Respiratory Diseases and Other Airborne Transmitted Infections

The vulnerable respiratory apparatus is easily invaded by microorganisms. Breathing is continuous and as respiratory gases are wafted in and out, infecting organisms find free passage deep inside the body. The site of entry is commonly the nasopharynx, but entry can also occur through the oropharynx and the conjunctiva. The lachrymal glands drain into the nasopharynx and experimental studies have shown that this is often a more certain method of infection than directly through the nose. The respiratory system also includes connections to the middle ear, the sinuses and the gastro-intestinal tract.

The ciliated lining and mucus-secreting cells of the respiratory tract can act as nonspecific host defence mechanisms entrapping microorganisms and passing them to the exterior. In attempting to expel these secretions from the body by coughing or spitting, organisms may be transmitted to another host. The lymphoid tissues, especially the tonsils and adenoids, guard the respiratory apparatus, but sometimes may themselves become foci of infection.

Respiratory infections are usually transmitted by direct contact between individuals and generally the closer the contact, the greater the chance of spread. As contact between human beings is a necessary part of life, control becomes more difficult and non-specific. Even so, the respiratory diseases are an enigma, the voluminous quantities of expelled organisms are sufficient to infect the entire population, yet only some individuals manifest disease. It is the infective dose and the host response, which determines whether infection will occur. Environmental factors that increase the infective dose (e.g. overcrowding) or reduce the host resistance (e.g. malnutrition or concomitant infections) can have a marked effect.

This chapter includes airborne transmitted infections that present as diseases of the respiratory system and also includes diseases of other systems of the body that are transmitted by the airborne route. Most of the skin infections, covered in Chapter 12, are also transmitted mainly by the airborne route.

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