Two Recent Studies On the Host Range of Hantaviruses In the United States

Credit CDC

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A week ago, in California: Mono County Reports 3rd Hantavirus Death, we looked at the unseasonably early start of Hantavirus transmission this year in the Eastern Sierras.  Mono County had previously reported only 24 cases over the past 32 years (since 1993), making 3 deaths in the space of a month (Feb-Mar) a tragic outlier. 

Hantavirus infections are most commonly reported in the spring or early summer, but sometimes into the fall. The 2012 outbreak in Yosemite began in August and ran through September, infecting 10 visitors to the park, and killing 3 (see CDC's MMWR: Yosemite Hantavirus).

`Hantavirus’ is a collective term for a group of viruses carried by various types of  rodents - that vary in distribution, symptomology, and severity around the world.

In Europe and Asia the hantavirus commonly presents as HFRS (Hemorrhagic Fever with Renal Syndrome), and the mortality rate varies from 1% to 15% depending upon the specific hantavirus involved (see ECDC Hantavirus Overview).  

In the Americas - while human infection is far less common - Hantavirus usually presents as Hantavirus Cardio-Pulmonary Syndrome (HCPS or sometimes just HPS), a more severe disease with a fatality rate of between 30% and 50%.

Most Hantavirus cases are sporadic, but occasionally we see clusters. Exposure is often linked to cleaning out sheds and garages in the late spring and summer when mouse activity is high. The CDC has a 20-page PDF guide on reducing exposure risks.

For many years it has been assumed that there are 4 main hosts of the Hantavirus in the United States (Deer Mice, Cotton, Rat, White-footed Mouse, and the Rice rat), and that the primary regions of concern are the American Southwest and California. 

But the more we look, the more we learn. And we've two recent studies indicating that the host and geographic range of Hantaviruses in the United States is larger than previously thought.  

Due to their length, I've only posted the links, and some excerpts (and a link to press releases). Follow these links to read these reports in their entirety. I'll have a postscript after the break.

Last January PLoS Pathogens published study out of New Mexico - where the North American Hantavirus was first identified in 1993 - which reports finding evidence of Hantavirus carriage in more than 30 species of rodents and other small mammals, including ground squirrels, chipmunks, gophers, rats and even house mice.

A human pathogenic hantavirus circulates and is shed in taxonomically diverse rodent reservoirs

Samuel M. Goodfellow, Robert A. Nofchissey, Chunyan Ye, Jaecy K. Banther-McConnell, Thanchira Suriyamongkol, Joseph A. Cook, Jonathan L. Dunnum, Ivana Mali, Steven B. Bradfute

Abstract

Background

Orthohantaviruses are negative-sense RNA viruses that can cause hantavirus cardiopulmonary syndrome (HCPS) in humans. In the United States, Sin Nombre orthohantavirus (SNV) is the primary cause of HCPS, with a fatality rate of 36% and most cases occuring in the southwestern states. The western deer mouse, Peromyscus sonoriensis, is the primary reservoir for SNV; however, it remains unclear if alternative reservoirs exist.

Results

We conducted an extensive survey of SNV genetic prevalence in wild-caught small mammal communities throughout New Mexico and observed that 27% of all animals were positive for SNV. Through longitudinal trapping at a site of patient exposure, we found that SNV circulates at a high rate in multiple species over time. Furthermore, we isolated live SNV from tissues and feces from multiple small mammal species, demonstrating infectious virus in alternative and novel reservoirs.

Significance

Altogether, this work shows that SNV is widely prevalent and persistent throughout New Mexico in multiple small mammal reservoirs that can harbor and shed infectious virus. This encourages future work for additional surviellance efforts and revaluates host-species dynamics for New World hantaviruses.

Author summary

The first reported hantavirus cases in the United States occurred in the Four Corners region (Arizona, New Mexico, Utah and Colorado) and was found to be transmitted by the droppings of western deer mice. This led to discovery of Sin Nombre virus (SNV). Unlike hantaviruses found through Europe and Asia, SNV causes hantavirus cardiopulmonary syndrome (HCPS), which has a high mortality rate. It is generally thought that only one small mammal host is capable of carrying and transmitting hantavirus to humans.

However, our group and others have found hantavirus genetic material in multiple small mammal species, but these studies have been fairly limited and did not determine if the virus could replicate in these species and be transmitted through them. Here, we conducted a large study to look for SNV in wild-caught rodents throughout New Mexico (NM) in counties with and without reported human HCPS cases. We found that SNV is widespread in all areas of NM and stably circulates in rodents at a site of human infection. Importantly, we show that multiple small mammal species can carry and shed infectious SNV. Altogether, our study provides a novel shift in the understanding of host reservoir dynamics for SNV.

  

         (Continue . . . )

You can read the University of New Mexico's press release at:

UNM researchers find live hantavirus is carried in more than 30 New Mexico small mammal species 

Our second study is published in Ecosphere  and comes, unexpectedly, from an Eastern State (Virginia) which is not normally associated with Hantavirus transmission. Virginia did report 1 probable case was reported in 1993 in a 61 y.o. hiker on the Appalachian Trail (see MMWR report), and neighboring West Virginia has reported 3 cases. 

Once again, Hantavirus was found in a number of unexpected species, and with surprisingly high seroprevalence in Virginia, Colorado, and Texas (see map below).

Hantavirus in rodents in the United States: Temporal and spatial trends and report of new hosts

Francisca Astorga, Abdelghafar Alkishe, Paanwaris Paansri, Gabriel Mantilla, Luis E. Escobar

First published: 16 March 2025 https://doi.org/10.1002/ecs2.70209

 

Abstract

In North America, the rodent-borne hantavirus pulmonary syndrome is predominantly caused by the Sin Nombre virus, typically associated with the deer mouse Peromyscus maniculatus. Utilizing data from the National Ecological Observatory Network (NEON) hantavirus program, we assessed factors that may influence the spatial and temporal distribution of hantavirus in rodent populations across the United States. Between 2014 and 2019, the NEON hantavirus program conducted 104,379 small mammal captures and collected 14,004 blood samples from 49 species at 45 field sites. 

Our study identified 296 seropositive samples across 15 rodent species, including 8 Peromyscus species. We describe six new species with hantavirus seropositive samples not previously reported as hantavirus hosts. The highest number of seropositive samples was obtained from Pe. maniculatus (n = 116; 2.9% seroprevalence), followed by Peromyscus leucopus (n = 96; 2.8%) and Microtus pennsylvanicus (n = 33; 4.2%).

Hantavirus seroprevalence showed an uneven spatial distribution, with the highest seroprevalence found in Virginia (7.8%, 99 seropositive samples), Colorado (5.7%, n = 37), and Texas (4.8%, n = 19). Hantavirus seropositive samples were obtained from 32 sites, 10 of which presented seropositive samples in species other than Pe. maniculatus or Pe. leucopus. Seroprevalence was inconsistent across years but showed intra-annual bimodal trends, and in Pe. maniculatus and Pe. leucopus, the number of captures correlated with seroprevalence in the following months.

Seroprevalence was higher in adult males, with only one seropositive sample obtained from a juvenile Peromyscus truei. Higher body mass, presence of scrotal testes, and nonpregnant status were associated with higher seropositivity. The NEON dataset, derived from a multiyear and structured surveillance system, revealed the extensive distribution of hantavirus across broad taxonomic and environmental ranges. Future research should consider winter season surveillance and continued analyses of stored samples for a comprehensive spatiotemporal study of hantavirus circulation in wildlife. Global changes are expected to affect the dynamics of rodent populations by affecting their availability of resources and demography and, consequently, may modify transmission rates of rodent-borne zoonotic pathogens such as hantavirus. This study can be considered a baseline to assess hantavirus patterns across host taxa, geographies, and seasons in the United States. 

         (Continue . . . )

The press release from Virginia Tech can be read at:

News Release 11-Apr-2025

Deadly rodent-borne hantavirus is an emerging disease with pandemic potential

It should be noted that we haven't seen any evidence of human-to-human transmission of the Sin Nombre (North American) Hantavirus, although such transmission of the South American Andes Hantavirus (ANDV) has been documented (see NEJM  “Super-Spreaders” and Person-to-Person Transmission of Andes Virus in Argentina).

We looked in at that outbreak a couple of  times in 2019 (see here and here).

While currently mostly a limited zoonotic threat, as the these Hantaviruses expand their host and geographic ranges, it is always possible their pandemic threat potential will increase.  

In the meantime, it is important that people understand that there are real risks from exposure to rodents and other types of small mammals, and try to avoid exposure whenever possible.