“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.
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.
