Short report: Decrease in seroprevalence of antibodies to hantavirus in rodents from 1993-1994 hantavirus pulmonary syndrome case sites.

Rodent trapping was conducted at seven hantavirus pulmonary syndrome (HPS) case sites from June 1993 to March 1994 during the HPS outbreak in the southwestern United States. To determine if there were changes in the rodent population or the hantavirus seroprevalence in rodents since the HPS outbreak, rodents were trapped at the same sites three years later using the same trapping protocol. The trap success decreased from the numbers trapped during the outbreak, however, the number of Peromyscus, as a percentage of the total rodents captured, did not noticeably decrease. In addition, the seroprevalence of hantavirus antibodies in Peromyscus decreased significantly (P , 0.0001). The outbreak of hantavirus pulmonary syndrome (HPS) in the Four Corners region in mid-1993 to early 1994 was linked to an increase in the number of rodents in the area. 1, 2 Rodent trapping and serologic testing led to the identification of Peromyscus maniculatus,the deer mouse, as the primary reservoir for the etiologic agent of HPS in the western Unit- ed States, now known as Sin Nombre virus. 3 Peromyscus mice trapped at HPS case sites had hantavirus seropreval- ence rates of up to 64%. To obtain a point-in-time estimate of changes in rodent density and hantavirus antibody sero- prevalence, seven of these sites were retrapped three years later, using the same trapping and testing protocol. 3, 4 Four of these locations are in Colorado and three are in Arizona. Follow-up trapping sessions were conducted during the same week of the year and in the exact location and manner as the original trapping sessions. Trapping teams from the two respective state health departments included at least one person who trapped during both time periods at each loca- tion. The number of traps used ranged from 80 to 100 per night for 2-4 nights. Sherman t-style box traps (H. B. Sher- man Trap Co., Tallahassee, FL) and Tomahawkt-style cage traps (Tomahawk Trap Co., Tomahawk, WI) baited with oats and peanut-butter were laid around the perimeter of the homesite and in north, south, east, and west transect lines extending out from the homesite. Rodent processing was done according to previously described methods. 4 Rodent sera were tested for hantavirus antibodies by using an ELISA previously described. 3, 4 Testing of the 1993 and 1994 sam- ples was done by the Centers for Disease Control and Pre- vention (CDC) in Atlanta, Georgia, whereas testing of the later samples was accomplished by CDC-trained laboratory personnel at the individual state health departments. In 1993-1994, during the original HPS outbreak, a total of 233 rodents from 1,803 trapnights (12.9% trap success) were trapped at these seven case sites, of which 145 (62.2%) were Peromyscus mice (Table 1). Fifty-seven (40.4%) of the Peromyscus were seropositive for antibodies to hantavirus (seroprevalence range