Molecular diagnosis of medical viruses

The diagnosis of infectious diseases has been revolutionized by the development of molecular techniques, foremost with the applications of the polymerase chain reaction (PCR). The achievable high sensitivity and ease with which the method can be used to detect any known genetic sequence have led to its wide application in the life sciences. More recently, real-time PCR assays have provided additional major contributions, with the inclusion of an additional fluorescent probe detection system resulting in an increase in sensitivity over conventional PCR, the ability to confirm the amplification product and to quantitate the target concentration. Further, nucleotide sequence analysis of the amplification products has facilitated epidemiological studies of infectious disease outbreaks, and the monitoring of treatment outcomes for infections, in particular with viruses which mutate at high frequency. This review discusses the applications of qualitative and quantitative real-time PCR, nested PCR, multiplex PCR, nucleotide sequence analysis of amplified products and quality assurance with nucleic acid testing (NAT) in diagnostic laboratories.

Incidence, etiology, and symptomatology of upper respiratory illness in elite athletes

PURPOSE

Upper respiratory illness (URI) is the most common medical condition affecting elite athletes. The aims of this study were to identify and evaluate the incidence, pathogenic etiology, and symptomatology of acute URI during a 5-month training and competition period.

METHODS

Thirty-two elite and 31 recreationally competitive triathletes and cyclists, and 20 sedentary controls (age range 18.0-34.1 yr) participated in a prospective surveillance study. Nasopharyngeal and throat swabs were collected from subjects presenting with two or more defined upper respiratory symptoms. Swabs were analyzed using microscopy, culture, and PCR testing for typical and atypical respiratory pathogens. The Wisconsin Upper Respiratory Symptom Survey (WURSS-44) was used to assess symptomatology and functional impairment.

RESULTS

Thirty-seven URI episodes were reported in 28 subjects. Incidence rate ratios for illness were higher in both the control subjects (1.93, 95% CI: 0.72-5.18) and elite athletes (4.50, 1.91-10.59) than in the recreationally competitive athletes. Infectious agents were identified in only 11 (two control, three recreationally competitive, and six elite) out of 37 illness episodes. Rhinovirus was the most common respiratory pathogen isolated. Symptom and functional impairment severity scores were higher in subjects with an infectious pathogen episode, particularly on illness days 3-4.

CONCLUSION

The results confirm a higher rate of URI among elite athletes than recreationally competitive athletes during this training and competition season. However, because pathogens were isolated in fewer than 30% of URI cases, further study is required to uncover the causes of unidentified but symptomatic URI in athletes. Despite the common perception that all URI are infections, physicians should consider both infectious and noninfectious causes when athletes present with symptoms.

Identification of a novel polyomavirus from patients with acute respiratory tract infections

We report the identification of a novel polyomavirus present in respiratory secretions from human patients with symptoms of acute respiratory tract infection. The virus was initially detected in a nasopharyngeal aspirate from a 3-year-old child from Australia diagnosed with pneumonia. A random library was generated from nucleic acids extracted from the nasopharyngeal aspirate and analyzed by high throughput DNA sequencing. Multiple DNA fragments were cloned that possessed limited homology to known polyomaviruses. We subsequently sequenced the entire virus genome of 5,229 bp, henceforth referred to as WU virus, and found it to have genomic features characteristic of the family Polyomaviridae. The genome was predicted to encode small T antigen, large T antigen, and three capsid proteins: VP1, VP2, and VP3. Phylogenetic analysis clearly revealed that the WU virus was divergent from all known polyomaviruses. Screening of 2,135 patients with acute respiratory tract infections in Brisbane, Queensland, Australia, and St. Louis, Missouri, United States, using WU virus–specific PCR primers resulted in the detection of 43 additional specimens that contained WU virus. The presence of multiple instances of the virus in two continents suggests that this virus is geographically widespread in the human population and raises the possibility that the WU virus may be a human pathogen.

We have identified a novel virus, referred to as WU virus, in the family Polyomaviridae by screening of human respiratory secretions. Two human polyomaviruses, BK and JC, were identified in 1971 and infect the majority of humans around the world. These two viruses are closely related to each other and are both are pathogenic in immunocompromised individuals. Earlier this year, a third polyomavirus, KI, was described in human clinical specimens, although its pathogenicity and prevalence in humans has not yet been established. The discovery of WU virus brings the number of polyomaviruses detected in humans to four. WU differs from BK and JC significantly in its genome sequence and in its relative tissue tropism, suggesting that it is likely to have unique biological properties. This discovery raises many questions for further investigation, such as, Is WU virus a human pathogen? If so, what kind of disease does it cause? Where in the body does WU virus reside? At what age does infection typically occur? Perhaps most importantly, there are likely to be many more as of yet unidentified viruses infecting the human body.

Impact of competitive inhibition and sequence variation upon the sensitivity of malaria PCR

Real-time PCR assays for Plasmodium species utilizing universal and species-specific primers were compared to investigate variables influencing decreased assay sensitivity. Sequence variation in oligomer targets and competitive inhibition of dual-species templates in universal-primer mixes were found to decrease assay sensitivity.

Tapsall J, D. Nissen M, P. Sloots T. Neisseria gonorrhoeae NAAT ? a problem down under

Nucleic acid amplification tests (NAATs) are used worldwide for the detection of Neisseria gonorrhoeae, either in conjunction with or in place of traditional bacterial culture techniques. There are numerous advantages of gonococcal NAATs, including increased sensitivity, that a viable organism is not needed for detection, and they can be used effectively on non-invasive specimens such as urine and self-collected specimens. For these reasons, NAATs have been particularly useful for patients in remote regions of Australia where sexual health services may not be available and where religious or cultural restrictions otherwise restrict opportunities for specimen collection. Australian studies have been at the forefront of investigating the use of self-collected NAAT specimens and particularly successful at introducing the use of tampon self-collected specimens in remote populations of Indigenous Australians.

Evidence that the gonococcal porA pseudogene is present in a broad range of Neisseria gonorrhoeae strains; suitability as a diagnostic target

AIMS

The primary aim of the study was to determine if the gonococcal porA pseudogene is a stable sequence target for the detection of Neisseria gonorrhoeae by PCR.

METHODS

A total of 240 gonococcal strains from various geographic locations were tested by porA pseudogene PCR. In addition, porA pseudogene PCR positivity rates were compared with established gonococcal assays in three Australian states.

RESULTS

All N. gonorrhoeae isolates provided positive results in the porA pseudogene PCR. Positivity rates compared favourably with established gonococcal assays, with increased N. gonorrhoeae detection in the Northern Territory and Western Australia.

CONCLUSIONS

The results of this multicentre study provide further evidence that the porA pseudogene is highly conserved across a diverse range N. gonorrhoeae strains and is a suitable PCR target for routine detection of N. gonorrhoeae.

Real-time PCR assays for detection of bocavirus in human specimens

The recently discovered human bocavirus (HBoV) is the first member of the family Parvoviridae, genus Bocavirus, to be potentially associated with human disease. Several studies have identified HBoV in respiratory specimens from children with acute respiratory disease, but the full spectrum of clinical disease and the epidemiology of HBoV infection remain unclear. The availability of rapid and reliable molecular diagnostics would therefore aid future studies of this novel virus. To address this, we developed two sensitive and specific real-time TaqMan PCR assays that target the HBoV NS1 and NP-1 genes. Both assays could reproducibly detect 10 copies of a recombinant DNA plasmid containing a partial region of the HBoV genome, with a dynamic range of 8 log units (10(1) to 10(8) copies). Eight blinded clinical specimen extracts positive for HBoV by an independent PCR assay were positive by both real-time assays. Among 1,178 NP swabs collected from hospitalized pneumonia patients in Sa Kaeo Province, Thailand, 53 (4.5%) were reproducibly positive for HBoV by one or both targets. Our data confirm the possible association of HBoV infection with pneumonia and demonstrate the utility of these real-time PCR assays for HBoV detection.

Human metapneumovirus, Australia, 2001-2004

We examined 10,025 respiratory samples collected for 4 years (2001-2004) and found a 7.1% average annual incidence of human metapneumovirus. The epidemic peak of infection was late winter to spring, and genotyping showed a change in predominant viral genotype in 3 of the 4 years.

Frequent detection of human rhinoviruses, paramyxoviruses, coronaviruses, and bocavirus during acute respiratory tract infections

Viruses are the major cause of pediatric acute respiratory tract infection (ARTI) and yet many suspected cases of infection remain uncharacterized. We employed 17 PCR assays and retrospectively screened 315 specimens selected by season from a predominantly pediatric hospital-based population. Before the Brisbane respiratory virus research study commenced, one or more predominantly viral pathogens had been detected in 15.2% (n = 48) of all specimens. The Brisbane study made an additional 206 viral detections, resulting in the identification of a microbe in 67.0% of specimens. After our study, the majority of microbes detected were RNA viruses (89.9%). Overall, human rhinoviruses (HRVs) were the most frequently identified target (n = 140) followed by human adenoviruses (HAdVs; n = 25), human metapneumovirus (HMPV; n = 18), human bocavirus (HBoV; n = 15), human respiratory syncytial virus (HRSV; n = 12), human coronaviruses (HCoVs; n = 11), and human herpesvirus-6 (n = 11). HRVs were the sole microbe detected in 37.8% (n = 31) of patients with suspected lower respiratory tract infection (LRTI). Genotyping of the HRV VP4/VP2 region resulted in a proposed subdivision of HRV type A into sublineages A1 and A2. Most of the genotyped HAdV strains were found to be type C. This study describes the high microbial burden imposed by HRVs, HMPV, HRSV, HCoVs, and the newly identified virus, HBoV on a predominantly paediatric hospital population with suspected acute respiratory tract infections and proposes a new formulation of viral targets for future diagnostic research studies.

Human metapneumovirus, Australia, 2001-2004

We examined 10,025 respiratory samples collected for 4 years (2001-2004) and found a 7.1% average annual incidence of human metapneumovirus. The epidemic peak of infection was late winter to spring, and genotyping showed a change in predominant viral genotype in 3 of the 4 years.

Genetic diversity of human metapneumovirus over 4 consecutive years in Australia

The molecular epidemiologic profile of human metapneumovirus (hMPV) infection has likely been skewed toward certain genetic subtypes because of assay-design issues, and no comprehensive studies have been conducted to date. Here, reverse-transcription polymerase chain reaction was used to screen 10,319 specimens from patients presenting to hospitals with suspected respiratory tract infections during 2001-2004. After analysis of 727 Australian hMPV strains, 640 were assigned to 1 of 4 previously described subtypes. hMPV was the most common pathogen detected, and subtype B1 was the most common lineage. Concurrent, annual circulation of all 4 hMPV subtypes in our study population was common, with a single, usually different hMPV subtype predominating in each year.

Detection and discrimination of herpes simplex viruses, Haemophilus ducreyi, Treponema pallidum, and Calymmatobacterium (Klebsiella) granulomatis from genital ulcers

BACKGROUND

Genital ulcer disease (GUD) is commonly caused by pathogens for which suitable therapies exist, but clinical and laboratory diagnoses may be problematic. This collaborative project was undertaken to address the need for a rapid, economical, and sensitive approach to the detection and diagnosis of GUD using noninvasive techniques to sample genital ulcers.

METHODS

The genital ulcer disease multiplex polymerase chain reaction (GUMP) was developed as an inhouse nucleic acid amplification technique targeting serious causes of GUD, namely, herpes simplex viruses (HSVs), H. ducreyi, Treponema pallidum, and Klebsiella species. In addition, the GUMP assay included an endogenous internal control. Amplification products from GUMP were detected by enzyme linked amplicon hybridization assay (ELAHA).

RESULTS

GUMP-ELAHA was sensitive and specific in detecting a target microbe in 34.3% of specimens, including 1 detection of HSV-1, three detections of HSV-2, and 18 detections of T. pallidum. No H. ducreyi has been detected in Australia since 1998, and none was detected here. No Calymmatobacterium (Klebsiella) granulomatis was detected in the study, but there were 3 detections during ongoing diagnostic use of GUMP-ELAHA in 2004 and 2005. The presence of C. granulomatis was confirmed by restriction enzyme digestion and nucleotide sequencing of the 16S rRNA gene for phylogenetic analysis.

CONCLUSIONS

GUMP-ELAHA permitted comprehensive detection of common and rare causes of GUD and incorporated noninvasive sampling techniques. Data obtained by using GUMP-ELAHA will aid specific treatment of GUD and better define the prevalence of each microbe among at-risk populations with a view to the eradication of chancroid and donovanosis in Australia.

Specific detection of enterovirus 71 directly from clinical specimens using real-time RT-PCR hybridization probe assay

Enterovirus 71 (EV71) is one of the main causative agents of hand, foot and mouth disease (HFMD) in young children. Infections caused by EV71 could lead to many complications, ranging from brainstem encephalitis to pulmonary oedema, resulting in high mortality. Thus, rapid detection of the virus is required to enable measures to be implemented in preventing widespread transmission. Based on primers and probes targeting at the VP1 region, a real-time reverse-transcriptase polymerase chain reaction (RT-PCR) hybridization probe assay was developed for specific detection of EV71 from clinical specimens. Quantitative analysis showed that the assay was able to detect as low as 5 EV71 viral copies and EV71 was detected from 46 of the 55 clinical specimens obtained from pediatric patients suffering from HFMD during the period from 2000 to 2003 in Singapore. This study showed that the single tube real-time RT-PCR assay developed in this study can be applied as a rapid and sensitive method for specific detection of EV71 directly from clinical specimens.

Cytotoxic T-lymphocyte epitope vaccination protects against human metapneumovirus infection and disease in mice

Human metapneumovirus (hMPV) has emerged as an important human respiratory pathogen causing upper and lower respiratory tract infections in young children and older adults. In addition, hMPV infection is associated with asthma exacerbation in young children. Recent epidemiological evidence indicates that hMPV may cocirculate with human respiratory syncytial virus (hRSV) and mediate clinical disease similar to that seen with hRSV. Therefore, a vaccine for hMPV is highly desirable. In the present study, we used predictive bioinformatics, peptide immunization, and functional T-cell assays to define hMPV cytotoxic T-lymphocyte (CTL) epitopes recognized by mouse T cells restricted through several major histocompatibility complex class I alleles, including HLA-A*0201. We demonstrate that peptide immunization with hMPV CTL epitopes reduces viral load and immunopathology in the lungs of hMPV-challenged mice and enhances the expression of Th1-type cytokines (gamma interferon and interleukin-12 [IL-12]) in lungs and regional lymph nodes. In addition, we show that levels of Th2-type cytokines (IL-10 and IL-4) are significantly lower in hMPV CTL epitope-vaccinated mice challenged with hMPV. These results demonstrate for the first time the efficacy of an hMPV CTL epitope vaccine in the control of hMPV infection in a murine model.

Sequence variation in primer targets affects the accuracy of viral quantitative PCR

This study was designed to assess the effect of sequence mismatches between primers and their targets on viral quantitative PCR. Numerous primers were constructed incorporating various mismatches with a target sequence on the BKV T antigen gene. When using these primers in standard Taqman two-step cycling conditions, as few as two mismatches in a single primer increased cycle threshold values and significantly influenced the calculation of viral load.

Nucleic acid amplification testing for Neisseria gonorrhoeae: an ongoing challenge

Nucleic acid amplification tests (NAATs) for the detection of Neisseria gonorrhoeae became available in the early 1990s. Although offering several advantages over traditional detection methods, N. gonorrhoeae NAATs do have some limitations. These include cost, risk of carryover contamination, inhibition, and inability to provide antibiotic resistance data. In addition, there are sequence-related limitations that are unique to N. gonorrhoeae NAATs. In particular, false-positive results are a major consideration. These primarily stem from the frequent horizontal genetic exchange occurring within the Neisseria genus, leading to commensal Neisseria species acquiring N. gonorrhoeae genes. Furthermore, some N. gonorrhoeae subtypes may lack specific sequences targeted by a particular NAAT. Therefore, NAAT false-negative results because of sequence variation may occur in some gonococcal populations. Overall, the N. gonorrhoeae species continues to present a considerable challenge for molecular diagnostics. The need to evaluate N. gonorrhoeae NAATs before their use in any new patient population and to educate physicians on the limitations of these tests is emphasized in this review.

A cluster of culture positive gonococcal infections but with false negative cppB gene based PCR

OBJECTIVES

To describe the prevalence and characteristics of isolates of Neisseria gonorrhoeae grown from urine samples that produced negative results with nucleic acid amplification assays (NAA) targeting the cppB gene.

METHODS

An initial cluster of culture positive, but cppB gene based NAA negative, gonococcal infections was recognised. Urine samples and suspensions of gonococci isolated over 9 months in the Northern Territory of Australia were examined using cppB gene based and other non-cppB gene based NAA. The gonococcal isolates were phenotyped by determining the auxotype/serovar (A/S) class and genotyped by pulsed field gel electrophoresis (PFGE).

RESULTS

14 (9.8%) of 143 gonococci isolated were of A/S class Pro(-/)Brpyut, indistinguishable on PFGE and negative in cppB gene based, but not other, NAA.

CONCLUSIONS

This cluster represents a temporal and geographic expansion of a gonococcal subtype lacking the cppB gene with consequent loss of sensitivity of NAA dependent on amplification of this target. Gonococci lacking the cppB gene have in the past been more commonly associated with the PAU-/PCU- auxotype, a gonococcal subtype hitherto infrequently encountered in Australia. NAA based on the cppB gene as a target may produce false positive as well as false negative NAA. This suggests that unless there is continuing comparison with culture to show their utility, cppB gene based NAA should be regarded as suboptimal for use either as a diagnostic or supplemental assay for diagnosis of gonorrhoea, and NAA with alternative amplification targets should be substituted.

Comparison of three in-house multiplex PCR assays for the detection of Neisseria gonorrhoeae and Chlamydia trachomatis using real-time and conventional detection methodologies

AIMS

To develop and evaluate multiplex PCR assays for Chlamydia trachomatis and Neisseria gonorrhoeae, using real-time and conventional PCR detection methodologies.

METHODS

Two real-time multiplex PCR assays, using nuclease (TaqMan-ABI7500) and hybridisation (LightCycler) probe formats, and a third assay using conventional PCR with solid-phase hybridisation and colour detection, were developed. The porA pseudogene was targeted for N. gonorrhoeae, and the major outer membrane protein gene for C. trachomatis. A total of 145 urogenital specimens were tested in all assays, and the results were compared with the Roche Cobas Amplicor assay.

RESULTS

There was little difference in clinical sensitivity and specificity, result discrimination and test cost for the three in-house assays. Our results showed that competitive inhibition of the PCR occurred in some samples that were positive for both organisms.

CONCLUSIONS

These results highlight the suitability and versatility of three multiplex PCR methods for the detection of C. trachomatis and N. gonorrhoeae.

A 5'-nuclease real-time reverse transcriptase-polymerase chain reaction assay for the detection of a broad range of influenza A subtypes, including H5N1

A 5'-nuclease real-time reverse transcriptase-polymerase chain reaction assay was developed for the detection of influenza type A and was validated using a range of influenza A subtypes, including avian strains, and 126 nasopharyngeal aspirate samples. The results show the assay is suitable for screening for influenza A infections, particularly in regions where avian strains may be circulating.

Evidence of human coronavirus HKU1 and human bocavirus in Australian children

Undiagnosed cases of respiratory tract disease suspected of an infectious aetiology peak during the winter months. Since studies applying molecular diagnostic assays usually report reductions in the number of undiagnosed cases of infectious disease compared to traditional techniques, we applied PCR assays to investigate the role of two recently described viruses, namely human coronavirus (HCoV) HKU1 and human bocavirus (HBoV), in a hospital-based paediatric population. Both viruses were found among Australia children with upper or lower respiratory tract disease during the autumn and winter of 2004, contributing to 21.1% of all microbial diagnoses, with individual incidences of 3.1% (HCoV-HKU1) and 5.6% (HBoV) among 324 specimens. HBoV was found to coincide with another virus in more than half of all instances and displayed a single genetic lineage, whilst HCoV-HKU1 was more likely to occur in the absence of another microbe and strains could be divided into two genetic lineages which we propose be termed HCoV-HKU1 type A and type B. Children under the age of 2 years were most at risk of infection by these viruses which contribute significantly to the microbial burden among patients with respiratory tract disease during the colder months.

Sequence variation can affect the performance of minor groove binder TaqMan probes in viral diagnostic assays

A minor groove binder (MGB) TaqMan real-time PCR assay was developed for the detection of respiratory syncytial virus (RSV) in clinical specimens. Upon evaluation of the assay, notable differences were observed in the overall fluorescent response obtained from RSV positive specimens, with some linear amplification curves deviating only slightly from baseline fluorescence. Sequencing of the probes targets in these RSV strains revealed single base mismatches with the MGB TaqMan probe. Overall, these results highlight the usefulness of MGB TaqMan probes for the detection of mismatches, but suggest that MGB Taqman probes have limitations for routine screening for uncharacterised viral strains.