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| ABSTRACT |
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| INTRODUCTION |
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| MATERIALS AND METHODS |
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Capture and processing of rodents. The rodents were captured in live traps (H. B. Sherman Traps, Inc., Tallahassee, FL, model LFATDG) as described in Texas Tech University Animal Care and Use Protocol #01178X. Four hundred traps were set each night during a 2-day period in July 2001. The traps were placed within grassy areas, set at 5-m intervals, and baited with a mixture of rice, millet, cracked corn, and wheat.
Each animal was assigned a unique museum (TK) number and then identified to species level based on external morphologic features.19 Samples of blood were dried on Nobuto strips (Advantec MFS, Inc., Pleasanton, CA), samples of heart, kidney, liver, lung, skeletal muscle, and spleen were stored individually in cryovials in liquid nitrogen, and the skins and skeletons were prepared as museum voucher specimens. The tissue samples and the skins and skeletons subsequently were deposited into the Natural Science Research Laboratory, Museum, Texas Tech University.
Antibody assays.
The blood samples were tested for immunoglobulin G (IgG) against the CADV prototype strain VHV-574, using an enzyme-linked immunosorbent assay (ELISA) described previously.16 The test antigen was a lysate of Vero E6 cells infected with strain VHV-574. The control (comparison) antigen was a lysate of uninfected Vero E6 cells. Serial 4-fold dilutions (from 1:80 through 1:5,120) of each blood sample were tested against the test antigen and the control antigen. Antibody bound to antigen was detected by using a mixture of a goat anti-Rat IgG peroxidase conjugate and a goat anti-Peromyscus leucopus IgG peroxidase conjugate in conjunction with the ABTS Microwell Peroxidase Substrate System (Kirkegaard and Perry Laboratories, Gaithersburg, MD). Optical densities (OD) at 405 nm (reference = 490 nm) were measured with a Dynex MRX II microplate reader (Dynatech Industries, Inc., McLean, VA). The adjusted OD (AOD) of a blood-antigen reaction was the optical density of the well coated with the test antigen less the OD of the well coated with the control antigen. A blood sample was considered to be antibody-positive if the AOD at 1:80 was
0.200, the AOD at 1:320 was
0.200, and the sum of the AODs for the series of 4-fold dilutions (from 1:80 through 1:5,120) was
0.750.20 The titer of a positive sample was the reciprocal of the highest dilution for which the AOD was
0.200.20
The blood samples were tested for IgG against hantavirus strain HV C1280001, using an indirect fluorescent antibody test (IFAT) described previously.21 (Strain HV C1280001 was isolated from a lung of rodent TK102040 in this study.) The cell spots were prepared from a suspension that contained a 1:1 mixture of Vero E6 cells infected with HV C1280001 and uninfected Vero E6 cells. Antibody (IgG) bound to cell-associated hantaviral antigen was revealed by using a goat anti-Peromyscus leucopus IgG fluorescein isothiocyanate conjugate (Kirkegaard and Perry Laboratories).
Virus assay. A lung of rodent TK102040 and the lungs of two other antibody-positive rodents, specifically TK102095 and TK102097, were tested for infectious hantavirus by cultivation in Vero E6 cells as described previously.16 Hantaviral antigen in the cultured cells was detected by using an IFAT in which the primary antibody was a hyperimmune mouse ascitic fluid raised against SNV and CADV. Mouse IgG bound to cell-associated hantaviral antigen was revealed by using a goat anti-mouse IgG fluorescein isothiocyanate conjugate (Kirkegaard and Perry Laboratories).
Genetic characterization of HV C1280001 and CADV strain VHV-574. The genomes of hantaviruses consist of 3 RNA segments, designated small (S), medium (M), and large (L), which encode the viral nucleocapsid (N) protein, glycoprotein precursor (GPC), and RNA-dependent RNA polymerase, respectively. Distinction between hantaviral species oftentimes is based on comparisons of the amino acid sequences of complete N proteins and comparisons of the amino acid sequences of complete GPCs.22
The nucleotide sequence of a 1943-nt fragment of the S segment and the nucleotide sequence of a 3616-nt fragment of the M segment of HV C1280001 were determined. The 1943-nt fragment of the S segment included the entire N protein gene. Similarly, the 3616-nt fragment of the M segment included the entire GPC gene.
Our knowledge of the genome of VHV-574 previously was limited to a 1130-nt fragment of the S segment, a 439-nt fragment of the 5' half of the GPC gene, and a 575-nt fragment of the 3' half of the GPC gene (GenBank accession nos. AF000140, AY953444, and AY953442, respectively). In this study, the lengths of the complete S segment and the complete M segment of VHV-574 were 1986 nucleotides and 3675 nucleotides, respectively.
Total RNA was isolated from monolayers of infected Vero E6 cells, using TRIzol® Reagent (Invitrogen Life Technologies, Inc., Carlsbad, CA). Reverse transcription of the S segment RNA and the M segment RNA was done by using SuperScript II RNase H Reverse Transcriptase (Invitrogen Life Technologies, Inc.) in conjunction with oligonucleotide 5'-GGTGGTTGTGGTAGTAGTAGACTCC-3' and HTM7 (5'-TAGTAGTAGACTCCGCAAGAAGAAGCA-3'), respectively.2 Amplicons (PCR products) were generated from 3 overlapping fragments of the S segment first-strand cDNA and from 2 overlapping fragments of the M segment first-strand cDNA by using the Master Taq Kit (Eppendorf North America, Inc., Westbury, NY) in conjunction with oligonucleotides described previously or designed based on sequence data generated in this study. The sequences of the termini of the S segment and the termini of the M segment of VHV-574 were determined from amplicons generated from circularized RNA. The termini were ligated together by using T4 RNA Ligase (Promega Corp., Madison, WI). Reverse transcription through the ligation site of the S segment RNA and through the ligation site of the M segment RNA was accomplished by using SuperScript II RNase H Reverse Transcriptase (Invitrogen Life Technologies, Inc.) in conjunction with HTS28 (5'-CAGAATCATCTCATTAGTCC-3') and HTM29 (5'-GAACATTCAGGCTCATTTCG-3'), respectively. Amplification of a 541-nt fragment of the S segment first-strand cDNA and a 1236-nt fragment of the M segment first-strand cDNA was done by using the Master Taq Kit (Eppendorf North America, Inc.) in conjunction with oligonucleotides HTS22 (5'-AGATCTGCCATCTGACGCT-3') and HTS28 and oligonucleotides HTM29 and HTM46 (5'-GTACAGCACCAGCTGCAACATG-3'), respectively. Amplicons of the expected size were purified from agarose gel slices by using the QIAquick Gel Extraction Kit (Qiagen, Inc., Valencia, CA). Both strands of each purified amplicon were sequenced directly, using the dye termination cycle sequencing technique (Applied Biosystems, Inc., Foster City, CA). The nucleotide sequences of the S and M segments of HV C1280001 and the S and M segments of VHV-574 were deposited into the GenBank nucleotide sequence database under accession nos. DQ256126 and DQ177347, and DQ285566 and DQ284451, respectively.
The nucleotide sequences of the N protein genes and GPC genes and the amino acid sequences of the N proteins and GPCs of HV C1280001 and VHV-574 were compared with the homologous sequences of ANDV strains AH-1, Chile-9717869, CHI-7913, Hu39694, Lechiguanas, and Oran, BAYV, BCCV, CHOV strain 588, ELMCV strain RM-97, LANV strain 510B, MAPV strain HV 97021050, MULV strain SH-Tx-339, NYV strain Rhode Island-1 (RI-1), RIOMV strain OM-556, SNV strain NM R11, Prospect Hill virus (PHV), Puumala virus (PUUV) strain CG1820, Hantaan virus (HTNV) strain 76-118, and Seoul virus (SEOV) strain SR11 (GenBank accession nos. AF324902 and AF324901, AF291702 and AF291703, AY228237 and AY228238, AF482711 and AF028023, AF482714 and AF028022, AF482715 and AF028024, L36929 and L36930, L39949 and L39950, DQ285046 and DQ285047, U11427 and U26828, AF005727 and AF005728, AY267347 and AY363179, U54575, U09488 and U36801, U5213600, L37904 and L37903, M34011 and X55129, M32750 and M29979, M14626 and M14627, and M34881 and M34882, respectively). Prospect Hill virus and PUUV are principally associated with arvicoline rodents (family Cricetidae, subfamily Arvicolinae) and HTNV and SEOV are principally associated with murine rodents (family Muridae, subfamily Murinae). The hantaviral species principally associated with sigmodontine rodents (New World rats and mice) are phylogenetically distinct from the hantaviral species principally associated with arvicoline rodents (voles and lemmings) and from the hantaviral species principally associated with murine rodents (Old World rats and mice).23 The amino acid sequences were aligned by using the computer program CLUSTALW (1.7).24 The nucleotide sequences were aligned manually based on the computer-generated multiple amino acid sequence alignments. The analyses of the multiple sequence alignments were done by using programs in the computer software packages MEGA2 and PAUP*, version 4.0b10.25,26 The neighbor-joining (NJ) analyses were carried out on uncorrected p model distances, with all 3 nucleotide positions included in the distance calculations. In the maximum parsimony (MP) analyses, third position nucleotides and uninformative first and second position nucleotides were excluded, and the characters were weighted in accordance with the transition/transversion (ti/tv) ratio calculated from the data. Bootstrap support for the NJ analyses was based on 1000 repetitions of the heuristic search and bootstrap support for the MP analyses was based on 500 repetitions of the heuristic search.27
Genetic characterization of rodents. Rodents TK102040 and TK102014 were identified at the study site as Coues oryzomys (Oryzomys couesi). The nucleotide sequences of the cytochrome b genes of TK102040 and TK102014, three other Coues oryzomys (TK93218, TK93244, and TK72660), and 4 marsh oryzomys (Oryzomys palustrisTK91240, TK51628, TK111000, and TK27995) were determined to improve our knowledge of the taxonomical relationship between O. couesi and O. palustris, the principal host of BAYV.28 Rodents TK93218 and TK93244 were captured at Las Minas in Oaxaca, Mexico, TK72660 was captured in Cameron County, Texas, TK91240 in Galveston County, Texas, TK51628 in Calhoun County, Texas, TK111000 in Brazoria County, Texas, and TK27995 in Okmulgee County, Oklahoma. Mitochondrial DNA was isolated from liver as described previously.29 The complete cytochrome b gene (1143-bp) was amplified by PCR, using Taq DNA Polymerase (Promega Corp.) in conjunction with oligonucleotides MVZ05 and MVZ14 or MVZ05 and 1115.30,31 Amplicons of the expected size were purified from agarose gel slices by using the QIAquick PCR Purification Kit (Qiagen, Inc.). Both strands of each purified amplicon were sequenced directly, using the dye termination cycle sequencing technique (Applied Biosystems, Inc.) in conjunction with oligonucleotides MVZ05 and MVZ14,30 1115,31 L14841,32 F1,33 400R,34 700H and 700L,35 or 870R.36 The nucleotide sequences of the cytochrome b genes of TK102040, TK102014, TK91240, TK93218, TK93244, TK51628, TK27995, TK111000, and TK72660 were deposited into the GenBank nucleotide sequence database under accession nos. DQ185383, DQ185384, DQ185382, DQ185385, DQ185386, DQ370031, DQ370032, DQ370033, and DQ370034, respectively, and then compared with the nucleotide sequences of the cytochrome b genes of a marsh oryzomys from Collier County, Florida, 4 russet oryzomys (Oryzomys russatus) captured at different localities in Brazil, 2 Emmons oryzomys (Oryzomys emmonsae) captured at a single locality in Brazil, 2 Azaras broad-headed oryzomys (Oryzomys megacephalus) captured at different localities in Brazil, 1 Azaras broad-headed oryzomys captured in Guyana, 1 Azaras broad-headed oryzomys captured in Suriname, 2 Atlantic Forest oryzomys (Oryzomys laticeps) captured at different localities in Brazil, and 1 Ucayali spiny rat (Scolomys ucayalensis) captured in Brazil (GenBank accession nos. L37388, AF181271, AF181272, AF251523, and AF251524, AF251525 and AF251526, AF251516 and AF251519, AF251518, AF251517, AF251521 and AF251522, and AF527420, respectively).37,38 A previous study established that O. russatus and O. emmonsae are sister species and that O. megacephalus and O. laticeps are sister species.38 The O. russatus, O. emmonsae, O. megacephalus, and O. laticeps sequences were included in the analyses to provide a metric for interpretation of the genetic distances between the Coues oryzomys and the marsh oryzomys. The analyses of the multiple sequence alignment were done by using programs in the computer software package PAUP*, version 4.0b10, and the computer program MrBayes 3.1.2.26,39 Sequence nonidentities were equivalent to uncorrected p model distances. The S. ucayalensis sequence was the designated outgroup taxon in the Bayesian analysis.39 A GTR+I+G model with a site-specific gamma distribution was used with the following options in MrBayes 3.1.2: two simultaneous runs of 4 Markov-chains, 10 million generations, and sample frequency = every 100th generation.40 The first 500 trees were discarded after review of the likelihood scores and the consensus tree (50% majority rule) was constructed from the remaining trees.
| RESULTS |
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Infectious hantavirus (strain HV C1280001) was isolated from the sample of lung tissue from rodent TK102040. Hantaviral antigen was not detected in the Vero E6 cells inoculated with the original suspension of lung tissue from TK102040 but was observed in 40% of the Vero E6 cells inoculated with first-passage (Vero E6 + 1) material. The attempts to isolate infectious hantavirus from rodents TK102095 and TK102097 were unsuccessful.
The alignment of complete N protein amino acid sequences was 433 characters in length. In pairwise comparisons, nonidentities (uncorrected p model distances) among the sigmodontine rodent-associated hantaviral species ranged from 4.717.8%, HV C1280001 exhibited the lowest nonidentity (4.7%) with BAYV, SNV exhibited the lowest nonidentity (6.3%) with NYV, and CADV strain VHV-574 exhibited the lowest nonidentity (13.8%) with MAPV (Table 1
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In pairwise comparisons of cytochrome b gene sequences, nonidentities (uncorrected p model distances) among the 5 Coues oryzomys ranged from 0.55.3%, nonidentities among the 5 marsh oryzomys ranged from 0.16.3%, nonidentities between the Coues oryzomys and the marsh oryzomys ranged from 9.911.3%, and nonidentities between the russet oryzomys and Emmons oryzomys and between the Azaras broad-headed oryzomys and Atlantic Forest oryzomys ranged from 10.711.7% and from 9.711.5%, respectively. The results of the Bayesian analysis of cytochrome b gene sequences indicated that the Coues oryzomys and marsh oryzomys represent different phylogenetic lineages and placed the Coues oryzomys lineage in a sister relationship to the marsh oryzomys lineage relative to the O. russatusO. emmonsae lineage and to the O. megacephalusO. laticeps lineage. Bootstrap support for monophyly of the Coues oryzomys and for monophyly of the marsh oryzomys in the Bayesian analysis was 100%.
| DISCUSSION |
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The Oryzomys species known to occur in Honduras are O. alfari (cane oryzomys), O. alfaroi, O. bolivaris (Bolivar oryzomys), O. couesi, and O. rostratus (long-nosed oryzomys).19,44 Oryzomys couesi can be distinguished from the 4 other species on the basis of external morphologic features.19 Rodent TK102040 and the 4 other antibody-positive rodents in this study were Coues oryzomys.
Antibody to HV C1280001 was found in 5 (20.8%) of the 24 Coues oryzomys captured at the study site. Collectively, the high prevalence of antibody to HV C1280001 in the Coues oryzomys, the absence of antibody to HV C1280001 in the other rodents captured at the study site, and the isolation of HV C1280001 from TK102040 indicate that O. couesi is the principal host of Catacamas virus (CATV).
The geographical range of O. palustris, the principal host of BAYV, extends from Kansas, New Jersey, and Florida to northeastern Mexico, and the geographical range of O. couesi extends from southern Texas to Colombia.28,4547 A previous study of oryzomys captured in Texas established that there are measurable differences between O. couesi and O. palustris in adult body size, pelage coloration, other anatomic features, and chromosomal morphology.48 The results of the analyses of cytochrome b gene sequence data in the present study support the separation of O. couesi from O. palustris and indicate that substantial evolutionary divergence has occurred between these rodent species and, as such, that CATV is ecologically as well as phylogenetically distinct from BAYV.22
As noted previously, 3 hantaviral species are naturally associated with Sigmodon (cotton rat) species. Black Creek Canal virus is principally associated with S. hispidus (hispid cotton rat) in southern Florida,41 MULV is naturally and perhaps principally associated with S. hispidus in northern Texas,14 and CADV is principally associated with Sigmodon alstoni (Alstons cotton rat) in western Venezuela.16 The results of the present study confirm the specific status of CADV and indicate that BCCV and MULV are phylogenetically more closely related to CATV and BAYV than to CADV (Fig. 1A
).
The present-day principal host relationships of many hantaviral species appear to be a consequence of a long-term shared evolutionary relationship between the genus Hantavirus and the rodent families Cricetidae and Muridae. Evidence for this ancient virus-host relationship includes the association of phylogenetically closely related hantaviral species with phylogenetically closely related rodent species, for exampleSNV with P. maniculatus and NYV with P. leucopus,4951 and ANDV, CHOV and MAPV, and RIOMV with Oligoryzomys longicaudatus (long-tailed colilargo),10,42,43 Oligoryzomys fulvescens (fulvous colilargo),7,17 and Oligoryzomys microtis (small-eared colilargo),18 respectively. The results of analyses of cytochrome b gene sequences in an earlier study indicated that Oryzomys species are phylogenetically more closely related to Oligoryzomys species than to Sigmodon species.29 The results of the phylogenetic analyses in the present study, specifically the monophyly of CATV, BAYV, BCCV, and MULV and the separation of the CATV-BAYV-BCCV-MULV lineage from the ANDV-CHOV-MAPV-RIOMV lineage, suggest that the association of CADV with S. alstoni or the association of CATV with O. couesi and BAYV with O. palustris is not the result of an ancient virus-host relationship. A plausible explanation for the discordance between the phylogeny of the viruses and the phylogeny of their rodent hosts is that the present-day association of CATV with O. couesi and BAYV with O. palustris is a consequence of inter-specific (cotton rat-to-oryzomys) virus transmission at some time after the last common ancestor of S. alstoni and S. hispidus. Alternatively, the association of CADV with S. alstoni was established after the last common ancestor of S. alstoni and S. hispidus.
The human health significance of CATV has not been investigated. The results of a recent study in Panama indicated that persons infected with CHOV usually do not develop severe HPS.52 In contrast, persons infected with SNV, ANDV, or some of the other sigmodontine rodent-associated hantaviruses frequently develop severe (if not fatal) HPS. Studies are needed to assess the risk of CATV infection in persons who live or work in rural areas of eastern Honduras and the severity of disease caused by CATV in these persons.
Received April 13, 2006. Accepted for publication July 10, 2006.
Acknowledgments: Members of the 2001 Field Methods Class, Texas Tech University, and members of the 2001 Sowell Expedition captured and processed the rodents. Mary Louise Milazzo, Maria N. B. Cajimat, and J. Delton Hanson contributed equally to this study.
Financial support: A grant from James Sowell to Robert J. Baker (Texas Tech University) and Robert D. Bradley provided financial support for the field component of this study. National Institutes of Health Grant AI-41435 ("Ecology of emerging arenaviruses in the southwestern United States") provided financial support for the laboratory work at UTMB and at Texas Tech University.
* Address correspondence to Charles F. Fulhorst, Department of Pathology, Delivery code L14686, University of Texas Medical Branch, 301 University Blvd., Galveston, Texas 77555-0609. E-mail:cfulhors{at}utmb.edu ![]()
Authors addresses: Mary Louise Milazzo, Department of Pathology, University of Texas Medical Branch, 301 University Blvd., Galveston, Texas 77555-0609, Telephone: (409) 747-2466, Fax: (409) 747-2437, E-mail: mamilazz{at}utmb.edu; Maria N.B. Cajimat, Department of Microbiology and Immunology, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-1019, Telephone: (409) 747-2466, Fax: (409) 747-2437, E-mail: nbcajirm{at}utmb.edu; J. Delton Hanson, Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409-3131, Telephone: (806) 742-2725, Fax: (806) 742-2963, E-mail: jdh95{at}yahoo.com; Robert D. Bradley, Department of Biological Sciences and Museum, Texas Tech University, Lubbock, TX 79409-3131, Telephone: (806) 742-2725, Fax: (806) 742-2963, E-mail: robert.bradley{at}ttu.edu; Miguel Quintana, USACHPPM-W, MCHB-AW, Box 339500, MS 115, Fort Lewis, WA 98433-9500, Telephone: (253) 966-3771, Fax: (253) 966-0163, E-mail: miguel.quintana{at}us.army.mil; Catalina Sherman, Dirección de Vigilancia de Salud, Secretaria de Salud de Honduras, Contiguo al Correo Nacional, Barrio El Jazmin, Tegucigalpa, M.D.C., Honduras, Telephone: 504-2381103; Fax: 504-2221036, E-mail: shermankaty{at}yahoo.com; Reina T. Velásquez, Dirección de Vigilancia de Salud, Secretaria de Salud de Honduras, Contiguo al Correo Nacional, Barrio El Jazmin, Tegucigalpa, M.D.C., Honduras, Telephone: 504-2381103, Fax: 504-2221036; Charles F. Fulhorst, Department of Pathology, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-0609, Telephone: (409) 772-9713, Fax: (409) 747-2400, E-mail: cfulhors{at}utmb.edu
Reprint requests: Charles F. Fulhorst, Department of Pathology, Delivery code L14686, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-0609 E-mail: cfulhors{at}utmb.edu.
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