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Seoul Virus Outbreak Highlights Ongoing Risk of Zoonotic Viruses

Amesh A. Adalja, MD, FACP, FACEP, FIDSA, January 27, 2017

The hantavirus genus of viruses are a zoonotic group of viruses endemic to the Americas and throughout the world. Known principally because of the ferocity that one of its members, the Sin Nombre virus, exhibits in causing hantavirus pulmonary syndrome (HPS), other members of this family have varying presentations ranging from asymptomatic infection to more severe forms.

In recent weeks, the Centers for Disease Control and Prevention (CDC) announced that it is assisting in a multistate outbreak of the Seoul hantavirus, and a health alert has been issued to physicians regarding the virus.1


Rat-Breeding Facility Link

Hantaviruses are spread to humans via rodents, with transmission occurring when people are exposed to infected body fluids or bites from rodents harboring the virus. The Seoul virus is found in wild in Norway rats, and human infections have been found almost exclusively in Asia.1

In the current US outbreak, 8 individuals in 2 states have been infected. The infections are tied to a Wisconsin-based home rat-breeding operation, which was supplied with rats purchased from Wisconsin and Illinois. Individuals in up to 10 other states may also have purchased infected rats2 and may be at risk of infection.


All Patients Recovered

Seoul virus is capable of causing a spectrum of clinical presentations, with many cases being entirely without symptoms and some exhibiting hemorrhagic fever with renal syndrome (HFRS). Symptoms from mild cases are nonspecific and can include fever, chills, headache, conjunctivitis, rash, and abdominal pain. Only 1% to 2% of cases are fatal.

Of the 8 cases currently identified, 2 required hospitalization. Serologic and viral nucleic acid testing is offered by the CDC (through state health laboratories) for people who report a compatible illness after handling a rat in which Seoul virus has been reported.1


The Continued Danger of Zoonotic Infection

This first US outbreak of Seoul virus illustrates the ubiquitous risk of zoonotic infections and how easily an outbreak can begin. Most human infections have zoonotic origins and, before becoming established as bona fide human pathogens, may have delimited and stuttering jumps into humans. 

That these jumps occur is not surprising; it is a well-established phenomenon. What these facts and the Seoul virus outbreak illustrate and imply, however, is that without meticulous surveillance and response, a small zoonotic outbreak can be missed and allowed the opportunity to amplify and cause widespread disease. Quick responses and rapid dissemination of information can minimize the impact of this outbreak and provide more details on the clinical manifestations of Seoul virus.



  1. 1. Centers for Disease Control and Prevention. Investigation of Seoul virus outbreak associated with home-based, rat-breeding facilities in Wisconsin and Illinois. CDC website. January 24, 2017. Accessed January 25, 2017.
  2. 2. Branswell H. CDC expands search for rats and people infected with Seoul virus. STAT January 24, 2017. Accessed January 25, 2017.