In medical segment, the vectors are those organisms which transmit pathogens from human to human and animals to human. These vectors are blood sucking organisms especially insect which suck blood along with pathogen from the host and then transfer this pathogen to new host while sucking blood. A very good example is mosquito. Other examples are ticks and snails. Mosquito specie called anopheles (Only females) transfer plasmodium to human while biting where it multiply. When the affected person is bitten by female anopheles then she take the plasmodium from the blood of host and can transfer to other person while biting.
