Pandemic Watch
Hantaan virus vs Seoul virus
A factual side-by-side comparison of two hantavirus strains: Hantaan virus and Seoul virus. Reservoir biology, geographic distribution, clinical course, case-fatality rate, and outbreak history.
Discovery and history
Hantaan virus
Between 1951 and 1954, roughly 3,000 United Nations soldiers near the Hantaan River in central Korea developed an unexplained hemorrhagic fever with renal involvement. The case-fatality rate approached 10 percent. The disease was given the descriptive name 'Korean hemorrhagic fever' and an etiology was sought for the next 25 years. Karl Johnson and Ho Wang Lee finally isolated the causative agent from striped field mice in 1976, naming it after the river. The discovery established hantaviruses as a coherent family and provided the type species against which all subsequent strains have been characterized.
Seoul virus
Seoul virus was isolated in 1980 from Norway rats trapped in the city for which it is named. The discovery completed an early picture of the hantavirus genus by adding an explicitly urban species to the previously wild-rodent-defined family. The recognition that an HFRS-causing virus could be carried by the cosmopolitan Norway rat — the same species that spread the bubonic plague historically and persists today in essentially every human-inhabited port — fundamentally changed how the geographic risk of hantaviruses was understood.
Reservoir and ecology
Hantaan virus
The reservoir is the striped field mouse (Apodemus agrarius), widely distributed across temperate East Asia in grasslands, agricultural fields, and forest margins. The species is intimately associated with grain agriculture across China, Korea, and the Russian Far East, which puts it in regular contact with farmers, harvesters, and rural residents. Seasonal peaks in HFRS cases track the autumn harvest and the spring planting cycles when human exposure to rodent-contaminated environments is highest.
Seoul virus
The Norway rat (Rattus norvegicus) is the primary reservoir, with the black rat (Rattus rattus) also documented as a carrier in some studies. Both species are cosmopolitan in distribution, following humans through trade, transportation, and habitation. Pet rat colonies — sometimes derived ultimately from wild-caught founders — can carry and transmit Seoul virus, and several documented human outbreaks have been traced to pet rat ownership rather than wild rat exposure.
Clinical course
Hantaan virus
HFRS classically progresses through five phases: febrile (fever, myalgia, headache, lasting 3-7 days), hypotensive (sudden drop in blood pressure, lasting hours to days), oliguric (acute kidney injury with reduced urine output, lasting 3-7 days — most deaths occur here), diuretic (recovery of urine output), and convalescent (gradual recovery over weeks to months). Hemorrhagic manifestations — petechial rash, conjunctival hemorrhage, gastrointestinal bleeding — give the syndrome its name. The case-fatality rate of 5 to 15 percent is lower than for HPS but the overall morbidity is substantial.
Seoul virus
Seoul-virus HFRS is milder than Hantaan-virus or Dobrava-virus disease. Patients develop the classic febrile prodrome — fever, myalgia, headache, abdominal pain — and a subset progress to a renal phase with proteinuria, mild renal impairment, and occasionally hemorrhagic manifestations. Severe disease requiring dialysis occurs but is uncommon. Case-fatality is 1 to 2 percent, the lowest among the HFRS-causing strains except for Puumala virus.
Notable outbreaks
Hantaan virus
The Korean War cases between 1951 and 1954 remain the largest documented Hantaan virus event. Modern outbreaks are smaller — clusters in agricultural workers, military trainees, or rural communities during harvest peaks. China has documented major HFRS outbreaks tied to flood-displacement of rodent populations.
Seoul virus
Several U.S. multi-state pet rat outbreaks have been investigated since 2017, involving home-breeder networks and rat fancier communities. United Kingdom investigations have linked pet rat ownership to sporadic Seoul virus cases as well. Wild-rat-associated cases occur in port cities globally but are typically sporadic rather than clustered.
Prevention
Hantaan virus
Inactivated HFRS vaccines have been licensed in South Korea since 1990 and in China shortly thereafter. They are recommended for high-risk occupational groups (military, agricultural workers, lab researchers) and provide partial protection against Hantaan and Seoul viruses. Uptake outside occupational programs is limited. Beyond vaccination, standard rodent-exposure precautions and grain-storage rodent-proofing reduce risk.
Seoul virus
Prevention focuses on rodent control in urban and peri-urban environments — sealing entry points, removing food sources, and integrated pest management. Pet rat owners should follow biosecurity practices (sourcing from reputable breeders with known disease status, hygiene during cage cleaning, avoiding contact with bedding aerosols). Healthcare workers caring for pet rat owners should be aware of Seoul virus as a differential diagnosis for unexplained febrile renal illness.
Full strain profiles: Hantaan virus · Seoul virus. For the broader disease guide, see hantavirus.
