This article describes the first detections of disease due to natural infection with highly pathogenic avian influenza virus (HPAIv) H5N1 of the Eurasian lineage goose/Guangdong clade 2.3.4.4b in wild terrestrial mammals throughout the United States during 2021-2022. Affected mammalian species include 50 red foxes (Vulpes vulpes), 6 striped skunks (Mephitis mephitis), 4 raccoons (Procyon lotor), 2 bobcats (Lynx rufus), 2 Virginia opossums (Didelphis virginiana), 1 coyote (Canis latrans), 1 fisher (Pekania pennanti), and 1 gray fox (Urocyon cinereoargenteus). Infected mammals primarily exhibited neurological signs. Necrotizing meningoencephalitis, interstitial pneumonia, and myocardial necrosis were the most common lesions; however, species variations in lesion distribution were observed. Genotype analysis of sequences from 48 animals indicates that these cases represent spillover infections from wild birds.

Chronic wasting disease (CWD) of white-tailed deer ( Odocoileus virginianus) is a fatal neurologic disease that is spreading across North America. A common surveillance protocol for CWD currently involves screening with an enzyme-linked immunosorbent assay (ELISA) followed by confirmatory testing with immunohistochemistry (IHC). Medial retropharyngeal lymph nodes (MRPLN) are the tissue of choice to diagnose CWD in free-ranging white-tailed deer. We examined left and right MRPLN from 101 ELISA-positive deer harvested from 2015 to 2019 to determine the incidence of cases in which prion protein was not detected by IHC as well as differences in IHC labeling between contralateral lymph nodes. Prion protein was not detected using IHC in either MRPLN in 5.9% (6/101) of cases. There was a significant but weak positive relationship between the number of IHC-positive follicles and ELISA optical density (OD) values ( R2=0.08, P=0.039). Mean optical density values in IHC-positive MRPLN were higher than in IHC-negative MRPLN; however, this was not statistically significant ( P=0.260). Failure to confirm ELISA diagnoses with IHC may have been because the methods tested different areas of MRPLN, or that there were differences in test sensitivity or antibody affinity. An additional 5.9% (6/101) of cases had one IHC-positive MRPLN, whereas the contralateral MRPLN was IHC negative. Therefore, testing a single MRPLN for CWD may lead to false-negative results, regardless of methodology, which highlights the importance of collecting and testing both MRPLN.

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Eastern equine encephalomyelitis (EEE) is a mosquito-borne viral disease that is an emerging public health concern in the state of Michigan. Although Michigan has one of the highest incidence rates of EEE in the United States, much of the information known about cases in humans, equines, and other animals residing in Michigan is unpublished. This article summarizes such information and explores spatial trends in the historic distribution of EEE in Michigan. Outbreaks in Michigan have occurred over an 80-yr interval, involving only horses in 1942–1943 and 1973–1976, and then episodically from 1980 to 2020, and involving horses, humans, and wild and domestic animals. An estimated 1,036 equine cases (confirmed and suspected) and 36 confirmed human cases have occurred, including 10 in 2019 (6 deaths) and 4 in 2020 (2 deaths). Human cases ranged in age from 1 to 81 yr; 70% were male, and fatality rate of 34.3%. Equine and human cases occurred from July to October, peaked in August, and cluster in space in southwestern and southeastern lower Michigan. Cases occurred in glacial outwash and ice-contact landscapes in glacial interlobate zones. EEE virus (EEEV) was recovered from Culiseta melanura, Coquillettidia perturbans, five species of Aedes, and other mosquito species near horse and human case sites. Virus isolations or presence of neutralizing antibodies in several passerine species of birds suggest broad EEEV–bird associations. White-tailed deer and other wildlife were also affected. Geographic spread to northern areas of the state suggests expansion of this disease system into new and unsuspected foci.