[Emerging Infectious Diseases * Volume 3 * Number 2 * April-June 1997]

Dispatches

Seroepidemiologic Studies of Hantavirus Infection Among Wild Rodents in
California

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      A total of 4,626 mammals were serologically tested for
      antibodies to Sin Nombre virus. All nonrodent species were
      antibody negative. Among wild rodents, antibody prevalence was
      8.5% in murids, 1.4% in heteromyids, and < 0.1% in sciurids. Of
      1,921 Peromyscus maniculatus (deer mice), 226 (11.8%) were
      antibody positive, including one collected in 1975. The highest
      antibody prevalence (71.4% of 35) was found among P.
      maniculatus on Santa Cruz Island, off the southern California
      coast. Prevalence of antibodies among deer mice trapped near
      sites of human cases (26.8% of 164) was significantly higher
      than that of mice from other sites (odds ratio = 4.5; 95%
      confidence interval = 1.7, 11.6). Antibody prevalence increased
      with rising elevation (>1,200 meters) and correlated with a
      spatial cluster of hantavirus pulmonary syndrome cases in the
      Sierra Nevada.

In spring 1993, a cluster of unexplained severe acute respiratory illnesses
associated with a high death rate was reported in the southwestern United
States (1). The outbreak was linked to a newly recognized hantavirus
strain, Sin Nombre virus (SNV), carried by the deer mouse, Peromyscus
maniculatus (2-5). Sporadic cases of the illness, hantavirus pulmonary
syndrome (HPS), were subsequently identified in other regions of North
America, especially the western United States (6,7). Three additional
pathogenic viruses associated with HPS were later discovered outside the
usual range of P. maniculatus: 1) Black Creek Canal virus, harbored by the
cotton rat, Sigmodon hispidus, in Florida; 2) Bayou virus, identified in
the rice rat, Oryzomys palustris, in Louisiana; and 3) New York virus,
isolated from the white-footed deer mouse, Peromyscus leucopus, in New York
(8-12). These viruses have not been found in California; however, two novel
hantaviruses, El Moro Canyon virus (EMCV) and Isla Vista virus (ISLA), were
recently discovered in that state (13-15). Genetic studies identified the
harvest mouse, Reithrodontomys megalotis, and the California meadow vole,
Microtus californicus, as the reservoirs for EMCV and ISLA, respectively.
Human infection with EMCV and ISLA has not been documented.

Through 31 January 1997, 156 cases of HPS were reported to the Centers for
Disease Control and Prevention (CDC); the case-fatality rate is
approximately 50% (T. Ksiazek, P. Rollin, unpub. data). HPS has been
confirmed in 26 states, with California reporting the third largest number
of cases (14 cases, 8 deaths), after New Mexico (29 cases) and Arizona (22
cases).

Hantaviruses are excreted in the urine, feces, and saliva of asymptomatic
infected rodents (16). Transmission to humans occurs when aerosols
contaminated with the virus are inhaled (16-18). Bites by infected rodents
or exposure to broken skin or mucous membranes may represent alternative
routes. Although specific risk factors are poorly defined, persons engaging
in activities that bring them in contact with rodents and/or their
excretions may be at a higher risk for infection (19).

The present study compiles retrospective and prospective serologic data to
1) confirm P. maniculatus as the primary reservoir of SNV and identify
alternative reservoirs, if any, in California; 2) assess differences in SNV
seroprevalence in vector populations from various geographic regions; and
3) compare seroprevalence rates of reservoirs collected near sites of human
cases with those from other sites.

The Study

Mammal Surveys
The California Department of Health Services (CDHS) contacted 18 agencies
(local vector control districts, local health and environmental health
departments, universities, state and national park and forest services, the
military, and wildlife refuges) involved in cross-sectional surveys of
California mammals to participate in developing a centralized, statewide
database of SNV serologic results and ecologic data.

Historical surveys used archived specimens collected in 1975, 1976, and
1988 and stored at the University of California, Berkeley, Museum of
Vertebrate Zoology, and specimens collected from 1989 through early 1993 by
local vector control districts. Prospective surveys and human case
investigations were conducted from late 1993 through the end of 1995. Wild
rodent trapping and processing methods were as previously described (20).

Reports by participating agencies included ecologic data on individual
mammals (species, age, and sex). Information on survey sites included
county, physical location of trapline, date of survey, elevation, and
habitat. Habitat was categorized by a single dominant vegetation type:
chaparral, conifer trees, grassland, hardwood trees, sage/scrub brush, or
urban environment (21).

Human Cases
Within 2 weeks after a confirmed diagnosis of HPS, the patient or a
surrogate was interviewed to determine potential sites of exposure to
infected rodents. An environmental/ecologic investigation was conducted at
possible sites of exposure (20,22).

Laboratory Studies
Rodent serum samples were tested by one or more of six laboratories (CDC;
CDHS; University of New Mexico; University of California, Davis; and
University of Nevada, Reno). Serum samples were examined for IgG antibodies
to the SNV nucleocapsid protein by Western blot and/or enzyme-linked
immunosorbent assay with CDC reagents (23,24). For archived specimens,
liver tissue from frozen carcasses was used for polymerase chain reaction
(PCR) (22,25).

Data Analysis
Descriptive data were analyzed by Epi Info, Version 6.0 (26). Frequency
distributions were obtained, and chi-square tests of homogeneity for
two-by-two contingency tables were used to examine the statistical
significance of any association. A crude relationship between altitude and
SNV-antibody prevalence was assessed by the Mantel-Cox test for trend.
Adjusted odds ratios and 95% confidence intervals were calculated by
logistic-binomial regression (27). A random effects model was chosen
because of the presence of important clustering effects from the sampling
design. The presence or absence of antibodies to SNV was the primary
dependent variable, and characteristics that were identified in the
descriptive analysis were the independent variables. Data from samples
collected on the Channel Islands were analyzed separately from mainland
data where indicated.

Sin Nombre Virus Antibody Prevalence

California Mammals
A total of 4,626 (4,549 rodent and 77 nonrodent species) mammals
representing 47 species were collected between 1975 and 1995 in California
and serologically tested for IgG antibodies to SNV (Table 1). Wild rodents
(most 3,109, from the family Muridae) made up 98% of the sample, followed
by Sciuridae (1,369), and Heteromyidae (71). Among the Muridae, 78% were
deer mice or related species, 11% were wood rats, 6% were domestic rodents
(house mice, rats), 3% were harvest mice, and fewer than 1% were meadow
voles or cotton rats. Antibodies to SNV were found only among wild rodents.
Prevalence of antibodies reactive with SNV was 8.5% among the Muridae, 1.4%
among the Heteromyidae, and less than 0.1% among the Sciuridae. Nonrodent
species tested included 74 carnivores (five domestic dogs, Canis
familiaris; 26 coyotes, Canis latrans; 25 Island foxes, Urocyon littoralis;
six domestic cats, Felis domesticus; two opossums, Didelphis virginiana;
three striped skunks, Mephitis mephitis; seven raccoons, Procyon lotor),
one black-tailed jackrabbit, Lepus californicus, one Nuttall's cottontail,
Silvilagus nuttallii, and one shrew, Sorex sp.

Table 1. Prevalence of antibodies to Sin Nombre virus among wild rodents
in California, 1975-1995
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Family/                        Common              No.      No.    %
Species                        Name                Tested   Pos.   Pos.
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Heteromyidae
    Dipodomys sp.              kangaroo rats       28       1      3.6
    Perognathus sp.            pocket mice         43       0      0.0
SUBTOTAL                                           71       1      1.4
Muridae
Microtus sp.                   meadow voles        29       5      17.2
    M. californicus            California          22       5      22.7
                               meadow vole
    M. montanus                Montane vole        3        0      0.0
    M. townsendii              Townsend's vole     1        0      0.0
Mus musculus                   house mouse         88       0      0.0
Neotoma sp.                    wood rats           330      2      0.6
    N. cinerea                 bushy-tailed        20       0      0.0
                               wood rat
    N. fuscipes                dusky-footed        215      2      0.9
                               wood rat
    N. lepida                  desert wood         95       0      0.0
                               rat
Peromyscus sp.                 deer mice           2430     236    9.7
    P. boylii                  brush mouse         98       0      0.0
    P. californicus            California          159      4      2.5
                               mouse
    P. crinitus                canyon mouse        29       2      6.9
    P. eremicus                cactus mouse        100      1      1.0
    P. maniculatus             deer mouse          1921     226    11.8
    P. truei                   pinyon mouse        123      7      5.7
Rattus norvegicus              Norway rat          11       0      0.0
Rattus rattus                  roof rat            99       0      0.0
Reithrodontomys megalotis      harvest mouse       108      16     14.8
Sigmondon hispidus             cotton rat          14       0      0.0
SUBTOTAL                                           3109     263    8.5
Sciuridae                                          1369     1      <0.1
Ammonospermophilus             antelope            4        0      0.0
leucurus                       ground
                               squirrel
Spermophilus sp.               ground              1205     1      <0.1
                               squirrels
    S. beecheyi                California          856      1      0.1
                               ground
                               squirrel
Tamias sp.                     chipmunks           152      0      0.0
Tamiascurus douglasii          Douglas'            5        0      0.0
                               squirrel
SUBTOTAL                                           1369     1      <0.1
TOTAL                                              4549     245    5.4
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Deer Mouse Populations
Of 1,921 P. maniculatus, 226 (11.8%) had antibodies to SNV (Table 1). Other
peromyscine-related species (e.g., cactus mice, canyon mice, California
mice, and pinyon mice) also had antibodies to SNV, but prevalence was
lower. In almost all instances, infected P. maniculatus were collected at
the same site as SNV-antibody-positive animals of other species.

Retrospectively, antibodies to SNV were identified in 3 (6.0%) of 50 deer
mice specimens collected in 1975 (1 of 22, 4.5%), 1976 (2 of 17, 11.8%),
1981 (0 of 2), 1992 (0 of 1), and early 1993 (0 of 8). The three
seropositive P. maniculatus collected by the University of California,
Berkeley in 1975 and 1976 were from Alameda, Kern, and Mono Counties.
Frozen liver tissue available from the seropositive Kern County specimen
yielded a PCR sequence of the G1 amplimer of SNV that differed from a P.
maniculatus collected in nearby Mono County in 1994 by only five residues
out of 274. The largest comparative protein dissimilarity was with a P.
maniculatus from the Channel Islands, which differed by seven amino acid
substitutions.

Among the deer mice for which age (1,165 animals, 87% adults) and sex
(1,239 animals, 57% male) were available, SNV antibody prevalence was,
respectively, 13.5% in adults and 6.7% in juveniles and 13.0% in males and
10.1% in females. Differences in age (chi-square = 5.5) and sex (chi-square
= 2.5) were not significant.

Geographic Distribution
Thirty-four of the state's 58 counties were surveyed (Table 2). Antibodies
to SNV were identified in deer mice from 21 (62%) of these counties (Figure
1). Most samples were from coastal counties (56%), followed by
foothill/mountainous (36%) and inland/valley (8%) counties. Among these,
the prevalence was 14.5% of 684 in the foothills/mountains, 11.6% of 112 on
the coast, and 0.7% of 151 in the inland/valley areas.

Table 2. Prevalence of antibodies to Sin Nombre virus among Peromyscus
maniculatus by county, California, 1975-1995
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                    No. survey   No.           No.        %
County              sites        tested        pos.       pos.
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COASTAL
Alameda             2            6             1          16.7
Contra Costa        1            36            0          0.0
Del Norte           2            19            0          0.0
Los Angeles         10(8)        112(71)       13(11)     11.6(15.5)
Marin               2            153           3          2.0
Mendocino           1            13            0          0.0
Monterey            2            52            5          9.6
Orange              8            52            3          5.8
San Diego           32           131           7          5.3
San Francisco       1            30            0          0.0
San Luis Obispo     2            4             0          0.0
San Mateo           1            40            8          20.0
Santa Barbara       6(2)         294(81)       86(7)      29.3(8.6)
Sonoma              1            7             0          0.0
Ventura             5(3)         137(9)        0(0)       0.0(0.0)
SUBTOTAL            76(68)       1086(704)     126(45)    11.6(6.4)
INLAND/VALLEY
Imperial            1            2             1          50.0
Riverside           10           57            0          0.0
Sacramento          1            36            0          0.0
San Bernardino      4            49            0          0.0
San Joaquin         1            7             0          0.0
SUBTOTAL            17           151           1          0.7
FOOTHILLS/MOUNTAINS
Butte               12           115           14         12.2
El Dorado           1            25            0          0.0
Glenn               1            4             0          0.0
Inyo                2            3             1          33.3
Kern                5            66            7          10.6
Mariposa            1            46            7          15.2
Mono                8            107           17         15.9
Nevada              1            52            26         50.0
Placer              2            29            2          6.9
Plumas              4            35            1          2.9
Shasta              3            30            4          13.3
Siskiyou            4            117           12         10.3
Tehama              1            35            5          14.3
Tulare              1            20            2          10.0
SUBTOTAL            46           684           99         14.5
TOTAL               139          1921          226        11.8
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*Numbers in parentheses exclude the Channel Islands in Los Angeles
(Catalina, San Clemente), Santa Barbara (San Miguel, Santa Barbara, Santa
Cruz, Santa Rosa), and Ventura (Anacapa, San Nicolas) counties.

 [Figure 1] [Figures not available in ASCII version]
 Figure 1. Geographical distribution of hantavirus pulmonary syndrome
 cases and occurrence of Sin Nombre virus antibodies among deer mice
 (Peromyscus maniculatus), California, 1975-1995 (n=1,921).

One hundred and thirty-nine individual sites were surveyed within 34
counties with a mean of four sites per county (Table 2). Antibody
prevalence at individual sites was 0.0% to 71.4% (25 of 35 tested on Santa
Cruz Island, Santa Barbara County). In the Sierras, the highest antibody
prevalence (50.0% of 52) was found in deer mice captured in Truckee, Nevada
County, during a human case-patient investigation (Table 3, Case 3). At
least one SNV-antibody-positive mouse was detected at each mainland site
where 38 or more mice were tested.

Table 3. Characteristics of selected hantavirus pulmonary syndrome cases
and prevalence of antibodies to Sin Nombre virus in Peromyscus maniculatus
collected at candidate sites of exposure, California, 1994-1995*
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        Onset  Outcome    Suspect     Predominant Elevation    No.      %
         Date              County      Vegetation  (meters)  Rodents  Pos.
 Patient                of Exposure                           Tested
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1       09/94 Nonfatal Mono          conifer,     1801-2100 34        14.7
                                     sage brush
2       03/95 Nonfatal Mono          conifer,     1801-2100 22        13.6
                                     sage brush
3       04/95 Nonfatal Nevada        sage brush   1801-2100 52        50.0
4       06/95 Fatal    Mono          conifer,     1801-2100 11        54.5
                                     sage brush
5       09/95 Fatal    Placer/Nevada conifer      1501-1800 26        7.7
6       10/95 Nonfatal Plumas        conifer      1201-1500 19        5.3
Total                                                       164       26.8
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*Rodent studies associated with California HPS cases described in greater
detail (20,22,29).

Channel Islands
The Channel Islands, a group of eight islands located south of the Santa
Barbara-Los Angeles coast, are 20 km (Anacapa) to 98 km (San Nicolas) from
the mainland and 5 km to 45 km from each other. Despite the proximity
between them, SNV-antibody prevalence varied significantly between islands.
Antibody prevalence in deer mice trapped on the islands (20.9% of 382) was
significantly higher than that of deer mice from the mainland (chi-square =
40.9, p < 0.001). In addition, Channel Island sequences differed by
approximately 17% to 19% from any mainland California sequences (22,25).
The highest prevalence was found on Santa Cruz and Santa Rosa Islands,
where, respectively, 25 (71.4%) of 35 and 47 (58%) of 81 deer mice were
SNV-antibody positive. Antibody prevalence among deer mice on the other
islands was 7 (17.9%) of 39 on San Miguel, 1 (14.3%) of 7 on Santa
Catalina, and 1 (2.9%) of 34 on San Clemente. However, deer mice sampled on
Anacapa (n=37), San Nicolas (n = 91), and Santa Barbara (n = 58) Islands
were all SNV-antibody negative.

Habitat
A higher SNV-antibody prevalence was observed in the Sierra Nevada, Great
Basin, and southern coastal habitats (Figure 1). Likewise, antibody
prevalence was higher among deer mice trapped in vegetation associated with
these environments: 15.1% of 531 in conifer, 14.8% of 597 in grassland,
13.4% of 86 in hardwood, 11.2% of 165 in sage/scrub brush, and 5.8% of 474
in chaparral. In urban environments, only 2.9% of 68 deer mice were
SNV-antibody positive.

Antibody prevalence among deer mice increased significantly (p < 0.001)
with rising altitude (Figure 2). In the regression model, adjusted odds
ratios steadily increased with elevation, peaking at 4.3 in the 1,800- to
2,100-meter range (95% confidence intervals = 1.3, 16.7) (Table 4). The
increased prevalence of SNV antibodies in deer mice trapped at higher
elevations correlated with an increased incidence of HPS cases at
elevations above 1,200 meters (Table 3).

Table 4. Odds ratios for Sin Nombre virus antibody prevalence among
Peromyscus maniculatus by association with human cases and elevation,
California, 1975-1995(a)
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                Cases      Controls     Adj.
                (+SNV)     (-SNV)       OR(c)    95% CI(c)     p value
---------------------------------------------------------------------------
Human
case(d)
Absent          101        1274         1.0      NA(c)         NA
Present         44         120          4.5      1.7-11.6      0.002
Elevation
(meters)
0-300           32         580          1.0      NA            NA
301-600         2          101          0.4      0.4-3.5       0.423
601-900         11         83           0.6      0.2-1.8       0.390
901-1200        8          85           2.4      0.7-8.6       0.168
1201-1500       26         234          3.2      1.0-10.0      0.044
1501-1800       23         152          2.6      0.7-9.2       0.151
1801-2100       26         103          4.3      1.3-16.7      0.032
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(a)Excludes Channel Islands; (b)Adjusted for trapline location and survey
date, vegetation, sex and age of deer mouse; (c)OR, odds ratio; CI,
confidence interval; NA, not applicable; (d)Deer mice collected at
candidate sites of exposure during human case investigations.

             [Figure 2] [Figures not available in ASCII version]
             Figure 2. Prevalence of Sin Nombre virus
             antibodies among deer mice (Peromyscus
             maniculatus) by elevation, California, 1975-1995
             (n=1,539, excluding Channel Islands).

Human Cases
HPS cases were spatially clustered in the state's Sierra Nevada region
(Figure 1). Results from antibody prevalence studies among rodents
collected during the investigation of six HPS cases in California are
presented in Table 3. Antibody prevalence in deer mice trapped at these
sites was significantly higher than at sites not associated with a human
case (odds ratio = 4.5; 95% confidence interval = 1.7, 11.6) (Table 4).

Reservoirs of Hantavirus in California

Extensive serologic testing unequivocally identified P. maniculatus as the
primary reservoir of SNV in California, as did previous studies in the
western United States (2,20,28-30). The overall prevalence of SNV
antibodies in deer mice (11.9%) in California is also comparable with
results published by nearby western states such as Montana (8.0%) and
Nevada (12.5%) (28,30). Other peromyscine rodents (e.g., canyon mice and
pinyon mice) may harbor the virus in California, but at much lower levels.
Because these related wild mice species frequently inhabit the same
environment as P. maniculatus, their infections may represent transmission
from the primary reservoir population rather than from each other, as would
occur in a permanent virus-species relationship. The extremely low
prevalence of SNV antibodies (Table 1) in heteromyids (kangaroo rats,
pocket mice), sciurids (ground squirrels, chipmunks), and Old World murids
(domestic mice and rats), despite a large sample size (> 1,600), suggests
that these animals are not important in the epidemiology of SNV in
California.

Positive serologic test results from California meadow voles and harvest
mice probably represent cross-reaction with SNV antigen by ISLA and EMCV,
respectively (13-15). The high prevalence of antibodies identified in
meadow voles (22.7% of 29) and harvest mice (14.8% of 108) is a cause for
concern, even though human infection by these viruses has not been
documented. Precautionary measures should be taken against exposure to
hantaviruses through all potential wild rodent reservoirs until more is
known about these newly discovered strains.

Temporal and Spatial Trends in Deer Mice Populations
Our data from historical surveys indicate that SNV was already circulating
in deer mice 20 years ago in parts of California. The antibody-positive
deer mouse originally trapped in Kern County in 1975 is the oldest
documented evidence of SNV infection in wild rodents. Notably,
SNV-antibody-positive deer mice identified retrospectively were captured
almost 20 years before the first HPS cases were recognized in California
and in some of the same geographic regions (20,22,29,31). The slight
difference (approximately 2%) between sequences from the Kern County deer
mouse trapped in 1976 and a Mono County deer mouse trapped in 1994
indicates a long-standing stability of the virus, as previously
demonstrated by Nerukar et al. in Mono County (32).

Although SNV infection in deer mice is widespread in California,
represented biotypes vary considerably in seroprevalence levels. For
example, deer mice in foothill/mountainous (14.5% of 684) counties have a
higher seroprevalence than those in inland/valley (0.7% of 151) and coastal
(6.4% of 704, excluding the Channel Islands) counties. The trend of
increasing prevalence with rising elevation found in this analysis has been
observed in other states (Jim Mills, pers. comm.).

The Channel Islands offered a unique opportunity to study SNV infection in
a relatively isolated population of deer mice. Deer mouse populations have
been on the Channel Islands long enough that each island has its own
subspecies and have considerable variation genetically within those
subspecies (33,34). Likewise, Hjelle et al. found significant divergence
between genetic sequences of virus from infected deer mice collected on the
islands and those from the nearby coastal mainland (25). Although travel
from the mainland to the islands and from island to island is common,
evidence suggests that SNV coevolved separately within the deer mouse
populations on each island (San Clemente, San Miguel, Santa Catalina, Santa
Cruz, Santa Rosa). It appears that the virus is not endemic or is present
at very low levels among deer mice on Anacapa, San Nicolas, and Santa
Barbara Islands.

Human Cases
The antibody prevalence of SNV in deer mice collected at potential exposure
sites during the investigation of sporadic HPS cases in California (26.8%)
was similar to the antibody prevalence (30.0%) in deer mice observed during
the 1993 HPS outbreak in the Four Corners region (2). Prevalence was
significantly higher (p = 0.002) in deer mice trapped near human case
exposure sites than in those from survey sites with no cases (Table 4).
Together these findings imply that the percentage of infected deer mice may
be a risk factor for human exposure to SNV. In addition, landscape features
such as high elevation may be another important predictor of hantavirus in
the state. The spatial clustering of HPS cases in the Sierra Nevada range
supports this conclusion.

Characteristics of the mouse population, the environment, or human
lifestyles may explain these geographic differences. The climate and
vegetation in the mountains could be conducive to large populations of deer
mice, a factor which might influence SNV prevalence. In addition, the
occupational and recreational activities of the inhabitants of rural,
mountainous environments bring them into frequent contact with rodents. In
addition, local residences (e.g., old log cabins) are prone to rodent
infestation, a possible risk factor for HPS infection (35).

Otteson et al. documented a higher SNV antibody prevalence among rodents
trapped near buildings, regardless of the presence of a human case; a
case-control study of the Four Corners outbreak had similar findings
(30,36). Information on proximity to human dwellings was not available for
our analysis; however, most mice were collected near buildings during
investigation of human cases. Since other survey sites were probably less
likely to be located near human dwellings, this factor may represent a
source of bias in our study. Other biases may have been introduced because
of nonrandom sampling and small sample size at some survey sites.
Systematic longitudinal studies of SNV infection in deer mice at the key
locations identified in this analysis are needed to further develop a
predictive model for hantavirus infection in California which could
elucidate the natural history of SNV and enhance prevention efforts.

Public Health Implications
Preliminary results indicate a need for health education of residents,
visitors, and workers at high risk, especially in the Sierra Nevada range.
Human dwellings in the mountains may be more vulnerable to deer mice
infestation, especially if the buildings are older and/or intermittently
occupied. In addition, persons working in or cleaning these structures may
be at an even higher risk (22,29,35,36). Local health care providers and
tertiary care centers should be aware of the potential for HPS cases in the
state.

Acknowledgments
The authors thank the many workers who conducted field surveys and
participated in the compilation of a state-wide mammal database; those
providing laboratory support, including David Cottam, Dale Dondero, CDHS;
Mary Lane Martin, George Gallucci, and Brad Hotard, CDC; Jeff Riolo,
University of Nevada, Reno; and Vicki Kramer for her helpful comments and
review of this manuscript. This work was supported in part by Public Health
Service Grant RO1 AI36336.

  Michele Jay,* Michael S. Ascher, Bruno B. Chomel, Minoo Madon, David
 Sesline, Barryett A. Enge, Brian Hjelle, Thomas G. Ksiazek, Pierre E.
                Rollin, Philip H. Kass, and Kevin Reilly*
  *California Department of Health Services, Sacramento, California, USA;
   Viral and Rickettsial Diseases Laboratory, Berkeley, California, USA;
 University of California, Davis, California, USA; California Department
  of Health Services, Ontario, California, USA; University of New Mexico,
 Albuquerque, New Mexico, USA; Centers for Disease Control and Prevention,
                           Atlanta, Georgia, USA

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Emerging Infectious Diseases
National Center for Infectious Diseases
Centers for Disease Control and Prevention
Atlanta, GA

URL: ftp://ftp.cdc.gov/pub/EID/vol3no2/ascii/jay.txt