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Vectorial capacity: Average number of potentially infective bites transmitted by one vector species from one infective host in one day.

Virulence: Degree of pathogenicity; disease-evoking power of a microorganism in a given host. Numerically, the ratio of the number of cases of overt disease in the total number infected.

Vulnerability: Extent to which a population is liable to be harmed by a hazard event. Depends on the population's exposure to the hazard and its capacity to adapt or otherwise mitigate adverse impacts.

Weather: Condition of the atmosphere at a particular place and time measured in terms of wind, temperature, humidity, atmospheric pressure, cloudiness, and precipitation. In most places, weather can change from hour to hour, from day to day, and from season to season.

Zoonosis: Infection that causes disease in human populations but that can be perpetuated solely in nonhuman host animals (e.g., bubonic plague).