We present a case of an 11-year-old male patient oriented to our unit with anore
ID: 3523385 • Letter: W
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We present a case of an 11-year-old male patient oriented to our unit with anorexia, weight loss and persistent cough with nocturnal paroxysms for 4 weeks. He also reported occasional wheezing and chest tightness. He denied fever, chills, myalgia, sore throat, or rhinorrhea. The patient presented to his primary care physician 1 week prior with the same complaint and was treated with amoxicillin and ebastine. Facing the persistence of the complaints he was oriented to our unit in order to exclude tuberculosis. Further study confirmed Bordetella pertussis infection and he started clarithromycin (15 mg/kg/day for 14 days). The patient's symptoms resolved after two weeks. Two of the patient's family members have developed symptoms of Bordetella pertussis infection and were treated.Explanation / Answer
Bordetella pertussis :
Morphology :It is a small ovoid coccobacillus (0.5 micrometer) and gram negative.Toluidine blue staining may show bipolar metachromatic granules. In culture films, the bacilli tend to be arranged in loose clumps, with clear spaces in between giving a ' thumb print ' appearance.
Cultural characteristics : It is an obligate aerobe.No growth occurs anaerobically, grows best at 35-360 c . Medium used is the Bordet-Gengou glycine-potato-blood agar or the Regan-Lowe media.Charcoal blood agar is also useful medium. In Bordet medium, after 48-72 hours it shows viscid, opaque colony resembling bisected pearl or mercury drop.
Virulence factors :
1. Agglutinogens : Bordetellae carry surface agglutinogens associated with fimbriae. Infectious strains belong to types 1,2 and 3. Factor-specific antibodies are present in the sera of convalescent and immunised person. Agglutinogens promote virulence by helping bacteria to attach to respiratory epithelial cells.
2. Pertussis toxin (PT) : This is present only in Bordetella pertussis and responsible for whooping cough. PT is expressed on the surface of the bacillus and secreted into the surrounding medium. Toxin exhibits diverse biological and biochemical activities, for example, lymphocytosis producing factor or LPF causing lymphocytosis in patients; and two other effects are seen in experimental animals are : histamine sensitising factor or HSF responsible for hightened sensitivity to histamine and islet activating protein or IAP inducing excessive insuline secretionby the pancreatic islet cells. PT is a 117000 molecular weight hexamer protein composed of 6 subunits with A-B structure ( A being the enzymatically active moiety and B the binding component). PT toxoid is the major component of acellular pertussis vaccines.
3.Filamentous hemagglutinin ( FHA) : Bordetella pertussis can produce 3 hemagglutinins : PT, lipid factor and FHA. FHA is present on the bacillary surface and is readily shed.It adheres to the cilia of the respiratory epithelium and to erythrocytes. Besides facilitating adhesion to the bacteria, FHA and PT also promote secondary infection by coating other bacteria such as Haemophilus influenzae and Streptococcus pneumoniae. This phenomenon has been termed piracy of adhesins.
4. Pertactin : It is an outer membrane protein antigen.
5. Heat labile toxin ( HLT) : Cytoplasmic protein which is dermonecrotic and lethal in mice.
6. Adenylate cyclase (AC) : It acts by catalysing the production of cAMP by various types of cells.
7. Treacheal cytotoxin (TCT) : Low molecular weight peptidoglycan which induces ciliary damage in hamster trachea.
8. Lipopolysaccharides : heat stable toxin.
Sources of infections : The disease has 3 phases : catarrhal paroxysmal and convalescent. In our case , the patient was treated with antibiotic and recovered from paroxysmal phase to convalescent. The disease is common in pediatric cases. Maternal antibodies do not give protection against the disease. Infection is transmitted by droplets and fomites contaminated with oropharyngeal secretions. The secondary attack rates are highest in close household contacts. In adolescents and adults, the disease is often atypical and may present as bronchitis. They may serve as a source of infection for infants and children. With universal immunization, childhood pertussis is on the decline but adolescent pertussis is on the rise due to waning of immunity at that age.
Laboratory diagnosis :
1. Collection and transport of specimen : respiratory samples can be collected by per-nasal swab, post-nasal swab or using cough plate method. Transport medium : modified Stuart's medium or Mischulow's charcoal agar.
2. Microscopy : demonstration of bacilli in respiratory secretions by fluorescent antibody technique.
3. Culture : Culture media had been discussed already in above para. Identification is confirmed by microscopy and slide agglutination of the colony.
4. Polymerase chain reaction : PCR based tests are more sensitive.
5. Serology : it is not helpful to be used for routine diagnosis. Rise in antibody titre may be demonstrated in paired serum samples by agglutination, gel precipitation or complement fixation tests.
6. Other lab parameters : blood changes in the disease are distinctive. Marked leucocytosis occurs and erythrocyte sedimentation rate or ESR increases if secondary infections are present.
Treatment : chloramphenicol, cotrimoxazole.
Prophylaxis : whole cell killed vaccine, acellular vaccine.
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