Mosquitoes (Diptera: Culicidae) are responsible for major human deaths, morbidity and economic lose, whereas others do not. Due to their blood-sucking behaviour, mosquitoes are able to acquire the pathogens or parasites from one vertebrate host and pass them to another. They can transmit number of medically important pathogens and parasites such as viruses (yellow fever, dengue, Rift Valley fever, myxomatosis; Eastern equine encephalomyelitis, estern equine encephalomyelitis, Venezuelan equine encephalomyelitis, St. Louis encephalitis, LaCrosse encephalitis, Japanese encephalitis, Murray Valley encephalitis, Chikungunya fever, Onyong nyong fever, Ross River fever, West Nile fever, Zika encephalitis), protozoans (malaria), and nematodes (Wuchererian filariasis, Bancroftian filariasis, dog heartworm).

Ticks (Ixodida) are well-known vectors of human and veterinary pathogens. They transmit a greater variety of infectious organisms than any other group of blood-sucking arthropods. Worldwide, they are the most important vectors in the veterinary field and are second only to mosquitoes in terms of their public health importance. Ticks transmit numerous protozoan (babesiosis), viral (tick-borne encephalitis, Powassan encephalitis, Colorado tick fever, Crimean-Congo hemorrhagic fever, African swine fever), and bacterial (Lyme disease, Rocky Mountain spotted fever, Boutonneuse fever, tick-borne ehrlichiosis, Q fever, heartwater fever, anaplasmosis, tick-borne relapsing fever, avian spirochetosis, theileriosis (East Coast fever), bovine dermatophilosus) pathogens.

Lice (Phthiraptera) can be a menace to humans, pets, and livestock, not only through their blood-feeding or chewing habits but also because of their ability to transmit debilitating pathogens. Lice can transmit viral (swine pox) and bacterial (epidemic typhus, trench fever, louse-borne relapsing fever) diseases.

Fleas (Siphonaptera) are members of the order Siphonaptera, named for their mouthparts and wingless condition. Most fleas of medical or veterinary importance are members of the family Pulicidae, with other important fleas belonging to the Tungidae, Ceratophyllidae, Leptopsyllidae, or Vermipsyllidae. Flea acts as a vector for virus (myxomatosis) and bacterial (plague, murine (endemic) typhus, tularemia, cat flea rickettsiosis, cat scratch disease) diseases.