Assessment of ecologic and biologic factors leading to hantavirus pulmonary syndrome, Colorado, U.S.A.

AIM: To understand the ecologic parameters of Sin Nombre virus (SNV; family Bunyaviridae, genus Hantavirus) infections in the deer mouse (Peromyscus maniculatus), environmental variables impacting the rodent populations, and the conditions under which SNV is amplified. This may help us understand the antecedents of human risk for developing hantavirus pulmonary syndrome (HPS) as a consequence of SNV infection. METHOD: Each 6 weeks, we trapped, measured, tagged, bled, and released rodents at three widely spaced sites in Colorado, USA: Fort Lewis (1994-2001), Molina (1994-2001), and Pinyon Canyon Maneuver Site (1995-2001). The ELISA method was used to test rodent blood samples for IgG antibody to SNV antigen. RESULTS: Where rodent species richness was high, the prevalence of infection of deer mice (as determined by the presence of antibody) with SNV was low, and vice versa. There was a higher prevalence of antibody to SNV in male than in female rodents, and seasonal differences were observed in acquisition of SNV between male and female deer mice. Long-lived infected deer mice served as transseasonal, over-winter reservoirs for the virus, providing the mechanism for its survival. CONCLUSION: Prevalence of rodent infection appears to be associated with fluctuations in deer mouse populations and, indirectly, with timing and amount of precipitation and the resulting biologic events (a trophic cascade). Together with information regarding transseasonal maintenance of SNV, seasonal differences in acquisition of SNV between sexes, group foraging, and various other factors may expand our understanding of the risk factors for acquiring HPS. Taken together and applied, we anticipate developing methods for preventing this disease as well as diseases caused by other rodent-borne viruses.

Experimental evaluation of rodent exclusion methods to reduce hantavirus transmission to residents in a Native American community in New Mexico.

We conducted a pilot study to evaluate the efficacy of rodent proofing continuously occupied homes as a method for lowering the risk for hantavirus pulmonary syndrome (HPS) among residents of a Native American community in northwestern New Mexico. Rodent proofing of dwellings was paired with culturally appropriate health education. Seventy homes were randomly assigned to treatment or control categories. Treatment homes were rodent-proofed by sealing openings around foundations, doors, roofs, and pipes and repairing screens and windows. Repairs to each dwelling were limited to $500 US. After repairs were completed, 15-20 snap traps were placed in each treatment and control home and checked approximately every 2 days for an average of 3-4 weeks. During 23,373 trap nights, one house mouse (Mus musculus) was captured in one treatment home, and 20 mice (16 deer mice, Peromyscus maniculatus, two Pinyon mice, Peromyscus truei, and two unidentified mice) were captured in five control homes (one house had 14 captures, two had two captures, and two had one capture). Trap success was 0.01% in treatment homes and 0.15% in controls. Intensity of infestation (mean number of mice captured per infested home) was 1 in treatment homes and 4 in controls. Observations of evidence of infestation (feces, nesting material, gnaw marks, or reports of infestation by occupant) per 100 days of observation were 1.2 in treatment homes and 3.1 in controls. Statistical power of the experiment was limited because it coincided with a period of low rodent abundance (August-November 2000). Nevertheless, these results suggest that inexpensive rodent proofing of occupied rural homes can decrease the frequency and intensity of rodent intrusion, thereby reducing the risk of HPS among rural residents in the southwestern United States.