Colorado endures a Dairy H5N1 Epizootic
New case today makes 17 in the last 20 days...but they are not alone
Colorado has nation's worst outbreak of bird flu among dairy cattle (coloradosun.com)
Colorado reported its 27th case this morning on-line HERE, making 17 new cases in the last 20 days! NASS data shows 62 dairy farms in Weld County in 2022, so it may be approaching a 30-50% infection rate, depending on its current dairy farm inventory and number of infected dairy farms in Colorado outside of Weld County. Aerosol or area spread is contentious and hard to prove; however, rapid spread in highly bio-secure conditions as described in the above article forces us to at least consider that possibility. Epidemiological phylogenetic analysis of all cattle isolates sourced from the local area would help clarify the picture.
This part of Colorado hosts some of the densest total cattle populations in the world. Is it possible that asymptomatic large feedlots could be generating large viral clouds overrunning most of the area dairy farms as wind directions shift about? Alternatively, the dairy farm populations themselves may be large enough to generate infectious plumes for area spread.
I think we're doing a disservice to the dairy farmers if we keep hammering them on biosecurity deficiencies without at least considering that existing dairy and feedlot densities may play a role in how they became infected. Producers’ biosecurity lapses shouldn't be cast as the sole etiology for explosive infectious spread when “inconvenient” alternative explanations are not investigated. Aerosol (area) spread from endemic H5N1 dairy and/or feedlot cattle has nasty implications for both industries that animal regulatory medicine would obviously prefer to ignore.
However, “hear no evil, see no evil, speak no evil” doesn’t work for long, even less so in today’s molecular diagnostic world with advanced analytical capabilities.
Consider for a moment the localities in 4 states where HPAI in dairy cattle has spread in an epizootic fashion. Michigan may count as the 5th, although I’m not as familiar with its beef feedlot segment. Here is a 2021 map of milk production. I’ve place green circles surrounding approximate areas for widespread H5N1 dairy herd outbreaks in the past few months. Texas came first and has now died down; Idaho, Colorado and Iowa have developed more recently as fulminant multi-herd outbreaks in relatively small areas.
Now here is a more dated (but still mostly accurate) map with USDA-derived data showing beef cattle concentrations by county. I’ve circled the areas affected by dairy outbreaks in green on this map. Note that in each case the fulminant dairy outbreaks have occurred in areas with high concentrations of feedlot cattle.
Just as with the recent CEAH epidemiological studies, association does not equal causation! We have areas (such as California and Wisconsin) with large feedlot populations and no reported dairy infections. Co-location with large feedlot cattle populations does not prove that to be the cause of the H5N1 outbreaks!
However, with the exception of the small Kansas State study failing to show onward oral-nasal transmission in cattle, we lack any data showing that ALL cattle cannot be infected by this virus and shed it at some level of risk for spread. We have no serological evidence regarding prevalence or lack of it in either dairy or feedlot cattle in the U.S. We have no aerosol or feedlot runoff studies for either dairies or feedlots documenting the degree of viral shedding (if any) in air or water leaving these facilities. Furthermore. in multiple other species and studies, high animal unit concentrations have increased risk for area spread of endemic pathogens, including influenza, PEDV in swine, and FMD.
I fully realize that many may look at these questions as “reckless” and beyond appropriate. I would ask the opposite- how can it not be appropriate to RULE OUT non-dairy cattle infections as complicating factors in managing dairy herd and poultry flock infections? Why should we limit ourselves to fomites and milk in our investigations because we are afraid of what the alternative explanations may reveal?
No one WANTS endemic cattle-wide H5N1 2.3.4.4b B3.13 influenza in the U.S. However, please prove to all of us that we do not have it or are not headed towards it because we lack courage to rule out alternatives. The jump to cattle was not our fault. Failing to respond appropriately will be.
John