USDA Statement On Mandatory Testing For Interstate Movement Of Cattle

#18,023

Earlier today the HHS hosted a teleconference with representatives from the CDC, FDA, USDA APHIS, and NIAID on the growing concerns of HPAI in dairy cattle, and while I was unable to attend I believe Lisa Schnirring will have details later today on the CIDRAP News site.

About an hour after the meeting, the USDA emailed out the following statement describing several steps - including new federal regulations on the testing of lactating cattle prior to interstate movement - that agency is taking to address the problem.

Today's statement also confirms (without providing details) that asymptomatic cattle have tested positive for the virus:

USDA has identified spread between cows within the same herd, spread from cows to poultry, spread between dairies associated with cattle movements, and cows without clinical signs that have tested positive. 

On nearly a daily basis, we continue to see signs that the scope of this outbreak is larger than has been previously assumed. I've reproduced the emailed statement below, which is also posted at this link.

USDA Actions to Protect Livestock Health From Highly Pathogenic H5N1 Avian Influenza

Federal Order to assist with developing a baseline of critical information and limiting the spread of H5N1 in dairy cattle

WASHINGTON, April 24, 2024 – To further protect the U.S. livestock industry from the threat posed by highly pathogenic H5N1 avian influenza, USDA is sharing a number of actions that we are taking with our federal partners to help us get ahead of this disease and limit its spread.    Today, USDA’s Animal and Plant Health Inspection Service (APHIS) announced a Federal Order requiring the following measures, effective Monday, April 29, 2024:    Mandatory Testing for Interstate Movement of Dairy Cattle Prior to interstate movement, dairy cattle are required to receive a negative test for Influenza A virus at an approved National Animal Health Laboratory Network (NAHLN) laboratory.  Owners of herds in which dairy cattle test positive for interstate movement will be required to provide epidemiological information, including animal movement tracing.  Dairy cattle moving interstate must adhere to conditions specified by APHIS.   As will be described in forthcoming guidance, these steps will be immediately required for lactating dairy cattle, while these requirements for other classes of dairy cattle will be based on scientific factors concerning the virus and its evolving risk profile.   Mandatory Reporting Laboratories and state veterinarians must report positive Influenza A nucleic acid detection diagnostic results (e.g. PCR or genetic sequencing) in livestock to USDA APHIS.  Laboratories and state veterinarians must report positive Influenza A serology diagnostic results in livestock to USDA APHIS.   USDA has identified spread between cows within the same herd, spread from cows to poultry, spread between dairies associated with cattle movements, and cows without clinical signs that have tested positive. On April 16, APHIS microbiologists identified a shift in an H5N1 sample from a cow in Kansas that could indicate that the virus has an adaptation to mammals. Centers for Disease Control and Prevention (CDC) conducted further analysis of the specimen sequence, which did not change their overall risk assessment for the general public, because the substitution has been seen previously in other mammalian infections and does not impact viral transmission. Additionally, APHIS’ National Veterinary Services Laboratories found H5N1 in a lung tissue sample from an asymptomatic cull dairy cow that originated from an affected herd and did not enter the food supply.    The novel movement of H5N1 between wild birds and dairy cows requires further testing and time to develop a critical understanding to support any future courses of action. This Federal Order is critical to increasing the information available for USDA. Requiring positive test reporting will help USDA better under this disease and testing before interstate movement will limit its spread.     While we are taking this action today, it is important to remember that thus far, we have not found changes to the virus that would make it more transmissible to humans and between people. While cases among humans in direct contact with infected animals are possible, our partners at the U.S. Centers for Disease Control and Prevention (CDC) believe that the current risk to the public remains low.    Additionally, we continue to see affected cows recover after supported care with little to no associated mortality. We also continue to work with our partners in the states and industry to emphasize the critical importance biosecurity plays in limiting disease spread for all livestock and poultry.    The Federal Order may be viewed here and is effective on Monday, April 29, 2024.    Further, in an effort to maximize understanding and research on H5N1 in dairy cattle, on April 21, APHIS made publicly available 239 genetic sequences from the U.S. H5N1 clade 2.3.4.4b influenza virus recently found in samples associated with the ongoing HPAI outbreak in poultry and wild birds, and the recent H5N1 event in dairy cattle. APHIS has also offered virus samples to interested researchers to facilitate epidemiological study. Increasing our understanding of this disease and how it spreads is critical to stopping it. This is why APHIS is urging dairy cattle producers and those who work in or with the industry to share epidemiological information from affected farms, even if they are not planning to move cattle interstate. APHIS further urges producer participation in public health assessments to continue to confirm worker safety and monitor for any potential changes in the virus that could impact transmissibility.      In addition, our partners in the U.S. Food and Drug Administration released an update on the ongoing work to ensure continued effectiveness of the federal-state milk safety system. It is important to emphasize that, based on the information and research available to us at this time, the U.S. Food and Drug Administration and USDA believe that our commercial milk supply is safe because of both the pasteurization process and the required diversion or destruction of milk from sick cows. Pasteurization has continuously proven to inactivate bacteria and viruses in milk. The FDA and USDA continue to work closely to collect and evaluate additional data and information specific to avian influenza in dairy cattle and to support state counterparts as this emerging disease in dairy cattle is managed.   As USDA continues to take steps to protect the health of livestock, the Department continues to work closely with federal partners at the CDC on protecting the health of people and FDA on protecting the safety of the food supply. The U.S. government is committed to addressing this situation with urgency.   To learn more about USDA’s response to HPAI in dairy cattle, visit https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/livestock.

FDA Statement On Investigation Of H5N1 Virus Particles Detected In Finished Milk

 

#18,022

As we've discussed many times (see here, here, and here), highly specific and sensitive PCR testing is great for detecting the presence of pathogens like influenza A, but it can also detect non-viable virus particles as well.   

So, despite the furor overnight in the media about the discovery of `HPAI virus' in pasteurized milk, we don't know whether it presents a public health hazard or not.  

It does, however, deflate repeated claims by the USDA/FDA that:

Dairies are required to send only milk from healthy animals into processing for human consumption; milk from impacted animals is being diverted or destroyed so that it does not enter the human food supply. 

Further testing, where attempts will be made to grow (culture) the virus, will tell us a lot more.  But that process could take days or (if the virus is toxic to the growth medium) weeks.  

While my guess is that pasteurization greatly reduces any risks of infection, it is a mystery why - a full month after the virus was confirmed in dairy cows - they don't have those answers yet.  

The FDA's low-key admission (see below) was buried well down the page in last night's Updates on Highly Pathogenic Avian Influenza (HPAI).

(Excerpt)

As noted by USDA and some press reports from the World Health Organization (WHO) and other sources, the presence of the virus has been detected in raw milk. Based on available information, pasteurization is likely to inactivate the virus, however the process is not expected to remove the presence of viral particles. Therefore, some of the samples collected have indicated the presence of HPAI using quantitative polymerase chain reaction (qPCR) testing.

During the course of the outbreak, the FDA has been evaluating milk from affected animals, in the processing system, and on the shelves. We are completing a large representative national sample, to better understand the extent of these findings. Because qPCR findings do not represent actual virus that may be a risk to consumers, the FDA is further assessing any positive findings through egg inoculation tests, a gold-standard for determining viable virus. To date, we have seen nothing that would change our assessment that the commercial milk supply is safe. Results from multiple studies will be made available in the next few days to weeks.

(Continue . . . )

Remarkably, this statement came only after repeated calls by researchers (see here, here, and here) for better surveillance and more disclosure. Under growing pressure, the USDA released  239 Sequences From HPAI H5N1 Viruses late Sunday night, but dates of collection and locations were notably absent. 

As reported by Lisa Schnirring on CIDRAP earlier this week (see Scientists find clues in early analysis of newly shared US H5N1 avian flu sequences), there is now evidence that HPAI H5 may have been circulating in cattle for weeks (or even months) longer than previously suspected.

A bias against testing cattle for influenza A (despite evidence of their susceptibility) allowed the virus to circulate undetected until a month ago.  Since then, further reluctance to test non-dairy cattle, or asymptomatic cows, has left us with no clear idea of how widespread this HPAI outbreak really is. 

This `don't test, don't tell' policy also extends to pigs, and other potentially susceptible livestock. 

We have a bad habit of assuming the `best case scenario' when it comes to emerging viruses. 

In 2020 it took weeks and even months for governments to accept that COVID couldn't be contained by travel restrictions, that it was spread via the `airborne' route, and early reports of asymptomatic spread and reinfections were dismissed by the experts.  

Those early overly-optimistic assumptions undoubtedly cost lives. 

While the jury is still out on whether HPAI H5 will spark the next global public health crisis, another pandemic is inevitable.   

Although I understand it may be politically and economically inconvenient, we have to be willing to actively look for the next threat, otherwise we'll never see it coming. 

Mixed Messaging On HPAI Food Safety

#18,021

Although the USDA and FDA continue to reassure the American public that the food chain (including milk) is safe from HPAI H5N1, there remain unanswered questions about how widespread the virus is in cattle, and how effective regular pasteurization is in killing the virus. 

While the extent of the spread in cattle remains unknown, 3 days ago the New York Times carried an article (see Scientists Fault Federal Response to Bird Flu Outbreaks on Dairy Farms) where they cite (so far, unverified) reports of positive tests from asymptomatic cattle in North Carolina.

Testing by the USDA of cattle has remained both limited and voluntary, and has so far only been recommended for symptomatic dairy cows (see APHIS/USDA Updated FAQ On Detection of HPAI (H5N1) in Dairy Herds).

This `don't test, don't tell' policy apparently extends to pigs as well, despite ongoing concerns that HPAI could find a home in swine herds (see EID Journal: Divergent Pathogenesis and Transmission of Highly Pathogenic Avian Influenza A(H5N1) in Swine).

An excellent overview by Jon Cohen in Science yesterday (see U.S. government in hot seat for response to growing cow flu outbreak) describes the parsimonious release of information by the U.S. government, along with the limited evidence on the effectiveness of standard pasteurization in deactivating the virus. 

Under what I assume to be an abundance of caution, the CDC recently revised their food safety advice (see below) regarding HPAI, which now includes guidance on safely cooking beef (which, according to the USDA, are unlikely to be infected).  

They recommend:

• Whole cuts of beef, veal, lamb, and pork, including fresh ham: 145°F
• Ground meats, such as beef and pork: 160°F
• All poultry, including ground chicken and turkey: 165°F

It is also worth mentioning that despite the mantra that `properly prepared foods are safe to consume', there may be some small risks entailed in the preparation of raw meat.  PAHO (the Pan-American Health Organization) mentions this on their Avian Influenza landing page:

Transmission

The most common way for the virus to enter a territory is through migratory wild birds. The main risk factor for transmission from birds to humans is direct or indirect contact with infected animals or with environments and surfaces contaminated by feces. Plucking, handling infected poultry carcasses, and preparing poultry for consumption, especially in domestic settings, may also be risk factors.

In Asia, more than a few human HPAI H5 infections have been linked to preparing and cooking poultry.  Although it gets mentioned, far more attention needs to be paid to safe food handling practices in this time of HPAI. 

While I fully understand the USDA's desire to reassure the public about the safety of the food supply - doing so while slow rolling the release of information is a risky strategy.

Particularly when dealing with a virus with a history of repeatedly doing the unexpected.

I&ORD: Evidence of Reverse Zoonotic Transmission of Human Seasonal Influenza A Virus (H1N1, H3N2) Among Cats

 

My strictly indoor companion

#18,020

Up until 20 years ago, cats (and dogs) were thought relatively immune to influenza A viruses.  All that changed when an equine H3N8 virus jumped to greyhounds at a racetrack in Florida in 2004, and half-way around the world, big cats in Asian zoos began to succumb to avian H5N1. 

Since then we've seen a second (avian H3N2) influenza A virus jump to dogs and begin a world tour, and dozens of reports of dogs and cats infected with a variety of (mostly novel) influenza A viruses.  

A small sampling includes:

Microorganisms: Case Report On Symptomatic H5N1 Infection In A Dog - Poland, 2023

J. Virology: Zoonotic Risk, Pathogenesis, and Transmission of Canine H3N2

Access Microbiology: Inter-Species Transmission of Avian Influenza Virus to Dogs

WHO Update & Risk Assessment On H5N1 In Cats - Poland

Nebraska Veterinary Diagnostic Center (NVDC) Report: 2 Domestic Cats Infected With HPAI H5N1

NYC Health Dept. Statement On Avian H7N2 In Cats

The most obvious concern is that a dog or a cat might pick up a novel influenza A virus (like H5N1) from exposure to birds, or a contaminated environment, and bring it home (zoonotic transmission). 

But it is equally possible that a companion animal (or farmed animals) could be infected by humans (aka `reverse zoonosis'), and even introduce that virus into the wild.  

Reverse zoonosis may help explain how SARS-COV ended up in North American deer and other peridomestic animals, and almost certainly how human influenza A viruses have spread so widely in swine (see Reverse zoonosis of influenza to swine: new perspectives on the human-animal interface). 

While we've seen a fair number of studies on novel flu infection in companion animals, relatively little is known about the spread of seasonal flu viruses to cats.  

• During the 2009 H1N1 pandemic we did see several reports of feline infection
• In late 2010 we saw a study (see EID Journal: Pandemic H1N1 Infection In Cats) that looked at the pathogenesis of novel H1N1 in domestic felines.
• Six years ago we looked at two rare fatal infections in cats from a single household in Connecticut. Reportedly, both cats had pre-existing conditions, and the owner of the cats had recently been sick with a flu-like illness. (see Connecticut: Two Cases Of Fatal H1N1 In Cats)

All of which brings us to a letter to the Editor published in Influenza & Other Respiratory Diseases, which provides details of evidence of reverse zoonotic transmission of seasonal flu viruses to cats in China, and discusses the potential for cats to serve as a `mixing vessel' . 

First, some excerpts from the letter (follow the link to read it in its entirety), after which I'll return with a postscript.

Evidence of Reverse Zoonotic Transmission of Human Seasonal Influenza A Virus (H1N1, H3N2) Among Cats

Sajid Umar, Semin Kim, Di Gao, Pu Chen
First published: 18 April 2024
https://doi.org/10.1111/irv.13296

Dear Editor,

Human–animal interactions are closely intertwined. The connection between animal, human, and environmental health is becoming increasingly complicated with globalization, industrialization, and climate change. Since the beginning of the 20th century, the number of domestic cats has increased rapidly worldwide, including in China. There are approximately 600 million domesticated cats worldwide, including 65 million cats in China, most of whom have close human contacts. 

These close contacts create more chances for pathogen spillover among humans and cats, which could lead to the emergence of new pathogenic strains or variants. Cats living in proximity to their owners carry a particular risk of catching pathogens, as they often share snuggles, kisses, dining, and beds [1, 2]. We share hundreds of pathogens with our animals, which they serve as intermediate or reservoir hosts for pathogens that affect human health. Cats, owing to their genetic similarity to humans, are more susceptible to catching diseases from their owners. Recently, it has been estimated that humans spillover far more pathogens to animals than animals transmit to humans [2, 3]. 

          (SNIP) 

The high susceptibility of cats to IAVs generates the possibility of zoonotic and reverse-zoonotic transmission events and can serve as a mixing vessel for the emergence of new IAV variants (Figure 1). A large population of animals and humans makes China an ideal location for the emergence of future IAV pandemics.

(SNIP)

IAV was detected in 2.8% of the samples (13/458), whereas influenza B virus was not detected during this study. Genetic analysis revealed the presence of A (H1N1) and A (H3N2). Among the positive strains, there were nine strains of A (H1N1) virus and four strains of A (H3N2) virus. A/H1N1 and A/H3N2 positive cats showed HAI titers against these viruses, which also supported the evidence of reverse zoonosis. Interestingly, a higher detection rate (84.61%) was observed in samples collected during autumn and winter, which could be linked to the peak flu season in Kunshan and Shanghai. Clinical signs, including sneezing, dyspnea, and coughing, varied from mild to moderate among influenza-positive cats. No deaths were reported among the positive cats.

Based on molecular and serological testing, we demonstrated human seasonal IAV-infected cats in this study. This is the first report to assess the reverse zoonotic events of influenza viruses in cats in Kunshan, China, and highlights the potential risk of catching IAV in cats living in close contact with their owners. Despite some limitations, such as the small sample size and geographical area, our study provides useful information to veterinarians, pet owners, and policymakers.

Cats could act as additional intermediate or reservoir hosts for endemic IVA evolution and thus may contribute to major public health issues. There are several reports on the natural transmission of different IAV subtypes in cats, including avian H5N1, canine H3N2, human H1N1, and H3N2 [8]. Anthroponotic spillover events for IAV have been documented among cats, suggesting close interactions between cats and owners suffering from influenza-like illness [1, 8-11]. In addition to cats, a variety of other animals (swine, dogs, turkeys, and ferrets) has been naturally infected with Influenza A/H1N1. Human-to-pig transmission of IAV is the most studied anthroponotic event. More IAVs jump from humans to swine than from swine to humans [1].

Several suggestions have been made to minimize the risk of IAV-reverse zoonosis.

First, flu vaccine shots are recommended to owners and susceptible cats to reduce anthroponotic events.

Second, people who are sick with seasonal flu need to modify their behaviors and should be more vigilant about the health of their cats. Pet owners can minimize reverse zoonotic transmission by keeping nasal discharges and other bodily secretions away from cats during the sickness period.

Third, owners can minimize their playing time and petting activities with their cats while they are sick.

Finally, they can also limit reverse zoonotic transmission by regularly cleaning and disinfecting the bedding area and providing fresh and healthy feed to their cats.

Reverse zoonotic events in IAV can pose significant health risks for cats and possibly human health if left unchecked. Therefore, it is important to keep the IAV under control before it imposes deadly consequences on the human population. Keeping in mind the close association of cats with humans and the high pandemic potential of IAV warrants a more integrated research approach to minimize reverse zoonoses. This could include greater testing and continuous human pathogen surveillance at the human-animal contact interface. This type of data could facilitate the mitigation, prevention, prediction, and preparation of future IAV pandemics.

          (Continue . . . .)

Twice in my lifetime (H2N2 in 1957 & H3N2 in 1968) pandemic influenza viruses have emerged from China that were a combination of avian and human flu viruses.  Presumably, some unknown host was co-infected with a seasonal flu virus and and avian flu virus, and produced a hybrid via reassortment.  

While that host might have been a human, it could just as easily have been a pig, a dog, a cat, or some other non-human host.

All reasons why, with the elevated amount of HPAI H5N1 virus in wild birds and the environment, it is more important than ever to heed the CDC's advice on how to keep your pets (and your family) safe. 

 CDC Updated Advice On Bird Flu in Pets and Other Animals

USDA Releases 239 Sequences From HPAI H5N1 Viruses

USDA - 32 Outbreaks of H5N1 in Cattle across 8 States
 

#18,019

The USDA, which has been criticized for being slow to release genetic sequences from H5N1 viruses affecting cattle (see Helen Branswell's STAT report) - published 239 genetic sequences on Sunday evening on the SRA - NCBI (nih.gov) website.

Sample From Database       

Sequences posted are from cattle, cats, chickens, skunk, raccoon, grackle, blackbird, and goose. However, some important epidemiological details on each sample (e.g. location, collection dates, etc) are not immediately apparent (see graphic above).

Each submission contains megabytes of cryptic data, so it will take time for researchers to fully analyse them.

The USDA announcement follows:

USDA Publishes H5N1 Influenza A Virus Genetic Sequences on publicly available site
Last Modified: April 21, 2024
 
Today, the APHIS National Veterinary Services Laboratories made available 239 genetic sequences from the U.S. H5N1 clade 2.3.4.4b influenza virus recently found in samples associated with the ongoing highly pathogenic avian influenza (HPAI) outbreak in poultry and wild birds, and the recent H5N1 event in dairy cattle. APHIS routinely publishes influenza genetic sequence data on GISAID (the Global Initiative on Sharing Avian Influenza Data); however, in the interest of public transparency and ensuring the scientific community has access to this information as quickly as possible to encourage disease research and development to benefit the U.S. dairy industry, APHIS is also rapidly sharing raw sequence data to the National Institute of Health’s National Library of Medicine, National Center for Biotechnology Information. Sequences posted are from cattle, cats, chickens, skunk, racoon, grackle, blackbird, and goose. APHIS will continue making additional raw genetic sequences available on a rolling basis at Home - SRA - NCBI (nih.gov); use the search term “WGS of H5N1”.

A Slight Case Of Deja Flu

“History Doesn't Repeat Itself, but It Often Rhymes” – Mark Twain.

#18,018

While the recent spillover of HPAI H5N1 into dairy cows in at least 8 states, and the discovery of `high concentrations' of the virus in raw milk, has been called unprecedented, it isn't that far afield from the events of a decade ago, when the MERS coronavirus was found to be endemic in Arabian camels, and shed in camel's milk and urine. 

WHO Update On MERS-CoV Transmission Risks From Animals To Humans

Eurosurveillance: MERS-CoV Antibodies & RNA In Camel’s Milk – Qatar 

CIDRAP: More Evidence for Camel-to-Human MERS-CoV Transmission

Despite an abundance of scientific evidence linking camels to the carriage and likely spread of the MERS virus (see here, here, & here) the Saudi Ministry of Agriculture spent months either evading or denying the issue (see Saudi MOA Spokesman: Camel Link Unproven, MERS-CoV Is MOH Problem).

Finally, in May of 2014 the Saudi Ministry Of Agriculture Issued Warnings On Camels, urging breeders and owners to limit their contact with camels, and to use PPEs (masks, gloves, protective clothing) when in close contact with their animals.

At first, this news was not well received (see Saudi Camel Owners Threaten Over MERS `Slander’) and many people (locals and tourists) continued to defiantly expose themselves to camels (rides and `kissing') and to camel products (meat, milk, urine, etc.) without taking recommended precautions.

The good news is, despite thousands of infections and hundreds of deaths (see chart above)  MERS-CoV never did acquire full transmissibility between humans.  Most outbreaks were household or nosocomial, although a few superspreader events did occur. 

Had MERS-CoV evolved to be as easily spread as COVID, the results would likely have been far different. 

While today we are dealing with an avian influenza virus, not a coronavirus, the similarities are striking.  Both viruses were thought unlikely to infect their respective intermediate hosts (cows and camels), and both were found to shed the virus via milk and other fluids (see USDA statement below). 

Has USDA confirmed at this point that cow-to-cow transmission is a factor? 

Yes, although it is unclear exactly how virus is being moved around. We know that the virus is shed in milk at high concentrations; therefore, anything that comes in contact with unpasteurized milk, spilled milk, etc. may spread the virus. Biosecurity is always extremely important, including movement of humans, other animals, vehicles, and other objects (like milking equipment) or materials that may physically carry virus.  

Although the outbreak in dairy cows has only been reported in 32 herds across 8 states so far, it is likely that some spillovers have not been documented.  Testing is voluntary, and is normally limited to dairy cattle.

While no other countries have reported similar outbreaks, if H5N1 can spillover to cows here, it can probably happen in other regions of the world as well. 

As we saw in Saudi Arabia with the continued consumption of raw camel's milk, there is a strong `raw milk' movement in the United States, with the following 2017 study published in the EID Journal suggesting that > 3% of the population regularly drinks unpasteurized milk. 

Outbreak-Related Disease Burden Associated with Consumption of Unpasteurized Cow’s Milk and Cheese, United States, 2009–2014

Solenne Costard , Luis Espejo, Huybert Groenendaal, and Francisco J. Zagmutt

Abstract

The growing popularity of unpasteurized milk in the United States raises public health concerns. We estimated outbreak-related illnesses and hospitalizations caused by the consumption of cow’s milk and cheese contaminated with Shiga toxin–producing Escherichia coli, Salmonella spp., Listeria monocytogenes, and Campylobacter spp. using a model relying on publicly available outbreak data.

In the United States, outbreaks associated with dairy consumption cause, on average, 760 illnesses/year and 22 hospitalizations/year, mostly from Salmonella spp. and Campylobacter spp. Unpasteurized milk, consumed by only 3.2% of the population, and cheese, consumed by only 1.6% of the population, caused 96% of illnesses caused by contaminated dairy products.

Unpasteurized dairy products thus cause 840 (95% CrI 611–1,158) times more illnesses and 45 (95% CrI 34–59) times more hospitalizations than pasteurized products. As consumption of unpasteurized dairy products grows, illnesses will increase steadily; a doubling in the consumption of unpasteurized milk or cheese could increase outbreak-related illnesses by 96%.

While heavily discouraged by most public health agencies (see CDC's Fast Facts: Why Is Raw Milk Unsafe?) there are enough loopholes in state laws that most American can buy raw milk if they want it. 

Milk pasteurization rules in Europe are much stricter than in the United States, with most milk subjected to ultra-high temperature (UHT) pasteurization, which makes it shelf stable.  

In many other countries, however, the consumption of `raw milk' is much higher than in the US. The USDA reported in 2019:

In Mexico, half of all fluid milk goes into the processing industry for the production of yogurt, cheeses, and other products. Between 40-45 percent of consumption is of fluid drinkable milk, such as pasteurized, ultra-high temperature processed (UHT), bottled, or packaged milk. Unpasteurized, raw milk accounts for between 5-10 percent of consumption.

Beyond that, accurate estimates of the consumption of raw milk around the globe are hard to come by. But it is safe to say in that in some countries, that number is likely to greatly exceed 10%. 

There are still a great many unknowns when it comes to HPAI's spillover into cattle, including:

• Whether the spillover of H5N1 to cows is currently limited to the B3.13 genotype found in Midwestern birds.

• Whether non-dairy cattle are being sub-clinically infected, and if so, what the risks to public health that might pose

• Whether standard pasteurization (as opposed to UHT) completely inactivates the virus in milk

• Whether other milk producing animals (e.g. goats, camels, buffaloes, etc.) carry the same risk of infection as dairy cows

• How long the virus is shed by these various milk producing species

• And perhaps most importantly, what is the range of illness experienced by humans who consume infected milk, and can they transmit it on to others via the respiratory route?

Hopefully we'll get the answers to these, and other pressing questions, sooner rather than later.

With luck, cattle may prove to be a `dead-end' host for avian flu  - and this outbreak can be contained by the USDA/FDA and the dairy industry - but the stakes would go up considerably if we started seeing evidence of similar spillovers in other parts of the world.

Or even more ominously, if we started seeing the virus turn up in domestic pigs. A year ago, the ECDC/EFSA Avian Influenza Overview December 2022 – March 2023 warned:

The additional reports of transmission events to and potentially between mammals, e.g. mink, sea lion, seals, foxes and other carnivores as well as seroepidemiological evidence of transmission to wild boar and domestic pigs, associated with evolutionary processes including mammalian adaptation are of concern and need to be closely followed up.

While it is always possible that there is some genetic barrier that prevents HPAI H5N1 from sparking a human pandemic, over the past 3 years the virus has greatly expanded its mammalian host range.  

And that is no small concern.

Stay tuned.