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Orthohantaviruses are negative-sense, enveloped RNA viruses that are transmitted by host reservoirs, such as rodents, to humans. Human infection occurs through inhalation of aerosolized viral particles from host excreta, such as urine or feces, often in enclosed spaces during infestations. New World orthohantavirus infection results in hantavirus cardiopulmonary syndrome (HCPS), which consists of febrile illness with edema and respiratory failure (1). In the United States, most HCPS cases occur in the Southwest and have a ≈35% mortality rate (2).

The dominant orthohantavirus that causes HCPS in the United States is Sin Nombre virus (SNV), which is thought to be carried and transmitted by the western deer mouse (Peromyscus sonoriensis). New York virus (NYV) is another pathogenic variant of orthohantavirus that is found in white-footed deer mice (Peromyscus leucopus); cases occur primarily in the Northeast region of the country (3). Although multiple host reservoirs for orthohantaviruses are distributed throughout the United States, most human cases are caused by SNV (4,5).

In early May 2021, a previously healthy 65-year-old woman visited an emergency department in Washtenaw County, Michigan, USA, with febrile prodrome of 3–6 days, thrombocytopenia, mild transaminase elevation, and acute hypoxic respiratory failure of unclear etiology requiring intubation. An extensive infectious disease workup was conducted, and physicians initially ruled out such pulmonary pathogens as SARS-CoV-2, common respiratory viruses, fungal agents, andLegionella spp. The family was interviewed to obtain a travel and animal exposure history, which revealed that the patient had not traveled outside of Michigan in the previous year. The interview also confirmed that the patient had not consumed unpasteurized dairy or undercooked meat, had a mostly indoor dog, lived near a natural area but used trails/sidewalks, and had no known rodent infestation in the home. However, the spouse reported that the patient had spent time recently cleaning out a relative’s home that had been uninhabited for 2 years and was infested with mice.

Results of a tickborne disease panel were negative, but hantavirus antibody testing performed at a commercial lab showed positive results for both IgM and IgG. The treating hospital notified the Michigan Department of Health and Human Services of a case of HCPS. Confirmatory hantavirus testing was arranged and confirmed with the Centers for Disease Control and Prevention, using serum samples collected from hospitalization.

Trapping was performed in and around the suspected site of exposure (relative’s home) using Sherman folding traps (https://shermantraps.com; 94 trap nights), resulting in 12 rodents captured (12.8% trap success) under an approved animal-use protocol (6). Trapping was conducted 12 days after the patient was released from the hospital. Researchers observed signs of previous trapping efforts; 5 unusablePeromyscus mouse carcasses were found in snap traps in the residential basement. Signs of infestation were evident. Of the 12 trapped rodents, 3 (25%) wereP. leucopus mice, 1 (8%) was a Northern short-tailed shrew (Blarina brevicauda), and 8 (67%) were Eastern chipmunks (Tamias striatus) (Table). The surrounding flora consisted of lawns, shrubs, and an evergreen windbreak near a public trail.

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Figure. Phylogenetic analysis of orthohantavirus sequence fragments from samples taken from a 65-year-old woman in Michigan, USA, and trapped rodents from the likely site of exposure (blue text). Trees displaying the...

Using quantitative reverse transcription PCR, we screened lung, liver, brown fat, or kidney tissue from captured rodents and from a plasma sample of the patient obtained during hospitalization (6). Brown fat and kidney tissue from 2P. leucopus mice and lung tissue from 2T. striatus chipmunks tested positive for SNV. Three fragments were obtained from the patient sample, 1 for the short segment (480 bp), 1 for the medium segment (283 bp), and 1 for the large segment (377 bp). Similar fragments were also generated from 3 of the 4 infected rodents; all sequences are publicly available in GenBank (accession nos. OR428177–88). We compared fragments by using phylogenetic analysis against several known orthohantavirus reference sequences to determine potential identification. The partial sequences of SNV short and medium segments from the patient formed a phylogenetic lineage with SNV sequences from the rodents collected in or near the suspected site of exposure in Michigan. However, the patient’s large fragment formed a lineage with NYV, suggesting that this species may be an SNV or NYV variant (Figure).

Previously, we identified the likely site of rodent-to-human SNV transmission in a patient case study (6). Here, we attempted a similar approach but were only able to generate partial sequences for the patient sample, which we compared with captured rodents. Orthohantavirus incubation periods can be up to several weeks after exposure (7), which may impact the timeliness of trapping efforts. We found infectedP. leucopus mice andT. striatus chipmunks at the site of exposure, both of which have been reported to carry NYV or SNV;P. leucopus mice are susceptible and capable vessels for SNV replication after laboratory infection (6,8–10). This finding suggests that orthohantaviruses may not be as species host–restricted as previously thought. Further studies are warranted to clarify (or define) orthohantavirus species in Michigan to anticipate the risk for patient infection. Increasing surveillance and diagnostic efforts can enable prospective detection of circulating viruses.

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We thank Michigan’s Department of Health and Human Services and Washtenaw County Health Department for collaboration, along with the Centers for Disease Control and Prevention Epidemiology and Ecology teams that participated in this response.

This work was supported in part by a University of New Mexico School of Medicine Research Allocation Committee (UNM SOM RAC) grant (S.B.B.) and an NIH/NIAID grant (AI-I7-042 U19, K.C.). S.M.G. was supported by UNM HSC Infectious Disease and Inflammation Program NIH grant T32AI007.

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