DENVER — Recognizing that Colorado has not been able to control the spread of highly pathogenic avian influenza among cattle since the virus was first detected at dairy farms in late April, state agriculture officials on Tuesday announced they would be mandating weekly testing of milk samples for bird flu at all commercial dairy farms in Colorado, effective immediately, in order to curb further spread of H5N1 in the state.
The move by the Colorado Department of Agriculture (CDA) is the first of its kind in the nation since the unprecedented outbreak of highly pathogenic avian influenza (HPAI) was first detected in U.S. dairy cattle on March 25, and comes nearly three months after the state detected its first outbreak of bird flu among dairy cows.
Citing difficulties in navigating a challenging, novel outbreak of HPAI in dairy operations, state veterinarian Dr. Maggie Baldwin said the order — which went into effect Monday — is aimed at protecting the dairy and poultry industries as well as public health in Colorado.
Can't view the document below? Click here to read the order from the CDA.
"What we're looking at right now is trying to identify where else the virus is in Colorado that might pose a risk for additional spillover," Dr. Maggie Baldwin said, adding the end goal is for Colorado to stop transmission as soon as possible. "There’s no way that we could live with this virus continually circulating in either our dairy or poultry operations in the state."
Colorado is leading the nation in both the number of bird flu outbreaks among dairy cattle as well as the number of infected workers, effectively becoming the current epicenter of the outbreak after the largest cluster of human cases in the country to date was detected at a Weld County egg-laying operation earlier this month.
As of Tuesday, Colorado had reported 48 bird flu outbreaks among dairy cattle, with more than half of those identified over the past 30 days, according to the U.S. Department of Agriculture (USDA). In all, bird flu has impacted 45% of Colorado’s herds since late April so far.
The weekly surveillance for H5N1 in bulk-tank milk samples will take place under the joint supervision of the CDA and the Colorado Department of Public Health and Environment (CDPHE), with support from a USDA epidemiological "strike team" who will do a deeper dive into how the virus is spreading among facilities and the potential connection between the outbreaks. Dairy producers will receive further guidance directly so they can meet the testing requirements as set by the order. Dairies currently under quarantine due to bird flu outbreaks or under orders for testing will be subject to those specific orders, a CDA spokesperson said.
So far, Baldwin said, she has not heard of any adaptions in the virus that could make it more transmissible among mammals from officials at the USDA and still believes spread among farms is happening through fomites — objects or materials which are likely to carry live virus particles — such as vehicles, equipment, and clothing from dairy or poultry workers exposed to sick cattle or poultry at these facilities.
The state does have research teams thanks to funding from the USDA provided to affected states that is looking into how exactly the virus might be moving among dairy cattle, but it's not clear when preliminary results on such research will be released.
In Colorado, between 10-30% of cows in herds with reported outbreaks show clinical symptoms, including decreased feed intake, decreased milk production, and discolored milk that is thicker in consistency, but affected cows return to milk production if the disease is caught early and they are provided supportive care, according to Baldwin. No cow is being provided antiviral treatment in Colorado unless the producer's veterinarian has other recommendations, she added.
Research is ongoing at the state level to determine how long dairy cows are sick and for how long they're shedding the virus once infected, Baldwin said, adding she hopes an early release on that data will come in the near future.
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Earlier in the outbreak, Colorado had implemented a 30-day quarantine period for lactating cattle but has since moved to releasing affected herds from quarantine after two consecutive negative tests for H5N1. Baldwin said she believes this approach is still a good standard for release, despite few herds being released from quarantine so far.
"We feel that doing the bulk-tank testing gives us the best assurance that a herd, as a whole, is not continuing to shed the virus," Baldwin said. "If we can't catch the virus on bulk milk tank testing, from what we've seen from some early research projects that were done, we feel pretty confident that that's a really good standard for release. I think that, for us, it gives us a lot of confidence in releasing that herd from quarantine and allowing lactating dairy cattle to move off of those premises without posing a risk for further disease transmission."
But if the goal is to prevent further chains of transmission, why isn't the state mandating the same type of testing for raw milk producers, considering studies have shown high levels of H5N1 in raw milk given to mice?
When asked about this particular exemption, Baldwin said the state has only had positive detections of H5N1 in commercially-licensed facilities, which for the most part, do not include any raw milk dairies.
"We feel that the risk — and we always want to make sure our policy decisions are based on science and risk — we feel that right now, our biggest risk and where we're currently seeing the virus circulating pretty heavily is in those commercially-licensed facilities in the state," Baldwin explained, saying the state is encouraging raw milk producers to participate in Colorado's voluntary surveillance program.
While only encouraging raw milk producers to participate voluntarily for now, things can change "if we learn that the risk for the raw milk facilities is different," she said. "Right now, we have not seen this virus circulating in our raw milk dairies; we've really seen it circulating in our commercial facilities."
Dairy producers under the order who do not comply could face criminal charges, according to the document.
Poultry facilities affected by spillover of H5N1 virus from infected cows
The latest effort by the state comes as the CDA simultaneously tries to prevent further spread of the virus in poultry, the species most affected by H5N1.
Spillover events from the strain of H5N1 that has been spreading among dairy cattle have been reported at two commercial poultry facilities in Weld County and the CDA is investigating a potential third spillover event from a dairy operation into a poultry farm.
Those infections have forced the state to wipe out more than 3.2 million egg-laying chickens during the month of July, the CDA spokesperson said.
When asked about what type of measures the state is implementing to ensure workers avoid infection when depopulating birds at these facilities, Baldwin said decisions on how depopulation happens and what methods are used is a joint decision between the USDA, the producer of the farm affected by an outbreak that must be eradicated, and the CDA.
"We have a lot of things that we have to carefully balance and so we work with the producer on identifying what the best method for the population is for that facility, and we do that in coordination with USDA and typically the producers who contracts with the actual contracting companies to bring in additional workers, if additional workers are needed at those facilities," Baldwin said. "A lot of it is people and resources and risk of exposure for zoonotic diseases."
Public health experts who have all eyes on Colorado due to the six human cases of H5N1 that have been confirmed here have been asking if the state will soon begin serologicial testing — testing farm workers infected with bird flu to see if any level of immunity is elicited following infection and what that may look like.
On that front, Baldwin said CDPHE was working with the U.S. Centers for Disease Control and Prevention (CDC) on trying to offer serologic surveys to the exposed farm workers.
"I know that they are actively pursuing that here in Colorado, and I do hope that we have some folks that are interested in that because it'll be really helpful to (determine) what is the true exposure rate on these facilities," she said.
The bird flu outbreaks at Colorado dairy farms account for nearly a third of all outbreaks in the U.S., per the USDA's tally, which shows 169 dairy herds have been infected across 13 states as of Tuesday.
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