Rickettsia prowazekii and real-time polymerase chain reaction

Comparative evaluation of two Rickettsia typhi-specific quantitative real-time PCRs for research and diagnostic purposes

Rickettsioses are caused by intracellular bacteria of the family of Rickettsiaceae. Rickettsia (R.) typhi is the causative agent of endemic typhus. The disease occurs worldwide and is one of the most prevalent rickettsioses. Rickettsial diseases, however, are generally underdiagnosed which is mainly due to the lack of sensitive and specific methods. In addition, methods for quantitative detection of the bacteria for research purposes are rare. We established two qPCRs for the detection of R. typhi by amplification of the outer membrane protein B (ompB) and parvulin-type PPIase (prsA) genes. Both qPCRs are specific and exclusively recognize R. typhi but no other rickettsiae including the closest relative, R. prowazekii. The prsA-based qPCR revealed to be much more sensitive than the amplification of ompB and provided highly reproducible results in the detection of R. typhi in organs of infected mice. Furthermore, as a nested PCR the prsA qPCR was applicable for the detection of R. typhi in human blood samples. Collectively, the prsA-based qPCR represents a reliable method for the quantitative detection of R. typhi for research purposes and is a promising candidate for differential diagnosis.

Strategies for detecting rickettsiae and diagnosing rickettsial diseases

Rickettsial diseases and scrub typhus constitute a group of the oldest known vector-borne diseases. The cosmopolitan distribution of the vectors that transmit rickettsiae and orientiae leads to a worldwide prevalence of these diseases. Despite their significant historical status, detection and diagnosis of these diseases are still evolving today. Serological methods remain among the most prevalent techniques used for the detection/diagnosis of rickettsial diseases and scrub typhus. Molecular techniques have been instrumental in increasing the sensitivity/specificity of diagnosis, identifying new Rickettsia and Orientia species and have enhanced epidemiological capabilities when used in combination with serological methods. In this review, we discuss these techniques and their associated pros and cons.

Negative impact of laws regarding biosecurity and bioterrorism on real diseases

Research on highly pathogenic microorganisms in biosafety level 3 and 4 laboratories is very important for human public health, as it provides opportunities for the development of vaccines and novel therapeutics as well as diagnostic methods to prevent epidemics. However, in recent years, after the anthrax and World Trade Center attacks in 2001 in the USA, the threat of bioterrorism has grown for both the public and the authorities. As a result, technical and physical containment measures and biosafety and biosecurity practices have been implemented in laboratories handling these dangerous pathogens. Working with selected biological agents and toxins is now highly regulated, owing to their potential to pose a threat to public health and safety, despite the fact that the anthrax attack was found to be the result of a lack of security at a US Army laboratory. Thus, these added regulations have been associated with a large amount of fruitless investment. Herein, we describe the limitations of research in these facilities, and the multiple consequences of the increased regulations. These limitations have seriously negatively impacted on the number of collaborations, the size of research projects, and, more generally, scientific research on microbial pathogens. Clearly, the actual number of known victims and fatalities caused by the intentional use of microorganisms has been negligible as compared with those caused by naturally acquired human infections.

Evidence of a louse-borne outbreak involving typhus in Douai, 1710-1712 during the war of Spanish succession

Background

The new field of paleomicrobiology allows past outbreaks to be identified by testing dental pulp of human remains with PCR.

Methods

We identified a mass grave in Douai, France dating from the early XVIII^th century. This city was besieged during the European war of Spanish succession. We tested dental pulp from 1192 teeth (including 40 from Douai) by quantitative PCR (qPCR) for R. prowazekii and B. quintana. We also used ultra-sensitive suicide PCR to detect R. prowazekii and genotyped positive samples.

Results and Discussion

In the Douai remains, we identified one case of B. quintana infection (by qPCR) and R. prowazekii (by suicide PCR) in 6/21 individuals (29%). The R. prowazekii was genotype B, a genotype previously found in a Spanish isolate obtained in the first part of the XX^th century.

Conclusion

Louse-borne outbreaks were raging during the XVIII^th century; our results support the hypothesis that typhus was imported into Europe by Spanish soldiers from America.

Rickettsial and ehrlichial infections

Rickettsial diseases represent a clinically homogeneous group of infections characterized by fever, headache myalgias, variable presence of a rash, and a broad spectrum of neurological manifestations. Epidemiological information including time of year, geography, history of arthropod exposure, and animal contact gives important clues to the diagnosis, and should be actively elicited. Abnormalities in hematological indices of liver function tests should also increase suspicion for illness. Delay in initiation of doxycycline therapy while awaiting laboratory confirmation of infection has been associated with progressive neurological impairment and death. Clinicians should maintain a low threshold to initiate empiric therapy for rickettsial diseases in any patient with neurological findings and compatible exposures, signs, or laboratories, as these syndromes represent readily treatable causes of neurological dysfunction.

Acceptance of a rapid herpes test in labour: survey of attitudes of patients and health care providers

OBJECTIVE

To determine the acceptability to pregnant women and their health care providers of a rapid test for genital herpes simplex virus (HSV) in labour.

METHODS

A cross-sectional survey was conducted with outpatient pregnant women and their health care providers (obstetricians, family physicians and midwives) at BC Women's Hospital and Health Centre.

RESULTS

Of pregnant women approached, 207 (92%) completed the survey; 90% reported no history of genital herpes. Rapid HSV testing in labour was acceptable to 85% of pregnant women. Among the 133 women who were planning a vaginal delivery, 63% were willing to consider delivery by Caesarean section and 53% were willing to consider intrapartum anti-viral medications if HSV was present in the genital tract. Of 51 health care providers surveyed, 98% indicated interest in knowing if their patient had a newly acquired HSV infection, while 84% indicated interest in knowing if the patient had a reactivation of infection. If HSV was detected in their patient's genital tract, 36% indicated they would recommend a Caesarean section, and 25% would consider antiviral medication as an investigational intrapartum treatment. Interestingly, both of these proportions increased if the patient had ruptured membranes for more than four hours.

CONCLUSION

Most pregnant women and their health care providers are receptive to the use of a rapid polymerase chain reaction test to detect genital HSV shedding in labour. This supports the development of HSV rapid testing and antiviral therapy trials in the labour setting.

Molecular diagnosis of bloodstream infections caused by non-cultivable bacteria

Bloodstream infections are an important cause of morbidity and mortality in patients. Blood culture is clearly the most important diagnostic procedure for identifying micro-organisms involved in bloodstream infections except when the patient has previously received antibiotics or in the presence of slow-growing or intracellular micro-organisms. Detection of micro-organisms, mainly in blood, using pathogen-specific or broad-range PCR assays is promising. However, it is very important to emphasise that the interpretation of this molecular tool is critical because of the risk of interfering contamination, underlining the necessity to interpret the results obtained with caution. Presently, due to more widely available data and to rapid advances in biotechnology, two significant improvements allow new perspectives for molecular diagnosis. Indeed, the complete sequences of genomes have provided an important source of gene sequences for PCR-based assays. In addition, the development of real-time PCR offers several advantages in comparison to conventional PCR, including speed, simplicity, quantitative capability and low risk of contamination. Herein, we review the usefulness of molecular diagnosis of highly fastidious micro-organisms in the context of three different bloodstream infections: systemic diseases (rickettsiosis, Q fever, bartonellosis, Whipple's disease), blood-culture-negative endocarditis and bioterrorism attack.

A murine model of infection with Rickettsia prowazekii: implications for pathogenesis of epidemic typhus

Epidemic typhus remains a major disease threat, furthermore, its etiologic agent, Rickettsia prowazekii, is classified as a bioterrorism agent. We describe here a murine model of epidemic typhus that reproduced some features of the human disease. When BALB/c mice were inoculated intravenously with R. prowazekii (Breinl strain), they survived but did not clear R. prowazekii infection. Immunohistological analysis of tissues and quantitative PCR showed that R. prowazekii was present in blood, liver, lungs and brain 1 day after infection and persisted for at least 9 days. Importantly, infected mice developed interstitial pneumonia, with consolidation of the alveoli, hemorrhages in lungs, multifocal granulomas in liver, and hemorrhages in brain, as seen in humans. Circulating antibodies directed against R. prowazekii were detected at day 4 post-infection and steadily increased for up to 21 days, demonstrating that R. prowazekii lesions were independent of humoral immune response. R. prowazekii-induced lesions were associated with inflammatory response, as demonstrated by elevated levels of inflammatory cytokines including interferon-gamma, tumor necrosis factor and the CC chemokine RANTES in the lesions. We concluded that the BALB/c mouse strain provides a useful model for studying the pathogenic mechanisms of epidemic typhus and its control by the immune system.