A path to virus elimination

In a continued effort to battle highly pathogenic avian influenza H5N1 in U.S. dairy herds, the U.S. Department of Agriculture announced a new federal order Dec. 6 — the National Milk Testing Strategy — that will grow surveillance efforts in an attempt to eradicate the virus.

As of Dec. 18, a total of 865 dairies in 16 states have had confirmed cases of H5N1 B3.13 strain of HPAI that has been affecting U.S. dairy farms since March. Nevada became the 16th state to confirm a case Dec. 6. California continues to experience the highest level of infection with 649 affected dairy farms, 313 of which have been confirmed in the past 30 days. A new case of H5N1 was reported in Texas Dec. 13, bringing the state’s total caseload to 27 dairies since March.

In a webinar Dec. 10 aimed at educating producers about the recently released federal order, Dr. Julie Gauthier, executive director of veterinary services field operations at USDA’s Animal & Plant Health Inspection Service, explained the NMTS.

“It is a very efficient way to screen a large number of herds using infrastructure that is already out there, with samplers collecting on a regular basis,” Gauthier said. “This will give us a quick snapshot of large numbers of herds, by focusing on milk at the processing facility. The test is extremely sensitive — we can identify a single infected cow contributing milk to a silo that might contain the milk of over 70,000 cows.”

Using the NMTS, the USDA will work with state regulatory agencies to collect samples in the 48 contiguous states.

“(They) are already sampling Grade A milk on a regular basis — at least four times every six months,” Gauthier said. “We are asking them to collect additional samples at the time they are making visits to each plant.”

Processing facilities of any size that receive raw, Grade A cows’ milk intended for pasteurization will be the focus of the NMTS sampling efforts. According to Gauthier, plants that manufacture raw milk cheese and other raw milk products will not be sampled.

“Focusing on Grade A milk intended for pasteurization gives us the vast majority of dairy herds in the country,” Gauthier said. “This is an effort to identify and control an animal health problem, not a food safety issue. We are not screening milk for the purpose of safety.”

Samples collected by state dairy regulatory collectors will be identified only by bulk tank units before being submitted for testing at National Veterinary Services Laboratories. NVSL will analyze milk samples by polymerase chain reaction for the presence of Influenza A virus genetic material and by enzyme-linked immunosorbent assay, looking for the presence of antibodies.

Scientists will be able to conduct genome sequencing on detected virus genetic material, allowing them to compare it to previously identified strains.

“We’ll be able to match that up with viruses detected in herds in other states, or know if it’s something new,” Gauthier said. “Antibodies present will give us additional data, that while not actionable, will give us an overall picture across the country of the level of disease.”

Testing results will be delivered to state animal health officials associated with the BTU numbers contained in the silo. They will work with their state’s dairy regulatory agencies to identify herds included in a positive silo.

The NMTS is broken down into five stages, the first of which is silo monitoring, which will lead to stages two and three — determining a state’s status and the detection and response to the virus in affected states.

“We’ll reach stage four when we have done enough testing for states to be considered unaffected,” Gauthier said. “Once we get all the states to stage four unaffected status, we’ll continue to conduct testing for a period of time — at least 90 days — to demonstrate that the entire country is free of infection, which is stage five.”

The goal of achieving virus elimination in the U.S. dairy herd is both achievable and necessary, according to Dr. Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory.

“We certainly can get to be virus free,” Poulsen said. “Our trading partners may not be saying things out loud, but they have shown interest in making sure this disease is not in products they import.”

Although Wisconsin has had no virus detected or reported in dairy herds, Poulsen is eager to begin surveillance for the virus using the NMTS.

“There is a lot we don’t know because the inability to do effective surveillance nine months ago has hampered the response,” Poulsen said. “Talking to dairy owners and veterinarians in the Texas panhandle area, Idaho, Colorado and California — they really want to do surveillance and eliminate the virus. They saw how damaging it really was and they want to make sure they have a farm to get to the next generation.”

The NMTS allows for flexibility in its administration on a state-by-state basis, Poulsen said.

“We can’t use what we use for HPAI for this H5N1 in dairy cattle — the poultry and swine industries are much more consolidated,” Poulsen said. “Our industry is so decentralized, and each state’s industry is just a little different — with 27,000 farms, a one-size-fits-all approach doesn’t work. There is no codified or statutory regulation for H5N1 in dairy cattle, either.” 

That flexibility will allow for states to learn from the experiences of others.

“Some states are already doing this,” Poulson said. “We can learn from those and move it to other high-producing dairy states and eventually everywhere. The goal is to declare virus elimination and disease freedom for the World Organisation for Animal Health. That is the important one, especially for trade reasons.”

Poulsen said ramping up surveillance efforts will potentially lead to an increased number of confirmed cases. State animal health officials in Wisconsin are preparing for that possibility.

Biosecurity will remain paramount for producers, Poulsen said.

“Creating a line of separation, keeping unnecessary traffic off the farm and knowing who is coming and going from the farm, using boot covers or boots that can be and are sanitized when people move from the dirty side of the farm at the road to inside the farm, along with clean clothes and washing hands — those basic biosecurity practices are vital,” Poulsen said.

Poulsen said one of the biggest concerns he has heard from farmers in states that have not seen the virus yet is the worry of losing milk markets because of a confirmed positive.

“Everyone should still be able to market milk — not one single farm has ever not been able to market their milk,” Poulsen said. “Pasteurization kills the virus. That is a key point we can’t repeat enough.”