Pertussis

Introduction to whooping cough Pertussis (whoopingcough) is a common acute respiratory infection in children. Bordetella pertussis is the causative agent of this disease. It is characterized by paroxysmal spasmodic cough, with a special inhalation snoring at the end of the cough. The course of the disease is long, up to several weeks or even 3 months, so it is called pertussis. Young children suffering from this disease are prone to suffocation, pneumonia, encephalopathy and other complications, and high mortality. In recent years, the incidence of infants and adults has increased. basic knowledge The proportion of illness: 0.005% Susceptible people: more common in children Mode of infection: respiratory transmission Complications: bronchial pneumonia, atelectasis

Cause of pertussis

(1) Causes of the disease

The pathogen is B. pertussis in Bordetella, commonly known as B. pertussis. It is known that B. genus has four bacilli, and there are also B. pertussis except for B. pertussis. (B. parapertussis), B. bronchiseptica and B. avium, B. avium, which does not cause human disease, causes only bird infection, and B. pertussis About 1.0 ~ 1.5m, width about 0.3 ~ 0.5m, with capsule, can not move, Gram stain negative, aerobic, no spores, no flagella, stained with toluidine blue stained at both ends, bacterial culture requires a lot of 15% to 25%) blood can only breed well, so the colonies are often isolated in Border-Gengous medium (ie blood, glycerin, potato), and the growth of B. pertussis is slow, in a humid environment of 35-37 ° C 3 ~ After 7 days, a small, opaque colony grows, the first colony is raised and smooth, and it is smooth (S) type, also known as Phase I bacteria. The morphology is consistent, with capsule and strong virulence and antigenicity. Strong disease, such as the isolation of the colony in the ordinary medium to continue cultivation, bacteria Falling from smooth to rough (R) type, called IV phase bacteria, no capsule, loss of virulence and antigenicity, and loss of pathogenicity, phase II, phase III is intermediate transition type, B. pertussis can produce many toxicity Factor, there are five toxins known:

1. Pertussis exotoxin (PT): is a protein in the cell wall of B. pertussis. It used to be called leukocytosis or lymphocyte promoting factor (LPE), histamine sensitizing factor (HSF). ), insulin activating protein (IAP), pertussis exotoxin consists of five non-covalent chain subunits (S1 ~ S5), subunit (S2 ~ S5) is a non-toxic unit, can be with the host cell membrane Binding, mediated by the subunit S1 with enzyme activity, S1 can catalyze the partial ADP-ribose from nicotinamide adenine dinucleotide (NAD) by the activity of adenosine diphosphate (ADP)-ribosyltransferase Separation, transfer to the cell membrane inhibits guanosine triphosphate (CTP) binding, ie G protein synthesis, leading to cell metaplasia, while also promoting lymphocyte elevation, activation of islet cells and enhancement of immune response.

2, heat-resistant endotoxin (endotoxin, ET), 100 ° C 60min can only be partially destroyed, 180 ° C can be inactivated, this toxin can cause fever and cough.

3, heat-resistant toxin (HLT) This toxin can destroy its toxic effects after heating at 55 ° C for 30 min. This toxin antibody has no protective effect on B. pertussis infection.

4, tracheal cytotoxin (TCT): can damage the host airway ciliated epithelial cells, denaturation, necrosis.

5. Adenosine cyclase toxin (ACT): An enzyme on the surface of B. pertussis cells. This enzyme is activated by calmodulin after entering phagocytic cells, catalyzes the production of cAMP, interferes with phagocytosis, and inhibits neutrophils. Chemotactic and phagocytic bactericidal ability to enable continuous infection, ACT is also a hemolysin, capable of hemolysis, the important antigen of pertussis is two hemagglutination active antigens of pertussis, one is filag hemagglutinin (filamentous hemagglutinin, FHA), also known as pilus antigen from the surface of the bacteria, FHA plays a decisive role in the adhesion of B. pertussis to the airway epithelial cells, which is the main cause of the disease. The experiment found that FHA-immunized mice can fight the lethal challenge of B. pertussis, so FHA is a protective antigen, and another agglutinogen (AGG) is a protein component of the outer membrane and pili of B. pertussis, mainly containing 1 , 2, 3 three serotype coagulation factors, AGG-1 is species-specific; AGG-2, 3 is type-specific, by detecting the type of agglutinogen to understand the local epidemic, currently considered two hemagglutinin The antigen-related antibody is a protective antibody, and B. pertussis is classified into a seven-type agglutinant according to the heat-resistant agglutination antigenicity, a type 1 agglutination is possessed by all B. pertussis, and a type 7 agglutinogen is a B. genus (including a pertussis). Bacillus bronchus, B. septicum) is shared. Types 2-6 divide B. pertussis into different serotypes. The serotypes are mainly used to study the serotypes of strains and the selection of special serotype strains for the production of vaccines. There is no cross-immunization between B. pertussis and B. pertussis, and it can also cause epidemics. B. pertussis has weak resistance to external physical and chemical factors, and is destroyed at 55 ° C for 30 min. To kill, the general disinfectant sensitive, weak resistance to ultraviolet light, but survived longer in 0 ~ 10 .

(two) pathogenesis

1. Pathogenesis: The pathogenesis of whooping cough is not clear. It is probably the result of the comprehensive action of pertussis toxin on the body. When the bacteria are immersed in the respiratory tract of the susceptible person with air droplets, the filamentous hemagglutinin of the bacteria adheres to the throat to fine. The surface of the ciliary epithelial cells of the bronchial mucosa; followed by the local reproduction of bacteria and the production of various toxins such as pertussis toxin, adenylate cyclase and other epithelial cell cilia palsy and cell degeneration, resulting in decreased protein synthesis, epithelial cell necrosis And systemic reactions, due to epithelial cell lesions and cilia paralysis, the mucus and necrotic epithelium in the small bronchi are piled up, the discharge of secretions is blocked, the peripheral nerves of the respiratory tract are constantly stimulated, the cerebral cortex and the medullary cough center are transmitted, and the reflex is caused. Spastic cough, due to long-term stimulation, the cough center forms an excitatory foci, so that non-specific stimuli, such as eating, pharyngeal examination, cold wind, smoke and injection pain, can cause reflex cough, and can also cry during recovery. Other infections, induced pertussis-like cough, recent studies have shown that pertussis occurs The mechanism is related to the damage of host cell immune function by pertussis toxins, and the immune response mediated by CD4+ T cells and cytokines secreted by Th1 cells plays an important role in B. pertussis infection.

2. Pathological anatomy: B. pertussis invades the nasopharynx, larynx, trachea, bronchial mucosa, mucosal congestion, polynuclear leukocytes at the base of epithelial cells, mononuclear cell infiltration and partial cell necrosis. In addition to inflammatory infiltration of the interstitial cells around the bronchi and alveoli, cytoplasmic vacuoles in the epithelial cells are formed, and even the nuclear membrane is ruptured, necrotic, and shedding, but rarely affects the alveoli. If the secretion is blocked, it can cause atelectasis, bronchiectasis, secondary infection, prone to bronchial pneumonia, sometimes interstitial pneumonia; if pertussis encephalopathy occurs, microscopic examination or macroscopic brain congestion and edema, spotted hemorrhage , cortical atrophy, neuronal degeneration, cerebral edema, etc., at this time, liver fat infiltration and other changes are often seen.

Pertussis prevention

1, control of the source of infection: in the epidemic season, if there are prodromal symptoms should be early antibiotic treatment.

2, cut off the transmission route: Because the pertussis bacillus is weak to the outside world, there is no need for disinfection treatment, but the indoor ventilation should be maintained, the clothes should be exposed to sunlight, and the sputum and mouth and nose secretions should be disinfected.

Pertussis complications Complications bronchopneumonia atelectasis

More common in children, rare in adults.

1, bronchial pneumonia: the most common complication, mostly caused by secondary infection, can occur in any period of the disease, but more common in the cough period, when bronchial pneumonia occurs, paroxysmal cough can temporarily disappear, The body temperature suddenly rises, the breathing is shallow and fast, the lips are cyanotic, the lungs are squeaky, the peripheral blood leukocytes are elevated, and the neutrophils are mainly elevated. X-ray chest radiographs show pneumonia lesions.

2, atelectasis: atelectasis is blocked by the thick secretions of the bronchi or bronchioles, more common in the middle and lower lobe of the lung, may be related to poor drainage of the secretions in the middle lobe.

3, emphysema and subcutaneous emphysema: due to cough and secretion obstruction, can lead to emphysema, when alveolar high pressure, alveolar rupture can cause pulmonary interstitial emphysema, through the trachea fascia to produce subcutaneous emphysema, Pneumothorax can be caused by the hilar, and pneumothorax can be produced through the pleural visceral layer.

4, pertussis brain.

Pertussis symptoms common symptoms dry cough convulsions chest tightness convulsions cough low heat lung yin deficiency inhalation

According to the history of contact and typical coughing period, if there is no typical cough, combined with typical blood changes, clinical diagnosis can be made. The pathogen diagnosis depends on bacterial culture and specific serological examination. It is unknown for all age groups. Persistent cough, especially those with cough symptoms, need to consider the possibility of this disease for further testing.

The incubation period is 3 to 21 days, with an average of 7 to 10 days. The typical clinical course is divided into 3 phases.

1, catarrh or pre-cough period: cough on the onset, sneezing, runny, tears, low fever or moderate fever, similar to cold symptoms, symptoms disappear after 3 to 4 days, heat retreat, but cough gradually worse Especially in the night, this period is the most contagious, sustainable 7 to 10 days, if timely treatment, can effectively control the development of this disease.

2, coughing period: catarrhal period failed to control, the patient developed paroxysmal spastic cough, which is characterized by frequent uninterrupted short cough more than 10 sounds, such as exhalation state, and finally deep exhale, at this time due to cough Caused by negative pressure in the chest, and inhalation, the vocal cords are still in a state of tension, the air flow quickly through the narrow glottis and a kind of snoring sound of a hoar-like high-pitched sound, followed by a series of coughs. Such repeated episodes, one time more than once, until a large amount of sticky sputum and vomiting stomach contents, coughing before the onset of cough, there are often itching, chest tightness and other signs of discomfort. The child feels that the cough is coming, showing fear, and the expression is painful when the cough occurs. When coughing, due to increased pressure in the thoracic cavity, the superior vena cava is blocked, the jugular vein is engorged, the eyelids and face are congested and edema, the lips are cyanotic, and the conjunctiva is congested. For example, capillary rupture can cause subconjunctival hemorrhage and nosebleeds. Some patients have tongue extension to the teeth, friction with the incisors, and often have tongue-belt ulcers. Some patients suffer from cough and abdominal pressure, which causes incontinence and appearance. Hysteria. In this period, if there is no complication, it usually lasts for 2 to 6 weeks, and it can last for 2 months or more. The symptoms of pertussis in infants and newborns are quite special, and there is no typical cough. Due to the small glottis, apnea may occur due to blockage of vocal cords and sticky secretions. Bleeding due to lack of oxygen, or even convulsions, can also die from suffocation. Adults or older children, pertussis symptoms are mild, and atypical, mainly for dry cough, no paroxysmal cough, white blood cells and lymphocytes are not obvious increase, mostly misdiagnosed as bronchitis or upper respiratory tract infection.

3, recovery period: the number of paroxysmal cough gradually reduced to disappear, lasting 2 to 3 weeks to improve recovery, if there is concurrent pneumonia, atelectasis and so on often delay, can last for several weeks.

Bronchial pneumonia is a common complication. It usually occurs in the coughing period. It can also be complicated by pertussis encephalopathy. Patients have disturbance of consciousness and convulsions, but there is no change in cerebrospinal fluid.

Pertussis check

1, blood test: at the end of catarrh and early cough, white blood cell count is as high as (20 ~ 40) × 10 ⁹ / L, up to 100 × 10 ⁹ / L, classified lymphocytes in more than 60%, also up to 90% The above.

2. Bacterial culture: At present, the nasopharyngeal swab culture method is superior to the cough method. The earlier the culture, the higher the positive rate, the positive rate of catarrhal culture can reach 90%, and the positive rate of the third to fourth week is only 50%. The positive rate of sampling after coughing or coughing is higher. If penicillin in the medium can reduce the growth of other bacteria, it is more conducive to the growth of B. pertussis.

3, serological examination

(1) Enzyme-linked immunosorbent assay: At present, the use of pertussis toxin and filamentous hemagglutinin as antigen to detect pertussis-specific IgM antibody can be used as an early diagnosis, the positive rate is 70%, and the seroprevalence rate in recovery period is increased, especially More meaningful for bacterial culture negative.

(2) Enzyme-linked dot blotting: The use of anti-pertussis toxin monoclonal antibody for the detection of pertussis toxin in nasopharyngeal secretions of pertussis patients by enzyme-linked dot blotting has high specificity and can be used as an early diagnosis.

(3) Monoclonal antibody colony imprinting method: anti-B. pertussis lipopolysaccharide and filamentous hemagglutinin monoclonal antibody colony ELISA for detection of B. pertussis, 48 hours can appear clear blue dot positive imprinting reaction on nitrocellulose membrane, As an early diagnosis.

(4) Fluorescent antibody method: Apply smear of nasopharyngeal swab secretion, and then add high-priced pertussis antiserum that absorbs fluorescence. After 30 minutes, observe the pathogen under fluorescence microscope, which is suitable for rapid diagnosis. 75%-80% of patients in early stage are positive. However, there is a false positive, so it cannot replace the culture method.

4, polymerase chain reaction (PCR): check the application of nasopharyngeal aspirate for PCR, is a rapid, sensitive and specific method for the detection of pertussis antigen, especially for atypical patients, early use It is of great value to have an antibiotic or a PCR check in an immunized person.

5, bronchial pneumonia: X-ray chest showed increased lung texture, and mixed with patchy shadows.

Pertussis diagnosis

According to the local epidemic situation, there is no history of contact with pertussis patients. If the child has had fever, but the symptoms of cough after heat retreat are worse, especially in the evening, the cough is severe, and there is no obvious pulmonary positive sign, which should be regarded as a suspected diagnosis; Cough, peripheral blood counts of white blood cells and lymphocytes are significantly increased, according to these characteristics can make a clinical diagnosis of pertussis, plus bacterial culture positive or serological immunology, PCR positive can confirm the diagnosis of whooping cough.

Differential diagnosis

1, acute bronchitis and pneumonia: bronchitis caused by influenza B, adenovirus, respiratory syncytial virus, parainfluenza virus, cough, severe cough, often cough, but severe cough appears within a few days of onset There is no echo of chicken sputum after coughing, and it is not necessarily aggravated at night. Symptoms of systemic infection in acute phase such as coughing and coughing are severe, and the lungs often have a fixed dry and wet voice, and the white blood cell count is normal or high. After treatment, the symptoms are alleviated or disappeared in the short term.

2, bronchial lymph node tuberculosis: swollen lymph nodes compress the bronchi, or erode the bronchial wall, can cause spastic cough, but no chicken-like echo. Diagnosis can be made according to the symptoms of tuberculosis poisoning, tuberculin test, lung X-ray changes, etc.

3, tracheobronchial foreign body: sudden onset of paroxysmal cough, a history of foreign body inhalation, white blood cells do not increase, X-ray visible segmental atelectasis, bronchoscopy can be found in foreign bodies.

4, whooping syndrome: in the general pertussis anti-immunization of the population, there may still be scattered "pertussis" cases, often isolated adenovirus, other respiratory viruses, Mycoplasma pneumoniae and B. pertussis, and no B. pertussis, Its clinical symptoms, lung X-ray findings and blood picture, similar to typical whooping cough, need to rely on pathogen examination to identify. It is estimated that about 20% of cases are caused by the above-mentioned pathogens. Chlamydia infection can be similar to a pertussis-like cough, but there is no echo of chicken sputum, and the symptoms caused by B. pertussis are mild and the course of disease is short.

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