Bird -> cow -> bird -> cow or bird -> cow -> cow?
May 3, 2024 8:52 PM Subscribe
This question is about the current spread of H5N1 influenza ("bird flu") among cattle in the United States. Is it known whether (a) this is a result of a single bird-to-cow transmission event, after which the (presumably new) cow-infecting sub-strain of H5N1 is spreading solely cow to cow, or (b) a cow-infecting sub-strain is also circulating among birds and each herd that is getting infected is being infected by separate bird-to-cow transmission events?
We know that it's circulating among cows; my question is whether birds are the infection vector between separate herds of cows.
We know that it's circulating among cows; my question is whether birds are the infection vector between separate herds of cows.
Best answer: According to this podcast from University of Minnesota Center for Infectious Disease Research and Policy, some cows (they think in the Texas panhandle) originally became infected either by wild birds or by domestic poultry that had been infected by wild birds, and then the virus spread among herds in multiple states via either by movement of cattle or by movement of equipment that carried the virus. So, it started from a bird but the spread is from cow to cow.
posted by SageTrail at 9:33 PM on May 3 [3 favorites]
posted by SageTrail at 9:33 PM on May 3 [3 favorites]
And cats on cow farms have died from drinking unpasteurized milk.
posted by tiny frying pan at 5:13 AM on May 4
posted by tiny frying pan at 5:13 AM on May 4
either by movement of cattle or by movement of equipment that carried the virus
There has also been some suggestion that infected human workers could be one vector transmitting the virus from farm to farm (there has been at least one confirmed case of an infected dairy worker, and anecdotal reports that an unusual number of people were sick at farms dealing with outbreaks) - but regardless, still just the one spillover event from birds to mammals.
posted by mskyle at 7:10 AM on May 4 [1 favorite]
There has also been some suggestion that infected human workers could be one vector transmitting the virus from farm to farm (there has been at least one confirmed case of an infected dairy worker, and anecdotal reports that an unusual number of people were sick at farms dealing with outbreaks) - but regardless, still just the one spillover event from birds to mammals.
posted by mskyle at 7:10 AM on May 4 [1 favorite]
Best answer: In addition to the human case report published in New England Journal of Medicine (linked above by mskyle), there is also a new epidemiology report on the dairy cattle outbreak.
They have a section in Results titled "Genomic epidemiology demonstrated a single interspecies transmission event" where they provide evidence that there was a single spillover event.
Also, they suggest that the spillover was preceded by a "reassortment event" that allowed for the easy transmission between cattle. In influenza, the genome of the virus is packaged as eight separate strands corresponding to the genetic instructions for different parts/capabilities of the virus. A reassortment occurs when the cell of an infected host is infected by virions of two different strains and a newly packaged virus receives a mixture of the strands from the two strains.
posted by pjenks at 8:13 AM on May 4 [1 favorite]
They have a section in Results titled "Genomic epidemiology demonstrated a single interspecies transmission event" where they provide evidence that there was a single spillover event.
Also, they suggest that the spillover was preceded by a "reassortment event" that allowed for the easy transmission between cattle. In influenza, the genome of the virus is packaged as eight separate strands corresponding to the genetic instructions for different parts/capabilities of the virus. A reassortment occurs when the cell of an infected host is infected by virions of two different strains and a newly packaged virus receives a mixture of the strands from the two strains.
posted by pjenks at 8:13 AM on May 4 [1 favorite]
The jump from a purely bird virus to easy transmission in one type of mammal is a big deal, but if it implied easy transmission in humans we'd already be in a pandemic. The single case report of the infected farmworker details an infection of the eye only; a complete absence of respiratory symptoms.
The route it took from birds to cattle, however, could easily happen again from cattle to pigs or cattle to humans. The apparent widespread epidemic among dairy cattle means that there are lots of reassortment events now happening in the cells of cattle, and one of those events could create a virus better adapted to humans (or to pigs/birds and then, by another event, to humans).
posted by pjenks at 8:24 AM on May 4
The route it took from birds to cattle, however, could easily happen again from cattle to pigs or cattle to humans. The apparent widespread epidemic among dairy cattle means that there are lots of reassortment events now happening in the cells of cattle, and one of those events could create a virus better adapted to humans (or to pigs/birds and then, by another event, to humans).
posted by pjenks at 8:24 AM on May 4
In fact, sequencing of cattle and bird viruses already shows that there have been jumps from cattle back to birds. These new widely circulating* bird strains carry mutations from their time in cattle are favorable to mammalian transmission.
* - the fact that they have been picked up in sampling of birds seems to imply wide circulation, unless they are just birds found on a dairy farm.
posted by pjenks at 8:55 AM on May 4 [1 favorite]
* - the fact that they have been picked up in sampling of birds seems to imply wide circulation, unless they are just birds found on a dairy farm.
posted by pjenks at 8:55 AM on May 4 [1 favorite]
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posted by peppercorn at 9:26 PM on May 3 [7 favorites]