There it releases a toxin that causes biochemical changes in the intestinal cells releasing a flood of water and electrolytes. This new induced environment favors the cholera organism over other intestinal organisms. The floods of fluids wash the competition away. Within hours, diarrheal discharges contain more than 100 billion cholera organisms per liter. This viral disease in modern in origin and attacks all available human hosts resulting in death or a life-long immunity.
Humans are the only host for measles.
It is perhaps the most infectious of all the specific human diseases. People of all races and all ages are infected readily by even a casual exposure. In most industrialized countries, measles is a childhood disease because most adults are immune as a result of a previous childhood infection. A population of at least 230,000 to 500,000 persons is needed to sustain the disease. In smaller populations as on islands or among the Eskimo, the disease will infect every susceptible person and then lacking other persons, the disease will 'burn itself out' and disappear.