Aedes albopictus distribution

http://ecdc.europa.eu/en/activities/diseaseprogrammes/emerging_and_vector_borne_diseases/Pages/index.aspx 

Vector-borne diseases rely upon organisms, named vectors, such as mosquitoes, ticks or sandflies that have an active role in the transmission of a pathogen from one host to the other, and also, in a broader sense, upon animals such as rodents, bats or pets, acting as reservoirs/carrier of pathogens of concern to human beings.

An emerging (or re-emerging) infectious disease generally is a disease (i) that arises through evolution or change in existing pathogens, (ii) was previously unrecognised  or (iii) is already known  but spreads to new geographic areas, or new populations, or reappears after having been eradicated.

Many factors that may facilitate the introduction and establishment of disease vectors, reservoirs or pathogens in new geographic areas could lead to the emergence of a disease in the European Union (EU). These factors include international travel and trade, e.g. legal and illegal trade in animals and animal products, new agricultural practices and land-use patterns, socio-demographic evolution and climatic changes.