Cocolitzli epidemic (1576)

The earliest recorded pandemic happened during the Peloponnesian War. It passed through Libya, Ethiopia, and Egypt,  and it reached Athens as the Spartans laid siege. Two-thirds of the population died.
The disease, suspected to have been typhoid fever, weakened the Athenians significantly and played a big role in their defeat by the Spartans.

It may have been an early appearance of smallpox that began with the Huns.
The Huns then infected the Germans, who passed it to the Romans and then returning troops spread it throughout the Roman empire.  This plague continued until about 180 A.D., claiming Emperor Marcus Aurelius as one of its victims.

Epidemiology is the branch of medicine that handles the following:

• Incidence: the occurrence of a disease over a specified period.
• Prevalence: how many people are affected within a population.
• Control of diseases: an appropriate public health response.

Two measurable factors mostly define the level of disease occurrence:

• The pattern and speed by which a disease moves.
• The size of the susceptible population.

• Sporadic refers to a disease that occurs infrequently or irregularly.
• Cluster refers to a disease that occurs in larger numbers even though the actual number or cause may be uncertain.
• Endemic refers to the constant presence and/or general prevalence of a disease in a geographic population.
• Hyperendemic refers to persistent, high levels of disease well above what is seen in other populations.
• Epidemic refers to a sudden increase in the number of cases of a disease above what is normally expected.
• Outbreak is the same as an epidemic but is often used to describe a more limited geographic event.
• Pandemic refers to an epidemic that has spread over several countries or continents, usually affecting a large number of people.

• The original use of the word Quarantine was the act of anchoring a ship arrived in Venice, Italy, for 40 days before landing.
• Infectiousness of any disease is measured by the reproduction number (R0, or R naught). For example, Smallpox has an R0 of 6 whereas Measles has an R0 of 16. 
• Vaccination, if available, and herd immunity can curb the spread of disease.
• Big cities, with exploding population and traffic, can lead to the rapid spread of any infectious disease.

The so-called Spanish flu did not originate in Spain. The geographic origin of the flu is debated to this day, though hypotheses have suggested East Asia, Europe, and even Kansas.
The influenza pandemic from 1918 got this name most likely because of the WWI context: The major countries involved in the war were keen to avoid encouraging their enemies, so reports of the extent of the flu were suppressed in Germany, Austria, France, the United Kingdom and the U.S. By contrast, neutral Spain had no need to keep the flu under wraps. That created the false impression that Spain was bearing the brunt of the disease.

The 1918 flu spread rapidly, killing 25 million people in just the first six months. This led some to fear the end of mankind and that the whole thing was caused by a form of super-virus.
Recent studies show that the high death rate can be attributed to crowding in military camps and urban environments, as well as poor nutrition and sanitation, which suffered during wartime.