Reference no: EM133442056

Diseases: Diphtheria, Pertussis, Tuberculosis. Potentially serious bacterial diseases of the respiratory system such as diphtheria, pertussis, and tuberculosis (TB) are rare diseases in most countries with a well-developed health care infrastructure because of effective prevention efforts; however, historically these diseases have been some of the world's leading causes of death from infectious disease. Today they continue to have a significant impact in areas where vaccinations, treatment, and the implementation of preventive health care efforts are lacking.
Diphtheria
Diphtheria is a serious disease that can lead to life-threatening complications. It has a mortality rate of 5-10%. In countries where childhood vaccinations are routinely given, diphtheria is rare (less than one case per year in the United States) and occurs mostly in unvaccinated children younger than 5 years of age and in adults older than age 40 whose immunity has waned and who have not had any booster immunizations. In countries without an adequate health care system or where vaccination programs are interrupted, diphtheria can cause large epidemics. For example, childhood vaccinations were largely interrupted from 1990-1994 in the former Soviet states. As a result, more than 150,000 cases of diphtheria and 5000 deaths were reported from 1990 to 1998. Etiology and Transmission Diphtheria is a rare disease caused by cytotoxin-producing strains of Corynebacterium diphtheriae, a gram-positive, club-shaped bacillus. The cytotoxin is produced only when C. diphtheriae is infected by a lysogenic bacteriophage that expresses a toxin-producing gene. As with other causes of pharyngitis, diphtheria is spread by the contact mode of transmission.
Clinical Features and Diagnosis
Diphtheria begins with a sore throat and fever. However, as the cytotoxin kills the tissues in the pharynx, a thick, gray pseudomembrane called the diphtheritic membrane develops and then turns black from tissue death. The cytotoxin can also damage cells in the lymph nodes, heart, and nervous tissues. Severe swelling of cervical lymph nodes can produce a bull neck appearance. A common cause of death is suffocation when the membrane is dislodged and blocks the airway. Other complications include heart and nervous system damage. The disease is initially diagnosed by clinical signs and symptoms. Lab tests that identify the toxin-producing pathogen are used to confirm the diagnosis.
Pathogenesis
Pathogenic strains of C. diphtheriae contain a lysogenic phage that codes for a cytotoxin. The cytotoxin inhibits protein synthesis and kills the cells to which it attaches, primarily those in the pharynx, heart, and nervous system.
Treatment
Diphtheria is treated with erythromycin and administration of diphtheria antitoxin. The antitoxin consists of antibodies that specifically bind to and inactivate the cytotoxin. They are derived from the serum of horses that have been immunized with the diphtheria toxoid.
Prevention
Diphtheria is prevented by childhood vaccination with the diphtheria, tetanus, acellular pertussis (DTaP) vaccine. The vaccine contains inactivated diphtheria toxin, which is immunogenic but not pathogenic. A local case of diphtheria can cause an outbreak among children who have not been vaccinated or adults who have not had boosters. To prevent an outbreak of diphtheria, an infected individual is isolated from others. Individuals in close contact with the infected person are given a booster immunization and treated with prophylactic antibiotics. A throat swab is taken after 2 weeks and analyzed to ensure that the infected person is no longer contagious. See Table 18.1 for an overview of diphtheria.
Disease Application
TABLE 18.1 D Etiology
Corynebacterium diphtheria
A micrograph shows several rod-shaped Corynebacterium diphtheria.
Diagnosis
Samples obtained from the throat and nose including a portion of the diphtheritic membrane (if possible). Samples are grown in special culture media (Loeffler's). The Elek test is an in vitro test used to evaluate toxin production from isolated strains of Corynebacterium. Treatmen An antibiotic such as erythromycin and an antitoxin.
Prevention Vaccines with the diphtheria toxoid are routinely given as part of childhood vaccination series. Risk of spread can be reduced by isolation of infected individuals and by consistent practice of excellent personal hygiene.
Pertussis
Pertussis, or whooping cough, is an intense respiratory disease that is characterized by three sequential stages and a chronic cough that can last for weeks or months (Figure 18.2). It is commonly called whooping cough because of the characteristic whooping sound a patient makes by inhaling rapidly between fits of coughing. Children younger than 6 months old have the most severe disease. The case fatality rate is about 1%.
Etiology
Pertussis is caused by Bordetella pertussis, a gram-negative, aerobic coccobacillus.
Transmission
B. pertussis is spread by both contact mode (respiratory droplets, fomites, and direct contact) and airborne transmission. One of the most contagious pathogens, it can travel more than 1 m through the air. Approximately 85% of people that live in the same household as someone with pertussis and are not immune to infection contract the disease. Pertussis transmission is most likely during the first 2 weeks after a patient begins coughing, when numerous bacteria-filled droplets are released; however, a patient may remain contagious for up to 6 weeks. Immediate antibiotic therapy can decrease the contagious period to approximately 5 days, significantly curtailing transmission.
Diseases: Diphtheria, Pertussis, Tuberculosis