Sin Nombre virus

SNV · Four Corners virus · HPS

Overview

Sin Nombre virus is the most clinically significant hantavirus in North America and the strain responsible for the original 1993 Four Corners outbreak that led to the recognition of hantavirus pulmonary syndrome (HPS). It is carried by the deer mouse (Peromyscus maniculatus), one of the most widely distributed rodents on the continent. Humans are infected almost exclusively by inhaling aerosolized particles from rodent urine, droppings, or saliva — typically while cleaning enclosed spaces with rodent activity (cabins, barns, sheds, crawl spaces). Person-to-person transmission has not been documented for SNV.

Discovery

Sin Nombre virus was identified in May 1993 after a cluster of previously healthy young adults — many of them Navajo — died of a rapidly progressive respiratory illness in the Four Corners region of New Mexico, Arizona, Colorado, and Utah. A joint investigation by the New Mexico Department of Health, the Indian Health Service, and CDC's Special Pathogens Branch traced the illness to aerosolized particles from deer-mouse excreta in homes with heavy rodent infestations. The virus was briefly proposed as "Muerto Canyon virus" and "Four Corners virus" before objections from local communities led to the placeholder name Sin Nombre — literally "without name" in Spanish — which has remained the accepted designation.

Rodent reservoir

The deer mouse (Peromyscus maniculatus) is among the most widely distributed mammals in North America, occupying habitats from boreal forest to alpine tundra to grassland across nearly every US state and most of Canada. Infected mice carry Sin Nombre virus for life without overt illness and shed virus continuously in urine, saliva, and droppings. Local infection prevalence in deer-mouse populations is heterogeneous but commonly ranges from 5% to 30%, with higher rates in years following heavy precipitation that boosts seed availability and rodent reproduction — the so-called trophic-cascade hypothesis used to explain the 1993 outbreak.

Transmission

Almost all documented Sin Nombre infections trace to inhaling aerosolized virus from rodent excreta in enclosed, poorly ventilated spaces — opening up a cabin after winter, cleaning a shed, sweeping a barn, working in a crawl space. Direct contact with mice or their bedding, contaminated food, or rodent bites can also transmit the virus, though these routes are uncommon. Unlike Andes virus, Sin Nombre has never been linked to person-to-person spread, and no documented airborne transmission between humans has been recorded in more than three decades of US surveillance.

Clinical course

Hantavirus pulmonary syndrome from Sin Nombre virus develops in two recognizable phases. After an incubation period of typically 1–4 weeks, the prodromal phase begins with fever, severe muscle aches (especially in the thighs, hips, and back), headache, fatigue, and gastrointestinal symptoms — nausea, vomiting, abdominal pain. This phase lasts 3–7 days. The cardiopulmonary phase then develops within hours: cough, shortness of breath, rapid-onset non-cardiogenic pulmonary edema, and shock. Untreated patients typically progress to respiratory failure within 24–48 hours of the first pulmonary symptoms.

Diagnosis

Diagnosis rests on serology — IgM and IgG antibodies to Sin Nombre virus by ELISA or strip immunoassay — supplemented by RT-PCR on blood or tissue at reference labs. Several lab findings are highly characteristic when HPS is suspected: marked thrombocytopenia (platelets often below 100,000), a left-shifted white-cell count with circulating immunoblasts on smear, hemoconcentration, elevated lactate dehydrogenase, and rapidly worsening hypoxia on chest imaging. Any patient with a flu-like illness plus thrombocytopenia and recent rodent exposure in an endemic state should be considered until proven otherwise.

Treatment & prognosis

No antiviral with proven efficacy against Sin Nombre virus exists; ribavirin, which is used for HFRS, has not shown benefit in HPS. Treatment is aggressive supportive care: early transfer to an ICU with experience in HPS, careful fluid management (over-resuscitation worsens pulmonary edema), vasopressor support, mechanical ventilation, and extracorporeal membrane oxygenation (ECMO) for the most severe cardiopulmonary collapse. Survival is closely tied to time-to-ICU; case-fatality is approximately 36–38% overall but drops substantially when patients reach a tertiary-care ICU before the cardiopulmonary phase.

Prevention

Prevention focuses on excluding deer mice from human dwellings and, when cleaning rodent-affected areas, avoiding aerosol generation. Ventilate enclosed spaces for at least 30 minutes before entering. Do not sweep or vacuum dry droppings. Wear an N95 or better respirator and rubber/plastic gloves. Spray droppings, nests, and contaminated surfaces with a 1:10 bleach-water solution and let stand five minutes before wiping up with paper towels; double-bag waste. Seal exterior openings ¼-inch or larger and store food in rodent-proof containers — exclusion is far more reliable than ongoing cleanup.

Tracked countries

Live risk index and news for countries where Sin Nombre virus is documented or surveilled.

Notable outbreaks

1. 1993
   Four Corners region (NM/AZ/CO/UT)

   Initial cluster of unexplained respiratory illness among healthy young adults; led to identification of SNV and the HPS case definition.

2. 2012
   Yosemite National Park, California

   Ten cases linked to deer-mouse contamination of double-walled tent cabins at Curry Village; three deaths. CDC investigation prompted park-wide tent-cabin redesign.

3. 2017
   Wisconsin

   Rare midwestern cluster linked to grain-elevator cleaning, illustrating that HPS can occur well outside the traditional western range.

4. 2024–2025
   California Eastern Sierra (Mono County)

   Multi-case cluster prompted state health-department warnings about deer-mouse exposure in rural and recreational settings.

References & primary sources

• CDC — Hantavirus Surveillance
• CDC — Cleaning Up After Rodents
• MMWR 1993 — Outbreak of Acute Illness, Southwestern United States
• NIAID — Hantavirus Research

Other hantavirus strains