Pertussis
Pertussis, commonly known as whooping cough, is a highly contagious disease caused by the bacteria Bordatella pertussis. It is characterized by classic paroxysms (spasms) of uncontrollable coughing, followed by a sharp intake of air which creates the characteristic "whoop" from which the name of the illness derives.
B. pertussis is uniquely a human pathogen (a disease causing agent, such as a bacteria, virus, fungus, etc.) meaning that it neither causes disease in other animals, nor survives in humans without resulting in disease. It exists worldwide as a disease-causing agent, and causes epidemics cyclically in all locations.
B. pertussis causes its most severe symptoms by attacking specifically those cells in the respiratory tract which have cilia. Cilia are small, hair-like projections that beat constantly, and serve to constantly sweep the respiratory tract clean of such debris as mucus, bacteria, viruses, and dead cells. When B. pertussis interferes with this janitorial function, mucus and cellular debris accumulate and cause constant irritation to the respiratory tract, triggering the cough reflex and increasing further mucus production.
Although the disease can occur at any age, children under the age of two, particularly infants, are greatest risk. Once an individual has been exposed to B. pertussis, subsequent exposures result in a mild illness similar to the common cold and are thus usually not identifiable as resulting from B. pertussis.
Whooping cough has four somewhat overlapping stages: incubation, catarrhal stage, paroxysmal stage, and convalescent stage.
An individual usually acquires B. pertussis by inhaling droplets infected with the bacteria, coughed into the air by an individual already suffering from whooping cough symptoms. Incubation occurs during a week to two week period following exposure to B. pertussis. During the incubation period, the bacteria penetrate the lining tissues of the entire respiratory tract.
The catarrhal stage is often mistaken for an exceedingly heavy cold. The patient has teary eyes, sneezing, fatigue, poor appetite, and a very runny nose. This stage lasts about eight days to two weeks.
The paroxysmal stage, lasting two to four weeks, is heralded by the development of the characteristic whooping cough. Spasms of uncontrollable coughing, the "whooping" sound of the sharp inspiration of air, and vomiting are hallmarks of this stage. The whoop is believed to occur due to inflammation and mucous which narrow the breathing tubes, causing the patient to struggle to get air in, and resulting in intense exhaustion. The paroxysms can be caused by over activity, feeding, crying, or even overhearing someone else cough.
The mucus that is produced during the paroxysmal stage is thicker and more difficult to clear than the waterier mucus of the catarrhal stage, and the patient becomes increasingly exhausted while attempting to cough clear the respiratory tract. Severely ill children may have great difficulty maintaining the normal level of oxygen in their systems, and may appear somewhat blue after a paroxysm of coughing due to the low oxygen content of their blood. Such children may also suffer from encephalopathy, a swelling and degeneration of the brain which is believed to be caused both by lack of oxygen to the brain during paroxysms, and also by bleeding into the brain caused by increased pressure during coughing. Seizures may result from decreased oxygen to the brain. Some children have such greatly increased abdominal pressure during coughing, that hernias result (hernias are the abnormal protrusion of a loop of intestine through a weaker area of muscle). Another complicating factor during this phase is the development of pneumonia from infection with another bacterial agent, which takes hold due to the patient's weakened condition.
If the patient survives the paroxysmal stage, recovery occurs gradually during the convalescent stage, and takes about three to four weeks. Spasms of coughing may continue to occur over a period of months, especially when a patient contracts a cold or any other respiratory infection.
By itself, pertussis is rarely fatal. Children who die of pertussis infection usually have other conditions (e.g., pneumonia, metabolic abnormalities, other infections, etc.) that complicate their illness.
The presence of a pertussis-like cough along with an increase of certain specific white blood cells (lymphocytes) is suggestive of B. pertussis infection, although it could occur with other pertussis-like viruses. The most accurate method of diagnosis is to culture (grow on a laboratory plate) the organisms obtained from swabbing mucus out of the nasopharynx (the breathing tube continuous with the nose). B. pertussis can then be identified during microscopic examination of the culture.
In addition to the treatment of symptoms, Treatment with the antibiotic erythromycin is helpful against B. pertussis infection only at very early stages of whooping cough: during incubation and early in the catarrhal stage. After the cilia, and the cells bearing those cilia, are damaged, the process cannot be reversed. Such a patient will experience the full progression of whooping cough symptoms, which will only abate when the old, damaged lining cells of the respiratory tract are replaced over time with new, healthy, cilia-bearing cells. However, treatment with erythromycin is still recommended to decrease the likelihood of B. pertussis spreading. In fact, it is not uncommon that all members of the household in which a patient with whooping cough lives are treated with erythromycin to prevent spread of B. pertussis throughout the community.
The mainstay of prevention lies in the mass immunization program that begins, in the United States, when an infant is two months old. The pertussis vaccine, most often given as one immunization together with diphtheria and tetanus, has greatly reduced the incidence of whooping cough. Unfortunately, there has been some concern about serious neurologic side effects from the vaccine itself. This concern led huge numbers of parents in England, Japan, and Sweden to avoid immunizing their children, which in turn led to epidemics of disease in those countries. Multiple carefully constructed research studies, however, have provided evidence that pertussis vaccine was not the cause of neurologic damage.
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