Where are We At? It's in the (Bulk) Tank

Massachusetts shows negative status; Colorado lowers the temperature (and the curve)

My blog this week is a bit short and early, since I’m off to visit family and also attend the Leman Conference in St. Paul MN. It’s their 50th Conference; I think I was there for the 2nd or 3rd one…in 1976 or 1977.

Massachusetts announced this week that they had completed bulk tank testing on all dairy herds in the state in August: No bird flu detected in Mass. dairy herds

DPH said it worked on the testing effort with the Massachusetts Department of Agricultural Resources, whose inspectors in August collected milk samples from bulk tanks. The Broad Institute at MIT and Harvard also helped with the testing.

"Massachusetts dairy farmers follow stringent safety protocols and take great pride in producing the highest-quality products," MDAR Commissioner Ashley Randle said. "That hard work protects all of us, and these test results demonstrate how supporting local agriculture and sourcing food from Massachusetts farms can keep our food supply strong and resilient."

This is a good example of a more localized niche market state doing its part to assure its customer base of freedom from a viral risk that has certainly been in the national news in 2024. There may be some other states with smaller localized production models that could benefit from a similar approach to establishing negative status to bolster consumer confidence in a local product. Bulk tank testing remains an economical and effective way for producers and officials to determine herd and area status for dairy H5N1 infection across defined areas.

Iowa and now California have also reportedly utilized bulk tank sampling of herds in proximity to poultry and dairy herd H5N1 outbreaks as a low cost and economical means for area surveillance following confirmed outbreaks. The high viral excretion in milk from infected cows makes the bulk tank an excellent pooled sample, even with fairly low incidence of infection within a herd. I am not aware of any published research regarding limits of detection with bulk tank sampling; that’s an area that will need increased research as we will see in the next section of this blog, reviewing the Colorado bulk tank monitoring experience.

As most readers realize, Colorado has been monitoring bulk tanks for H5 in commercial dairy herds since late July 2024 and began publicly reporting positive results by herd number as of August 5th, 2024, at the following site:

HPAI in Dairy Cattle | Department of Agriculture (colorado.gov)

This table does not include results for any herds that have been negative for H5 since case reporting began in late April 2024. And herds selling raw milk directly to consumers are exempted from testing by state law, so are not included.

We now have enough “real world” data available voluntarily shared by the Colorado Department of Agriculture (kudos to them!) to make some tentative conclusions regarding longer term viral status in herds earlier infected with H5. This is tremendously important information, because if H5 “hangs around” in infected herds, hopes for eradication of infection are illusory as new susceptible animals are brought into virus-positive environments.

The following table is clunky and herd to decipher, so please bear with me. Column 1 is the 64 infected herds, with the date confirmed positive next to it. The third column is the latest herd status available on the web site (9/13/24). The 4th column is herd status for many of the 64 herds I captured back on 8/30/2024 when I wrote another column on CO bulk tank testing.

All of the herd numbers in red are those established by bulk tank testing. Note that 7 herds (green highlight) that were earlier quarantined and released (5, 10, 14, 17, 20, 28, and 33) were re-quarantined on August 9th, most likely due to positive bulk tank test results. All seven subsequently returned to negative herd status.

Two herds (Yellow) -13 and 61 - are in reality new reinfections since August 30 with new positive bulk tank results after earlier negative status. Finally, 1 herd has been positive since June 12 and another 5 since July 23.

It’s not a bad picture, all in all - only 11 positive herds remain out of 64 originally infected! However, something is amiss in some herds, where the virus persists. Herd 13 is particularly concerning, since it recently returned to positive status after being negative since an initial June infection.

The biggest take home to me is the demonstrated value of bulk tank testing. We have no information on possible clinical signs or production parameters in these herds. However, if these H5 signals are “silent”, then knowing they are there is important information for the producer and the veterinarian to possess from a biosecurity standpoint. If vaccines become available, positive viral status may be the signal that changes in a vaccine program are required.

Lowering the Bar (CT cut-off)

In talking with a veterinary contact I learned that Colorado recently lowered its bulk tank CT cut-off value for quarantining a herd to 35 from the high 30’s (38-39?). Apparently, herds have been cycling too often between positive and negative status - i.e. CT’s can fluctuate in the mid-to-high 30’s but never go completely negative or definitively positive. This makes the quarantine imposition and release process cumbersome.

On the other hand, it’s dangerous to ignore herds with positive CT values at any level, especially if repeated over more than one week. Barring contamination issues, virus is in the herd at some level, threatening to remerge in susceptible stock at some point. Whether quarantined or not, moving animals from herds with positive bulk tank CT values at any level should be fully discussed by regulatory officials and herd veterinarians and owners for both shipping and receiving herds.

In summary, the Colorado data tells me that in the short term weekly bulk tank testing is a necessary precaution for all herds to be utilized as a monitor for H5 status in the lactating line. Recovery from clinical signs does not guarantee that a herd will not be reinfected or remain infected, even months later. Combined with on-farm clinical and serological information, owners and veterinarians have an opportunity to gain some valuable information on how this virus behaves in naive, newly infected, recovering, and “fully recovered” herds. We’re reaching the point where we’ll have herds in all those categories; each one will likely behave differently. Monitoring viral load by bulk tank testing will be critical in those assessments.

Until next week,

John