Leonard P. Wasieloski

Smallpox and pan-Orthopox Virus Detection by Real-Time 3′-Minor Groove Binder TaqMan Assays on the Roche LightCycler and the Cepheid Smart Cycler Platforms

ABSTRACT We designed, optimized, and extensively tested several sensitive and specific real-time PCR assays for rapid detection of both smallpox and pan-orthopox virus DNAs. The assays are based on TaqMan 3′-minor groove binder chemistry and were performed on both the rapid-cycling Roche LightCycler and the Cepheid Smart Cycler platforms. The hemagglutinin (HA) J7R, B9R, and B10R genes were used as targets for the variola virus-specific assays, and the HA and DNA polymerase-E9L genes were used as targets for the pan-orthopox virus assays. The five orthopox virus assays were tested against a panel of orthopox virus DNAs (both genomic and cloned) at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID). The results indicated that each assay was capable of detecting both the appropriate cloned gene and genomic DNA. The assays showed no cross-reactivity to the 78 DNAs in the USAMRIID bacterial cross-reactivity panel. The limit of detection (LOD) of each assay was determined to be between 12 and 25 copies of target DNA. The assays were also run against a blind panel of DNAs at the Centers for Disease Control and Prevention (CDC) on both the LightCycler and the Smart Cycler. The panel consisted of eight different variola virus isolates, five non-variola virus orthopox virus isolates, two varicella-zoster virus isolates, and one herpes simplex virus isolate. Each sample was tested in triplicate at 2.5 ng, 25 pg, 250 fg, and 2.5 fg, which represent 1.24 × 107, 1.24 × 105, 1.24 × 103, and 1.24 × 101 genome equivalents, respectively. The results indicated that each of the five assays was 100% specific (no false positives) when tested against both the USAMRIID panels and the CDC blind panel. With the CDC blind panel, the LightCycler was capable of detecting 96.2% of the orthopox virus DNAs and 93.8% of the variola virus DNAs. The Smart Cycler was capable of detecting 92.3% of the orthopox virus DNAs and between 75 and 93.8% of the variola virus DNAs. However, all five assays had nearly 100% sensitivity on both machines with samples above the LOD (>12 gene copies). These real-time PCR assays represent a battery of tests to screen for and confirm the presence of variola virus DNA. The early detection of a smallpox outbreak is crucial whether the incident is an act of bioterrorism or an accidental occurrence.

Cynomolgus macaque as an animal model for severe acute respiratory syndrome

Background The emergence of severe acute respiratory syndrome (SARS) in 2002 and 2003 affected global health and caused major economic disruption. Adequate animal models are required to study the underlying pathogenesis of SARS-associated coronavirus (SARS-CoV) infection and to develop effective vaccines and therapeutics. We report the first findings of measurable clinical disease in nonhuman primates (NHPs) infected with SARS-CoV. Methods and Findings In order to characterize clinically relevant parameters of SARS-CoV infection in NHPs, we infected cynomolgus macaques with SARS-CoV in three groups: Group I was infected in the nares and bronchus, group II in the nares and conjunctiva, and group III intravenously. Nonhuman primates in groups I and II developed mild to moderate symptomatic illness. All NHPs demonstrated evidence of viral replication and developed neutralizing antibodies. Chest radiographs from several animals in groups I and II revealed unifocal or multifocal pneumonia that peaked between days 8 and 10 postinfection. Clinical laboratory tests were not significantly changed. Overall, inoculation by a mucosal route produced more prominent disease than did intravenous inoculation. Half of the group I animals were infected with a recombinant infectious clone SARS-CoV derived from the SARS-CoV Urbani strain. This infectious clone produced disease indistinguishable from wild-type Urbani strain. Conclusions SARS-CoV infection of cynomolgus macaques did not reproduce the severe illness seen in the majority of adult human cases of SARS; however, our results suggest similarities to the milder syndrome of SARS-CoV infection characteristically seen in young children.

Monkeypox virus detection in rodents using real-time 3′-minor groove binder TaqMan ® assays on the Roche LightCycler

During the summer of 2003, an outbreak of human monkeypox occurred in the Midwest region of the United States. In all, 52 rodents suspected of being infected with monkeypox virus were collected from an exotic pet dealer and from private homes. The rodents were euthanized and submitted for testing to the United States Army Medical Research Institute of Infectious Diseases by the Galesburg Animal Disease Laboratory, Illinois Department of Agriculture. The rodent tissue samples were appropriately processed and then tested by using an integrated approach involving real-time polymerase chain reaction (PCR) assays, an antigen-detection immunoassay, and virus culture. We designed and extensively tested two specific real-time PCR assays for rapidly detecting monkeypox virus DNA using the Vaccinia virus F3L and N3R genes as targets. The assays were validated against panels of orthopox viral and miscellaneous bacterial DNAs. A pan-orthopox electrochemiluminescence (ECL) assay was used to further confirm the presence of Orthopoxvirus infection of the rodents. Seven of 12 (58%) animals (seven of 52 (15%) of all animals) tested positive in both monkeypox-specific PCR assays and two additional pan-orthopox PCR assays (in at least one tissue). The ECL results showed varying degrees of agreement with PCR. One hamster and three gerbils were positive by both PCR and ECL for all tissues tested. In addition, we attempted to verify the presence of monkeypox virus by culture on multiple cell lines, by immunohistology, and by electron microscopy, with negative results. Sequencing the PCR products from the samples indicated 100% identity with monkeypox virus strain Zaire-96-I-16 (a human isolate from the Congo). These real-time PCR and ECL assays represent a significant addition to the battery of tests for the detection of various orthopoxviruses. In light of the recent monkeypox virus transmissions, early detection of the virus is crucial for both natural outbreaks and potential acts of bioterrorism.

Identification of ciprofloxacin resistance by SimpleProbe™, High Resolution Melt and Pyrosequencing™ nucleic acid analysis in biothreat agents: Bacillus anthracis, Yersinia pestis and Francisella tularensis

The potential for genetic modification of biological warfare agents makes rapid identification of antibiotic resistant strains critical for the implementation of suitable infection control measures. The fluorinated quinolone, ciprofloxacin, is an antibiotic effective for treating bacterial infections by inhibiting the enzyme activity of the DNA type II topoisomerases DNA gyrase and topoisomerase IV. The genes that encode the subunits of DNA gyrase (gyrA and gyrB) and topo IV (par C and parE) contain hotspots within an area known as the quinolone resistance-determining region (QRDR). Base pair changes within this region give rise to mutations that cause resistance to the antibiotic by altering amino acids within the enzymes. Ciprofloxacin-resistant (cipro(r)) strains of Bacillus anthracis, Yersinia pestis, and Francisella tularensis with one or more known mutations within the QRDR of gyrA, gyrB, parC, and parE genes were tested with SimpleProbe and High Resolution Melt (HRM) dye chemistries and Pyrosequencing genetic analysis to evaluate the ability to rapidly detect ciprofloxacin-induced mutations. While SimpleProbe and Pyrosequencing successfully identified all known mutants, the HRM assay identified all but those resulting from G<-->C or A<-->T substitutions.

In silico microarray probe design for diagnosis of multiple pathogens

BackgroundWith multiple strains of various pathogens being sequenced, it is necessary to develop high-throughput methods that can simultaneously process multiple bacterial or viral genomes to find common fingerprints as well as fingerprints that are unique to each individual genome. We present algorithmic enhancements to an existing single-genome pipeline that allows for efficient design of microarray probes common to groups of target genomes. The enhanced pipeline takes advantage of the similarities in the input genomes to narrow the search to short, nonredundant regions of the target genomes and, thereby, significantly reduces the computation time. The pipeline also computes a three-state hybridization matrix, which gives the expected hybridization of each probe with each target.ResultsDesign of microarray probes for eight pathogenic Burkholderia genomes shows that the multiple-genome pipeline is nearly four-times faster than the single-genome pipeline for this application. The probes designed for these eight genomes were experimentally tested with one non-target and three target genomes. Hybridization experiments show that less than 10% of the designed probes cross hybridize with non-targets. Also, more than 65% of the probes designed to identify all Burkholderia mallei and B. pseudomallei strains successfully hybridize with a B. pseudomallei strain not used for probe design.ConclusionThe savings in runtime suggest that the enhanced pipeline can be used to design fingerprints for tens or even hundreds of related genomes in a single run. Hybridization results with an unsequenced B. pseudomallei strain indicate that the designed probes might be useful in identifying unsequenced strains of B. mallei and B. pseudomallei.

Identification of Genomic Signatures for the Design of Assays for the Detection and Monitoring of Anthrax Threats

Sequences that are present in a given species or strain while absent from or different in any other organisms can be used to distinguish the target organism from other related or un-related species. Such DNA signatures are particularly important for the identification of genetic source of drug resistance of a strain or for the detection of organisms that can be used as biological agents in warfare or terrorism. Most approaches used to find DNA signatures are laboratory based, require a great deal of effort and can only distinguish between two organisms at a time. We propose a more efficient and cost-effective bioinformatics approach that allows identification of genomic fingerprints for a target organism. We validated our approach using a custom microarray, using sequences identified as DNA fingerprints of Bacillus anthracis. Hybridization results showed that the sequences found using our algorithm were truly unique to B. anthracis and were able to distinguish B. anthracis from its close relatives B. cereus and B. thuringiensis.

Inactivation of West Nile virus in serum with heat, ionic detergent, and reducing agent for proteomic applications

Research involving biosafety level 3 pathogens such as West Nile virus (WNV) is often limited by the limited space and technical constraints of these environments. To conduct complex analytical studies outside of high containment, robust and reliable inactivation methods are needed that maintain compatibility with downstream assays. Here we report the inactivation of WNV in spiked serum samples using a commercially available SDS-PAGE sample buffer for proteomic studies. Using this method, we demonstrate its utility by identification proteins differentially expressed in the serum of mice experimentally infected with WNV.