A<unk>  is a place containing whatever epidemiological factors are needed for transmission of an<unk> . Any<unk>  will have a source of<unk> , and other common traits of such a place include a human community, a vector population, and environmental characteristics adequate for spreading<unk> .
Focus of infection
Disease vector
Anatomy of an Epidemic
Epidemiology of bed bugs
Strain 
Biological specimen
Vaccine shedding
Natural reservoir