#19,286
The USDA maintains a public database of wild and captive mammals (excludes livestock) infected with HPAI H5 across the country since its arrival in 2022; one which is highly dependent upon investigations and submissions by individual states and/or veterinarians.
Last December, in Declining Mammalian Spillover Submissions To USDA Over Past 8 Months, we looked at a 90% drop in reported infections of HPAI H5 to mammalian wildlife during the 2nd half of 2025, despite increased detections in wild birds.
What the above chart did not reflect was the existing backlog, and gaps (between collection and confirmation dates) and/or delays in reporting cases (see chart below). Delays of 2 to 3 months are common (see graph below), and delays of 6 to 8 months are not unheard of.
Graph created by Gemini using USDA data
Since April of this year, only 3 cases (2 skunks and 1 domestic cat from Utah) have been confirmed by the USDA. While there may be as-yet unpublished data in the pipeline, the decline in case reports appears to be ongoing.
Graph created by Gemini using USDA data
Graph created by Gemini using USDA data
But after 4 years, there are still 8 states which have yet to report a single detection.
These disparities may come down to differences in climate and terrain (swamps vs. forests vs. deserts), varying activity by migratory flyways, and the fact that infected wildlife quite often die in remote, difficult to access places where their carcasses are quickly scavenged by other animals, making them unlikely to be discovered or tested.
- Alabama
- Arkansas
- Hawaii
- Maryland
- Mississippi
- New Hampshire
- South Carolina
- West Virginia
But it is also possible that some states are simply more proactive in investigating, and reporting suspected cases, than others.
As far as host range is concerned, there are 54 different species listed in the USDA database, with the top 3; Domestic cat (155), Red fox (126), and House mouse (111) make up nearly half (48.0%) of all reported mammal submissions.
- There are, altogether, 16 different feline species (wild/captive/domestic) - which combined account for 238 submissions or (29.2%) of confirmed cases.
- Marine mammals make up another large chunk of the data accounting for 13.7% of all submissions (n=112), led by Northern Elephant Seal (57), Harbor seal (27), and Bottlenose dolphins (11)
(Excludes 22 one-off single detections)
Graph created by Gemini using USDA data
All of these numbers are presumed to represent a small fraction of the actual number of infections, as limited seroprevalence studies have found antibodies in a large array of wildlife species (see Virology: Susceptibilities & Viral Shedding of Peridomestic Wildlife Infected with Clade 2.3.4.4b HPAI Virus (H5N1).
Meanwhile, the public remains largely oblivious to the threat of HPAI (see Two Surveys (UK & U.S.) Illustrating The Public's Lack of Concern Over Avian Flu), while some state and local governments appear not to have prioritized surveillance, testing, and reporting.
Although the decline in reported wildlife infections to the USDA may turn out to be a good sign, a lack of evidence is not evidence of lack.
