Seoul virus

SEOV · HFRS

Overview

Seoul virus is unique among hantaviruses for its global distribution: its host, the brown rat (Rattus norvegicus), follows human commerce and is now established in port cities and urban areas worldwide. Seoul virus causes a generally milder form of hemorrhagic fever with renal syndrome (HFRS) than Hantaan virus, but with prominent liver involvement. Human cases have been linked both to wild urban-rat exposure and to pet rats — the 2017 multi-state outbreak in the United States traced infections to a network of breeders and home rat owners.

Discovery

Seoul virus was identified in 1980 by Lee Ho-Wang's group at Korea University — the same team that had isolated Hantaan virus four years earlier — when they detected hantavirus antigen in brown rats trapped in urban Seoul, in contrast to the rural striped field mice that hosted Hantaan virus. The finding was important for two reasons: it showed that hantaviruses were carried by a commensal urban rodent already established globally, and it provided an explanation for clusters of mild HFRS occurring in cities far from typical Hantaan-virus agricultural settings.

Rodent reservoir

The brown rat (Rattus norvegicus) — also called the Norway rat, sewer rat, or common rat — is among the most successful commensal mammals on Earth, established on every continent except Antarctica. Brown rats colonise sewers, ports, food-processing facilities, agricultural buildings, and any human environment that offers food and shelter. Seoul virus prevalence in brown-rat populations varies from a few percent in some cities to 30% or more in port and slum areas of East and Southeast Asia. Pet rats, derived from selectively bred lines of Rattus norvegicus, can also carry Seoul virus when introduced into a colony.

Transmission

Most Seoul virus infections occur through inhalation of aerosolized excreta from wild urban brown rats — workers in port facilities, sewer maintenance, food storage, and unsanitary housing have elevated risk. Beginning in 2017, multi-country outbreaks have been linked to pet-rat networks, with infections traced through breeders, owners, and rescue groups. Rat bites and direct mucosal contact with rodent fluids can also transmit infection. Person-to-person transmission has not been documented for Seoul virus.

Clinical course

Seoul virus disease is generally a milder HFRS than Hantaan-virus infection: fever, headache, abdominal pain, and acute kidney injury are common, but haemorrhage and shock are less prominent. A distinguishing clinical feature is prominent hepatic involvement — elevated transaminases, hyperbilirubinaemia, and clinical hepatitis — that is uncommon with other hantaviruses. Severe cases occur but are unusual; the majority of patients recover fully with supportive care over 2–3 weeks.

Diagnosis

Diagnosis is by serology and PCR. Hantavirus serology cross-reacts among related strains, so confirmation typically requires either Seoul-virus-specific assays or comparative testing against multiple antigen panels at reference labs. In a febrile patient with acute kidney injury, transaminitis, and a history of rat exposure — wild or pet — Seoul virus should be considered. Routine bloodwork shows thrombocytopenia, leukocytosis, elevated transaminases and creatinine, and proteinuria.

Treatment & prognosis

Treatment is supportive: fluid management, electrolyte correction, and renal replacement therapy in the small proportion of patients who develop severe AKI. Ribavirin has been used selectively in Asia for severe HFRS but is not routinely indicated for Seoul virus given the typically mild course. Case-fatality is approximately 1–2% and is strongly tied to comorbidities and delayed recognition.

Prevention

Prevention combines urban rat control (sanitation, exclusion, professional pest management) and personal hygiene measures: hand washing after any rat contact, ventilation of rat-housed spaces, and use of gloves and respiratory protection when handling pet rats, cleaning enclosures, or working in rat-infested environments. Pet-rat owners should be aware that imported or rescued rats may carry Seoul virus and that public-health agencies in the United States, the UK, and Canada provide voluntary testing programmes for at-risk colonies.

Tracked countries

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

Notable outbreaks

1. 1980s–1990s
   Seoul, Busan, and other Asian port cities

   Recognition that urban brown rats sustained an endemic hantavirus distinct from rural Hantaan virus; case counts in the hundreds to low thousands annually.

2. 2017
   United States and Canada (multistate)

   First confirmed Seoul virus cases linked to pet rats in the US, with infections traced through a network of breeders and home rat owners; followed by linked cases in Canada.

3. 2018
   United Kingdom

   Multi-case cluster also tied to pet rats, prompting Public Health England guidance on rat-handling hygiene.

References & primary sources

• CDC — Seoul Virus Outbreak (2017)
• UK Health Security Agency — Hantavirus Guidance
• WHO — Hantavirus Fact Sheet
• CDC — Hantavirus in the United States

Other hantavirus strains