Am. J. Trop. Med. Hyg., 67(3), 2002, pp. 310–318
Copyright © 2002 by The American Society of Tropical Medicine and Hygiene
INFECTION DYNAMICS OF SIN NOMBRE VIRUS AFTER A WIDESPREAD
DECLINE IN HOST POPULATIONS
JOHN D. BOONE, KENNETH C. MCGWIRE, ELMER W. OTTESON, ROBERT S. DEBACA, EDWARD A. KUHN,
STEPHEN C. ST. JEOR
Department of Microbiology, University of Nevada Reno; Desert Research Institute, Reno, Nevada
AND
Abstract. Many researchers have speculated that infection dynamics of Sin Nombre virus are driven by density
patterns of its major host, Peromyscus maniculatus. Few, if any, studies have examined this question systematically at a
realistically large spatial scale, however. We collected data from 159 independent field sites within a 1 million-hectare
study area in Nevada and California, from 1995–1998. In 1997, there was a widespread and substantial reduction in host
density. This reduction in host density did not reduce seroprevalence of antibody to Sin Nombre virus within host
populations. During this period, however, there was a significant reduction in the likelihood that antibody-positive mice
had detectable virus in their blood, as determined by reverse-transcriptase polymerase chain reaction. Our findings
suggest 2 possible causal mechanisms for this reduction: an apparent change in the age structure of host populations and
landscape-scale patterns of host density. This study indicates that a relationship does exist between host density and
infection dynamics and that this relationship concurrently operates at different spatial scales. It also highlights the
limitations of antibody seroprevalence as a metric of infections, especially during transient host-density fluctuations.
mechanisms by which host density may influence natural infection dynamics is poorly understood. Most studies to date
have failed to detect a clear linear correlation between concurrently measured host density and antibody seroprevalence
(i.e., percent of animals with antibody to SNV) at local sampling sites.4–5,9 There are reported exceptions to this pattern,
although they typically are based on data from a few sites.10,11
In 1995–1998, we conducted field studies to characterize
the ecology of the deer mouse/SNV system in the Walker
River Basin of Nevada and California.5,15 Our study design
emphasized sampling many independent sites to capture the
ecologic diversity present within our study area, as opposed to
more intense study of a few sites. This article addresses the
effects of a 1-year, large-scale decline in host density on SNV
infection patterns. Although other Peromyscus species that
can host SNV were present within our study area, deer mice
were the only species that occurred at most sites (see Appendix), and we focus on them. In addition to testing blood from
all captured deer mice for antibody to SNV, we tested a subset of blood samples for SNV RNA, which more accurately
indicates an acute, relatively new infection. In this article, we
make a distinction between these acute (i.e., highly transmissible) infections and low-grade chronic infections that seem to
persist for life after animals have cleared virus from the blood.
Current evidence suggests that virus titers are much higher in
mice during the initial acute phase and that human exposure
to SNV and rodent-to-rodent transmission occur primarily
during this period.6 We also distinguish between the local
spatial scale (which we define as the area sampled by a single,
typical live-trapping site, within which all rodents have the
opportunity to interact) and the large, or regional, spatial
scale (an area at least several orders of magnitude greater
than a local site, with component local host populations exhibiting varying degrees of contact with neighboring populations).
INTRODUCTION
In 1993, an unexplained respiratory distress syndrome was
reported in the Four Corners area of the southwestern United
States, ultimately resulting in a few dozen human fatalities.
Sin Nombre virus (SNV), a previously unknown hantavirus
(family Bunyaviridae), was rapidly identified and confirmed
as the causative agent of the human disease, hantavirus pulmonary syndrome (HPS).1,2 The primary natural hosts of
SNV were found to be rodents of the genus Peromyscus,
especially the deer mouse, Peromyscus maniculatus.2,3 Humans were thought to become infected primarily by inhaling
aerosolized rodent excreta containing infectious virus. Subsequent field studies revealed that SNV is widespread and common in deer mouse populations across much of the species’
geographic range.4,5 Further investigations revealed that deer
mice infected with SNV experience an initial acute phase,
when SNV is most likely to be shed in blood, urine, and saliva.
This phase is followed by a chronic low-grade infection without severe pathology, during which virus seems to be absent
in the blood but is present at relatively low levels in several
organs.6 Other New World hantaviruses similar to SNV have
been found in other rodent hosts (some of which may cooccur with deer mice), but only a subset of these viruses are
known to produce human disease.7 Since 1993, >240 human
cases of HPS have been confirmed in the United States, with
a mortality rate of approximately 40% (Mills J, Centers for
Disease Control and Prevention, personal communication).
HPS outbreaks comparable to the original 1993 incident
have not recurred in the United States, although large outbreaks attributed to other hantaviruses have been reported in
South America.8 Given the relatively sporadic nature of HPS
cases since 1993 and concerns about future outbreaks, there is
interest in documenting and understanding the temporal dynamics of this host-virus system. Field studies conducted after
the initial outbreak indicated that SNV infection patterns are
variable over time at some sites but are relatively stable at
others.5,9–11 It has been suggested that variations in infection
rates within host populations or risk of human exposure to
hantaviruses may be a function of host-density patterns.7,12–14
Although it seems logical that elevated host density increases
the opportunities for human-rodent contact, the specific
METHODS
Study area and site selection. The Walker River Basin of
Nevada and California (1.02 million hectares) is located south
of Reno, Nevada, and northeast of Yosemite National Park
(Figure 1). At least 10 cases of HPS have occurred in or near
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HOST POPULATIONS AND SIN NOMBRE VIRUS
FIGURE 1. Location of the Walker River Basin study area (heavy
outline) within the Great Basin (shaded area).
Walker River Basin since 1993. The eastern half of the study
area comprises the arid basin-and-range topography typical of
much of Nevada, whereas the western portion extends
through foothills to the crest of the Sierra Nevada range.
Ecologic diversity within Walker River Basin is substantial.
Major habitat types associated with ascending elevations
(1,200–3,760 m) include salt desert scrub, sagebrush-grass
steppe, pinyon-juniper woodland, coniferous forest, montane
shrubland, and limited amounts of alpine tundra at the highest elevations. Riparian habitat and meadows occur across a
wide range of altitudes.
To sample systematically a wide range of the ecologic variability present within this region, field-sampling sites were
selected using a geographic information system that incorporated remotely sensed data, elevation maps, and vegetation
maps. Each of the 8 major vegetation types (see earlier) was
subdivided into a number of strata, each representing a
unique combination of above-median or below-median values
for altitude, slope, vegetation density, vegetation structure,
and distance from stream corridors. During each year, sample
sites were selected randomly within each of these strata (see
Boone et al15 for complete details). Because this procedure
was repeated exactly for every year, each year’s data set represents an unbiased, randomized-stratified sample of the entire study area. In 1995, 42 sites were sampled; 92 sites were
sampled in 1996; 47 sites were sampled in 1997; and 46 sites
were sampled in 1998. Sample size among years differed (especially 1996) because of varying availability of resources and
trained technical personnel and the demands of other ongoing
studies. Although most sites were sampled only once, 41 were
sampled in ⱖ2 years, including 11 that were sampled longitudinally (multiple times within ⱖ2 years). Thus, our total of
159 independent sites over the 4 years is less than the sum of
each year’s sample size. The positions occupied in the sampling stratification by the repeat-visit sites were withdrawn
when selecting new sites for each year. Results from multiple
311
visits to longitudinally sampled sites within a given year were
averaged to produce a single data point for that year so that
these sites did not exert disproportionate influence.
Live-trapping and collection of blood samples. Field sampling during each year (1995–1998) occurred in June–
September. Rodents at every site were live-trapped according
to a standardized protocol. A total of 48 Ugglan (Grahnab,
Marieholm, Sweden) mesh live-traps were used at each trapping site, placed in 2 identical subgrids that were separated by
70 m. Two subgrids were used to characterize each site to
avoid reliance on a single, potentially atypical, habitat patch.
Each subgrid had 24 traps in a 6 × 4 pattern with 10-m spacing
between traps. Results from subgrid pairs were combined to
produce site-level data. Traps were operated for 2–5 days,
depending on capture success. We standardized our estimate
of population density of deer mice by counting only the number of unique animals captured during the first 2 days of
trapping (i.e., relative density; see Slade and Blair20 for justification and rationale for this approach). Therefore, our
relative, standardized estimates of population density were
sometimes lower than the actual number of individual animals that were captured and processed on a given site. After
weighing, sexing, and species identification, a blood sample
was collected from each deer mouse (and other potential
SNV hosts) at the trap station by retro-orbital puncture with
a heparinized capillary tube or Pasteur pipette. Animals were
marked with ear tags or fur clips to avoid collection of duplicate blood samples in later days of the trapping session. Rodents were released at point of capture. Blood samples were
placed immediately on dry ice until they could be returned to
the laboratory for analysis.
Laboratory analysis. Every blood sample was tested for antibody to SNV by enzyme-linked immunosorbent assay
(ELISA), using SNV recombinant antigen and secondary antibody developed at the Centers for Disease Control and Prevention (Atlanta, GA).21 Each sample was paired with a
negative control sample using negative recombinant antigen,
and each ELISA plate was run with a known positive control
sample. All details of ELISA testing and evaluation procedures are given in Otteson et al.22
We also tested a subset of samples for the presence of virus
RNA in the blood using reverse-transcriptase polymerase
chain reaction (RT-PCR). We initially tested antibodypositive and antibody-negative samples. By the end of 1996,
we found only 16 of 673 samples from antibody-negative rodents that were positive by RT-PCR (2.4%) (see Boone et al5
and Rowe et al23 for further discussion). Because of these
results and the expense and time involved in PCR testing, we
concentrated thereafter on testing randomly selected subsets
of antibody-positive samples, which are the focus of this article. Positive ELISA tests have been reported to have a concordance of 50–70% with the presence of virus RNA in blood
as determined by RT-PCR in previous studies,22,23 but we
suspected that this rate might vary considerably at different
sites depending on whether an acute infection exists. RNA
extraction and RT-PCR were conducted according to the protocols in Rowe et al.23 To avoid RNA template or PCR product cross-contamination, RNA extraction and purification
was conducted in a biohazard containment hood in a biosafety level 3 laboratory, and RT-PCR reactions were performed in a biohazard containment hood in a separate laboratory. Previously designed primer sets specific to Nevada
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BOONE AND OTHERS
SNV sequences were used.23 To confirm positive results, purified PCR products were sequenced directly by dye deoxy
automatic sequencing23 (ABI Prism 310 automatic sequencer,
Applied Biosystems, Foster City, CA).
Data analysis. Data sets from each year were compared
with one another with regard to host relative density, mean
animal weight, sex ratio, percent juveniles, antibody prevalence, and frequency of positive RT-PCR results in antibodypositive animals. Among-year sampling bias was minimized
by the randomized-stratified site selection criteria that were
used every year, as described earlier. Antibody prevalences
were calculated for each individual sampling site (number
animals positive/number animals tested), and a mean prevalence was calculated for each year. For the sites that were
sampled more than once in a given year, raw data were combined to produce a single value for overall antibody prevalence and mean relative density for that site and year. Analysis of variance (ANOVA), Kruskal-Wallis tests, and categorical analyses with multiple comparisons were used to compare
variables among years (Systat version 9, SPSS Science, Chicago, IL). Variables that were candidates for parametric procedures (ANOVA) were evaluated for normality using the
tests and criteria provided in Systat 9 (skewness/skewness SE;
kurtosis/kurtosis SE). Weight of adult deer mice was acceptably normal, and relative density became acceptably normal
for a robust parametric procedure (ANOVA) after a squareroot transformation ([relative density + 1]1/2). Antibody
prevalence could not be transformed to an acceptable approximation of normality and was tested nonparametrically
(Kruskal-Wallis test). RT-PCR results, sex ratios, and percent
juveniles were frequency counts that were tested using ␹2
procedures with multiple comparisons.24 Finally, to allow
graphic examination of temporal trends, relative density and
antibody seroprevalence were plotted over time for the 18
sites that were sampled in ⱖ3 years.
RESULTS
We collected 3,577 blood samples from deer mice during
the study. Yearly data on relative density, antibody prevalence, RT-PCR results, host demography, and site status are
summarized in Table 1. In 1997, we observed a substantial
decline in deer mouse density across our entire study area.
Mean relative density of deer mice in 1997 was less than one
third that of any other year (Table 1, Figure 2A) (one-way
ANOVA on transformed data, F ⳱ 8.70, P < 0.001). According to pairwise multiple comparisons with Bonferronicorrections, relative density in 1997 differed from all other
years (P < 0.007 for all comparisons), but 1995, 1996, and 1998
were statistically equivalent to one another. Mean antibody
prevalence of sampling sites did not differ among years
(Kruskal-Wallis test statistic ⳱ 1.929, P ⳱ 0.59), contrary to
a priori expectations. It was higher in 1997 (the low-density
year) than in other years.
A total of 226 antibody-positive samples (from different
individual rodents) were tested by RT-PCR for virus RNA in
the blood (21 from 1995, 99 from 1996, 75 from 1997, and 31
from 1998). There was a significant and substantial drop in
1997 in the frequency of antibody-positive animals that were
positive by RT-PCR (Table 1) (Pearson ␹2 ⳱ 19.74, P < 0.01).
A multiple comparison procedure for proportions from Zar24
indicated that RT-PCR prevalence among antibody-positive
deer mice was significantly lower in 1997 than in any other
year (P < 0.001 for all 3 comparisons), but that there was no
difference between any of the normal-density years. Thus, in
1997, a significantly smaller proportion of antibody-positive
mice were experiencing an acute infection than was the case
in other years.
There was an apparent change in host age structure in 1997,
relative to other years. Mean weight of adult deer mice was
significantly different among years, with the highest weight
occurring in 1997 (Table 1) (one-way ANOVA, F ⳱ 51.67, P
< 0.001). Pairwise multiple comparison procedures with Bonferroni-corrections indicated that weights differed among all
pairs of years (P < 0.001) except for 1995 versus 1998. Ratio
of males in each year varied between 47.5% and 55.9%, and
ratios of juveniles varied from 12.6–17.7% (Table 1). Differences in these variables among years were significant (Pearson ␹2 ⳱ 8.38, P ⳱ 0.04 for sex ratio; ␹2 ⳱ 22.53, P < 0.001
for juveniles) but did not seem to be associated with the population decline of 1997 (Table 1).
DISCUSSION
Major findings. In 1997, when population densities of deer
mice were relatively low across the entire study region, there
was a significant reduction in the frequency of acute infections among antibody-positive animals, although antibody
TABLE 1
Yearly summaries of deer mouse relative density (number of unique animals caught per site during the first 2 days of trapping), mean antibody
(AB) prevalence, site infection status based on antibody results, proportion of antibody-positive animals that were positive by RT-PCR, mean
weight of adult deer mice, sex ratios, and percent juveniles*
Year
Mean density
Mean AB prevalence
Total no. sites (sample size)
No. AB-positive sites (%)
No. AB-negative sites (%)
No. sites without deer mice (%)
Proportion of AB-positive animals that
were RT-PCR positive (%)
Mean weight of adults
Sex ratio (% male)
Percent juveniles
1995
1996
1997
1998
11.1 [10.9]
0.16 [0.19]
42
22 (52%)
16 (38%)
4 (10%)
13/21
(62%)
17.8 (n ⳱ 446)
55.9 (n ⳱ 528)
12.6 (n ⳱ 549)
10.3 [10.4]
0.18 [0.16]
92
59 (64%)
22 (24%)
11 (12%)
49/99
(49%)
16.8 (n ⳱ 1,031)
49.9 (n ⳱ 1,212)
13.8 (n ⳱ 1,207)
2.4 [3.2]
0.22 [0.23]
47
21 (45%)
12 (26%)
14 (30%)
19/75
(25%)
19.5 (n ⳱ 371)
47.5 (n ⳱ 455)
17.7 (n ⳱ 452)
8.9 [9.9]
0.17 [0.20]
46
23 (50%)
12 (26%)
11 (24%)
20/31
(65%)
17.6 (n ⳱ 1,099)
49.6 (n ⳱ 1,340)
17.4 (n ⳱ 1,337)
* SDs of relative density and antibody prevalence are given in brackets. Number of antibody-positive mice tested by RT-PCR each year is in the denominator of the proportions. Sample sizes
for weight, sex ratio, and percent juveniles are listed for each year. Although most animals had their weight, sex, and age assessed, occasional escapes or ambiguous cases resulted in partial data
for a few animals. Results of all statistical comparisons are given in the text.
HOST POPULATIONS AND SIN NOMBRE VIRUS
313
FIGURE 2. Yearly trends for (A) relative density and (B) antibody seroprevalence, using only the 18 sites that were sampled in ⱖ3 years. Each
line represents the trajectory of 1 site over time.
prevalence itself did not decline. Synchronous fluctuations in
the density of deer mice and other rodents across large regions were noted previously,16–18 but there is no universally
accepted theory for their causal mechanisms. Similarly the
cause of the 1997 decline is unknown, but we speculate that it
resulted from climatic conditions that negatively affected production of preferred food sources (insects or seeds).19 The
increased mean weight of adult animals in 1997 suggested that
younger animals born in later 1996 experienced unusual mortality in the winter of 1996–1997, whereas older, heavier animals survived at higher rates. An alternative explanation
would be that surviving animals were not age biased but
gained weight more rapidly in early 1997 than typically would
be the case. We consider the first explanation more likely,
given the general association between weight and age in these
relatively short-lived animals. Older, heavier, and more experienced animals, with better-established home ranges, might
easily have a survival advantage during food shortages or
other unusually stressful periods. Older animals are more apt
to have experienced past infections than younger animals,
leaving them antibody-positive and RT-PCR negative.4,5 If
such differential survival occurred in 1996–1997, the resulting
enrichment of host populations in previously infected animals
could have contributed to the reduction in the frequency of
acute infections (a second possible explanation is given subsequently). Eventually, reproduction in 1997 restored a more
typical balance of previously infected versus susceptible animals, and by 1998, frequency of acute infections returned to
more normal levels.
Differences existed among years with regard to sex ratio
and percent juveniles (especially for 1995). Based on the extent and the chronology of these differences, however, it is
not clear that they were related to the population decline of
1997 (Table 1). It is possible that changes in sex ratio and
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BOONE AND OTHERS
percent juveniles reflected the operation of distinct demographic processes. The statistical analyses of weight, sex ratio,
and percent juveniles were based on data sets characterizing
individual animals (not trapping sites) and involved large
sample sizes (Table 1). Larger sample sizes make statistical
tests increasingly sensitive to small differences, and the results
of these analyses should be interpreted with this in mind.
Effects of spatial scale. The relationship between temporal
host-density patterns and acute SNV infections was apparent
when we combined data from all of our sites to characterize
the entire study region as a single entity. When we previously
looked for similar relationships at the local scale, however, we
found no significant results using either ELISA or RT-PCR
data.5 Most other studies of local site dynamics also failed to
find clear relationships between host density and infections,
although there are exceptions.4–5,9–11 It is suggested that
changes in host density must occur at sufficiently large spatial
and temporal scales before predictable changes in infection
dynamics occur. We hypothesize that large-scale and relatively synchronous fluctuations in host density can affect infection dynamics by altering the efficiency with which infections can travel across space, from recently infected to susceptible populations. During unfavorable periods, host
animals often disappear from marginal sites (Table 1), leaving
surviving populations more isolated from one another than
would otherwise be the case. Without a pathway occupied by
susceptible animals, infections are more likely to be contained
effectively in these local pockets, and infection-free populations have a decreased likelihood of becoming infected. Under this scenario, specific host-density levels within a local
area may be relatively unimportant because the likelihood of
an acute infection being present is determined by the hostdensity patterns of surrounding regions through which a potential infection initially must pass. Studies attempting to relate variations in local host density (within a normal-density
year) to variations in antibody prevalence generally would fail
to find a relationship. This possibility deserves additional consideration because most SNV field studies to date have focused on longitudinal sampling of one or a few local sites, a
technique that might not efficiently capture large-scale dynamics of host populations. This hypothesized mechanism requires a host animal with limited dispersal capabilities (such
as a rodent) that cannot travel easily between isolated populations.
Limitations of the antibody prevalence metric. Antibodypositive status of animals at a local site can indicate any combination of acute infections, recent infections, or low-grade
chronic infections that presumably pose little risk of transmission to humans or other rodents. Although antibody prevalence is an undeniably useful measurement, it has limitations
in terms of assessing risk of human exposure or likelihood of
rodent-to-rodent transmission. Specifically, during periods of
unusual host population density, the normal interpretation of
a given antibody prevalence value may need to be reevaluated. In 1997, a serologic study would have found no
significant changes in SNV infection patterns. An atypically
high proportion of deer mice were in the chronic low-grade
state (i.e., virus RNA not present in blood), however, presumably as a result of infections initiated in 1996 or earlier.
Because of its postinfection temporal inertia, an analysis relying only on antibody prevalence might fail to detect the true
impact of population fluctuations on infection dynamics. If
major shifts in host population density were maintained over
a long period, however, we would expect antibody prevalence
eventually to reflect the associated changes in infection dynamics. The antibody response experiences only a brief temporal inertia (of approximately 1 month)5 before accurately
reflecting newly initiated infections. Thus, there is relatively
little risk of misinterpreting the meaning of a low antibody
prevalence, unless the sampling period is short.
Conclusions. There has been considerable speculation and
discussion about the potential effects of host-density fluctuations on SNV infections. This study provides the first spatially
extensive description, using RT-PCR and ELISA data, of the
nature of these effects. Specifically, large-scale population declines seem to affect not only the likelihood of rodent-human
encounters, but also the likelihood that a given encounter
involves a rodent that is shedding large amounts of virus. The
strength of this relationship would be expected to degrade
progressively at smaller scales of spatial resolution, at least in
landscapes characterized by heterogeneous patterns of host
population density. We would expect large-scale increases in
population density initially to produce a significant increase in
the frequency of acutely infected animals, with increases in
antibody prevalence lagging behind by approximately 1
month.5,23 Carefully designed and fortuitous field studies
might capture a wave of increasing disease prevalence as it
travels from an initial focal point.
Given the ecologic complexity of this host-virus system,
additional well-replicated and spatially extensive studies need
to be conducted in different geographic regions during host
population fluctuations. The deer mouse uses an unusually
wide variety of habitats and biomes, where it exhibits considerable demographic, ecologic, behavioral, and physiologic
plasticity, all of which presumably can affect susceptibility to
infections and the likelihood of virus transmission. Further
complications occur in regions where multiple hosts for SNV
frequently coexist (i.e., the southwestern United States). Only
a meta-analysis of several robust studies ultimately can confirm the general properties of SNV/host dynamics and the
effects of host-density fluctuations. We believe that our study
can serve as a model for further investigations of these questions.
Acknowledgments: The authors thank Dale Netski, Joan Rowe, and
Monica Borucki for laboratory analysis and advice, and Joe Blattman
and Pascal Villard for extensive field work.
Financial support: This work was supported by NIH grants R01
AI36418-04 to Stephen C. St. Jeor and F32 AI09621 to John D.
Boone. We thank NIH for its past and continuing support.
Authors’ addresses: John D. Boone, Elmer W. Otteson, and Stephen
C. St. Jeor, Department of Microbiology/320, University of Nevada
Reno, Reno, NV 89557, Telephone: 775-784-6161. Kenneth C. McGwire, Division of Earth and Ecosystem Sciences, Desert Research
Institute, 2215 Raggio Parkway, Reno, NV 89512. Robert S. DeBaca,
Department of Biologic Sciences, Texas Tech University, Lubbock
TX 79409. Edward A. Kuhn, Washington State University, School of
Molecular Biosciences, PO Box 644234, Pullman, WA 99164-4234.
Reprint requests: John D. Boone, Department of Microbiology/320,
University of Nevada Reno, Reno, NV 89557, E-mail: boone@
unr.nevada.edu
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Otteson EW, Riolo J, Rowe JE, Nichol ST, Ksiazek TG, Rollin
TG, St. Jeor SC, 1996. Occurrence of hantavirus within the
rodent population of northeastern California and Nevada. Am
J Trop Med Hyg 54: 127–133.
Rowe JE, St. Jeor SC, Riolo J, Otteson EW, Monroe MC, Henderson WW, Ksiazek TG, Rollin PE, Nichol ST, 1995. Coexistence of several novel hantaviruses in rodents indigenous to
North America. Virology 213: 122–130.
Zar JH, 1984. Biostatistical Analysis, 2nd ed. Englewood Cliffs,
NJ: Prentice-Hall, 401–402.
APPENDIX 1
SITE-LEVEL DATA USED FOR THIS STUDY, PLUS DATA FOR POTENTIAL SNV CARRIERS THAT WERE
CAPTURED AND TESTED BUT NOT OTHERWISE DISCUSSED, GROUPED BY YEAR
Grid
Visits/
Year
Year
PM
Density
PM
Sampled
PM
Positive
PM
AB%
PT
Density
PT
Sampled
PT
AB%
PC/B
Density
PC/B
Sampled
PC/B
AB%
1
2
3
4
8
9
10
11
12
13
14
15
16
17
18
19
20
23
24
25
26
27
28
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
9
3
1
6
3
6
0
0
12
25
13
39
4
10
5
8
4
7
19
14
16
8
18
12
2
1
10
3
6
0
0
12
22
13
37
3
11
5
13
4
6
7
12
14
8
15
0
0
0
0
0
0
0
0
6
12
4
13
0
2
2
1
2
2
1
4
4
1
4
0.00
0.00
0.00
0.00
0.00
0.00
—
—
0.50
0.55
0.31
0.35
0.00
0.18
0.40
0.08
0.50
0.33
0.14
0.33
0.29
0.13
0.27
23
1
0
4
0
6
1
3
0
0
0
0
2
0
0
0
0
0
0
0
0
0
0
22
1
0
4
0
6
1
2
0
0
0
0
2
0
0
0
0
0
0
0
0
0
0
0.00
0.00
—
0.25
—
0.00
1.00
0.00
—
—
—
—
0.50
—
—
—
—
—
—
—
—
—
—
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
316
BOONE AND OTHERS
APPENDIX 1
(CONTINUED)
Grid
Visits/
Year
Year
PM
Density
PM
Sampled
PM
Positive
PM
AB%
PT
Density
PT
Sampled
PT
AB%
PC/B
Density
PC/B
Sampled
PC/B
AB%
29
30a
30b
31
32
33
34
35
36
37
D1
D2
D3
H1a
H1b
H2
R1
R2
R3
1
4
13
14
15
23
24
26
30a
30b
31
42
44
45
46
47
50
51
53
54
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
76
80
81
83
84
85
87
88
89
90
91
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
4
4
1
1
1
1
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
95
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
5
16
36
1
1
0
12
3
1
0
10
18
8
46
6
8
29.25
18.25
18
6
26
3
4.5
10.5
6
29
36
22
36
2
0
27
9
2
1
3
21
4
24
6
8
12
16
15
6
17
18
17
5
8
4
6
13
5
0
7
2
40
0
0
1
3
1
10
1
4
1
47
5
3
6
15
1
1
0
12
3
1
0
11
20
7
21
3
7
121
84
17
6
21
3
12
26
6
28
35
7
18
2
0
22
9
1
1
3
16
4
16
6
6
12
16
15
6
17
15
16
5
8
4
5
11
5
0
7
2
35
0
0
1
3
1
9
1
4
1
35
5
0
0
5
0
0
0
3
2
0
0
0
1
1
1
0
0
5
14
0
0
3
2
2
8
1
11
7
2
0
0
0
1
2
0
0
0
3
0
0
2
0
0
4
5
2
4
2
1
1
1
1
1
2
4
0
2
0
11
0
0
0
1
0
1
0
0
0
2
1
0.00
0.00
0.33
0.00
0.00
—
0.25
0.67
0.00
—
0.00
0.05
0.14
0.05
0.00
0.00
0.04
0.17
0.00
0.00
0.14
0.67
0.17
0.31
0.17
0.39
0.20
0.29
0.00
0.00
—
0.05
0.22
0.00
0.00
0.00
0.19
0.00
0.00
0.33
0.00
0.00
0.25
0.33
0.33
0.24
0.13
0.06
0.20
0.13
0.25
0.20
0.18
0.80
—
0.29
0.00
0.31
—
—
0.00
0.33
0.00
0.11
0.00
0.00
0.00
0.06
0.20
0
0
2
3
0
0
5
0
0
0
3
0
0
0
0
8
0.25
2
0
3
5
0
0
0
0
0
16
8
2
4
0
1
2
0
1
0
6
0
0
3
5
0
1
0
0
0
0
0
0
0
8
3
0
0
0
0
1
0
3
0
0
1
0
1
0
0
0
1
0
0
0
1
3
0
0
4
0
0
0
2
0
0
0
0
7
0
7
0
2
5
0
0
0
0
0
14
4
1
4
0
1
2
0
1
0
6
0
0
3
4
0
1
0
0
0
0
0
0
0
8
3
0
0
0
0
1
0
3
0
0
1
0
1
0
0
0
1
0
—
—
0.00
0.00
—
—
0.25
—
—
—
0.00
—
—
—
—
0.00
—
0.14
—
0.00
0.00
—
—
—
—
—
0.00
0.25
0.00
0.00
—
0.00
0.00
—
0.00
—
0.17
—
—
0.00
0.00
—
0.00
—
—
—
—
—
—
—
0.13
0.00
—
—
—
—
0.00
—
0.33
—
—
0.00
—
0.00
—
—
—
0.00
—
0
0
0
4
0
0
0
0
0
0
0
0
0
0
4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
—
—
—
4
—
—
—
—
—
—
—
—
—
—
2
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0.00
—
—
—
—
—
—
—
—
—
—
0.00
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
317
HOST POPULATIONS AND SIN NOMBRE VIRUS
APPENDIX 1
(CONTINUED)
Grid
Visits/
Year
Year
PM
Density
PM
Sampled
PM
Positive
PM
AB%
PT
Density
PT
Sampled
PT
AB%
PC/B
Density
PC/B
Sampled
PC/B
AB%
92
94
95
98
99
101
102
103
104
105
106
107
108
109
110
111
114
117
118
120
121
122
123
124
125
126
127
128
129
130
132
133
D1
D2
D3
H1a
H1b
H2
R1
R2
R3
T1
1
14
15
24
26
21C
21E
21N
21S
30a
30b
30E
30N
30S
30W
45
51
54
54C
54W
58
58E
58N
58S
58W
64
70
85
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
5
5
1
7
7
7
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
2
1
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
96
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
5
1
6
5
13
9
14
9
6
6
8
16
5
7
15
1
20
18
1
0
2
0
0
4
0
0
1
0
5
15
1
23
19
33.5
13
33.2
7.6
12
20.57
18.57
9.86
12
0
0
4
1.5
2.5
0
0
0
0
0
2
3
14.5
1
0.5
0
0
1
0.5
0
1.5
2.5
3.5
2.5
4
1
4
0
5
1
6
5
13
9
13
8
6
6
8
16
5
7
13
1
20
17
0
0
2
0
0
4
0
0
1
0
5
15
1
22
38
65
23
67
17
11
120
123
61
11
0
0
4
3
5
0
0
0
0
0
3
6
29
2
1
0
0
2
1
0
3
5
5
5
8
1
11
0
0
0
1
2
2
2
7
1
1
1
2
2
2
2
3
0
3
4
0
0
0
0
0
1
0
0
0
0
2
3
0
9
13
26
4
5
4
1
35
29
9
1
0
0
2
0
0
0
0
0
0
0
1
1
3
0
0
0
0
1
0
0
0
0
1
1
0
0
0
0
0.00
0.00
0.17
0.40
0.15
0.22
0.54
0.13
0.17
0.17
0.25
0.13
0.40
0.29
0.23
0.00
0.15
0.24
—
—
0.00
—
—
0.25
—
—
0.00
—
0.40
0.20
0.00
0.41
0.34
0.40
0.17
0.07
0.24
0.09
0.29
0.24
0.15
0.09
—
—
0.50
0.00
0.00
—
—
—
—
—
0.33
0.17
0.10
0.00
0.00
—
—
0.50
0.00
—
0.00
0.00
0.20
0.20
0.00
0.00
0.00
—
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
0
1
0
0
0
0
0
0
0
0
5.5
2
0.5
12.4
1.2
5
1.29
5.29
0.57
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.5
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
0
0
0
0
0
0
0
0
10
4
1
22
3
5
9
36
4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0.00
—
0.00
—
—
—
—
—
—
—
—
0.20
0.00
0.00
0.09
0.00
0.00
0.11
0.11
0.25
—
—
—
—
—
—
0.00
—
0.00
—
—
—
—
—
0.00
—
—
—
—
—
—
—
—
—
—
0.00
—
—
—
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1.2
1.6
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
3
3
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0.00
0.00
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
318
BOONE AND OTHERS
APPENDIX 1
(CONTINUED)
Grid
Visits/
Year
Year
PM
Density
PM
Sampled
PM
Positive
PM
AB%
PT
Density
PT
Sampled
PT
AB%
PC/B
Density
PC/B
Sampled
PC/B
AB%
85E
85W
86S
130
133
D1
D2
D3
H1a
H1b
H2
J1
J2
R1
R2
R3
T1
T2
T3
1
8
12
14
15
51
61
62
65
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
58N
58W
D1
D2
D3
J1
J2
J3
R1
R2
R3
T1
T2
T3
1
1
3
2
2
4
4
4
3
3
2
2
2
8
8
4
6
6
6
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
8
8
8
7
7
3
6
6
6
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
97
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
98
0
1
4.67
3
9.5
3
0.5
0.5
0.67
0
4
0
1
4.88
7.63
0.75
10.17
7.83
6
7
13
14
3
31
12
24
29
5
1
0
2
0
1
0
0
1
0
8
5
0
0
0
0
11
1
1
4
6
0
1
0
24
23
10
15
6
3.88
6.75
20.63
16.57
14.57
1.33
29
23.67
34.33
0
1
24
9
22
11
2
2
1
0
8
0
2
38
59
3
79
60
40
7
22
14
5
31
12
33
40
5
0
0
2
0
1
0
0
1
0
8
5
0
0
0
0
11
1
1
4
4
0
1
0
24
23
15
24
9
35
51
167
112
93
4
191
159
226
0
1
8
1
6
4
1
1
0
0
1
0
1
13
18
0
31
14
11
1
4
2
0
4
1
4
5
0
0
0
2
0
0
0
0
0
0
0
1
0
0
0
0
1
0
0
1
0
0
0
0
4
2
3
10
4
0
10
4
49
8
0
76
57
94
—
1.00
0.33
0.11
0.27
0.36
0.50
0.50
0.00
—
0.13
—
0.50
0.34
0.31
0.00
0.39
0.23
0.28
0.14
0.18
0.14
0.00
0.13
0.08
0.12
0.13
0.00
—
—
1.00
—
0.00
—
—
0.00
—
0.00
0.20
—
—
—
—
0.09
0.00
0.00
0.25
0.00
—
0.00
—
0.17
0.09
0.20
0.42
0.44
0.00
0.20
0.02
0.44
0.09
0.00
0.40
0.36
0.42
0
0
0
0
0
0
0
0
0
0
1
2
10.5
0
0.13
0
0
0
0
15
12
0
0
0
2
0
0
0
0
0
0
0
0
0
0
0
0
3
0
0
0
0
0
0
0
0
0
2
0
0
0
1
2
1
0
0
17.5
44.75
45.5
0
0.86
0
0
0
1
0
0
0
0
0
0
0
0
0
0
1
3
19
0
1
0
0
0
0
14
18
0
0
0
2
0
0
0
0
0
0
0
0
0
0
0
0
3
0
0
0
0
0
0
0
0
0
2
0
0
0
1
2
1
0
0
135
362
378
0
6
0
0
0
1
—
—
—
—
—
—
—
—
—
—
0.00
0.00
0.00
—
1.00
—
—
—
—
0.00
0.00
—
—
—
0.00
—
—
—
—
—
—
—
—
—
—
—
—
0.00
—
—
—
—
—
—
—
—
—
0.00
—
—
—
0.00
0.00
0.00
—
—
0.00
0.08
0.01
—
0.50
—
—
—
0.00
0
0
0
0
0
0
0
0
0.67
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4
0
0
0
0
7
0
0
0
0
0
0
0
0
1
5
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
—
—
—
—
—
—
—
—
1
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
4
—
—
—
—
7
—
—
—
—
—
—
—
—
—
5
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0.00
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0.00
—
—
—
—
0.00
—
—
—
—
—
—
—
—
—
0.00
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
PM ⳱ Peromyscus maniculatus, PT ⳱ P. truei (pinyon mouse), PC/B ⳱ P. crinitus (canyon mouse) and or P. boylei (brush mouse). Density is relative density, as defined in the text, and AB%
is antibody prevalence. Number sampled may exceed the relative density estimate as explained in the text. For sites sampled >1 time within a year, density is a yearly average.