Includes insects, arachnids, crustaceans. Some diptera are vectors of diseases such as malaria, yellow fever, filariasis, and the arboviruses, while others are important pollinators and pest predators and parasites. Used to refer to diseases that are not consistently present in an area, and which are brought in from the outside or a temporary increase in the number of cases of an endemic disease.
Parasites are organisms that are metabolically dependent upon the host.
The form of the insect during the larval stage differs radically from the adult. E.g., Some scientists hypothesize that West Nile virus may be a chronic infection in birds that recrudesces during times of stress for the bird, such as migration, mating and when establishing territory. Although human populations can form reservoirs of this kind, the concept is usually applied to non-human populations from which the pathogen periodically escapes, causing individual infections or epidemics in humans or epizootics in other animals. A secondary result. In describing any species as a vector, what is meant is that some individuals of a species are capable of carrying a given pathogen.