Thank you for the opportunity to help you with your question!
A vector is an invertebrate animal that actively transmits an infectious agent between infected and susceptible vertebrates.
Epidemiologists follow a pre determined method to identify the vector in a disease.Inherent in the epidemiological approach is the belief that the frequency of occurrence of a disease in a population is governed by the interaction of a large number of different factors or determinants. The epidemiologist believes that by studying these interactions it may become possible to manipulate some of the determinants involved, and so reduce the frequency with which the disease in question occurs in a population.
a)A specific organism must be always be observed in association with the disease. (regular presence)
b)The organism must be isolated from an infected host and grown in pure culture in the laboratory. (exclusive presence)
c)When organisms from the pure culture are inoculated into a susceptible host organism, it must cause the disease. (sufficient cause)