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Public Health Ontario
RAPID REVIEW
Survivability of Influenza A (H5N1) in Milk
Published: June 2024
Key Findings
• In March, 2024 avian influenza A(H5N1) was detected in raw (unpasteurized) milk, and in nasal
swabs and tissue samples collected from dairy cattle in the US,1 and on April 24, 2024, the US Food
and Drug Administration (US FDA) announced that samples of pasteurized milk had tested positive
by polymerase chain reaction (PCR) for influenza A(H5N1).2
• Detecting viral genetic material in pasteurized milk does not necessarily mean that someone could
become ill with influenza A(H5N1) from drinking pasteurized milk, as PCR testing cannot distinguish
between live and inactivated virus.3 Further testing of different types of pasteurized dairy products
sold at retail in the US (via a different testing method that looked for the presence of live virus) did
not detect any live, infectious virus. 2,3 The US FDA asserts that the totality of available evidence
(including recent testing of commercial milk and studies on the effectiveness of pasteurization in
eggs) indicates that the commercial milk supply is safe.3
• As of May 22, 2024, the Canadian Food Inspection Agency reported that retail milk samples from
across Canada have tested negative for influenza A(H5N1), indicating that there is no evidence of
disease in Canadian dairy cattle.4
• There appears to be some evidence from the published literature that a high viral load (large
amount of virus) of influenza A has an impact on pasteurization time and temperatures, requiring a
longer duration of heat treatment or use of higher temperature to inactivate the virus, with the
virus potentially having a higher resistance to inactivation in liquid media (e.g., suspension, water
or serum).5–8
• A combination of precautionary measures in the US, including disposing of milk from cattle with
signs of influenza A(H5N1) infection, dilution of milk from various farms in bulk milk tanks prior to
pasteurization, and pasteurization, are currently considered by the US FDA as sufficient means to
inactivate any virus that may be present in the raw milk.3 The Canadian Food Inspection Agency
(CFIA) has similarly noted that milk from dairy cattle in Canada is required to be pasteurized prior
to sale, and that pasteurized milk and milk products remain safe for consumption.9
Scope
This rapid review aimed to assess the survivability of influenza A(H5N1) in fluid milk from cattle and
other small ruminants that may be infected with the virus, including goats and sheep. Other dairy
products (e.g., cheese and sour cream) and meat from susceptible food-producing species (e.g., cattle,
poultry) were out-of-scope.
...
Conclusion
Although there is a lack of published literature specifically assessing the inactivation of influenza
A(H5N1) in milk, several studies have explored thermal inactivation of various avian influenza A subtypes
in eggs, and other liquid media. 27,28 These studies have found that in liquid egg products the virus is
inactivated within the time and temperature parameters required for pasteurization of milk, however
there is some evidence that the virus may be more heat-stable in mammalian cells compared to avian
cells,27 and that increasing viral load may affect the time and temperature required for viral
inactivation. 28 The most common method of pasteurization of milk in Ontario is continuous flow
pasteurization (72°C for 15 seconds for products with <10% milk fat). Several of the studies outlined
herein studied heat inactivation of various influenza A subtypes at temperatures of 70°C and above and
noted that full inactivation of the virus required exposure to 70°C for at least 1-5 minutes or 80°C for 2.5
minutes, depending on test media and viral load.6–8
Some studies have noted that influenza A in liquid media may be resistant to inactivation at industry
standard milk pasteurization temperatures (particularly when viral loads are high).29,30 One study found
that influenza A(H1N1) in water required heat treatment at 70°C for 5 minutes to reduce the virus below
detectable levels, 8 and another found that influenza A(H7N9) virus stock solution required heat
treatment at 70°C for 1 minute for infectivity to be completely lost.7 Studies exploring the effectiveness
of pasteurization on different viruses, including influenza, in human milk found that pasteurization at
62.5°C for 30 minutes should be effective to inactivate heat-sensitive viruses in human milk, although no
studies specifically tested the effectiveness of pasteurization on influenza A viruses.25
There appears to be some evidence that a high viral load (regardless of the medium) has an impact on
pasteurization time and temperatures, requiring a longer duration of heat treatment for inactivation,
with the virus potentially having a higher resistance to inactivation in some liquid media.
The recent finding that influenza A(H5N1) appears to have tropism for mammary tissue in cattle,
potentially increasing the viral load in milk from infected cattle, has prompted research by the US FDA,
in collaboration with the USDA and other partners to further explore and confirm the effectiveness of
pasteurization and other technologies (e.g., reverse osmosis, filtration) in inactivating any virus that may
be present.
...
RAPID REVIEW
Survivability of Influenza A (H5N1) in Milk
Published: June 2024
Key Findings
• In March, 2024 avian influenza A(H5N1) was detected in raw (unpasteurized) milk, and in nasal
swabs and tissue samples collected from dairy cattle in the US,1 and on April 24, 2024, the US Food
and Drug Administration (US FDA) announced that samples of pasteurized milk had tested positive
by polymerase chain reaction (PCR) for influenza A(H5N1).2
• Detecting viral genetic material in pasteurized milk does not necessarily mean that someone could
become ill with influenza A(H5N1) from drinking pasteurized milk, as PCR testing cannot distinguish
between live and inactivated virus.3 Further testing of different types of pasteurized dairy products
sold at retail in the US (via a different testing method that looked for the presence of live virus) did
not detect any live, infectious virus. 2,3 The US FDA asserts that the totality of available evidence
(including recent testing of commercial milk and studies on the effectiveness of pasteurization in
eggs) indicates that the commercial milk supply is safe.3
• As of May 22, 2024, the Canadian Food Inspection Agency reported that retail milk samples from
across Canada have tested negative for influenza A(H5N1), indicating that there is no evidence of
disease in Canadian dairy cattle.4
• There appears to be some evidence from the published literature that a high viral load (large
amount of virus) of influenza A has an impact on pasteurization time and temperatures, requiring a
longer duration of heat treatment or use of higher temperature to inactivate the virus, with the
virus potentially having a higher resistance to inactivation in liquid media (e.g., suspension, water
or serum).5–8
• A combination of precautionary measures in the US, including disposing of milk from cattle with
signs of influenza A(H5N1) infection, dilution of milk from various farms in bulk milk tanks prior to
pasteurization, and pasteurization, are currently considered by the US FDA as sufficient means to
inactivate any virus that may be present in the raw milk.3 The Canadian Food Inspection Agency
(CFIA) has similarly noted that milk from dairy cattle in Canada is required to be pasteurized prior
to sale, and that pasteurized milk and milk products remain safe for consumption.9
Scope
This rapid review aimed to assess the survivability of influenza A(H5N1) in fluid milk from cattle and
other small ruminants that may be infected with the virus, including goats and sheep. Other dairy
products (e.g., cheese and sour cream) and meat from susceptible food-producing species (e.g., cattle,
poultry) were out-of-scope.
...
Conclusion
Although there is a lack of published literature specifically assessing the inactivation of influenza
A(H5N1) in milk, several studies have explored thermal inactivation of various avian influenza A subtypes
in eggs, and other liquid media. 27,28 These studies have found that in liquid egg products the virus is
inactivated within the time and temperature parameters required for pasteurization of milk, however
there is some evidence that the virus may be more heat-stable in mammalian cells compared to avian
cells,27 and that increasing viral load may affect the time and temperature required for viral
inactivation. 28 The most common method of pasteurization of milk in Ontario is continuous flow
pasteurization (72°C for 15 seconds for products with <10% milk fat). Several of the studies outlined
herein studied heat inactivation of various influenza A subtypes at temperatures of 70°C and above and
noted that full inactivation of the virus required exposure to 70°C for at least 1-5 minutes or 80°C for 2.5
minutes, depending on test media and viral load.6–8
Some studies have noted that influenza A in liquid media may be resistant to inactivation at industry
standard milk pasteurization temperatures (particularly when viral loads are high).29,30 One study found
that influenza A(H1N1) in water required heat treatment at 70°C for 5 minutes to reduce the virus below
detectable levels, 8 and another found that influenza A(H7N9) virus stock solution required heat
treatment at 70°C for 1 minute for infectivity to be completely lost.7 Studies exploring the effectiveness
of pasteurization on different viruses, including influenza, in human milk found that pasteurization at
62.5°C for 30 minutes should be effective to inactivate heat-sensitive viruses in human milk, although no
studies specifically tested the effectiveness of pasteurization on influenza A viruses.25
There appears to be some evidence that a high viral load (regardless of the medium) has an impact on
pasteurization time and temperatures, requiring a longer duration of heat treatment for inactivation,
with the virus potentially having a higher resistance to inactivation in some liquid media.
The recent finding that influenza A(H5N1) appears to have tropism for mammary tissue in cattle,
potentially increasing the viral load in milk from infected cattle, has prompted research by the US FDA,
in collaboration with the USDA and other partners to further explore and confirm the effectiveness of
pasteurization and other technologies (e.g., reverse osmosis, filtration) in inactivating any virus that may
be present.
...
