All 12 of the tail snip samples matched the species P. leucopus with a probability of placement between 99.1% and 99.8%. Hence, it is highly likely that the dominant species in our study sites is P. leucopus, which is consistent with the morphological determination in the field.
The total number of trap-nights for 2005, 2006, and 2007 were 1920, 2560, and 1792, respectively. In most cases only 1 mouse was captured per trap. In addition to P. leucopus, other nontarget rodents were also caught in the traps, including Tamias striatus, Clethrionomys gapperi, Microtus pinetorum, and Blarina brevicauda; blood samples were not taken from these animals. We collected and examined a total of 2142 serum samples from P. leucopus: 741 samples from 379 individuals in 2005, 941 samples from 495 individuals in 2006, and 460 samples from 282 individual mice in 2007. The average prevalence of detectable hantavirus antibody in Peromyscus was 5% (range: 0%–16%), and varied by year and site ().
Prevalence of hantavirus antibodies across three study sites over 3 years. The three sites examined were Broken Arrow (gray bars), Yellow Hickory (hatched bars), and Rothrock (white bars).
Overall, year alone was not a statistically significant factor (deviance [=sum of squares]=1.49, p=0.22), but site (deviance=39.3, p<0.001), sex (deviance=10.5, p<0.001), and the interaction between year and site (deviance=23.3, p<0.001) were significant factors; month was not significant and was deleted from the model. The overall sex ratio (male:female) was 1.27 and was not statistically different by site (deviance=3.94, p=0.14) or year (deviance=1.19, p=0.13). Overall, Rothrock had the lowest prevalence for all years (pooled across all months) with <1% of mice found positive for hantavirus-specific antibodies. Broken Arrow had the highest prevalence, with 16.1% of mice expressing hantavirus-specific antibodies in 2005; however, in subsequent years antibody prevalence dropped below 1%. In contrast, antibody prevalence remained fairly constant across all 3 years in Yellow Hickory with a range of 7.2%–10.3% ().
Mouse abundance, estimated as MNA, varied by site (deviance=61.7, p<0.001), but not year (deviance=1.85, p=0.17); however, the site–year interaction was significant (deviance=23.7, p<0.001); month was not significant and was deleted from the minimal model. An a posteriori Tukey test by site and year (pooled across all months) showed that in the first year, mouse abundance was significantly higher in Rothrock (p<0.001) and Yellow Hickory (p<0.001) than in Broken Arrow. However, there was no significant difference in mouse abundance between sites in the following year. In the third year of the study, abundance reached its highest level in Yellow Hickory, and was significantly higher than either of the two sites (p=0.01, p=0.01). The proportion of mice antibody positive for a hantavirus in a given site and year was not associated with MNA (deviance=0.03, p=0.68). Even when the site with near-zero antibody prevalence (Rothrock) was excluded from the analysis, mouse abundance still did not predict antibody prevalence (deviance=0.05, p=0.81).
Prevalence of hantavirus-specific antibodies increased linearly with mass class, which served as a proxy for age (Coefficient=0.87, standard error [SE]=0.25, p<0.001) (). Antibody prevalence was significantly higher (deviance=10.5, p<0.001) in male mice (7.1%±1.0% s.e.) than in female mice (2.7%±0.7% s.e.). Other host factors such as wounding also increased with host mass class: the data fit a second-order polynomial function (linear coefficient: 1.22, SE=0.25, p<0.001; quadratic coefficient: −0.14, SE=0.04, p<0.001) (). Wounding, however, was not correlated with host sex (linear coefficient: 0.12, SE=0.14, p=0.36). Although incidence (proportion of mice found positive for the first time) increased with mass class (deviance=17.04, p<0.001), it was not directly correlated with wounding (deviance=0.15, p=0.70) (). Wounds appeared to have healed in 6% of the mice (out the 426 individuals with mutliple captures), as they were not detected in subsequent trap sessions.
Relationship between mass class (indicator for age) and incidence (proportion of first time antibody-positive mice) of hantavirus in P. leucopus. The dashed line is a fitted linear regression for hantavirus-specific antibody incidence.
The relationship between wounding status and host mass class (indicator for age). Mice were grouped into mass classes representing age groups. The dashed line represents a best fit second-order polynomial fit to the data.