Bayou virus-associated hantavirus pulmonary syndrome in Eastern Texas: identification of the rice rat, Oryzomys palustris, as reservoir host

Understanding Viral Haemorrhagic Fevers: Virus Diversity, Vector Ecology, and Public Health Strategies

Viral haemorrhagic fevers encompass a diverse group of severe, often life-threatening illnesses caused by viruses from multiple families, including Arenaviridae, Filoviridae, Flaviviridae, Hantaviridae, Nairoviridae, Peribunyaviridae, and Phenuiviridae. Characterised by fever and haemorrhagic symptoms, these diseases challenge public health systems by overwhelming healthcare facilities, complicating diagnostic processes, and requiring extensive resources for containment and treatment, especially in resource-limited settings. This discussion explores the intricate relationships between VHFs and their transmission vectors-both animal and arthropod-and examines the impact of ecological and geographic factors on disease spread. The primary transmission of VHFs typically occurs through direct contact with infected animals or via bites from haematophagous arthropods, facilitating zoonotic and, at times, human-to-human transmission. With an emphasis on the role of diverse wildlife, domesticated animals, and vectors such as mosquitoes and ticks in the epidemiology of VHFs, there is a recognised need for robust surveillance and strategic public health responses to manage outbreaks. This review discusses the necessity of interdisciplinary approaches that integrate virology, ecology, and public health to enhance diagnostic capabilities, develop vaccines and antivirals, and improve outbreak interventions. Exploring the ecological and biological dynamics of VHFs will help bolster a deeper understanding of these emerging viruses and underpin preparation for future outbreaks. The importance of enhanced global cooperation, continuous research, and collaboration to mitigate the public health threats posed by these complex infections is a central theme, serving as a foundational strategy to reinforce worldwide preparedness and response efforts. Future directions include addressing gaps in vaccine development and tailoring public health strategies to the unique challenges of managing VHFs, such as the rapid mutation rates of viruses, the need for cold chain logistics for vaccine distribution, and socio-economic barriers to healthcare access, in order to ensure readiness for and effective response to emerging threats worldwide.

Genetic variants associated with hantavirus infection in a reservoir host are related to regulation of inflammation and immune surveillance

The immunogenetics of wildlife populations influence the epidemiology and evolutionary dynamic of the host-pathogen system. Profiling immune gene diversity present in wildlife may be especially important for those species that, while not at risk of disease or extinction themselves, are host to diseases that are a threat to humans, other wildlife, or livestock. Hantaviruses (genus: Orthohantavirus) are globally distributed zoonotic RNA viruses with pathogenic strains carried by a diverse group of rodent hosts. The marsh rice rat (Oryzomys palustris) is the reservoir host of Orthohantavirus bayoui, a hantavirus that causes fatal cases of hantavirus cardiopulmonary syndrome in humans. We performed a genome wide association study (GWAS) using the rice rat "immunome" (i.e., all exons related to the immune response) to identify genetic variants associated with infection status in wild-caught rice rats naturally infected with their endemic strain of hantavirus. First, we created an annotated reference genome using 10× Chromium Linked Reads sequencing technology. This reference genome was used to create custom baits which were then used to target enrich prepared rice rat libraries (n = 128) and isolate their immunomes prior to sequencing. Top SNPs in the association test were present in four genes (Socs5, Eprs, Mrc1, and Il1f8) which have not been previously implicated in hantavirus infections. However, these genes correspond with other loci or pathways with established importance in hantavirus susceptibility or infection tolerance in reservoir hosts: the JAK/STAT, MHC, and NFκB. These results serve as informative markers for future exploration and highlight the importance of immune pathways that repeatedly emerge across hantavirus systems. Our work aids in creating cross-species comparisons for better understanding mechanisms of genetic susceptibility and host-pathogen coevolution in hantavirus systems.

Deep Sequencing to Reveal Phylo-Geographic Relationships of Juquitiba Virus in Paraguay

Several hantaviruses result in zoonotic infections of significant public health concern, causing hemorrhagic fever with renal syndrome (HFRS) or hantavirus cardiopulmonary syndrome (HCPS) in the Old and New World, respectively. Given a 35% case fatality rate, disease-causing New World hantaviruses require a greater understanding of their biology, genetic diversity, and geographical distribution. Juquitiba hantaviruses have been identified in Oligoryzomys nigripes in Brazil, Paraguay, and Uruguay. Brazil has reported the most HCPS cases associated with this virus. We used a multiplexed, amplicon-based PCR strategy to screen and deep-sequence the virus harbored within lung tissues collected from Oligoryzomys species during rodent field collections in southern (Itapúa) and western (Boquerón) Paraguay. No Juquitiba-like hantaviruses were identified in Boquerón. Herein, we report the full-length S and M segments of the Juquitiba hantaviruses identified in Paraguay from O. nigripes. We also report the phylogenetic relationships of the Juquitiba hantaviruses in rodents collected from Itapúa with those previously collected in Canindeyú. We showed, using the TN93 nucleotide substitution model, the coalescent (constant-size) population tree model, and Bayesian inference implemented in the Bayesian evolutionary analysis by sampling trees (BEAST) framework, that the Juquitiba virus lineage in Itapúa is distinct from that in Canindeyú. Our spatiotemporal analysis showed significantly different time to the most recent ancestor (TMRA) estimates between the M and S segments, but a common geographic origin. Our estimates suggest the additional geographic diversity of the Juquitiba virus within the Interior Atlantic Forest and highlight the need for more extensive sampling across this biome.

Global Diversity and Distribution of Hantaviruses and Their Hosts

Rodents represent 42% of the world's mammalian biodiversity encompassing 2,277 species populating every continent (except Antarctica) and are reservoir hosts for a wide diversity of disease agents. Thus, knowing the identity, diversity, host-pathogen relationships, and geographic distribution of rodent-borne zoonotic pathogens, is essential for predicting and mitigating zoonotic disease outbreaks. Hantaviruses are hosted by numerous rodent reservoirs. However, the diversity of rodents harboring hantaviruses is likely unknown because research is biased toward specific reservoir hosts and viruses. An up-to-date, systematic review covering all known rodent hosts is lacking. Herein, we document gaps in our knowledge of the diversity and distribution of rodent species that host hantaviruses. Of the currently recognized 681 cricetid, 730 murid, 61 nesomyid, and 278 sciurid species, we determined that 11.3, 2.1, 1.6, and 1.1%, respectively, have known associations with hantaviruses. The diversity of hantaviruses hosted by rodents and their distribution among host species supports a reassessment of the paradigm that each virus is associated with a single-host species. We examine these host-virus associations on a global taxonomic and geographical scale with emphasis on the rodent host diversity and distribution. Previous reviews have been centered on the viruses and not the mammalian hosts. Thus, we provide a perspective not previously addressed.

Muleshoe Virus and Other Hantaviruses Associated with Neotomine or Sigmodontine Rodents in Texas

The broad objective of this study was to increase our knowledge of Muleshoe virus and other hantaviruses associated with cricetid rodents in Texas. Anti-hantavirus antibody was found in 38 (3.2%) of 1171 neotomine rodents and 6 (1.8%) of 332 sigmodontine rodents from 10 Texas counties; hantaviral RNA was detected in 23 (71.9%) of 32 antibody-positive rodents. Analyses of nucleocapsid protein gene sequences indicated Muleshoe virus infection in four hispid cotton rats (Sigmodon hispidus) from northern Texas; Bayou virus, three Texas marsh oryzomys (Oryzomys texensis) from the Gulf Coast; Limestone Canyon virus, five brush mice (Peromyscus boylii) from western Texas; and Sin Nombre virus-five Texas mice (P. attwateri), one Lacey's white-ankled deer mouse (P. laceianus), four white-footed mice (P. leucopus), and one fulvous harvest mouse (Reithrodontomys fulvescens) from northern, central, or southern Texas. The results of this study together with the results of a previous study revealed that Muleshoe virus, perhaps in association with S. hispidus, is distributed across northern Texas. Finally, the results of Bayesian analyses of glycoprotein precursor (GPC) gene sequences and pairwise comparisons of complete GPC (amino acid) sequences strengthened support for the notion that Muleshoe virus is distinct from Black Creek Canal virus, Bayou virus, and all other species included in the Bunyaviridae, genus Hantavirus.

Prediction of Pan-Specific B-Cell Epitopes From Nucleocapsid Protein of Hantaviruses Causing Hantavirus Cardiopulmonary Syndrome

Hantaviruses are emerging viral pathogens that causes hantavirus cardiopulmonary syndrome (HCPS) in the Americas, a severe, sometimes fatal, respiratory disease in humans with a case fatality rate of ≥50%. IgM and IgG-based serological detection methods are the most common approaches used for laboratory diagnosis of hantaviruses. Such emerging viral pathogens emphasizes the need for improved rapid diagnostic devices and vaccines incorporating pan-specific epitopes of genotypes. We predicted linear B-cell epitopes for hantaviruses that are specific to genotypes causing HCPS in humans using in silico prediction servers. We modeled the Andes and Sin Nombre hantavirus nucleocapsid protein to locate the identified epitopes. Based on the mean percent prediction probability score, epitope IMASKSVGS/TAEEKLKKKSAF was identified as the best candidate B-cell epitope specific for hantaviruses causing HCPS. Promiscuous epitopes were identified in the C-terminal of the protein. Our study for the first time has reported pan-specific B-cell epitopes for developing immunoassays in the detection of antibodies to hantaviruses causing HCPS. Identification of epitopes with pan-specific recognition of all genotypes causing HCPS could be valuable for the development of immunodiagnositic tools toward pan-detection of hantavirus antibodies in ELISA. J. Cell. Biochem. 118: 2320-2324, 2017. © 2017 Wiley Periodicals, Inc.

Hantavirus pulmonary syndrome

Hantavirus pulmonary syndrome (HPS) is a severe disease characterized by a rapid onset of pulmonary edema followed by respiratory failure and cardiogenic shock. The HPS associated viruses are members of the genus Hantavirus, family Bunyaviridae. Hantaviruses have a worldwide distribution and are broadly split into the New World hantaviruses, which includes those causing HPS, and the Old World hantaviruses [including the prototype Hantaan virus (HTNV)], which are associated with a different disease, hemorrhagic fever with renal syndrome (HFRS). Sin Nombre virus (SNV) and Andes virus (ANDV) are the most common causes of HPS in North and South America, respectively. Case fatality of HPS is approximately 40%. Pathogenic New World hantaviruses infect the lung microvascular endothelium without causing any virus induced cytopathic effect. However, virus infection results in microvascular leakage, which is the hallmark of HPS. This article briefly reviews the knowledge on HPS-associated hantaviruses accumulated since their discovery, less than 20 years ago.

Hantaviruses in the americas and their role as emerging pathogens

The continued emergence and re-emergence of pathogens represent an ongoing, sometimes major, threat to populations. Hantaviruses (family Bunyaviridae) and their associated human diseases were considered to be confined to Eurasia, but the occurrence of an outbreak in 1993–94 in the southwestern United States led to a great increase in their study among virologists worldwide. Well over 40 hantaviral genotypes have been described, the large majority since 1993, and nearly half of them pathogenic for humans. Hantaviruses cause persistent infections in their reservoir hosts, and in the Americas, human disease is manifest as a cardiopulmonary compromise, hantavirus cardiopulmonary syndrome (HCPS), with case-fatality ratios, for the most common viral serotypes, between 30% and 40%. Habitat disturbance and larger-scale ecological disturbances, perhaps including climate change, are among the factors that may have increased the human caseload of HCPS between 1993 and the present. We consider here the features that influence the structure of host population dynamics that may lead to viral outbreaks, as well as the macromolecular determinants of hantaviruses that have been regarded as having potential contribution to pathogenicity.

Sympatry of 2 hantavirus strains, paraguay, 2003-2007

To explore geographic and host-taxonomic patterns of hantaviruses in Paraguay, we established sampling sites in the Mbaracayu Biosphere Reserve. We detected Jabora virus and Itapua37/Juquitiba-related virus in locations approximately 20 m apart in different years, which suggested sympatry of 2 distinct hantaviruses.

A habitat-based model for the spread of hantavirus between reservoir and spillover species

New habitat-based models for spread of hantavirus are developed which account for interspecies interaction. Existing habitat-based models do not consider interspecies pathogen transmission, a primary route for emergence of new infectious diseases and reservoirs in wildlife and man. The modeling of interspecies transmission has the potential to provide more accurate predictions of disease persistence and emergence dynamics. The new models are motivated by our recent work on hantavirus in rodent communities in Paraguay. Our Paraguayan data illustrate the spatial and temporal overlaps among rodent species, one of which is the reservoir species for Jabora virus and others which are spillover species. Disease transmission occurs when their habitats overlap. Two mathematical models, a system of ordinary differential equations (ODE) and a continuous-time Markov chain (CTMC) model, are developed for spread of hantavirus between a reservoir and a spillover species. Analysis of a special case of the ODE model provides an explicit expression for the basic reproduction number, R(0), such that if R(0)<1, then the pathogen does not persist in either population but if R(0)>1, pathogen outbreaks or persistence may occur. Numerical simulations of the CTMC model display sporadic disease incidence, a new behavior of our habitat-based model, not present in other models, but which is a prominent feature of the seroprevalence data from Paraguay. Environmental changes that result in greater habitat overlap result in more encounters among various species that may lead to pathogen outbreaks and pathogen establishment in a new host.

Potential renal sequelae in survivors of hantavirus cardiopulmonary syndrome

Although other hantaviruses are associated with renal manifestations, hantavirus cardiopulmonary syndrome (HCPS) has not been associated with such sequelae. The HCPS survivors were prospectively evaluated for renal complications. Subjects underwent yearly evaluation, laboratory studies, and 24-hour urine collection. Thirty subjects were evaluated after recovery from HCPS with the first follow-up at a median of 7.4 months after discharge. Subjects were a wide age range (18-51) but had an equal gender composition. Eighteen of 30 (60%) returned for > 1 evaluation. Half (15/30) had a 24-hour urine collection with > 150 mg of total protein and 6 had > 300 mg. Seven had a Cockcroft-Gault creatinine clearance (CrClCG) < 90 mL/min/1.73 m2 and 2 were < 60. Fifty-three percent met the definition of chronic kidney disease. Those treated with extracorporeal membrane oxygenation had less renal sequelae (P = 0.035). Our data suggest that renal sequelae may occur in HCPS. Further study of renal complications of New World hantavirus infections are needed.

Defense Against Biological Weapons (Biodefense)

Biological warfare (germ warfare) is defined as the use of any disease-causing organism or toxin(s) found in nature as weapons of war with the intent to destroy an adversary. Though rare, the use of biological weapons has occurred throughout the centuries.

Hantavirus and arenavirus antibodies in persons with occupational rodent exposure

Risk for infection was low among those who handled neotomine or sigmodontine rodents on the job.

Rodents are the principal hosts of Sin Nombre virus, 4 other hantaviruses known to cause hantavirus pulmonary syndrome in North America, and the 3 North American arenaviruses. Serum samples from 757 persons who had worked with rodents in North America and handled neotomine or sigmodontine rodents were tested for antibodies against Sin Nombre virus, Whitewater Arroyo virus, Guanarito virus, and lymphocytic choriomeningitis virus. Antibodies against Sin Nombre virus were found in 4 persons, against Whitewater Arroyo virus or Guanarito virus in 2 persons, and against lymphocytic choriomeningitis virus in none. These results suggest that risk for infection with hantaviruses or arenaviruses usually is low in persons whose occupations entail close physical contact with neotomine or sigmodontine rodents in North America.

Hantavirus N protein exhibits genus-specific recognition of the viral RNA panhandle

A key genomic characteristic that helps define Hantavirus as a genus of the family Bunyaviridae is the presence of distinctive terminal complementary nucleotides that promote the folding of the viral genomic segments into "panhandle" hairpin structures. The hantavirus nucleocapsid protein (N protein), which is encoded by the smallest of the three negative-sense genomic RNA segments, undergoes in vivo and in vitro trimerization. Trimeric hantavirus N protein specifically recognizes the panhandle structure formed by complementary base sequence of 5' and 3' ends of viral genomic RNA. N protein trimers from the Andes, Puumala, Prospect Hill, Seoul, and Sin Nombre viruses recognize their individual homologous panhandles as well as other hantavirus panhandles with high affinity. In contrast, these hantavirus N proteins bind with markedly reduced affinity to the panhandles from the genera Bunyavirus, Tospovirus, and Phlebovirus or Nairovirus. Interactions between most hantavirus N and heterologous hantavirus viral RNA panhandles are mediated by the nine terminal conserved nucleotides of the panhandle, whereas Sin Nombre virus N requires the first 23 nucleotides for high-affinity binding. Trimeric hantavirus N complexes undergo a prominent conformational change while interacting with panhandles from members of the genus Hantavirus but not while interacting with panhandles from viruses of other genera of the family Bunyaviridae. These data indicate that high-affinity interactions between trimeric N and hantavirus panhandles are conserved within the genus Hantavirus.

Development and evaluation of serological assays for detection of human hantavirus infections caused by Sin Nombre virus

BACKGROUND

The hantavirus cardiopulmonary syndrome (HCPS) was first recognized in 1993 after a cluster of acute respiratory distress syndrome deaths in the southwestern of the United States. The major causative agent of HCPS in North America is the Sin Nombre virus (SNV) carried by the deer mouse Peromyscus maniculatus. The first HCPS case imported to Europe was reported in 2002.

OBJECTIVES

The objective of the study was to develop and evaluate ELISA and Western blot tests for the serological detection of human infections caused by SNV including those imported to Europe.

STUDY DESIGN

A polyhistidine (His)-tagged recombinant nucleocapsid (rN) protein of SNV was expressed in Saccharomyces cerevisiae and purified by nickel chelation chromatography. On the basis of the purified SNV rN protein mu-capture and indirect IgM and IgG ELISAs and an IgG Western blot were developed. The evaluation of the tests was performed using a negative serum panel and a blinded serum panel from the US containing acute-phase sera from HCPS patients.

RESULTS

Based upon the results obtained using a panel of negative control sera the specificity for SNV mu-capture and indirect IgM and IgG ELISAs were found to be 100%. All 33 sera from SNV-infected HCPS patients included in the blinded panel were detected by the SNV mu-capture and indirect IgM ELISAs. Twenty-nine out of the 33 SNV-IgM positive sera reacted also in the SNV-IgG ELISA. An SNV-IgG Western blot confirmed the data of the SNV-IgG ELISA. Although the majority of anti-SNV positive sera cross-reacted with rN proteins of Puumala virus and Dobrava virus, the lacking reactivity of a few sera with these heterologous rN antigens in the corresponding IgM and IgG ELISAs demonstrates the value of virus-specific test formats for acute-phase sera.

CONCLUSIONS

The novel SNV ELISA and Western blot tests represent a useful tool for the serological detection of SNV infections.

Outbreak of hantavirus pulmonary syndrome, Los Santos, Panama, 1999-2000

An outbreak of hantavirus pulmonary syndrome occurred in the province of Los Santos, Panama, in late 1999 and early 2000. Eleven cases were identified; 9 were confirmed by serology. Three cases were fatal; however, no confirmed case-patient died. Case-neighborhood serologic surveys resulted in an overall hantavirus antibody prevalence of 13% among household and neighborhood members from the outbreak foci. Epidemiologic investigations did not suggest person-to-person transmission of hantavirus infection. By use of Sin Nombre virus antigen, hantavirus antibodies were detected in Oligoryzomys fulvescens and Zygodontomys brevicauda cherriei. This outbreak resulted in the first documented cases of human hantavirus infections in Central America.

Maporal virus, a hantavirus associated with the fulvous pygmy rice rat (Oligoryzomys fulvescens) in western Venezuela

Oryzomine rodents in the southeastern United States, Panama, and southern South America are natural hosts of 6 of the 13 viruses known to cause hantavirus pulmonary syndrome. The purpose of this study was to extend our knowledge of the geographical distribution and genetic diversity of the hantaviruses associated with oryzomine rodents in South America. An infectious hantavirus was isolated from two fulvous pygmy rice rats captured in western Venezuela. Analyses of complete nucleocapsid protein and glycoprotein precursor sequences indicated that the isolates are strains of a novel hantavirus (proposed name "Maporal") which is phylogenetically most closely related to the viruses known to cause hantavirus pulmonary syndrome in southern South America.

Tropical dermatology: viral tropical diseases

Viruses are important pathogens in tropical areas; most of them, especially the tropical hemorrhagic fevers, produce mucocutaneous manifestations. More than any other kind of pathogen, viruses have the possibility for being widespread, since they have a greater probability of mutation than do bacteria, can cross species barriers easily, and infect both human beings and animals in habitats with a great biodiversity. Tropical habitats also have been subject to major ecologic changes in the last few decades, exposing humans to direct contact with these viruses and allowing hemorrhagic fevers due to new emergent viruses such as flaviviruses, filoviruses, arenaviruses, and hantaviruses to become major threats to public health. The collapse of eradication programs in many countries, as well as population increases and ecologic modifications, have led to the spread of dengue and yellow fever to large portions of the world owing to the dissemination of vectors, especially mosquitoes, with broad ecologic ranges. Viruses previously restricted to some geographic areas, such as Rift Valley fever, Crimean-Congo hemorrhagic fever, West Nile fever, and monkeypox are now affecting new countries and populations. Other viruses such as herpes B infection often affect travelers and animal handlers in most parts of the world. Dermatologic lesions occur in all these diseases and can facilitate a rapid diagnosis, leading to control of the virus and helping prevent possible outbreaks.

Hantavirus transmission: potential role of ectoparasites

Hantavirus pulmonary syndrome is an often-fatal disease thought to be transmitted exclusively by rodents. We report the first evidence of hantavirus-specific RNA (Bayou) from two trombiculid mites (chiggers) and an ixodid tick parasitizing wild-caught rodents at a field site in Texas and also from a trombiculid mite in the free-living predatory stage of the chigger life cycle collected from the same site.

Vaccines against hantaviruses

Rodent-borne hantaviruses are etiologic agents for hemorrhagic fever with renal syndrome and hantavirus cardiopulmonary syndrome in the Old World and New World, respectively. These often severe diseases are relatively uncommon in most parts of the world and are sufficiently genetically variable that widely cross-protective vaccines will probably need to be polyvalent. The current status of hantavirus vaccines shall be reviewed and both conventional and speculative new vaccine technologies that may evolve within the field shall be considered.

Purification and characterization of the Sin Nombre virus nucleocapsid protein expressed in Escherichia coli

Sin Nombre virus is a member of the Hantavirus genus, family Bunyaviridae, and is an etiologic agent of hantavirus pulmonary syndrome. The hantavirus nucleocapsid (N) protein plays an important role in the encapsidation and assembly of the viral negative-sense genomic RNA. The Sin Nombre N protein was expressed as a C-terminal hexahistidine fusion in Escherichia coli and initially purified by nickel-affinity chromatography. We developed methods to extract the soluble fraction and to solubilize the remainder of the N protein using denaturants. Maximal expression of protein from native purification was observed after a 1.5-h induction with IPTG (2.4 mg/L). The zwitterionic detergent Chaps did not enhance the yield of native purifications, but increased the yield of protein obtained from insoluble purifications. Both soluble and insoluble materials, purified by nickel-affinity chromatography, were also subjected to Hi Trap SP Sepharose fast-flow (FF) chromatography. Both soluble and insoluble proteins had a similar A(280) profile on the Sepharose FF column, and both suggested the presence of a nucleic acid contaminant. The apparent dissociation constant of the N protein, purified by nickel-affinity and SP Sepharose FF chromatography, and the 5' end of the viral S-segment genome were measured using a filter binding assay. The N protein-vRNA complex had an apparent dissociation constant of 140 nM.

Spectrum of hantavirus infection: hemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome

Hantaviruses chronically infect rodents without apparent disease, but when they are spread by aerosolized excreta to humans, two major clinical syndromes result: hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). Both diseases appear to be immunopathologic, and inflammatory mediators are important in causing the clinical manifestations. In HPS, T cells act on heavily infected pulmonary endothelium, and it is suspected that gamma interferon and tumor necrosis factor are major agents of a reversible increase in vascular permeability that leads to severe, noncardiogenic pulmonary edema. HFRS has prominent systemic manifestations. The retroperitoneum is a major site of vascular leak and the kidneys suffer tubular necrosis. Both syndromes are accompanied by myocardial depression and hypotension or shock. HFRS is primarily a Eurasian disease, whereas HPS appears to be confined to the Americas; these geographic distinctions correlate with the phylogenies of the rodent hosts and the viruses that coevolved with them.

Sin Nombre virus pathogenesis in Peromyscus maniculatus

Sin Nombre virus (SNV), a member of the Hantavirus genus, causes acute viral pneumonia in humans and is thought to persistently infect mice. The deer mouse, Peromyscus maniculatus, has been identified as the primary reservoir host for SNV. To understand SNV infection of P. maniculatus, we examined wild deer mice for localization of viral antigens and nucleic acid. Morphologic examination consistently revealed septal edema within lung tissue and mononuclear cell infiltrates in portal areas of the liver. Immunohistochemical analysis of SNV-infected deer mice identified viral antigens within lung, liver, kidney, and spleen. The lungs consistently presented with the highest levels of viral antigen by immunohistochemistry and with the highest levels of nucleic acid by reverse transcriptase (RT) PCR. The mononuclear cell infiltrates surrounding liver portal triads were positive for SNV antigens in addition to resident macrophages in liver sinuses. Spleen tissue contained antigens in both the red pulp and the periartereolar region of the white pulp. The kidney presented with no gross pathology, although antigens could be localized to glomeruli. Virus antigen levels within the kidney were highest in deer mice that did not have antibodies to SNV but contained viral nucleic acid detectable by RT PCR. Since transmission is thought to occur via urine, our results suggest that virus transmission may be highest in the early stages of infection. In addition, these results indicate that SNV does cause some pathology within its reservoir host.