Evaluation of specificity of BP3385 for Bordetella pertussis detection

Bordetella bronchiseptica and Bordetella pertussis: Similarities and Differences in Infection, Immuno-Modulation, and Vaccine Considerations

Bordetella pertussis and Bordetella bronchiseptica belong to the genus Bordetella, which comprises 14 other species. B. pertussis is responsible for whooping cough in humans, a severe infection in children and less severe or chronic in adults. These infections are restricted to humans and currently increasing worldwide. B. bronchiseptica is involved in diverse respiratory infections in a wide range of mammals. For instance, the canine infectious respiratory disease complex (CIRDC), characterized by a chronic cough in dogs. At the same time, it is increasingly implicated in human infections, while remaining an important pathogen in the veterinary field. Both Bordetella can evade and modulate host immune responses to support their persistence, although it is more pronounced in B. bronchiseptica infection. The protective immune responses elicited by both pathogens are comparable, while there are important characteristics in the mechanisms that differ. However, B. pertussis pathogenesis is more difficult to decipher in animal models than those of B. bronchiseptica because of its restriction to humans. Nevertheless, the licensed vaccines for each Bordetella are different in terms of formulation, route of administration and immune responses induced, with no known cross-reaction between them. Moreover, the target of the mucosal tissues and the induction of long-lasting cellular and humoral responses are required to control and eliminate Bordetella. In addition, the interaction between both veterinary and human fields are essential for the control of this genus, by preventing the infections in animals and the subsequent zoonotic transmission to humans.

Laboratory Diagnosis of Pertussis

The introduction of vaccination in the 1950s significantly reduced the morbidity and mortality of pertussis. However, since the 1990s, a resurgence of pertussis has been observed in vaccinated populations, and a number of causes have been proposed for this phenomenon, including improved diagnostics, increased awareness, waning immunity, and pathogen adaptation. The resurgence of pertussis highlights the importance of standardized, sensitive, and specific laboratory diagnoses, the lack of which is responsible for the large differences in pertussis notifications between countries. Accurate laboratory diagnosis is also important for distinguishing between the several etiologic agents of pertussis-like diseases, which involve both viruses and bacteria. If pertussis is diagnosed in a timely manner, antibiotic treatment of the patient can mitigate the symptoms and prevent transmission. During an outbreak, timely diagnosis of pertussis allows prophylactic treatment of infants too young to be (fully) vaccinated, for whom pertussis is a severe, sometimes fatal disease. Finally, reliable diagnosis of pertussis is required to reveal trends in the (age-specific) disease incidence, which may point to changes in vaccine efficacy, waning immunity, and the emergence of vaccine-adapted strains. Here we review current approaches to the diagnosis of pertussis and discuss their limitations and strengths. In particular, we emphasize that the optimal diagnostic procedure depends on the stage of the disease, the age of the patient, and the vaccination status of the patient.

Bordetella holmesii: an under-recognised Bordetella species

Bordetella holmesii, first described in 1995, is believed to cause both invasive infections (bacteraemia, meningitis, endocarditis, pericarditis, pneumonia, and arthritis) and pertussis-like symptoms. Infection with B holmesii is frequently misidentified as being with B pertussis, the cause of whooping cough, because routine diagnostic tests for pertussis are not species-specific. In this Review, we summarise knowledge about B holmesii diagnosis and treatment, and assess research needs. Although no fatal cases of B holmesii have been reported, associated invasive infections can cause substantial morbidities, even in previously healthy individuals. Antimicrobial treatment can be problematic because B holmesii's susceptibility to macrolides (used empirically to treat B pertussis) and third-generation cephalosporins (often used to treat invasive infections) is lower than would be expected. B holmesii's adaptation to human beings is continuing, and virulence might increase, causing the need for better diagnostic assays and epidemiological surveillance.

Insertion sequences shared by Bordetella species and implications for the biological diagnosis of pertussis syndrome

The molecular diagnosis of pertussis and parapertussis syndromes is based on the detection of insertion sequences (IS) 481 and 1001, respectively. However, these IS are also detected in the genomes of various Bordetella species, such that they are not specific for either B. pertussis or B. parapertussis. Therefore, we screened the genome of recently circulating isolates of Bordetella species to compare the prevalence of IS481, IS1001 and, also IS1002 with previously published data and to sequence all IS detected. We also investigated whether the numbers of IS481 and IS1001 copies vary in recently circulating isolates of the different Bordetella species. We used the polymerase chain reaction (PCR) method for screening the genome of circulating isolates and to prepare the fragments for sequencing. We used Southern blotting and quantitative real-time PCR for quantification of the numbers of IS. We found no significant diversity in the sequences of the IS harboured in the genomes of the Bordetella isolates screened, except for a 71-nucleotide deletion from IS1002 in B. bronchiseptica. The IS copy numbers in the genome of recently circulating isolates were similar to those in reference strains. Our results confirm that biological diagnosis targeting the IS481 and IS1001 elements are not specific and detect the species B. pertussis, B. holmesii and B. bronchiseptica (IS481), and B. parapertussis and B. bronchiseptica (IS1001).

Towards improved accuracy of Bordetella pertussis nucleic acid amplification tests

In many clinical microbiology laboratories, nucleic acid amplification tests such as PCR have become the routine methods for the diagnosis of pertussis. While PCR has greatly increased the ability of laboratories to detect Bordetella pertussis infections, it has also been associated with false-positive results that can, given the tendency of B. pertussis to cause outbreaks, result in unnecessary and costly control measures. The species specificity of Bordetella gene targets and their number of copies per genome greatly impact the performance characteristics of nucleic acid amplification tests for B. pertussis. It is crucial that laboratorians recognize these characteristics, to limit false-positive test results and prevent pseudo-outbreaks.

Significant finding of Bordetella holmesii DNA in nasopharyngeal samples from French patients with suspected pertussis

Pertussis is routinely diagnosed with real-time PCR based on insertion sequence IS481, which is not specific for Bordetella pertussis. We conducted a retrospective study using real-time PCRs specific for Bordetella pertussis and for Bordetella holmesii on 177 samples positive for IS481 PCR. Bordetella holmesii DNA was detected in 20.3% samples collected from adolescents and adults.

Evaluation of four commercial real-time PCR assays for detection of Bordetella spp. in nasopharyngeal aspirates

We evaluated the performances of 4 commercial real-time PCR kits for Bordetella pertussis IS481 sequence detection in nasopharyngeal aspirates by comparison with an in-house real-time PCR assay. Among them, the Simplexa Bordetella pertussis/parapertussis assay (Focus Diagnostics), the SmartCycler Bordetella pertussis/parapertussis assay (Cepheid), and Bordetella R-gene (Argene) present sensitivities over 90%. One kit proved unsuitable for routine clinical use.