Update: Outbreak of Hantavirus Infection -- Southwestern United States, 1993

Since May 1993, the New Mexico Department of Health, the Arizona Department of Health, the Colorado Department of Health, the Utah Department of Health, the Indian Health Service, and CDC, with the assistance of the Navajo Nation Division of Health, have been investigating an outbreak of illness associated with hantavirus infection (1,2). This report updates information regarding the relation between illness and infection with a previously unrecognized hantavirus.

Through June 21, laboratory evidence of hantavirus infection had been confirmed in 12 patients meeting the case definition (2); of these, nine (75%) persons have died. Of the 12 cases, nine occurred in New Mexico, two in Arizona, and one in Colorado. Ten (83%) cases occurred in persons aged 20-40 years. Similar illnesses in an additional 20 persons, eight of whom died, are being investigated for possible hantavirus infection. As of June 21, cases of acute illness associated with hantavirus infection had been documented only in persons residing in Arizona, Colorado, and New Mexico.

The laboratory evidence of hantavirus infection in the 12 case-patients includes demonstration of antibody to hantavirus antigens (eight case-patients), immunohistochemical evidence of hantavirus antigen in autopsy specimens (five case-patients), and amplification of hantavirus-specific RNA sequences by polymerase chain reaction (PCR) performed on RNA extracted from autopsy specimens (three case-patients). Hantavirus-related antigens were immunohistochemically detected in formalin-fixed lung and kidney tissue using a monoclonal antibody that cross-reacts with conserved hantavirus nucleoprotein epitopes (3). Immunostaining did not occur when a battery of other hantavirus-specific monoclonal and polyclonal antibodies was used for case-patients. Immunostaining did not occur with any of the monoclonal antibodies for tissue from seven persons who died from other illnesses.

Since June 6, 191 animals of 12 species have been collected from peridomestic settings in areas where cases have occurred and tested for evidence of hantavirus antibodies at CDC. Hantavirus antibodies were present in 32 (30%) of 107 deer mice (Peromyscus maniculatus), one (9%) of 11 piĺon mice (P. truei), and one (2%) of 48 chipmunks (Eutamias dorsalis).

Hantavirus sequences from nine (75%) of 12 antibody-positive Peromyscus rodents have been amplified using PCR. Nucleotide sequence analysis of amplified DNA products from three PCR-positive humans and six PCR-positive Peromyscus rodents are closely related and provide a direct genetic link between the hantavirus sequence in the rodents and in the human case-patients.

Reported by: F Koster, MD, H Levy, MD, G Mertz, MD, A Cushing, MD, S Young, PhD, K Foucar, MD, J McLaughlin, PhD, B Bryt, MD, Univ of New Mexico School of Medicine, T Merlin, MD, Lovelace Medical Center, Albuquerque; R Zumwalt, MD, P McFeeley, MD, K Nolte, MD, New Mexico Office of the Medical Investigator; MJ Burkhardt, MPH, Secretary of Health, N Kalishman, MD, M Gallaher, MD, R Voorhees, MD, M Samuel, DrPH, M Tanuz, G Simpson, MD, L Hughes, PhD, E Umland, MD, G Oty, MS, L Nims, MS, CM Sewell, DrPH, State Epidemiologist, New Mexico Dept of Health. R Levinson, MD, F Yerger, MD, B Allan, MD, Scottsdale; P Rubin, Phoenix; L Sands, DO, K Komatsu, MPH, C Kioski, MPH, K Fleming, MA, J Doll, PhD, C Levy, MS, TM Fink, P Murphy, B England, MD, M Smolinski, MD, B Erickson, PhD, W Slanta, G Gellert, MD, State Epidemiologist, Arizona Dept of Health Svcs. P Shillam, MSPH, RE Hoffman, MD, State Epidemiologist, Colorado Dept of Health. S Lanser, MPH, CR Nichols, MPA, State Epidemiologist, Utah Dept of Health. L Hubbard-Pourier, MPH, Div of Health, Navajo Nation, Window Rock, Arizona. J Cheek, MD, A Craig, MD, R Haskins, MPH, B Muneta, MD, B Tempest, MD, M Carroll, MD, LA Shands, MPH, JP Sarisky, MPH, RE Turner, L White, P Bohan, MS, Indian Health Svc. Div of Field Epidemiology, Epidemiology Program Office; National Center for Environmental Health; Div of Bacterial and Mycotic Diseases, Div of Vector-Borne Infectious Diseases, Scientific Resources Program, and Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The patterns of cross-reactivity in the human convalescent and rodent serum specimens, the pattern of immunohistochemical reactivity, and the clinical syndrome in which adult respiratory distress syndrome is a prominent feature of the disease (1,2) suggest that a previously unrecognized hantavirus is responsible for this outbreak. Additional studies of sequences from the viral genome and studies of the virus, once it is isolated, will be necessary for further characterization of the agent.

The high prevalence of hantavirus antibodies in the deer mice and the similarity of PCR products in the deer mice and human case-patients suggest that this species may be involved in hantavirus transmission to humans. Studies of other rodent species have been initiated. P. maniculatus is distributed in all parts of the United States, except in the Southeast (4). Although serologic evidence of hantavirus infection was detected during 1985 in 11 (5%) of 218 P. maniculatus rodents collected from California, Colorado, and New Mexico (5), additional studies are needed to determine the current distribution of hantavirus infection in Peromyscus species in the United States.

Previously described transmission of hantavirus infection has been associated with exposure to rodent excreta and saliva; evidence thus far suggests rodents also are likely the primary source of infection for the hantavirus associated with this outbreak. Reports concerning previously identified hantaviruses have not documented person-to-person transmission of these viruses, nor has there been evidence of person-to-person transmission in the current outbreak. Nonetheless, an investigation of contacts of case-patients, including health-care workers, has been initiated along with other studies of risk factors for infection in this outbreak.

The findings implicating a hantavirus in this outbreak and knowledge regarding modes of hantavirus transmission support the previous recommendation that restriction of travel to areas affected by this outbreak is not considered necessary. However, activities that may disrupt rodent burrows or result in contact with rodents or aerosolization of rodent excreta should be avoided (1).

References

1. CDC. Outbreak of acute illness -- Southwestern United States, 1993. MMWR 1993;42:421-4.

2. CDC. Update: outbreak of hantavirus infection -- Southwestern United States, 1993. MMWR 1993;42:441-3.

3. Ruo S, Sanchez AS, Elliot LH, et al. Monoclonal antibodies to three strains of hantaviruses: Hantaan, R22, and Puumula. Arch Virol 1991;119:1-11.

4. Hall RE. Peromyscus maniculatus. In: Mammals of North America. 2nd ed. New York: Wiley, 1981:670-83.

5. Tsai TF, Bauer SP, Sasso DR, et al. Serological and virological evidence of a Hantaan virus-related enzootic in the United States. J Infect Dis 1985;152:126-36.

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