing
negative for any viral particles.
The NAHLN is a key component for managing this disease
event. NAHLN is a network of 63 federal, state, and
FSIS is collecting muscle samples from culled dairy cows
university veterinary diagnostic laboratories in 42 states
condemned at slaughter facilities for systemic pathologies.
that test for foreign animal diseases, including avian
APHIS plans to test the samples for viral particles and post
influenza. NAHLN personnel work with APHIS’s National
the results when available.
Veterinary Services Laboratory (Ames, IA, and Plum
Island, NY) on diagnostic testing and surveillance of animal
USDA’s Agricultural Research Service is conducting
disease.
studies to evaluate how a HPAI virus surrogate is affected
by different cooking temperatures of ground beef. USDA
In the case of dairy herd infections with H5N1, APHIS
plans to report these results when they available.
announced that the NAHLN laboratories will be reimbursed
for (1) testing suspect dairy cattle, (2) pre-movement
According to FSIS, Colombia is the only country that has
testing, (3) tests requested by producers of asymptomatic
banned beef shipments from the nine states with HPAI
cattle, and (4) testing of samples from other animals on
infected dairy herds. Thus far, other U.S. beef trading
dairies with HPAI infections.
partners have not imposed any restrictions.
FDA Milk Safety
Impact on Dairy Industry
FDA is responsible for the safety of the U.S. milk supply.
To date, there has been little impact on dairy markets. One
Almost all commercial milk is produced under the Grade
initial analysis indicates a minimal impact on milk
“A” Pasteurized Milk Ordinance (PMO) that regulates milk
production and markets. According to USDA statistics,
safety and sanitary conditions of milk facilities. The PMO
there are 9.4 million dairy cows in the United States,
specifies that milk from sick dairy cows should not enter
producing about 226 billion pounds of milk annually. In
the milk supply.
2023, USDA reported that there were 26,290 licensed dairy
herds (commercial operations) in the United States
FDA has concluded that the PMO and the pasteurization of
producing a majority of the milk. About 0.1% of dairies
milk kills the H5N1 virus, making the milk safe for
have been affected by the current HPAI outbreak to date.
consumption. Initial FDA PCR tests of milk found that 20%
of commercial milk samples contained viral HPAI
Joel L. Greene, Analyst in Agricultural Policy
fragments, with more positive results in areas with infected
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Highly Pathogenic Avian Influenza in Dairy Herds

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