Vector-borne diseases are primarily spread by arthropods, including mosquitoes, sand flies, tsetse flies, and ticks. Whilst each of these groups of arthropod has many species, not all are capable of disease transmission. Indeed, there are over 3,500 species of mosquito, but only 60-100 of these species are able to transmit malaria, and even individuals within a population of mosquitoes show variability in infection and transmission rates.