FAQs: Seoul virus

Yes. Seoul virus is a member of the hantavirus family of rodent-borne viruses. This family also includes Sin Nombre virus, which is the most common hantavirus causing disease in the United States.  Most hantaviruses have only one or two rodent species as their natural host.  For Seoul virus, the natural host is the Norway rat (Rattus norvegicus) and the black rat (Rattus rattus), whereas for Sin Nombre it’s the deer mouse (Peromyscus maniculatus). In the rodents that carry them, these viruses don’t cause disease, but do cause life-long infection and shedding of the virus.  These viruses can occasionally spill over into other species of rodents, but they don’t cause chronic virus infections and shedding.

The severe disease associated with Sin Nombre virus infections is called hantavirus pulmonary syndrome (HPS). Most HPS infections lead to fever and body aches, progressing to severe breathing difficulties that frequently require hospitalization. Death occurs in approximately 38% of cases (or 38  of every 100 patients).  In contrast, the severe disease associated with Seoul virus is called hemorrhagic fever with renal syndrome (HFRS).  Most people who get infected with Seoul virus experience mild or even no symptoms.  However, in the severe form of the disease, patients can exhibit bleeding and kidney involvement, and death occurs in approximately 1-2% of cases (or 1-2 of every 100 sick individuals).

CDC worked with state health departments and others to investigate an outbreak of Seoul virus infections in pet rodents and humans. CDC and its partners traced shipments and transport of rats, some of which were infected with Seoul virus, to better understand how the virus entered the pet trade, and to interrupt transmission of Seoul virus to other rats or people.

While Seoul virus infection in humans is generally considered less severe than some other types of hantavirus infections, it can still cause a severe illness in some cases. Some people may develop a severe form of infection known as hemorrhagic fever with renal syndrome (HFRS), and an estimated 1-2% of people may die after being infected with Seoul virus. Because there is presently no effective treatment for Seoul virus infection, preventing infections in people is important.

Seoul virus diagnostic testing can be done on live rats by taking a small blood sample and testing it in a laboratory. Rats do not have to be euthanized to collect a blood sample. The blood sample is sent to CDC or to another laboratory to perform the diagnostic test for Seoul virus infection. CDC and the other lab perform tests looking for antibodies (serologic tests) and/or evidence of virus genetic material [by polymerase chain reaction (PCR)]. A positive result means that the rat has been infected with Seoul virus and is presumed to pose a risk for transmitting the virus to other rats or to people. Infected rats are believed to remain infectious for life with permanent or intermittent shedding of virus. A negative result means there is no evidence of Seoul virus infection in the rat at the time of the sampling.

State and local departments of health are reaching out to breeders and owners of rats from suspected or confirmed facilities. Teams working with the state department of health will visit suspected facilities, and—working with the owners—will take blood samples for testing. Owners of rats that are not linked to a confirmed facility but who want their rats to be tested may choose to do so independently through commercial laboratories.

Serologic testing is the most accurate and sensitive test for Seoul virus. The accuracy of PCR testing as a screening tool is not yet established. Thus, negative results from PCR testing of blood, urine, fecal pellets, bedding, or organs should not be interpreted to mean that a rat is not infected with Seoul virus.