How to become a vector

Most, if not all, species of arthropods feeding on blood or other body fluids of vertebrates transmit microorganisms, be them viruses, bacteria, protozoa or helminths. Differing, however, are the species and pathogenicity of microorganism, the developmental routes in the vector, the modes of transmission, the susceptibility of host species and the geographical region where transmission occurs. The interactions and mutual adaptations of vector, host and microorganism are extremely complex and usually a result of long-lasting evolutionary processes. Decisive for or against a vectorial role of an arthropod species are numerous factors such as physiological, receptor-mediated, behavioural and climatic traits. Microorganisms inadvertently imported into regions where they do not occur naturally (e. g., by infected vertebrate hosts or by introduction of infected vectors) might encounter hematophagous arthropods closely related to their native vectors and being vector-competent although no coevolution has taken place. Such scenarios will tend to cause unexpected outbreaks of disease and should be reason to carefully monitor the indigenous hematophagous arthropod fauna and to identify those species able to vector pathogens.