Bordetella pertussis

 

PT (Pertussis Toxin) is an exotoxin with six subunits (named S1 through S5—each complex contains two copies of S4).The subunits are arranged in a A-B structure: the A component is enzymatically active and is formed from the S1 subunit, while the B component is the receptor-binding portion and is made up of subunits S2–S5.The subunits are encoded by ptx genes encoded on a large PT operon that also includes additional genes which encode Ptl proteins: Together these proteins form the PT secretion complex.

PT is released from B. pertussis in an inactive form. When the B subunit binds to a cell membrane receptor, the A subunit (or protomer) becomes activated, perhaps through the action of glutathione and ATP. PT catalyzes the ADP-ribosylation of the α subunits of the heterotrimeric guanine nucleotide regulatory proteins G_i, G_o, and G_t. This prevents the G-proteins from interacting with cell membrane receptors, thus interfering with intracellular communication. Since the Gα subunits remain in their GDP-bound, inactive state, they are unable to inactivate adenylyl cyclase or open potassium channels.

Illness: if high index of suspicion the HPA must be informed. Contact tracing can be performed using salivary PCR, with vaccine offered as appropriate.

Catarrhal Phase - cough, 1-2 weeks of rhinorrhea, conjunctivitis.

Paroxsysmal Phase - cough (chronic cough is the only symptom found in adults), wheeze, conjunctival haemorrhage, lymphocytosis.

Convalescent Phase - slow resolution, increasing incidence in adults & kids. Kids younger than 3 months or older than 1 year might need ECMO.

Complications - FTT, vomiting, pneumonia and atelectasis. Low FiO2/Fits/Low Glu/Hyperinsulinaemia. Classically referred to as the "100 day" cough.

Diagnosis - done during acute and convalescent phases, NPA on calcium alginate tip for PCR (some false +ves for PCR), use serum for detection of pertussis antibody, antibody to filamenteous haemaglutinnin and raised IgG. Use selective media for culture.

Bordet Gengou Agar is used for the primary isolation of Bordetella pertussis and Bordetella parapertussis from clinical specimens. This is the "Cough Plate" (yes, they do actually cough on it - it is reserved for in patients due to contamination). The "pernasal swab" has the calcium alginate tip on the end of a bendy wire so that the pharynx is sampled not the anterior nares.

1) Bordet Gengou Agar (charcoal based - cefalexin added) - this forms the basis of the cough plate:

2a) Here is the pernasal swab - with my pen for comparison:

2b) And here is the plate with a useful illustration:

Treatment - Erythromycin, Clarithromycin, Doxycycline, Trim/sulfamethoxazole, Ciprofloxacin (locally). Antibiotics may lessen the severity of the illness if begun early on. Otherwise, treatment focuses on simple supportive measures.

Vaccination -   whole-cell vs acellular vaccine. The pertussis vaccine protects for only a few years, at most. As vaccination coverage has increased over the past 20 years, so has the number of reported cases of pertussis. It is unclear at this time whether this is reflective of an actual increase in disease incidence or whether more reports are being made, as physicians are realizing pertussis frequently occurs even in vaccinated communities and have begun actively looking for it in ill patients. The pertussis vaccinevaccine, the whole-cell pertussisacellular version that produces fewer reactions. Pertussis-containing vaccines are never administered to children over seven years of age (in the USA), due to an increased risk of such reactions. component has been linked with the development of neurologic disorders, as well. Due to the high number of adverse reactions to this component has been replaced in recent years by an acellular version that produces fewer reactions. Pertussis-containing vaccines are never administered to children over seven years of age, due to an increased risk of such reactions. In the UK, the vaccination profile is: the first year, aged 13-15 months, then preschool. We may start boosing at 15 years old.