By Lisa Schnirring
The Michigan Department of Agriculture and Rural Development (MDRAD) today reported three more H5N1 avian flu outbreaks in dairy herds, noting that it will send results to the US Department of Agriculture (USDA) National Veterinary Services Laboratory (NVSL) for confirmation.
Also, H5N1 has been detected in two domestic cats in South Dakota, neither of them from affected poultry farms or dairy farms, according to a notification from US government officials to the World Organization for Animal Health (WOAH).
In other developments, the Food and Drug Administration (FDA) recently detailed its next steps for monitoring the virus in that nation’s milk supply and the Centers for Disease Control and Prevention (CDC) posted an update on its response steps, which includes an evaluation of the dairy outbreak virus with its Influenza Risk Assessment Tool (IRAT).
Regarding wastewater monitoring for influenza A, the CDC said it compares the most recent weekly levels with those reported from the same site the previous season. Sites in the “high” category prompt CDC outreach to local jurisdictions and intensive surveillance review.
In the most recent week, there were four locations in the high category: two in California (San Francisco/San Mateo and Sonoma), and one each in Kansas (Saline County) and Texas (Dallas) The CDC said so far there are no unusual flu indicators in people, including for H5N1.
In a statement, the MDARD said the three newly affected dairy herds are in Clinton, Gratiot, and Ionia counties, all of which were affected in recent outbreaks. Samples from the farms were positive in tests at Michigan State University’s Veterinary Diagnostic Laboratory, and samples have been sent to the NVSL for further confirmation.
According to the MDARD’s line list, Michigan has now reported 18 outbreaks in dairy cows in nine counties, the most of any state.
In a May 16 update, the USDA reported 51 dairy herd outbreaks in nine states, which included 2 newly affected herds, one in Michigan and one in Idaho.
A few H5N1 detections in cats were reported earlier in the US dairy farm outbreaks, and some of the animals were known to have consumed raw milk from infected cows. However, officials have now reported two infections in domestic cats without links to poultry or dairy cow outbreak farms. The two cats are from South Dakota’s Campbell County, which is in the northern part of the state on the border with North Dakota.
South Dakota has one outbreak in dairy cattle, which occurred in Brown County, which is also on the North Dakota border.
The WOAH report didn’t say if the domestic cats in South Dakota showed clinical symptoms. Earlier reports on H5N1 in cats, both in the United States and abroad, described respiratory and neurologic symptoms in infected animals, which were often fatal.
Since the Eurasian H5N1 strain was first detected in the United States in early 2022, the virus has been detected several times in mammals, mostly wildlife including bobcats and mountain lions—species known to feed on infected wild birds.
The FDA today in an update outlined its next scientific studies to validate the impact of pasteurization on H5N1, which will include tests using the same pasteurization equipment that milk processors use. The agency noted that follow-up inoculation tests on 297 retail milk samples that had fragments of virus on PCR resting were all negative for live virus.
Testing is under way on pooled raw milk slated for shipment for commercial processing, with the goal of characterizing virus levels before pasteurization. The FDA said the study will better replicate real-world conditions and more clearly gauge how effective pasteurization is at inactivating H5N1 in milk and other dairy products.
Also, the FDA announced an additional $8 million to bolster ongoing work to ensure the safety of the milk supply, which will support the studies to validate pasteurization criteria, conduct surveillance at different points in the milk production system, boost lab capacity, and train staff on biosecurity procedures.
The funding will help partnership activities with states and may allow the FDA to partner with universities to answer key research questions.
Meanwhile, in its latest update on its response to the H5N1 outbreaks in dairy herds, the CDC said it is developing a plan for enhanced surveillance over the summer, which will include increasing the number of flu specimens tested and subtyped at public health laboratories.
“While influenza testing typically declines over the summer, this approach would maintain an increased level of testing,” it said.
The CDC also said it has started the process of conducting a pandemic risk assessment of the H5N1 virus linked to the outbreak in dairy cattle using IRAT. CDC scientists measure 10 risk elements, which can take months to complete.
The CDC’s last IRAT assessment was posted in July 2023 and involved the H5N1 virus that triggered an outbreak at a Spanish mink farm. Though that virus scored higher on some of the CDC’s risk measures, the overall threat is moderate and similar to the earlier version of the virus.
Lisa Schnirring is news editor for University of Minnesota Center for Infectious Disease Research & Policy.