Parapertussis: an abortive pertussis infection?

Of mice and men: asymmetric interactions between Bordetella pathogen species

In a recent experiment, we found that mice previously infected with Bordetella pertussis were not protected against a later infection with Bordetella parapertussis, while primary infection with B. parapertussis conferred cross-protection. This challenges the common assumption made in most mathematical models for pathogenic strain dynamics that cross-immunity between strains is symmetric. Here we investigate the potential consequences of this pattern on the circulation of the two pathogens in human populations. To match the empirical dominance of B. pertussis, we made the additional assumption that B. parapertussis pays a cost in terms of reduced fitness. We begin by exploring the range of parameter values that allow the coexistence of the two pathogens, with or without vaccination. We then track the dynamics of the system following the introduction of anti-pertussis vaccination. Our results suggest that (1) in order for B. pertussis to be more prevalent than B. parapertussis, the former must have a strong competitive advantage, possibly in the form of higher infectivity, and (2) because of asymmetric cross-immunity, the introduction of anti-pertussis vaccination should have little effect on the absolute prevalence of B. parapertussis. We discuss the evidence supporting these predictions, and the potential relevance of this model for other pathogens.

Bacterial Infections

In Osier’s time, bacterial pneumonia was a dreaded event, so important that he borrowed John Bunyan’s characterization of tuberculosis and anointed the pneumococcus, as the prime pathogen, “Captain of the men of death.”1 One hundred years later much has changed, but much remains the same. Pneumonia is now the sixth most common cause of death and the most common lethal infection in the United States. Hospital-acquired pneumonia is now the second most common nosocomial infection.2 It was documented as a complication in 0.6% of patients in a national surveillance study,3 and has been reported in as many as 20% of patients in critical care units.4 Furthermore, it is the leading cause of death among nosocomial infections.5 Leu and colleagues6 were able to associate one third of the mortality in patients with nosocomial pneumonia to the infection itself. The increase in hospital stay, which averaged 7 days, was statistically significant. It has been estimated that nosocomial pneumonia produces costs in excess of $500 million each year in the United States, largely related to the increased length of hospital stay.

Role of pertussis toxin in causing symptoms of Bordetella parapertussis infection

Whooping cough can be caused by either Bordetella pertussis or Bordetella parapertussis. Although the two species share an almost complete DNA identity, Bordetella parapertussis does not produce pertussis toxin, which is thought to be the main virulence factor of Bordetella pertussis. In order to elucidate the role of pertussis toxin in causing the typical symptoms of whooping cough, clinical information from 33 patients with culture-positive Bordetella parapertussis infection was collected and compared to that from 331 patients with infection caused by Bordetella pertussis. Isolated strains of Bordetella parapertussis lacked pertussis toxin expression, as was demonstrated by negative tests for histamine sensitization. This was further substantiated in vivo by a significantly lower leukocyte count in the parapertussis group as compared to the pertussis group. Frequencies of typical symptoms of whooping cough, such as paroxysmal coughing, whooping and vomiting, were almost identical in the two groups. Nocturnal coughing and contact anamnesis were noted more often in the Bordetella pertussis group. Children in the parapertussis group were significantly more often vaccinated with whole-cell pertussis vaccine than children infected with Bordetella pertussis. The results indicate that pertussis toxin may not play a decisive role in causing the typical symptoms of whooping cough, such as paroxysmal coughing, whooping and vomiting.

Human infections associated with Bordetella bronchiseptica

This study examines the potential of Bordetella bronchiseptica to act as a human pathogen. After encountering two patients from whom B. bronchiseptica was isolated, we searched the literature and found 23 reports in which a human infection was reported in association with B. bronchiseptica. As a basis for evaluating these cases, we summarize the literature about the current microbiological status of B. bronchiseptica, the pathology and pathogenic mechanisms associated with the microorganism, and the likelihood of it acting as a commensal or colonizer. From this review we conclude that B. bronchiseptica has been rarely isolated from humans despite their considerable exposure to animal sources. Evidence suggests that B. bronchiseptica may be rarely encountered as a commensal or colonizer of the respiratory tract of humans and rarely in association with infection. When found as a probable pathogen, most infections have been respiratory tract in origin and have occurred in severely compromised hosts.

A DNA hybridization test for detection of Bordetella in nasopharyngeal specimens

A cloned Bam H1 fragment of genomic Bordetella pertussis DNA which recognized a frequently repeated sequence in the genome of B. pertussis was used as a probe in a DNA hybridization assay for the detection of Bordetella. Extensive studies on cross-reactivity were carried out in standardized strains and in cultured swab specimens from patients without suspected pertussis. Hybridizations of cultured clinical specimens from 142 patients with suspected pertussis were in complete agreement with the standard identification methods. The recovery rate of B. pertussis from nasopharyngeal swabs was less than 50%. Therefore the possibility to detect low numbers of B. pertussis in solution (nasopharyngeal aspirates) was investigated. The detection limit of direct hybridization by dot-blot technique was 5 x 10(3)-10(4) B. pertussis. Culturing bacteria on membranes placed on agar plates prior to hybridization showed that the detection limit could be lowered to 10(4), 10(2), and 10(1) cfu after 1, 2 and 3 days' culture, respectively. DNA hybridization under these conditions was found to be sufficiently sensitive and specific for further evaluation in clinical specimens for diagnosis of pertussis.

All species of the genus Bordetella contain genes for pertussis toxin of Bordetella pertussis

A molecular probe for the PT-operon of B. pertussis hybridized with 4.7 Kb EcoRI-fragments of chromosomal DNAs of B. pertussis strain 475 phase I, phase IV, B. parapertussis strains 504 and 17903, B. bronchiseptica strain 214, B. parapertussis strain 17903-convertant of B. pertussis phage 134 but not with phage 134 DNA under stringent conditions of DNA-DNA hybridization. This fact indicates the presence of PT-genes in all Bordetella species. Since there is no production of PT in B. parapertussis and B. bronchiseptica, a presence of regulatory mutations in the PT-operon or absence of the functionally active vir-gene product in these species is suggested.

Bacteriophages of Bordetella sp.: features of lysogeny and conversion

It has been the purpose of this paper to study molecular-biological features of the Bordetella bacteriophage interaction with the host cell during lysogeny and conversion as well as to determine the degree of homology between genomes of homologous and heterologous bacteriophages. Genomes of bacteriophages from B. pertussis 134, 41405 and B. bronchiseptica 214 were studied. Heteroduplex and restriction analyses revealed a heterogeneity of bacteriophage populations, and their DNAs were found to differ in size and position of inserts. As shown by blot hybridization, the bacteriophage genome is not inserted into the chromosome of the lysogenic cell but apparently exists as an autonomous plasmid replicon. It has been established that during conversion only a part of the phage genome is inserted into the chromosome of the recipient cell.

Evolutionary relationships in the genus Bordetella

The nucleotide sequence of the pertussis toxin operon of Bordetella pertussis, Bordetella parapertussis and Bordetella bronchiseptica, has shown that the last two species contain many common mutations and are likely to derive from a common ancestor (Aricò and Rappuoli, 1987). To elucidate further the evolutionary relationships between the Bordetella species, we have cloned and sequenced the promoter region and the gene coding for the S1 subunit of pertussis toxin from additional B. pertussis strains, such as the type strain BP 18323 and two recent clinical isolates, namely strain BP 13456 from Sweden and strain BP SA1 from Italy. While the strains BP SA1 and BP 13456 are shown to differ from the published B. pertussis sequences by only one base pair, the type strain BP 18323 contains a total of 11 base-pair substitutions. Remarkably, 9 of the 11 substitutions found in BP 18323 are also common to B. parapertussis and B. bronchiseptica, strongly suggesting that this strain derives from the same ancestor as B. parapertussis and B. bronchiseptica. Computer analysis of the sequence data allows the construction of an evolutionary 'tree' showing that the B. pertussis strains are very homogeneous and significantly distant from B. parapertussis and B. bronchiseptica. Therefore the proposed conversion from B. parapertussis to B. pertussis appears highly improbable.

Bordetella parapertussis and Bordetella bronchiseptica contain transcriptionally silent pertussis toxin genes

Pertussis toxin, the major virulence factor of Bordetella pertussis, is not produced by the closely related species Bordetella parapertussis and Bordetella bronchiseptica. It is shown here that these two species possess but do not express the complete toxin operon. Nucleotide sequencing of an EcoRI fragment of 5 kilobases comprising the regions homologous to the pertussis toxin genes shows that in this region, B. parapertussis and B. bronchiseptica are 98.5% and 96% homologous, respectively, to B. pertussis. The changes (mostly base pair substitutions) in many cases are identical in B. parapertussis and B. bronchiseptica, suggesting that these two species derive from a common ancestor. Many of the mutations common to B. parapertussis and B. bronchiseptica involve the promoter region, which becomes very inefficient. The S1 subunits of both species, when expressed in Escherichia coli, have the same ADP-ribosylating activity as the S1 subunit from B. pertussis, indicating that the mutations in the S1 gene described here do not affect its function.

Nucleotide sequence homology to pertussis toxin gene in Bordetella bronchiseptica and Bordetella parapertussis

Multiple strains of Bordetella parapertussis and B. bronchiseptica were examined for the presence of nucleotide sequences which hybridized with a cloned 4.5-kilobase (kb) fragment of B. pertussis DNA containing the genes responsible for pertussis toxin expression. All six B. parapertussis strains tested had nucleic acid sequences that hybridized with the cloned 4.5-kb fragment in Southern blot analyses. When the B. parapertussis DNA was digested with restriction endonuclease PstI, the pattern of hybridization was identical to that obtained with B. pertussis. Only five of the seven B. bronchiseptica strains tested had sequences that hybridized with the 4.5-kb fragment. Three of these B. bronchiseptica strains had a hybridization pattern identical to B. pertussis upon PstI digestion and Southern blot analyses. Two B. bronchiseptica strains were shown to lack a PstI cleavage site downstream from the region analogous to that coding for the pertussis toxin structural genes. Monoclonal antibody analyses were unable to detect pertussis toxin subunits S1 and S2 in Western blots with cellular material or culture supernatant from several B. bronchiseptica and B. parapertussis strains that possessed the DNA homologies. In addition, preliminary Northern hybridizations with RNA isolated from B. bronchiseptica and B. parapertussis strains suggested that the homologous regions were not transcribed. The data show that the gene coding for the toxic component of B. pertussis is common in other Bordetella species, though the gene probably is not expressed.

Genetic diversity and relationships in populations of Bordetella spp

Genetic diversity in 60 strains of three nominal Bordetella species recovered from humans and other mammalian hosts was assessed by analyzing electrophoretically demonstrable allelic variation at structural genes encoding 15 enzymes. Eleven of the loci were polymorphic, and 14 distinctive electrophoretic types, representing multilocus genotypes, were identified. The population structure of Bordetella spp. is clonal, and genetic diversity is relatively limited compared with most other pathogenic bacteria and is insufficient to justify recognition of three species. All isolates of Bordetella parapertussis were of one electrophoretic type, which was closely similar to 9 of the 10 electrophoretic types represented by isolates of Bordetella bronchiseptica. Bordetella pertussis 18-323, which is used in mouse potency tests of vaccines, is more similar genetically to isolates of B. bronchiseptica and B. parapertussis than to other isolates currently assigned to the species B. pertussis. Apart from strain 18-323, the isolates of B. pertussis represented only two closely related clones, and all isolates of B. pertussis from North America (except strain 18-323) were genotypically identical. Strain Dejong, which has been classified as B. bronchiseptica, was strongly differentiated from all of the other Bordetella isolates examined.

Mixed outbreak of Bordetella pertussis and Bordetella parapertussis infection in Finland

The epidemiology of whooping cough in a vaccinated population was studied during an outbreak of paroxysmal cough in an elementary school with 258 pupils in Turku, Finland. Nasopharyngeal specimens for isolation of Bordetella pertussis and/or sera for ELISA detection of antipertussis immunoglobulin M, A and G antibodies were taken from 94% of children who were prospectively followed for two months. Bordetella pertussis was isolated in six patients, and 17 culture-positive cases with Bordetella parapertussis were identified. Patients with Bordetella pertussis or Bordetella parapertussis were found simultaneously in the same classrooms. Comparison of immunoglobulin M responses to Bordetella pertussis and Bordetella parapertussis was used for differential diagnosis of these two infections. Twenty-six cases with pertussis and 27 cases with parapertussis were diagnosed. The results of this prospective study suggest that Bordetella parapertussis is a more common etiologic agent of mild respiratory tract infection among vaccinated school-aged children than is generally recognised. The possibility that Bordetella pertussis was converted to Bordetella parapertussis during this outbreak is discussed.

Diagnosis of whooping cough--a comparison of culture, immunofluorescence and serology with ELISA

Three methods for diagnosis of whooping cough--culture, immunofluorescence (IF) technique on nasopharyngeal secretion and serology with ELISA--were compared. 52 patients with symptoms of upper respiratory tract infection, which could not exclude pertussis as a differential diagnosis, were investigated. Pertussis infection was confirmed in 30 patients. Of these 16 (53%) were found by culture, 19 (63%) by IF and 28 (93%) by serology. It is concluded that IF analysis of nasopharyngeal secretion is a valuable tool for rapid diagnosis of whooping cough with a sensitivity similar to that of culture. Serodiagnosis with ELISA added a significant number of positive patients in which culture and IF were negative.