Rubulavirus
If not vaccinated against mumps, susceptible individuals catch the disease by breathing around an infected person who has coughed or sneezed, releasing their contaminated saliva. Those who have had mumps are usually immune to future infections of the disease. Children have the highest risk of catching mumps, and it is rare for an adult to contract mumps. The incubation period for mumps can range from a couple weeks to a month, while the illness period is a few weeks. The swelling of the salivary glands is caused when the virus travels from the respiratory tract to the salivary glands and multiplies within the glands, causing the glands to swell.
Measles
Estimates based on modern molecular biology place the emergence of measles as a human disease sometime after 500 AD (the former speculation that the Antonine Plague of 165–180 AD was caused by measles is now discounted). The first systematic description of measles, and its distinction from smallpox and chickenpox, is credited to the Persian physician Rhazes (860–932), who published "The Book of Smallpox and Measles". Given what is now known about the evolution of measles, Rhazes' account is remarkably timely, as recent work that examined the mutation rate of the virus indicates the measles virus emerged from rinderpest (cattle plague) as a zoonotic disease between 1100 and 1200 AD, a period that may have been preceded by limited outbreaks involving a virus not yet fully acclimated to humans. This agrees with the observation that measles requires a susceptible population of >500,000 to sustain an epidemic, a situation that occurred in historic times following the growth of medieval European cities.
Measles is an endemic disease, meaning it has been continually present in a community, and many people develop resistance. In populations not exposed to measles, exposure to the new disease can be devastating. In 1529, a measles outbreak in Cuba killed two-thirds of those natives who had previously survived smallpox. Two years later, measles was responsible for the deaths of half the population of Honduras, and it had ravaged Mexico, Central America, and the Inca civilization.