TeacherOfMedicine: [Infectiology] Introduction

Usually called infectious disease, infectious diseases, or infectious disease medicine.

Infectiologists specialise in infectious diseases. The infectious agents which cause diseases are called pathogens.
There is significant overlap with microbiology, genitourinary medicine, tropical medicine and travel medicine.

Etymology

Latin infectiō, infectiōnis = infection
Ancient Greek λογία (logia) = study of

Physiology of infectious diseases and immunity

The ecosystems of the planet Earth contain a huge population of diverse organisms. Some of these organisms accidentally enter the human body, but some of them are obligated to infect it as an essential phase of their lifecycle.

In health, harmful organisms trigger a response from the immune system. As a general rule, greater extents of tissue damage produce greater inflammatory responses. This increases the traffic of immune cells to the area.

Pathophysiology of infectious diseases and immunity

Despite the large range of diverse organisms in the world, there is a small range of common human infectious diseases. This is a testament to the ability of the human immune system to neutralise and destroy threats. Most types of infectious disease occur as a result of atypical circumstances (e.g. trauma, immunosupression).

Several pathogens are highly transmissible (e.g. influenzaviruses), but the vast majority of healthy patients will eradicate an infection relatively quickly, with permanent defence (immunity) against that strain.

Several pathogens are highly virulent and pathogenic (e.g. ebolaviruses). They can overwhelm the immune response by causing rapid tissue destruction in healthy hosts. Patients are often quickly symptomatic. The symptoms are often dramatic and mortality is high. These properties make them relatively poor at persisting in human populations.

Pathogens can be bacteria, fungi, unicellular eukaryotic parasites (e.g. protozoa, chromista), multicellular parasites (e.g. helminthiasis: nematodes, trematoda, cestoda), viruses, and prions.

All known organisms (including pathogens) are being continuously researched and categorised in the field of taxonomy.