The genus Bordetella has been enriched in recent years with new species. However, predominant B. pertussis, pertussis agent and pathogen only in humans; B. parapertussis, much rarer, also a pertussis agent clinically indistinguishable from pertussis but for a shorter time.
The species B. bronchiseptica is responsible for respiratory infection in a large number of mammals such as the pig (atrophic rhinitis, bronchopneumonia) or the dog (kennel cough) or the cat or especially immunocompromised man. B. avium (turkey coryza) and B. hinzii are responsible for respiratory infections in birds. B. holmesii responsible for bacteremia in humans. B. petrii is the only species in the environment.
History of the disease
It was in 1570, by Guillaume de Baillou that pertussis was described for the first time during an epidemic in Paris. In the XVIIth century, Willis and Sydenham describe pertussis syndrome under the name of pertussis (ethymologically: severe cough).
It was Jules Bordet, inventor of the Bordet-Wasserman (BW) reaction to detect syphilis, who, with Octave Gengou, developed the isolation of pertussis bacillus in 1906 on an extract-based medium. potatoes (middle of Bordet and Gengou). Was Nobel Prize in Medicine and Physiology in 1919.
Pathogenicity
In humans, B. pertussis and B. parapertussis are strict parasitic species of the respiratory mucosa. Other species have preferential hosts, animal species such as pigs and hens: B. bronchiseptica, B. avium and B. hinzii.
Whooping cough is a highly contagious childhood respiratory disease. The term whooping cough derives its name from the noisy character of the inspiratory recovery which resembles the song of the rooster. Its seriousness is due to bronchopulmonary complications and its possible mortality in infants. In well-vaccinated countries like France, mortality and morbidity have decreased by 95%.
However, in the absence of natural booster and vaccine booster, there has been a change in the transmission of the disease for several years. It is no longer from child to child but from adults and adolescents to unvaccinated infants. This disease is a very serious disease and can be fatal in newborns less than 3 months old. It can affect men regardless of their age.
In vaccinated populations, its immunity is evaluated at ten years without any vaccine or natural booster and for this reason one can have pertussis several times in his life. Because of this problem, the vaccination schedule was modified in 1998 with the addition of a booster at 11-13 years of age following the primary vaccination at 2-3-4 months and the booster at 16-18 months. Its surveillance has been carried out in France since 1996 by the pediatric hospital network, RENACOQ.
Classically, four phases are described: silent incubation (2-3 weeks), catarrhal (a few days), state phase (30 to 40 days) and finally convalescence (several months).
The classic disease is defined above all by a cough evolving for more than a week, or even 2 or 3 with fifths, characterized by difficult inspiratory recovery (rooster crowing), apneas, attacks of cyanosis or vomiting after the fifths. Hyperlymphocytosis is often associated.
In France, coughing for more than 21 days has been noted in almost 90% of cases with difficult inspiratory recovery (73%), vomiting after fifths (63%), cyanosis episodes (48%), hyperlymphocytosis> 104 / mm3 (45%), rooster crowing (33%) and apneas (21%), in unvaccinated individuals. However, it should be noted atypical forms, in adolescents and adults who were vaccinated in childhood.
Pathogenesis
The Bordet-Gengou bacillus induces a single infection by its manifestations and the duration of its symptoms. The bacteria will interact (colonization) with the tracheal cells ciliated by proteins of the adhesin type.
This first period of invasion or proliferation will lead to the production of various toxins expressing their biological effects resulting in the elimination of hair cells, the accumulation of mucus by paralysis of the ciliary purification system and an inflammatory reaction. Lymphocytosis is a systemic effect.
The genome of the species pertussis, parapertussis and bronchiseptica has been sequenced. B. pertussis is the most suitable species for humans. It would come from the species B. bronchiseptica, animal species, and would have adapted to humans after loss of chromosomal material
Diagnostic
Clinical diagnosis:
Whooping cough is most often diagnosed in the presence of the following signs: nocturnal cough of more than 14 days with fifths and difficult inspiratory recovery without fever, rooster crowing, apnea, attacks of cyanosis, vomiting after fifths or even hyperlymphocytosis. But it can be clinically atypical in adolescents and adults, hence biological confirmation is necessary.
The biological diagnosis is bacteriological (direct), genomic (PCR) or serological (indirect) but the diagnostic value varies according to data (%) from RENACOQ.
Bacteriological diagnosis:
. Collect using a dacron swab and culture quickly from nasopharyngeal aspirations or sputum in the case of an adult.
The sample must be taken, if possible, within the first 3 weeks of the onset of the disease and before antibiotic treatment. After agreement with the biologist, it must be sent immediately to the laboratory.
Isolation of the bacteria is infrequent in practice, due to the need to temporarily prepare a potato-based agar with mutton fibrous blood which will be incubated at least 7 days at 37 ° C and in a humid atmosphere. Culture remains the benchmark diagnosis but not very sensitive.
The advantage of isolating strains is to be able to follow the evolution of virulence factors such as pertussis toxin, adenyl cyclase-hemolysin, adhesins such as filamentous hemagglutinin, fimbriae, or even pertactin. These are small Gram-negative coccobacilli, bi-polar in color, often in diplococci.
Strictly aerobic, this bacterium is catalase +, oxidase + and has no glucidolytic activity. The appearance of the colonies is characteristic, in a mercury and hemolytic droplet (phase I).
Genomic diagnosis (PCR):
this diagnostic approach obtained directly from pathological product is the best as evidenced by the results over several years, the frequencies of positivity varying from 79 to 90%. However, several PCR techniques are currently used in France without all of them having been subject to validation of their performance.
The one whose primers makes it possible to amplify the promoter of the genes coding for PT is the only one which has been the subject of a validation.
Serological diagnosis:
By detection of various antibodies. In particular, the seroconversion observed after a second sample (1 month later) is defined by an increase or decrease in anti-PTX antibodies, in the absence of any recent vaccination. The antibodies sought are of various specificities:
Agglutinins, i.e. antibodies that bind bacteria, in the serum of patients.
Anti-toxin and anti-adhesin antibodies in the serum of patients by immunoblot or ELISA.
Treatment & Antibiotic Sensitivity
If the antibiogram is not necessary, antibiotic treatment based on erythromycin has its place in the first 3 weeks of evolution, given orally at a dose of 50 mg / kg / day in 3 to 4 doses during 14 days. Cotrimoxazole can be used during allergies, but its effectiveness has not been clearly established.
Antibiotic treatment makes it possible to quickly reduce the contagiousness allowing the return to community after 5 days of treatment. After the start of the fifths, the effect of the treatment on the evolution of the cough remains uncertain. Finally, hospital care for infants (<6 months) is justified during the acute phase.
Polyvalent immunoglobulins have not been shown to be effective in either prophylaxis or treatment, unlike erythromycin.
Vaccination:
The role of vaccination has been essential in reducing the incidence of pertussis. The introduction of the vaccine with whole germs killed in 1959 and especially its diffusion in 1966 thus resulted in a spectacular fall in the number of cases in France.
However, the term of protection is limited to a few years, hence the vaccine booster. The vaccine is presented in isolated form (Vaxicoq®) or combined with others (DTCOQ®, DTCP®, Tétracoq® or pentavalent including the vaccine against Haemophilus influenzae: Pentacoq® or Pent-HIBest®).
Following the re-emergence of cases in adolescents (see figure below), a booster with an “acellular” vaccine consisting of purified proteins was proposed from the age of 11 in the French vaccination calendar in 1998. In 2004 these new recommendations recommend vaccination of adults in professional contact with infants too young to be vaccinated and adults likely to become parents.