USDA H5N1 Epidemiology Reports - Great Efforts Lead Me to "Air" More Questions
Meanwhile 6 new confirmed herds in Colorado in last 3 days suggests the possibility of a common source for area infection
USDA released 2 complete epidemiological studies on their H5N1 in Livestock website on Thursday:
This report is an overarching summary of epidemiological data collected from all participating farms across the U.S. through June 8, 2024. I won’t repeat contents from the report but would urge all to read it carefully for yourselves. Many of the outbreaks can be linked directly to cattle movements. However, as I’ll discuss further regarding the following detailed Michigan report, a significant number of cattle outbreaks, as well as phylogenetically linked poultry outbreaks cannot be explained through movements of at risk or infected animals. Both reports discuss potential transmission links or risk factors for spread of infection to naive herds or poultry flocks.
The second report is a much more detailed dive into the epidemiological data collected from 15 herds in Michigan, where substantial USDA-APHIS resources were deployed at the request of state officials in response to both the poultry and dairy herd outbreaks:
Please also read this report in detail; it has some truly impressive analyses drawn from data made available by producers and associated groups.
Here are some issues that drew my attention:
I was struck by the fact that 9 of 15 farms had NO importation of any animals into their herds prior to infection, and of the 6 that did import animals, on only one farm was it shown that the importation had definitively led to the infection (index herd?). That means that on somewhere between 9 and 14 dairy farms and all poultry farms, spread of virus onto farms was indirect (not by animal movement). To me that was the headline finding not covered - In the cases studied, Most H5N1 outbreaks in dairy herds (and poultry flocks) studied were indirectly spread! Movement of infected animals was not a major factor in spread of disease. This is not good news for those hoping that the virus will simply die out on infected farms. It seems quite capable of devising ways under current production practices to hop a ride in one way or another to other dairy and poultry production facilities, at least in spring climatic conditions in Michigan.
Personnel and equipment sharing is more widespread between farms than assumed. These are undoubtedly risk factors to varying degrees, but we need more data on viral loads, infectious doses required, animal routes of infection, etc. to really assess the likelihood that a bulk milk truck itself for example, that never touches an animal anywhere is a viable risk for spread. Now if the driver dribbles milk on his shoes and walks through pens on another farm, that’s another matter altogether! Each transmission link will need to be broken down into component parts to get at where the real risk resides.
A related question would relate to cleaning and clothing, boots, showering, etc., between farms. What is the survivability of this virus as a fomite? People themselves likely do not carry it intranasally. A lot of the transmission links depend heavily on the virus maintaining itself on equipment or clothing, then somehow being ingested or inhaled by a susceptible animal. Can that cycle be broken to allow behaviors that the industry requires without adding to risk of viral spread?
Don’t be a cat on an infected farm! 12 of 15 farms had cats, and cats died on 7 of those 12 farms. From a welfare standpoint, pets need to be separated from infected herds quickly.
Finally, I want to turn to a section of the report that I feel is in need of a lot more research, not because I know it is a smoking gun, but because I DON’T know - that is waste milk and urine, especially from infected cows, discharged into lagoons, then spread onto area land for disposal. Please remember this all highly speculative, flowing partly from some old data with novel flu strains in swine from nearby lagoon water. I’ll return to the influenza in swine work in a bit, but first, looking at the Michigan report, note that 11 of 15 producers disposed of waste milk in lagoons (mostly unpasteurized). Further 9 of 15 premises applied or removed, gave away, or sold manure after clinical signs were observed:
We need some research soon on viral levels (if any) in lagoon waste on affected farms, as well as survival times for H5N1 in lagoon substrates under field conditions. We at least have the potential for aerosolized virus in cattle and poultry dense areas as a risk factor for spread of H5N1 2.3.4.4b B3.13 to uninfected herds/flocks.
For those of you interested in further reading here are 4 references from swine literature related to both lagoon-related transmission of influenza virus to nearby swine populations and risks for aerosol transmission of influenza (and other pathogens) in swine:
Aerosol transmission and “area spread” remain extremely contentious and difficult to prove/disprove. All “transmission links” face that difficulty to varying degrees. I simply throw “aerosol spread” and “lagoon waste” out there as two more transmission links to consider and test scientifically for probability of risk.
All of that brings me to disheartening news from the H5N1 in dairy case list yesterday. NVSL and Colorado reported 5 more cases to add to the one reported a day earlier, making 6 new cases in 2 days:
I have heard unofficially that these 6 cases may be fairly closely located geographically - confirmation of that will await word from state officials or later OIE reporting. Regardless, such a case load in a short period suggests a “common source” infection of multiple herds. I have a lot of faith that Dr. Maggie Baldwin, Colorado State Veterinarian, and her team, along with APHIS, Colorado State, and industry colleagues will soon have us all apprised of the situation as it unfolds.
This disease continues to wreak havoc with everyone it touches. Minnesota and Iowa are under the H5N1 gun in both cattle and poultry, Idaho has a pickup in dairy cases, Wyoming recorded a dairy case, and now Colorado just got slammed. Please, let’s remember to monitor the employees and responders everywhere! No one wants another human case, but better a case than a hospitalization or a cluster. Let’s all be safe out there!
John