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Journal of Clinical Microbiology, September 2008, p. 2874-2878, Vol. 46, No. 9
0095-1137/08/$08.00+0 doi:10.1128/JCM.00074-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Polio and Picornavirus Laboratory Branch,1 Gastroenteritis and Respiratory Virus Laboratory Branch, Division of Viral Diseases, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia,2 Yerkes National Primate Research Center, Emory University, Atlanta, Georgia3
Received 14 January 2008/ Returned for modification 6 March 2008/ Accepted 22 June 2008
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In a recent study, we investigated cases of diarrheal disease among monkeys at a U.S. primate center (25). In that study, fecal specimens were tested for enteric viruses, including rotavirus, adenovirus, and enterovirus. Of 56 animals tested, enteroviruses were detected in 75% of rhesus macaques (30/40) and 45% of pigtail macaques (5/11), while adenovirus was detected only in rhesus macaques and there were no rotaviruses detected. To determine whether the enterovirus detections represented circulation of one or more simian enteroviruses within the colony or transmission of human enteroviruses from animal handlers, we determined here the serotype identity of each virus by reverse transcription-PCR (RT-PCR) and sequencing of a portion of the VP1 gene, a region whose sequence corresponds to antigenic type (16, 19).
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Enterovirus identification by RT-PCR and sequencing.
Of the original 59 fecal specimens (25), 56 were available for further virologic investigation. RNA was extracted from stool specimens by using guanidine isothiocyanate and silica, as described previously (2). Enterovirus VP1-specific RT-PCR and sequencing were carried out as previously described (15). Briefly, cDNA was synthesized using primers in VP1 and PCR was performed using primers in VP3 and VP1 to produce a first-round product of
700 bp. One microliter of the first PCR product was added to a second PCR containing nested primers within VP1 to produce a product of approximately 320 to 350 bp (
35% of the VP1 region). Reaction products were separated and visualized on an agarose gel, and purified by using the QIAquick gel extraction kit (Qiagen, Inc., Valencia, CA). The resulting DNA templates were sequenced on both strands with the second-reaction primers using the BigDye Terminator v1.1 ready-reaction cycle sequencing kit on an ABI Prism 3100 automated sequencer (both from Applied Biosystems, Foster City, CA). Amplicon sequences were compared to the VP1 sequences of enterovirus reference strains, including at least one representative of each recognized serotype, by script-driven sequential pairwise comparison using the program Gap (Wisconsin Sequence Analysis Package, version 10.3; Accelrys, Inc., San Diego, CA), as described previously (15, 19). In this scheme, a VP1 nucleotide sequence identity of greater than 75% confirms the enterovirus serotype present in the specimen. This approach has been shown to be suitable for complete VP1 sequences and for partial sequences of at least 300 nucleotides (nt) (15-16, 18-19).
A portion of the 3D (polymerase) region was amplified by RT-nested PCR. 3D-specific cDNA was synthesized with Superscript II reverse transcriptase (Invitrogen, Carlsbad, CA) using primer AN368 (AAACAACTAGACTTRTCNGCNGGNGTCAT, nt 6957 to 6929 relative to SV19) in a 10-µl reaction. The reaction was incubated at 42°C for 1 h, followed by 5 min at 95°C. The first-round PCR used primers AN392 (TTCCCAACCAAAGCNGGNCARTG, nt 5735 to 5757 relative to SV19) and AN368, Taq polymerase (Roche Applied Science, Indianapolis, IN), and the entire cDNA reaction in a 50-µl reaction. The reaction was carried out by performing 40 cycles of 95°C for 30 s, 55°C for 20 s, and 60°C for 50 s. One microliter of first-round PCR product was added to a 50-µl reaction containing primers AN366 (GGCAATGGAAGCCARGGNTTYTGYGC, nt 5807 to 5832 relative to SV19) and AN367 (CCAGAAAGTATCTGGGTTRCANCCNACNGC, nt 6520 to 6491 relative to SV19), and FastStart Taq (Roche Applied Science), with initial denaturation at 95°C for 6 min, followed by 40 cycles of 95°C for 30 s, 60°C for 15 s, and 70°C for 40 s. Amplicon sequences were determined as described above using the primers AN366 and AN367.
Sequence analysis. The partial VP1 sequences were compared to a database of complete enterovirus VP1 sequences of all serotypes to determine whether the isolates were genetically related to any known enterovirus serotype. Multiple alignments and phylogenetic relationships of VP1 and 3D sequences, including the Yerkes sequences and those of EV reference strains, were constructed by using the neighbor-joining method implemented in CLUSTAL W (23). Phylogenetic analysis of the 3D sequences was conducted on 26 of the 37 VP1-positive samples. Eleven specimens were excluded due to the lack of sufficient sample, failed 3D sequencing, or because they were mixtures of viruses and the 3D sequence could not unambiguously be assigned to the correct VP1 sequence.
Nucleotide sequences. The sequences described here have been deposited in the GenBank database, accession no. EU194488 to EU194550.
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320-nt amplicon and comparison of the sequence to a database of reference sequences yields a type identification (15, 19). The VP1 assay was positive for 37 of 56 (66%) specimens tested (Table 1). The sensitivity and specificity of the 5'-nontranslated region (5'NTR) PCR/hybridization assay (25) and the VP1 assay were approximately equal, as the 5'NTR assay detected enterovirus genome in 36 of 53 (68%) specimens tested (Table 1). One specimen was positive only in the PCR-hybridization assay (25), and one specimen was positive only in the VP1 assay. Of the three specimens not tested by the 5'NTR PCR-hybridization assay, one was positive in the VP1 assay, and two were negative. The VP1-positive animals included 30 of 40 rhesus macaques (75%), 5 of 11 pigtails (45%), and 2 of 4 mangabeys (50%). There were no detections of known human enteroviruses, indicating that human-to-primate transmission was unlikely to have occurred during the study period. All five control animals were among those that were negative by the VP1 assay (data not shown). |
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TABLE 1. Detection of enteroviruses by two different RT-PCR assaysa
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TABLE 2. Enteroviruses identified in captive primates grouped by host speciesa
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FIG. 1. Phylogenetic relationships in the VP1 region based on analysis of partial VP1 sequences of Yerkes enteroviruses and reference strains of other enteroviruses. Phylogenetic trees were generated by the neighbor-joining algorithm implemented in CLUSTAL W (23), with 1,000 bootstrap replicates, based on analysis of partial VP1 sequences of Yerkes enteroviruses and reference strains of other enteroviruses. Bootstrap values over 60% are indicated at the respective nodes on the tree. For clarity, subtrees containing only nonsimian sequences (e.g., other HEV-A) have been collapsed and are indicated by elongated triangles, the length of which depicts the overall diversity within the subtree. Sequences determined in the present study are indicated by an animal identifier (e.g., RHp-4). Reference sequences are indicated by serotype and GenBank accession number. HEV, human enterovirus species A, B, C, or D; HRV, human rhinovirus A or B; PEV, porcine enterovirus; BEV, bovine enterovirus.
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FIG. 2. Phylogenetic relationships in the 3D region based on analysis of partial VP1 sequences of Yerkes enteroviruses and reference strains of other enteroviruses. Phylogenetic trees were generated by the neighbor-joining algorithm implemented in CLUSTAL W (23), with 1,000 bootstrap replicates, based on analysis of partial 3D sequences of Yerkes enteroviruses and reference strains of other enteroviruses. Bootstrap values over 60% are indicated at the respective nodes on the tree. For clarity, subtrees containing only nonsimian sequences (e.g., other HEV-A) have been collapsed and are indicated by elongated triangles, the length of which depicts the overall diversity within the subtree. Sequences determined in the present study are indicated by an animal identifier (e.g., RHp-4). Reference sequences are indicated by serotype and GenBank accession number. HEV, human enterovirus species A, B, C, or D; HRV, human rhinovirus A or B; PEV, porcine enterovirus; BEV, bovine enterovirus.
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SV19, EV92, and EV103 were found in both rhesus and pigtail macaques (Table 2). The close genetic relationships between viruses of a given type in the two monkey species (e.g., EV92 strains RFk-5 [rhesus] and PJf-1 [pigtail]) suggests that these viruses have been transmitted between the two host species and that the two monkey populations probably represent a single virus reservoir. Interspecies transmission is considered likely because the two species are often housed together when they are inside. Interestingly, SV19, EV92, and EV103 were not detected in mangabeys, a species that is kept separate from the macaques at the Yerkes field station; however, the number of mangabeys in the study (n = 4) was too small to allow us to determine whether SV19, EV92, and EV103 circulated exclusively in the macaque populations. On the other hand, one can conclude that SV6 was probably present only in the mangabeys and not in the macaques.
There are few data to associate simian enterovirus infection with specific diseases in primates (10). There have been reports of minor central nervous system lesions in experimentally infected animals (10), but most simian enterovirus isolations have been from specimens derived from healthy animals (1, 3, 4, 6, 7, 14). For example, SV4 and SV6 were identified by the observation of cytopathic effect in normal primary monkey kidney cells that were being prepared for the production of polio vaccine (7). On the other hand, SV6 and SV19 have also been isolated from monkeys with acute gastroenteritis, but there was no clear association between infection and disease (4). The vast majority of human enterovirus infections are asymptomatic (21), and the same may be true for the simian enteroviruses. If this is the case, it may be difficult to link infection with disease in primates, particularly since the infections appear to be relatively common.
The origin of the enterovirus infections in the Yerkes colony remains unclear. Since no human enteroviruses were detected, it is unlikely that the viruses were introduced by animal handlers in the facility. No wild-caught animals have been introduced into the colony in approximately 25 years, so it is also unlikely that the viruses were recently introduced from a wild reservoir. Introduction from another primate facility is possible, since animals are sometimes received from other primate colonies, but those facilities would also be expected to have ceased primate importation many years ago. It is more likely that the viruses have been circulating at Yerkes and/or another colony for many years, probably since the time when importation of wild-caught primates from South Asia was common (i.e., the 1950s or 1960s). The range of VP1 sequence diversity within a given type suggests that individual founder strains of the different virus types were introduced once and have subsequently circulated and evolved within the colony for many years. Alternatively, multiple strains of each type may have been introduced at different times, resulting in cocirculation of several strains of a given type. Unfortunately, there is insufficient information about natural simian enterovirus transmission and diversity to distinguish between these possibilities.
Additional studies are needed to assess the prevalence of simian enterovirus infections in wild and captive primate populations to determine whether the viruses cause disease in primates and to investigate the potential for their zoonotic transmission to humans. Studies are under way to survey picornaviruses excreted by wild and captive primates to better understand the diversity, natural history, and ecology of simian enteroviruses in their native environment.
This study was supported in part by Yerkes Base Grant RR00165.
The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.
Published ahead of print on 2 July 2008. ![]()
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