Vector (epidemiology)

The mosquito is a vector for Malaria.

In epidemiology, a vector is any agent (person, animal or microorganism) that carries and transmits an infectious agent.^[1][2][3] Vectors are vehicles by which infections are transmitted from one host to another. Most commonly known vectors consist of arthropods, domestic animals or mammals that assist in transmitting parasitic organisms to humans or other mammals. A vector is not only required for part of the parasite's developmental cycle, but it also transmits the parasite directly to subsequent hosts.

Arthropods as vector

The deer tick, a vector for lyme disease.

Arthropods form a major group of disease vectors with mosquitoes, flies, sand flies, lice, fleas, ticks and mites transmitting a huge number of diseases. Many such vectors are haematophagous, which feed on blood at some or all stages of their lives. When the insects blood feed, the parasite enters the blood stream of the host. This can happen in different ways.

The Anopheles mosquito, a vector for Malaria, Filariasis and various arthropod-borne-viruses (arboviruses), inserts its delicate mouthpart under the skin and feeds on its host's blood. The parasites the mosquito carries are usually located in its salivary glands (used by mosquitoes to anaesthetise the host). Therefore, the parasites are transmitted directly into the host's blood stream. Pool feeders such as the sand fly and black fly, vectors for Leishmaniasis and Onchocerciasis respectively, will chew a well in the host's skin, forming a small pool of blood from which they feed. Leishmania parasites then infect the host through the saliva of the sand fly. Onchocerca force their own way out of the insect's head into the pool of blood.

Triatomine bugs are responsible for the transmission of a trypanosome, 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.

Examples of vectors

• Aedes mosquitoes are vectors of avian malaria, dengue fever, yellow fever and chikungunya.^[4]
• Aphids are the vectors of many viral diseases in plants.^[5]
• Bats which represent about 20% of all known mammalian species act as both a natural reservoirs for viruses such as the Hendra virus (HeV) and the SARS like coronaviruses^[6][7]and in many cases as a vector for various viruses such as the lyssaviruses including the rabies virus.^[8][9]
• Cyclopoid copepods; a number of species transmit the nematode Dracunculus medinensis.^[10]
• Domestic cats are the primary host species for Toxoplasma gondii a species of parasitic protozoa which causes Toxoplasmosis.^[11]Approximately 30% of the human population is infected with Toxoplasmosis.^[12]
• Fleas such as the human flea, Pulex irritans and the Oriental rat flea, Xenopsylla cheopis, transmit bubonic plague, murine typhus and tapeworms.^[13]
• Glassy-winged sharpshooter transmits the Xylella fastidiosa bacterium among plants, resulting in diseases of grapes, almonds, and many other cultivated plants.^[14]
• Mosquitoes of the Anopheles genus transmit human malaria^[15]
• Phlebotomine sand flies transmit leishmaniasis, bartonellosis, sandfly fever and pappataci fever.^[16]
• Ticks of the genus Ixodes are vectors of Lyme disease and babesiosis.^[17]and along with lice transmit various members of the bacterial genus Rickettsia.^[18]
• Triatomine bugs such as Rhodnius prolixus are vectors of Chagas disease.^[19]
• Tsetse flies Several genera are vectors of human African trypanosomiasis also known as "African sleeping sickness".^[20]
• Mabelocking birds have been known to transmit many airborne human diseases diseases including Streptococcus .

See also

• Globalization and disease
• VectorBase: genomic database of invertebrate vectors of human pathogens
• Water-borne disease

Footnotes

1. ^ WordNet Search
2. ^ Last, James, ed (2001). A Dictionary of Epidemiology. New York: Oxford University Press. p. 185. ISBN 978-0195141696. OCLC 207797812. http://books.google.com/books?id=RPaQY8cG4N4C&lpg=PP1&dq=editions%3AISBN0195314492&client=firefox-a&pg=PP1#v=onepage&q=&f=false. 
3. ^ Roberts, Larry S.; John, Janovy; Gerald D., Schmidt (2008). Foundations of Parasitology. McGraw Hill. ISBN 978-0073028279. OCLC 226356765. 
4. ^ CDC: Aedes albopictus
5. ^ MetaPathogen.com/Aphid
6. ^ Halpin K, Young PL, Field HE, Mackenzie JS. Isolation of Hendra virus from pteropid bats: a natural reservoir of Hendra virus. J Gen Virol. 2000 Aug;81(Pt 8):1927-32. PMID 10900029
7. ^ Li W, Shi Z, Yu M, Ren W, et al. Bats are natural reservoirs of SARS-like coronaviruses. Science. 2005 Oct 28;310(5748):676-9. Epub 2005 Sep 29. PMID 16195424
8. ^ McColl KA, Tordo N, Aguilar Setién AA. Bat lyssavirus infections. Rev Sci Tech. 2000 Apr;19(1):177-96. PMID 11189715
9. ^ Arellano-Sota C. Rev Infect Dis. 1988 Nov-Dec;10 Suppl 4:S707-9. Vampire bat-transmitted rabies in cattle. PMID 3206085
10. ^ The intermediate hosts of Dracunculus medinensis in northern region, Ghana.
11. ^ Ryan KJ, Ray CG (eds) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. pp. 722–7. ISBN 0838585299. 
12. ^ Vivan AL, Caceres RA, Basso LA, et al.Structural studies of PNP from Toxoplasma gondii. Int J Bioinform Res Appl. 2009;5(2):154-62. PMID 19324601
13. ^ http://www.ttlntl.co.uk/3/Diseases/fleas.htm Taking the Lead: Fleas
14. ^ Vector Transmission of Xylella fastidiosa
15. ^ MicrobiologyBytes: Malaria
16. ^ Stages in the identification of phlebotomine sandflies as vectors of leishmaniases and other tropical diseases
17. ^ MetaPathogen.com/Deer tick
18. ^ Online Textbook of Bacteriology
19. ^ WHO Chagas disease (American trypanosomiasis)
20. ^ WHO African trypanosomiasis (sleeping sickness)

References

• Pawan, J.L. (1936). "Transmission of the Paralytic Rabies in Trinidad of the Vampire Bat: Desmodus rotundus murinus Wagner, 1840." Annual Tropical Medicine and Parasitol, 30, April 8, 1936:137-156.
• Pawan, J.L. "Rabies in the Vampire Bat of Trinidad with Special Reference to the Clinical Course and the Latency of Infection." Annals of Tropical Medicine and Parisitology. Vol. 30, No. 4. December, 1936