Geographic distribution and genetic diversity of Whitewater Arroyo virus in the southwestern United States.

Abstract

The purpose of this study was to extend our knowledge of the geographic distribution and genetic diversity of the arenavirus(es) associated with Neotoma species (woodrats) in the southwestern United States. Infectious arenavirus was recovered from 14 (3.3%) of 425 woodrats. The virus-positive species included N. albigula in New Mexico and Oklahoma, N. cinerea in Utah, N. mexicana in New Mexico and Utah, and N. micropus in Texas. Analyses of viral nucleocapsid protein gene sequence data indicated that all the isolates were strains of the Whitewater Arroyo virus, an arenavirus previously known only from northwestern New Mexico. Analyses of the sequence data also indicated that there can be substantial genetic diversity among strains of Whitewater Arroyo virus from conspecific woodrats collected from different localities and substantial genetic diversity among strains from different woodrat species collected from the same locality.

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Vol. 7, No. 3, May–June 2001Emerging Infectious Diseases
403
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The virus family Arenaviridae comprises two serocom-
plexes. The lymphocytic choriomeningitis-Lassa (Old World)
complex includes lymphocytic choriomeningitis (LCM),
Lassa, Mopeia, Mobala, and Ippy viruses. The Tacaribe (New
World) complex includes Tamiami (TAM), Whitewater Arroyo
(WWA), Pichindé (PIC), Amapari, Flexal, Guanarito, Junin,
Latino, Machupo, Oliveros, Parana, Pirital, Sabiá, and
Tacaribe viruses.
The arenaviruses have bipartite, single-stranded RNA
genomes (1). The large (L) genomic segment encodes the viral
RNA-dependent RNA polymerase and a zinc-binding protein.
The small (S) genomic segment encodes the nucleocapsid (N)
protein and glycoprotein precursor. The most comprehensive
knowledge of the phylogeny of the family Arenaviridae is
based on a fragment of the N protein gene (2-4).
Six arenaviruses are known to cause severe disease in
humans. LCM virus is an agent of acute central nervous
system disease (5) and congenital malformations (6). Lassa,
Junin, Machupo, Guanarito, and Sabiá viruses are etiologic
agents of hemorrhagic fever in western Africa, Argentina,
Bolivia, Venezuela, and Brazil, respectively (7).
The arenaviruses known to occur in North America are
LCM, TAM, and WWA. LCM virus was introduced into the
Americas along with its principal rodent host, Mus musculus
(house mouse) (8). TAM virus is known only from Sigmodon
hispidus (hispid cotton rat) in southern Florida (9-11). WWA
virus was originally recovered from Neotoma albigula (white-
throated woodrat) collected from northwestern New Mexico (12).
In a recent study (13), antibody to an arenavirus was
found in five Neotoma species in the southwestern United
States: N. albigula in Arizona, Colorado, and New Mexico;
N. stephensi (Stephen’s woodrat) in Arizona and New Mexico;
N. mexicana (Mexican woodrat) in Arizona and Utah; and
N. fuscipes (dusky-footed woodrat) and N. lepida (desert
woodrat) in California. The purpose of the present study was
to extend our knowledge of the geographic distribution and
genetic diversity of the arenavirus(es) associated with
Neotoma rodents in the southwestern United States.
Materials and Methods
All work with rodent tissues and infectious arenavirus
was performed in a biosafety level 3 laboratory at the Centers
for Disease Control and Prevention (Atlanta, GA) or
University of Texas Medical Branch, Galveston.
Rodent Tissues
Five hundred sixty-six tissue specimens (74 spleen, 225
liver, and 267 kidney) from 425 woodrats were tested for
infectious arenavirus. The specimens were from the Museum
of Texas Tech University (Lubbock, TX) or Museum of
Southwestern Biology (University of New Mexico, Albuquer-
que, NM). The specimens from the Museum of Southwestern
Biology were chosen to represent localities in which antibody
to an arenavirus was found in one or more Neotoma species in
a previous study (13).
Virus Assay
Tissue specimens were tested for infectious arenavirus as
described previously (12). Briefly, 0.2 mL of a 10% w/v crude
tissue homogenate was inoculated onto a monolayer of Vero
E6 cells in a 25-cm2 plastic culture flask (Corning, Inc.,
Geographic Distribution and Genetic Diversity
of Whitewater Arroyo Virus in
the Southwestern United States
Charles F . F ulhorst,* R emi N. Charrel,*† Scott C. Weaver,* T homas G. K siazek,‡
R obert D. Bradley,§ Mary L . Milazzo,* R obert B. T esh,* and Michael D. Bowen‡
*University of Texas Medical Branch, Galveston, Texas, USA; †Faculté de Médecine, Marseille,
France; ‡Centers for Disease Control and Prevention, Atlanta, Georgia, USA; and
§Texas Tech University, Lubbock, Texas, USA
Address for correspondence: Charles F. Fulhorst, Department of
Pathology, Route 0609, University of Texas Medical Branch,
Galveston, Texas 77555-0609, USA; fax: 409-747-2415; e-mail:
cfulhors@utmb.edu
The purpose of this study was to extend our knowledge of the geographic
distribution and genetic diversity of the arenavirus(es) associated with Neotoma
species (woodrats) in the southwestern United States. Infectious arenavirus was
recovered from 14 (3.3%) of 425 woodrats. The virus-positive species included
N. albigula in New Mexico and Oklahoma, N. cinerea in Utah, N. mexicana in
New Mexico and Utah, and N. micropus in Texas. Analyses of viral nucleocapsid
protein gene sequence data indicated that all the isolates were strains of the
Whitewater Arroyo virus, an arenavirus previously known only from
northwestern New Mexico. Analyses of the sequence data also indicated that
there can be substantial genetic diversity among strains of Whitewater Arroyo
virus from conspecific woodrats collected from different localities and substantial
genetic diversity among strains from different woodrat species collected from the
same locality.

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Emerging Infectious Diseases Vol. 7, No. 3, May–June 2001
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Corning, NY). The inoculum was incubated on the cell
monolayer at 37°C for 60 minutes; then the monolayer was
overlaid with 7.0 mL of a minimum essential medium
containing Earle’s salts, 1.5 mg/mL sodium bicarbonate, 2%
v/v heat-inactivated (56ºC for 30 minutes) fetal bovine serum,
0.29 mg/mL L-glutamine, 100 U/mL penicillin G, 100 µg/mL
streptomycin sulfate, and 100 U/mL nystatin. The cell culture
was maintained at 37°C in a humidified atmosphere of 5%
CO2 in air for 13 days. Half the culture medium was replaced
with fresh maintenance medium on day 6 or 7 after
inoculation. Cells were scraped from the monolayer on day 13
after inoculation and coated onto 12-well glass microscope
slides (Cel-Line Associates, Inc., Newfield, NJ). The cell spots
were air-dried, fixed in cold acetone, and then tested for
arenaviral antigen by using an indirect fluorescent antibody
test (12). In that test, cell spots were stained with a
hyperimmune mouse ascitic fluid prepared against the WWA
virus prototype strain AV 9310135, and mouse immunoglobulin
G (IgG) bound to cell-associated arenaviral antigen was detected
by using a goat anti-mouse IgG fluorescein isothiocyanate
conjugate (Cappel Laboratories, West Chester, PA).
Genetic Characterization of Viral Isolates
The nucleotide sequence of a fragment of the N protein
gene of each of 12 isolates was determined. Four of the 12
isolates were from the spleens and kidneys of two animals,
rodents 62425 and 62439 (Table 1). Total RNA was extracted
from monolayers of infected Vero E6 cells by using TRIzol
Reagent (Life Technologies, Inc., Grand Island, NY). Reverse
transcription of RNA from isolates AV 96010149, AV
96010151, AV 96010025, and AV 96010024 was carried out by
using Superscript II RTase (Life Technologies) in conjunction
with oligonucleotide ARE-3'END (14). This oligonucleotide
apparently is complementary to the 19-nt fragment at the 3'
terminus of the S genomic segment of all arenaviruses.
Polymerase chain reaction (PCR) amplification of the first-
strand cDNA was carried out by using Taq DNA polymerase
(Promega Corp., Madison, WI) in conjunction with
oligonucleotides 1010C and NW1696R (2-3), which flank a
616-nt region of the N protein gene of WWA virus prototype
strain AV 9310135 (12). Reverse transcription and PCR (RT-
PCR) amplification of a fragment of the N protein gene of each
of the eight other isolates was carried out by using the Access
RT-PCR Kit (Promega Corp.) in conjunction with oligonucle-
otides AVNP1 (5'-CCCTTCTTYTTNYTCTTRATGACTA-3')
and AVNP2 (5'-GGKAGRGCNTGGGAYAACAC-3'). AVNP1
and AVNP2 flank a 518-nt region in the fragment of the WWA
virus N protein gene that is amplified by using
oligonucleotides 1010C and NW1696R. They were designed
based on N protein gene sequence data for the WWA virus
prototype strain AV 9310135 (GenBank Accession No.
U52180), WWA virus strains AV 96010149, AV 96010151, AV
96010025, and AV 96010024, TAM virus strain W-10777
(U43690), and PIC virus strain An 3739 (K02734). Size
separation of PCR products was done by agarose gel
electrophoresis; the products of the expected size were
purified from gel slices by using QIAquick Gel Extraction Kit
(Qiagen, Inc., Valencia, CA). One strand of each 1010C-
NW1696R PCR product was sequenced directly by using the
dye termination cycle sequencing technique (Applied
Biosystems, Inc., Foster City, CA) in conjunction with
oligonucleotide 1010C. The sequence of the other (i.e.,
complementary) strand of each of these products was
determined by cloning the PCR product in the TA cloning
vector PCRII (Invitrogen Corp., Carlsbad, CA) and then using
a plasmid-specific oligonucleotide (M13) to initiate the cycle
sequencing reaction. Both strands of the AVNP1-AVNP2 PCR
products were sequenced directly by using the same
oligonucleotides that were used to prime the RT-PCR, i.e.,
AVNP1 and AVNP2. The 12 nucleotide sequences generated
in this study were deposited with the GenBank nucleotide
sequence database under Accession Nos. AY012710-
AY012721.
Data Analysis
The analyses of nucleotide sequence data were restricted
to the 518-nt fragment of the WWA virus N protein gene that
is flanked by oligonucleotides AVNP1 and AVNP2. The
GenBank database sequences included in the analyses were
Accession Nos. U52180 (WWA virus, strain AV 9310135),
U43690 (TAM, W-10777), K02734 (PIC, An 3739), U43689
(Parana, 12056), U43687 (Flexal, BeAn 293022), U62561
(Pirital, VAV-488), U43688 (Latino, 10924), U34248
(Oliveros, 3229-1), U70802 (Junin, XJ), X62616 (Machupo,
AA288-77), U43686 (Guanarito, INH-95551), U41071 (Sabiá,
SPH 114202), U43685 (Amapari, BeAn 70563), M20304
(Tacaribe, TRVL 11573), M20869 (LCM, Armstrong), and
U80004 (Lassa, LP). The computer software package
Table 1. Recovery of infectious arenavirus from tissues of virus-positive woodrats (Neotoma species)
Date
Rodent Speciescollected
1627
N. albigula
07/15/93
1626
N. albigula
07/15/93
62415
N. mexicana
09/24/94
62425
N. mexicana
09/24/94
62439
N. mexicana
09/24/94
28731
N. albigula
10/12/85
28742
N. albigula
10/12/85
84648
N. micropus
07/18/99
84703
N. micropus
07/19/99
84708
N. micropus
07/19/99
84761
N. micropus
07/18/99
84816
N. micropus
07/20/99
36287
N. cinerea
07/06/94
36282
N. mexicana
07/05/94
ant = not tested. The WWA virus prototype strain is bolded. Isolates (strains) included in the (phylo-) genetic analyses are underlined.
Collected from
County
McKinley
McKinley
Socorro
Socorro
Socorro
Cimarron
Cimarron
Dimmit
Dimmit
Dimmit
Dimmit
La Salle
San Juan
San Juan
Virus (strain) recovered froma
Spleen Kidney
AV 9310041
AV 9310135
nt AV 9310040
nt AV 96010149
nt AV 96010151
nt AV 96010154
nt AV 98490013
nt AV 97130039
NegativeAV A0400098
AV A0400337 AV A0400135
ntAV A0400140
AV A0400373 AV A0400174
AV A0400412AV A0400212
nt AV 96010025
nt AV 96010024
State
NM
NM
NM
NM
NM
OK
OK
TX
TX
TX
TX
TX
UT
UT
Liver
nt
nt
nt
AV 98360019
AV 98360020
Negative
TVP-6038
nt
nt
nt
nt
nt
AV 96010206
AV 96010205

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405
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CLUSTAL W1.7 (15) was used to construct an alignment of
the predicted amino acid sequences, and the computer
program TransAlign (16) was used to generate a multiple
nucleotide sequence alignment from the amino acid sequence
alignment. Pairwise genetic distances were computed by
using the p distance model as implemented in the computer
program MEGA, version 1.02 (17). Percent sequence
identities were calculated by subtracting the genetic
distances from 1.0 and multiplying by 100. Phylogenetic
analysis was carried out on the multiple amino acid sequence
alignment by using the neighbor-joining method (gamma
model, alpha = 2) as implemented in MEGA, version 1.02.
Bootstrap support (18) for the results of the phylogenetic
analysis was based on 500 pseudoreplicate datasets
generated from the original multiple amino acid sequence
alignment.
Results
Viral Isolates
Twenty-three arenaviral isolates were recovered from
tissues of 14 (3.3%) of 425 Neotoma rodents (Table 1). The 23
isolates included three WWA virus strains (AV 9310135, AV
9310041, and AV 9310040) that were reported previously (12).
The virus-positive animals included two N. albigula from
McKinley County, northwestern New Mexico; two N. albigula
from Cimarron County, western Oklahoma; three N. mexicana
from Socorro County, central New Mexico; five N. micropus
from the Chaparral Wildlife Management Area (Dimmit and
La Salle counties), southern Texas; and one N. mexicana and
one N. cinerea from San Juan County, southeastern Utah
(Table 2, Figure 1). The virus-positive animals from McKinley
County were two (50%) of four woodrats (all N. albigula)
collected on July 15, 1993, from Whitewater Arroyo. The
positive N. albigula from Cimarron County were two (22.2%)
of nine woodrats (seven N. albigula and two N. mexicana)
collected on October 12, 1985, from a site near Kenton. The
positive N. mexicana from Socorro County were three (42.9%)
of seven woodrats (all N. mexicana) collected on September
24, 1994, from a site in the Magdalena Mountains. The
positive N. micropus from Dimmit County were 4 (13.8%) of 29
woodrats (all N. micropus) collected in a 3-day period (July 17
through July 19, 1999) from the western region of the
Chaparral Wildlife Management Area. The positive
N. micropus from La Salle County was one (25.0%) of four
woodrats (all N. micropus) collected on July 20, 1999, from the
eastern region of the Chaparral Wildlife Management Area.
The positive N. mexicana and N. cinerea from San Juan
County were 2 (12.5%) of 16 woodrats (11 N. mexicana, 2
N. cinerea, and 3 N. albigula) collected in an 8-day period
(June 29 through July 6, 1994) from Natural Bridges National
Monument. Information from the Museum of Southwestern
Biology indicated that the positive N. mexicana and N. cinerea
were collected from different sites in Natural Bridges
National Monument.
The nucleotide sequences of the isolates from rodent
62425 (one isolate each from kidney and liver; strains AV
96010151 and AV 98360019, respectively) were identical. In
contrast, the nucleotide sequences of the isolates from rodent
62439 (again, one isolate each from kidney and liver; strains
AV 96010154 and AV 98360020, respectively) were 99.6%
identical. Further study is needed to determine whether the
differences between the isolates from rodent 62439 represent
the coexistence of multiple virus genotypes (alleles) in the
same rodent. An alternative explanation is that the sequence
differences are the result of adaptation of the isolates to
growth in cultured (Vero E6) cells or manipulation of viral
nucleic acid extracted from cultured cells.
Nucleotide and amino acid sequence identities among
WWA virus prototype strain AV 9310135 and 12 other
Table 2. Results of virus isolation attempts on tissues from 425 woodrats
Neotoma speciesa
Countyb
State Nalb Ncin Nflo Nme Nmic Nste Total
Apache (1)AZ- -
Cochise (2)AZ0/31 -
Coconino (2) AZ 0/6 -
Maricopa (1) AZ0/23 -
Navajo (1) AZ 0/290/1
Yavapai (2)AZ0/5 -
McKinley (3)NM 2/16 -
Otero (9) NM0/33 -
Socorro (3)NM0/31 -
Cimarron (4) OK2/11 -
Major (4) OK - -
McIntosh (2) OK - -
Pottawatomie (2) OK - -
Dimmit (1)TX - -
La Salle (1) TX - -
San Juan (8) UT 0/31/2
Total4/188 1/3
aNalb = Neotoma albigula, Ncin = N. cinerea, Nflo = N. floridana, Nmex = N.
mexicana, Nmic = N. micropus, Nste = N. stephensi. Values are the number
positive/number tested; “-” = none tested.
bNumber in parentheses indicates the number of sites sampled in the county.
-
-
-
-
-
-
-
-
-
-
0/45 -
0/12 -
0/7
-
-
-
0/64 4/48
0/6
-
-
-
0/5
0/2
-
0/9
3/10
0/5
-
-
-
-
-
-
-
0/35
0/1
-
0/38
-
-
4/29
1/4
-
5/107 0/15 14/425
0/5
-
0/3
-
0/7
-
-
-
-
-
-
-
-
-
-
-
0/11
0/31
0/9
0/23
0/42
0/7
2/16
0/77
3/42
2/16
0/83
0/12
0/7
4/29
1/4
2/16
-
-
-
1/11
Figure 1. Locations of 14 arenavirus-positive Neotoma rodent
collections. San Juan County, southeastern Utah = N. cinerea and N.
mexicana (one virus-positive animal each species); Cimarron County,
western Oklahoma = N. albigula (2); McKinley County, northwestern
New Mexico = N. albigula (2); Socorro County, central New Mexico =
N. mexicana (3); Dimmit and La Salle counties (Chaparral Wildlife
Management Area), southern Texas = N. micropus (5). The map inset
shows the location of study area.

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isolates from Neotoma rodents ranged from 74.7% to 100.0%
and 84.9% to 100.0%, respectively (Table 3). When compared
with other arenaviruses, the isolates from the Neotoma
rodents exhibited 69.9% to 73.7% nucleotide sequence
identity with TAM virus, 61.0% to 63.3% identity with PIC
virus, and less than 62.0% sequence identity with all other
arenaviruses.
Phylogenetic analysis of N protein amino acid sequence
data indicated that isolates from Neotoma rodents represent a
phylogenetic lineage (viral species) that is in a sister
relationship to the lineage represented by TAM virus (Figure
2). We concluded that all isolates recovered from the Neotoma
rodents were strains of WWA virus.
Discussion
Before the present study, WWA virus was known only
from N. albigula in northwestern New Mexico (12). The
present work provides unequivocal evidence that the virus
also is naturally associated with N. cinerea, N. mexicana, and
N. micropus, and that it occurs in Utah, central New Mexico,
Oklahoma, and Texas. The recovery of WWA virus strains AV
98490013 and TVP-6083 from N. albigula is the first evidence
that a Tacaribe complex virus occurs in Oklahoma. Likewise,
the recovery of strains AV A0400174 and AV A0400212 from
woodrats collected from southern Texas (Chaparral Wildlife
Management Area) is the first evidence that N. micropus is
naturally associated with a Tacaribe complex virus and that
WWA virus occurs in Texas.
In a previous study (13), antibody to an arenavirus was
found in N. fuscipes and N. lepida in southern California;
N. albigula, N. mexicana, and N. stephensi in Arizona; and
N. albigula in southwestern Colorado. Although the results of
the present study indicate that WWA virus is geographically
widely distributed in association with Neotoma rodents,
further work is needed to determine whether the arenavirus
associated with Neotoma rodents in California, Arizona, and
Colorado is in fact WWA virus.
The results of the present study indicate that there can be
substantial genetic heterogeneity among strains of WWA
virus from different woodrat species from the same locality
and among strains from conspecific woodrats collected from
different localities. For example, nucleotide sequence identity
between the strains recovered from N. mexicana and
N. cinerea from Natural Bridges National Monument (San
Juan County, Utah; strains AV 96010024 and AV 96010025,
respectively) was 82.8%, and nucleotide sequence identity
between strain AV 96010024 and the three strains recovered
from N. mexicana collected from the Magdalena Mountains
(Socorro County, New Mexico; strains AV 96010149, AV
96010151, and AV 96010154) was from 85.1% to 85.5%. In
contrast, nucleotide sequence identity in strains recovered
from conspecific rodents collected from the same locality (e.g.,
strains AV 9310135 and AV 9310040 from N. albigula from
Whitewater Arroyo, and strains AV A0400174 and AV
Figure 2. Phylogeny of the North American arenaviruses based on a
neighbor-joining analysis of nucleocapsid protein amino acid sequence
data. Distances and groupings were determined by using the gamma
distance algorithm (alpha = 2). Branch lengths are proportional to the
gamma distance between amino acid sequences. Numbers indicate the
percentage of 500 bootstrap replicates that supported each labeled
interior branch. The WWA virus prototype strain AV 9310135 is in bold
type. Nmex = Neotoma mexicana, Nalb = N. albigula, Ncin = N. cinerea,
Nmic = N. micropus, and Shisp = Sigmodon hispidus.
Table 3. Nucleotide and amino acid sequence identities among 13 arenavirus isolates recovered from 11 woodrats and Tamiami virusa
Virus or strain
AV 98 AV 93 AV 93 AV 96
1013510040
--100.0
100.0 --
95.3 95.3
95.3 95.3
95.3 95.3
94.8 94.8
95.3 95.3
91.9 91.9
91.9 91.9
88.4 88.4
88.9 88.9
90.7 90.7
93.0 93.0
77.9 77.9
AV 96 AV 98 AV 96 AV 98 TVP- AV A0 AV A0 AV 96 AV 96 TAM
400212 400174 010025 010024
79.179.183.4
79.179.1 83.4
79.578.8 84.4
79.578.884.4
79.5 78.884.4
79.378.684.4
79.5 78.884.4
79.077.880.9
79.1 78.081.1
-- 95.777.2
98.3 --74.7
84.984.9 --
86.086.089.5
80.280.277.3
Virusb
WWA
WWA
WWA
WWA
WWA
WWA
WWA
WWA
WWA
WWA
WWA
WWA
WWA
TAM
Strain
AV 9310135
AV 9310040
AV 96010149
AV 96010151
AV 98360019
AV 96010154
AV 98360020
AV 98490013
TVP-6038
AV A0400212
AV A0400174
AV 96010025
AV 96010024
W-10777
010149 010151 360019 010154 360020 490013 6038
86.5 86.5 86.585.3
86.5 86.5 86.585.3
--100.0100.0 98.1
100.0 --100.0 98.1
100.0100.0 --98.1
98.8 98.8 98.8 --
99.4 99.4 99.499.4
90.7 90.7 90.790.7
90.7 90.7 90.7 90.7
88.9 88.9 88.988.9
89.5 89.5 89.589.5
91.3 91.3 91.391.3
94.2 94.2 94.294.2
78.5 78.5 78.578.5
85.3
85.3
98.5
98.5
98.5
99.6
--
91.3
91.3
89.5
88.9
91.3
94.2
78.5
82.3
82.3
80.1
80.1
80.1
81.3
81.3
--
98.8
86.6
85.5
87.8
88.4
78.5
82.6
82.6
80.3
80.3
80.3
81.5
81.5
99.4
--
86.6
85.5
87.8
88.4
78.5
85.1
85.1
85.5
85.5
85.5
85.1
85.1
80.7
80.1
77.0
75.5
82.8
--
78.5
71.6
71.6
73.7
73.7
73.7
73.2
73.4
72.2
72.4
69.9
69.9
71.6
72.2
--
aNucleotide and amino acid sequence identities are listed above and below the dashes, respectively.
bWWA = Whitewater Arroyo, TAM = Tamiami.

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A0400212 from N. micropus from the Chaparral Wildlife
Management Area) was >95.0%.
The results of previous studies (3,19,20) suggested that
the present-day diversity of the arenaviruses is a product of
long-term coevolution of the various viruses with their
respective principal rodent hosts. In the present study, WWA
viral strains AV 9310135 and AV 9310040 (both from
N. albigula, northwestern New Mexico) appeared to be
phylogenetically more closely related to strain AV 96010024
(N. mexicana, southeastern Utah) than to strains AV
98490013 and TVP-6038 (both from N. albigula, western
Oklahoma). This situation suggests that the present-day
association of WWA virus with N. albigula and N. mexicana
does not represent a long-term shared evolutionary
relationship between virus and rodent species. However, this
conclusion assumes that recovery of WWA virus from a rodent
represents a principal virus-host relationship. Perhaps some
of the virus-positive rodents in the present study were
infected by contact with other Neotoma species or even non-
Neotoma rodent species.
The geographic range of the genus Neotoma extends from
western Canada south to Guatemala, Honduras, and
Nicaragua, and includes 33 states in the contiguous United
States and 26 of the 32 states in Mexico (21). Thus, if the
present-day association of WWA virus with the genus
Neotoma represents a long-term shared evolutionary
relationship between virus and rodent host, the geographic
range of the virus may extend far beyond the southwestern
United States. WWA virus recently was associated with
several human deaths in California (22). Further study is
needed to assess the human health significance of this virus
in the southwestern United States and other regions in North
America in which woodrats are indigenous.
Acknowledgments
Robert Baker and Terry Yates provided the tissue specimens
that were tested for infectious arenavirus; Wen Li Kang amplified
and cloned the PCR products generated from isolates AV 96010149,
AV 96010151, AV 96010025, and AV 96010024.
This research was supported by the National Institutes of
Health grant AI-41435 (“Ecology of emerging arenaviruses in the
southwestern United States”).
Dr. Fulhorst is assistant professor and member of the World Health
Organization Collaborating Center for Tropical Diseases, University of
Texas Medical Branch, Galveston. His research interests include the
epidemiology of the arenaviruses, hantaviruses, and other viral zoonoses.
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