Hantavirus Syndrome

Discovery of Hantavirus Syndrome in Washington State

Illustration from: Christensen JR, Larrison EJ.Mammals of the Pacific Northwest, Boise: University of Idaho press,1982; reprinted with permission

John H. Grendon
Marcia J. Goldoft

A series of unexplained deaths in young adults focused attention on the southwestern United States during the spring of 1993. First recognized in the Four Corners region, the new illness caused a cluster of fatal cases of acute respiratory distress syndrome. Subsequent investigation identified a new pathogenic strain of hantavirus, Sin Nombre, which causes the hantavirus pulmonary syndrome (HPS). Hantaviruses were previously recognized as a cause of human illness in Europe and Asia. In those parts of the world hantaviruses cause both mild and severe hemorrhagic fevers, with renal syndrome.

HPS Cases in Washington

Eight HPS confirmed cases and one probable case have been identified in Washington State residents. The earliest occurred in 1985 in Lincoln County and was retrospectively confirmed in 1994 with the assistance of the hospital, the local health department, and Centers for Disease Control and Prevention (CDC). Also in 1994 a case occurred in a Lewis County resident who may have been exposed to rodents during travel outside the state. Four cases occurred in 1995, one in Yakima County in July, two unrelated cases in Stevens County (in July and August), and one in Grant County in December. To date, three cases have been reported in 1996: in Franklin County (January), Snohomish County March), and a probable case in Lewis County (June). Six cases have been fatal. All cases lived in rural areas and only one had traveled out of state during the incubation period.

Epidemiology

All hantaviruses have rodent reservoirs. The deer mouse, Peromyscus maniculatus, is the primary reservoir of the Sin Nombre virus. Rodents carry and excrete the virus without adverse health effects. Transmission to humans occurs by inhalation of aerosolized virus and possibly by bites. Person-to-person transmission has never been documented, nor has transmission from insects, cats,dogs, or predators (e.g., snakes).

Based on the available exposure information, most persons with HPS in the United States appear to have been exposed to infected rodents in or around rural homes. Several HPS cases in North America probably were caused by occupational exposures. HPS has been identified in three biologists/mammalogists; in the United States and one in British Columbia. Cases also occurred in a shepherd who slept in rarely used cabins and a farmhand who trapped deer mice daily. Exposure during recreational activities such as camping and hiking is also suspected in several HPS cases.

HPS is not a new disease. A suspected occurred case in Utah in 1959; the 1985 case in Washington and a 1992 case in Oregon were confirmed retrospectively as of May 1996, HPS has been confirmed in 135 persons in 24 states. Case-patients are slightly more likely to be male (59%). The mean age of patients is 35 years (range I I to 69 years). One significant change between the newer cases and all cases is a somewhat lower fatality rate, nearly 40% for new cases -and about 50% for all cases.

The Disease

HPS associated with hantavirus infection begins as a nonspecific illness resembling influenza or gastroenteritis. The incubation period usually is one to three weeks, but may range from three to 42 days. Almost all casepatients have a fever and muscle aches. Many have a cough, chills, headache, and gastrointestinal symptoms such as nausea, vomiting, or diarrhea. After three to four days of nonspecific symptoms, the disease worsens rapidly. Patients develop difficulty breathing, a rapid heart rate, and decreased blood pressure. Fluid enters the lungs, causing acute respiratory distress syndrome. White blood cell and platelet counts are abnormal. Treatment consists of providing supplemental oxygen and ventilator support. Even with intensive care, mortality is high. Experimental treatment protocols are being tested.

Rodent Reservoir

Deer mice had the highest prevalence of the Sin Nombre strain of hantavirus antibody of all rodents tested in the southwestern United States, although other rodent species have antibody indicating exposure to the virus. Slightly different hantavirus strains in the eastern United States are carried by other rodents. In Florida a case of HPS led to the discovery of the Black Creek Canal hantavirus and the identification of the cotton rat as its rodent reservoir. Investigations have identified two additional rodent reservoirs for different hantavirus strains linked to HPS cases in Rhode Island and Louisiana.

In 1993 in Arizona, New Mexico, and Colorado, 30% of 813 deer mice tested were seropositive for antibody In general, the prevalence of hantavirus infection in deer mice from other parts of the United States is lower than in the Southwest. In Washington, seropositive deer mice have been found in one western county (Whatcom) and in four eastern counties (Grant, Kittitas, Lincoln, and Whitman). Overall, 5-10% of deer mice tested in 10 counties have been seropositive, similar to findings in other western states.

Prevention and Education

Public interest in hantavirus has increased following media coverage of confirmed cases in Washington and other western states. The Department of Health (DOH) regularly receives requests for hantavirus information. DOH staff have given many presentations to groups with occupational exposure concerns including biologists, mammalogists, foresters, and pest control exports.

The CDC has issued prevention measures to reduce exposure to rodents and hantavirus in and around the home and in occupational and recreational settings (Table 1). This information has been provided to all local health jurisdictions and to state agencies that may receive inquiries or have employee exposure concerns. They include the departments of Agriculture, Fish and Wildlife, Natural Resources, State Parks, Labor and Industries, and the Washington State University Cooperative Extension Service. DOH staff have worked with the media in both Western and Eastern Washington to provide hantavirus prevention information and have written several articles for professional association newsletters.

Prevention table

Recommended Reading Centers for Disease Control and Prevention: Hantavirus infection, southwestern United States: Interim recommendations for risk reduction. MMWR 1993;42(RR-11):1-13.

Centers for Disease Control and Prevention: Newly identified hantavirus, Florida. MMWR 1994;43(6): 99-105.

Childs JE, Mills JN, Glass GE: Rodent-borne hemorrhagic fever viruses: A special risk for mammalogists? Journal of Mammalogy 1995; 76:664 680.

Childs JE, Ksiazek TG, Spiropoulou CF, et al: Serotogic and genetic identification of Peromyscus maniculatus as the primary rodent reservoir for a new hantavirus in the southwestern United States. J Infect Dis 1994;169:1271-1280.

Duchin JS, Koster FT, Peters CJ, et al Hantavirus pulmonary syndrome: A clinical description of 17 patients with a newly recognized disease. N Engl J Med 1994;330:949-955.

Nichol ST, Spiropoulou CF, Morzunov S, et al: Genetic identification of a novel hantavirus associated with an outbreak of acute respiratory illness in the southwestern United States. Science 1993; 262:914-917.

Simonsen L, Dalton M and Breiman R, et al: Evaluation of the magnitude of the 1993 hantavirus outbreak in the southwestern United States. J Infect Dis 1995;172:729-733.

Zietz PS, Butler JC,Cheek JE,et al: Epidemiology and risk factors for hantavirus pulmonary syndrome in the southwestern United States. J Infect Dis 1995;171:864 870.

Authors

John H. Grendon, D.V.M., M.PH., is an epidemiologist with Environmental Health Programs, Washington State Department of Health.

Marcia Goldoft, M.D., M.P.H., is an epidemiologist with the Office of Communicable Disease Epidemiology, Washington State Department of Health.

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Last update: 02/03/97