Chapter 24: Microbial Diseases of the Respiratory System

The upper respiratory system consists of the nose, the pharynx (throat), larynx (voice box), and the structures associated with them, including the middle ear and the auditory (eustachian) tubes
The lower respiratory system consists of the trachea (windpipe), bronchial tubes, and alveoli

Pharyngitis, inflammation of the mucous membranes of the throat, or sore throat.
When the larynx is the site of infection, we suffer from laryngitis, which affects our ability to speak.
==The microbes that cause pharyngitis also can cause inflamed tonsils, or tonsillitis==
- They have a mucous membrane lining that is continuous with that of the nasal cavity. Infection of a sinus involving heavy nasal discharge of mucus is called sinusitis.
Probably the most threatening infectious disease of the upper respiratory system is epiglottitis, inflammation of the epiglottis.

Streptococcal pharyngitis (strep throat) is an upper respiratory infection caused by group A streptococci (GAS).
- When the Streptococcus pyogenes strain causing streptococcal pharyngitis produces an erythrogenic (reddening) toxin, the resulting infection is called scarlet fever.
Another bacterial infection of the upper respiratory system is diphtheria.
- Diphtheria is also expressed as cutaneous diphtheria. In this form of the disease, C. diphtheriae infects the skin, usually at a wound or similar skin lesion, and there is minimal systemic circulation of the toxin.
Part of the normal immunization program for children in the United States is the DTaP vaccine, which protects against diphtheria, tetanus, and pertussis.
One of the more uncomfortable complications of the common cold, or of any infection of the nose or throat, is infection of the middle ear, otitis media, or earache.

More than one virus is involved in the etiology of the common cold
- Enterovirus D68 (EV-D68) causes cold like symptoms. In 2014, the United States experienced a nationwide outbreak of EV-D68 associated with severe respiratory illness.
As the bronchi become involved, bronchitis or bronchiolitis develops.

Infection by the bacterium Bordetella pertussis results in pertussis, or whooping cough.
In Europe during the seventeenth through the nineteenth centuries, tuberculosis (TB) was responsible for an estimated 20–30% of all deaths
- Another mycobacterial species, Mycobacterium bovis (BO-vis), is a pathogen mainly of cattle. M. bovis is the cause of bovine tuberculosis, which is transmitted to humans via contaminated milk or food.
This immunity, involving sensitized T cells, is the basis for the tuberculin skin test, a screening test for infection.
- There are a number of second-line drugs that can be used, mainly if resistance develops to alternatives
These cases, defined as extensively drug-resistant (XDR), are virtually untreatable and are emerging globally.
Not surprisingly, problems have arisen with cases of TB that are caused by multi-drug-resistant (MDR) strains.
==The term psittacosis is derived from the disease’s association with psittacine birds, such as parakeets and other parrots.==

Viral pneumonia can occur as a complication of influenza, measles, or even chickenpox.
- Middle East respiratory syndrome coronavirus (MERS-CoV) was first reported in Saudi Arabia and then spread to several other countries
Respiratory syncytial virus (RSV) is probably the most common cause of viral respiratory disease in infants.
The developed countries of the world are probably more aware of influenza (flu) than any other disease except the common cold.
Antigenic shifts mark changes great enough to evade most of the immunity developed in the human population.

Histoplasmosis superficially resembles tuberculosis.
Another fungal pulmonary disease, also rather restricted geographically, is coccidioidomycosis.
Blastomycosis is usually called North American blastomycosis to differentiate it from a similar South American blastomycosis.
- ==Aspergillosis is an important example; it is airborne by the conidia of Aspergillus fumigatus and other species of Aspergillus, which are widespread in decaying vegetation.==