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In epidemiology, a disease vector is any living agent that carries and transmits an infectious pathogen such as a parasite or microbe, to another living organism. (2025). 9780199976720 ISBN 9780199976720 Agents regarded as vectors are mostly blood-sucking (Hematophagy) arthropods such as mosquitoes. The first major discovery of a disease vector came from Ronald Ross in 1897, who discovered the malaria pathogen when he dissected the stomach tissue of a mosquito.
The process of proving that a vector is responsible for transmitting pathogens is called vector incrimination.
The Anopheles mosquito, a vector for malaria, filariasis, and various arthropod-borne-viruses (), inserts its delicate mouthpart under the skin and feeds on its host's blood. The parasites the mosquito carries are usually located in its (mosquito saliva contains a cocktail of proteins that facilitate blood feeding by anaesthetizing the bite site, preventing blood clotting and modulating the host immune system among other things). Therefore, the parasites are transmitted directly into the host's blood stream. Pool feeders such as the Phlebotominae, Tsetse fly and black fly, vectors for pathogens causing leishmaniasis, African trypanosomiasis and onchocerciasis respectively, will chew a well in the host's skin, forming a small pool of blood from which they feed. Leishmania and trypanosome parasites then infect the host through the saliva of the sandfly or tsetse, respectively. Onchocerca force their own way out of the insect's head into the pool of blood.
Triatominae are responsible for the transmission of a Trypanosoma, Trypanosoma cruzi, which causes Chagas disease. The Triatomine bugs defecate during feeding and the excrement contains the parasites, which are accidentally smeared into the open wound by the host responding to pain and irritation from the bite.
There are several species of Thrips that act as vectors for over 20 viruses, especially Tospoviruses, and cause all sorts of plant diseases. (2025). 9780128186541 ISBN 9780128186541 (2025). 9780323953399 ISBN 9780323953399
Many plant pests that seriously damage important crops depend on other plants, often weeds, to harbour or vector them; the distinction is not always clear. In the case of Stem rust for example, Berberis and related genera act as alternate hosts in a cycle of infection of grain.
More directly, when they twine from one plant to another, parasitic plants such as Cuscuta and Cassytha have been shown to convey and between plants.
Examples of vector-borne zoonotic diseases include:
Several factors influence the incidence of vector-borne diseases, including environmental conditions, animal hosts, and the movement of people. The expansion of human settlements into previously undisturbed areas creates new habitats for vectors and animals that are potential hosts. Vector-borne zoonotic diseases are transmitted by a variety of vectors, including arthropods (mosquitoes, ticks, fleas) and rodents, with humans often acting as incidental hosts.
Humans can act as mechanical vectors for some diseases, such as Tobacco mosaic virus. TMV is a single-stranded RNA virus spread spread through physical contact. Humans physically transmit the virus with their hands or tools from plant to plant. The concept of humans acting as a vector for TMV requires understanding the transmission dynamics and how human activity can play a role in spreading the virus among plants. Humans do not usually act as primary vectors for zoonotic diseases; however, they contribute to indirect transmission via human travel or trade aiding the spread of vector-borne diseases.
In April 2014, WHO launched a campaign called "Small bite, big threat" to educate people about vector-borne illnesses. WHO issued reports indicating that vector-borne illnesses affect poor people, especially people living in areas that do not have adequate levels of sanitation, drinking water and housing. It is estimated that over 80% of the world's population resides in areas under threat of at least one vector borne disease.
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