Résumé
The number of already known arthropod species is almost two million and account for over 80% of all living animal species. Most of them do not affect humans and are essential in the maintenance of the ecosystem. However, some arthropods are pests of cultivated plants and pests of stored products. Some can be pathogen themselves as ectoparasites. Some, like several fly species and cockroaches, carry bacteria or helminths from fecal matter, garbage heaps, animal secretions to food products or human and animal body. Others, insects and Acari, are hematophagous and can be mechanical or biological vectors of pathogens. Besides, arthropods maintain complex interactions with different microorganisms they harbor. Some of these microorganisms can be simple symbionts, some have mutualistic behavior, and others can be infectious agents transmitted to a vertebrate host. These various microorganisms can elicit an innate immunity, which is more and more investigated in the context of arthropod-borne diseases. Nuisance and vector aspects are defined and discussed in this chapter, and main vectors and vector-borne pathogens are presented.