Vector (epidemiology)

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A mosquito shortly after obtaining blood from a human (note the droplet of blood plasma being expelled as the mosquito squeezes out excess water). Mosquitos are a vector for several diseases, including malaria. Anopheles stephensi.jpeg
A mosquito shortly after obtaining blood from a human (note the droplet of blood plasma being expelled as the mosquito squeezes out excess water). Mosquitos are a vector for several diseases, including malaria.

In epidemiology, a disease vector is any agent which carries and transmits an infectious pathogen into another living organism; [1] [2] agents regarded as vectors are organisms, such as intermediate parasites or microbes. The first major discovery of a disease vector came from Ronald Ross in 1897, who discovered the malaria pathogen when he dissected a mosquito. [3]



The deer tick, a vector for Lyme disease pathogens. Adult deer tick(cropped).jpg
The deer tick, a vector for Lyme disease pathogens.

Arthropods form a major group of pathogen vectors with mosquitoes, flies, sand flies, lice, fleas, ticks, and mites transmitting a huge number of pathogens. Many such vectors are haematophagous, which feed on blood at some or all stages of their lives. When the insects blood feed, the pathogen enters the blood stream of the host. This can happen in different ways. [4] [5]

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 pathogens causing 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.[ citation needed ]

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.[ citation needed ]

There are several species of Thrips that act as vectors for over 20 viruses, especially Tospoviruses, and cause all sorts of plant diseases.

Plants and fungi

Some plants and fungi act as vectors for various pathogens. For example, the big-vein disease of lettuce was long thought to be caused by a member of the fungal division Chytridiomycota, namely Olpidium brassicae . Eventually however, the disease was shown to be viral. Later it transpired that the virus was transmitted by the zoospores of the fungus and also survived in the resting spores. Since then, many other fungi in the Chytridiomycota have been shown to vector plant viruses. [6]

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 Puccinia graminis for example, Berberis and related genera act as alternate hosts in a cycle of infection of grain. [7]

More directly, when they twine from one plant to another, parasitic plants such as Cuscuta and Cassytha have been shown to convey phytoplasmal and viral diseases between plants. [8] [6]

World Health Organization and vector-borne disease

The World Health Organization (WHO) states that control and prevention of vector-borne diseases are emphasizing "Integrated Vector Management (IVM)", [9] which is an approach that looks at the links between health and environment, optimizing benefits to both. [lower-alpha 1] [10]

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. [11]

Vector-borne zoonotic disease and human activity

Figure 1. This figure shows how the Flavivirus is carried by mosquitos in the West Nile Virus and Dengue fever. The mosquito would be considered a disease vector. Disease Vector.jpg
Figure 1. This figure shows how the Flavivirus is carried by mosquitos in the West Nile Virus and Dengue fever. The mosquito would be considered a disease vector.

Several articles, recent to early 2014, warn that human activities are spreading vector-borne zoonotic diseases. [lower-alpha 2] Several articles were published in the medical journal The Lancet , and discuss how rapid changes in land use, trade globalization, and "social upheaval" are causing a resurgence in zoonotic disease across the world. [12]

Examples of vector-borne zoonotic diseases include: [13]

Many factors affect the incidence of vector-borne diseases. These factors include animals hosting the disease, vectors, and people. [13]

Humans can also be vectors for some diseases, such as Tobacco mosaic virus , physically transmitting the virus with their hands from plant to plant.

See also


  1. "IVM strategies are designed to achieve the greatest disease control benefit in the most cost-effective manner, while minimizing negative impacts on ecosystems (e.g. depletion of biodiversity) and adverse side-effects on public health from the excessive use of chemicals in vector control." [10]
  2. "Vector-borne zoonotic diseases are those that naturally infect wildlife and are then transmitted to humans through carriers, or vectors, such as mosquitoes or ticks." [12]

Related Research Articles

Zoonosis Disease that can be transmitted from other species to humans

A zoonosis is an infectious disease caused by a pathogen that has jumped from an animal to a human. Typically, the first infected human transmits the infectious agent to at least one other human, who, in turn, infects others.

Mosquito Family of flies

A mosquito is any member of a group of about 3,500 species of small insects belonging to the order Diptera (flies). Within Diptera, mosquitoes constitute the family Culicidae. The word "mosquito" is Spanish and Portuguese for "little fly". Mosquitoes have a slender segmented body, one pair of wings, one pair of halteres, three pairs of long hair-like legs, and elongated mouthparts.

West Nile fever Human disease caused by West Nile virus infection

West Nile fever is an infection by the West Nile virus, which is typically spread by mosquitoes. In about 80% of infections people have few or no symptoms. About 20% of people develop a fever, headache, vomiting, or a rash. In less than 1% of people, encephalitis or meningitis occurs, with associated neck stiffness, confusion, or seizures. Recovery may take weeks to months. The risk of death among those in whom the nervous system is affected is about 10%.

Parasitism relationship between species where one organism lives on or in another organism, causing it harm

Parasitism is a symbiotic relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has characterised parasites as "predators that eat prey in units of less than one". Parasites include single-celled protozoans such as the agents of malaria, sleeping sickness, and amoebic dysentery; animals such as hookworms, lice, mosquitoes, and vampire bats; fungi such as honey fungus and the agents of ringworm; and plants such as mistletoe, dodder, and the broomrapes. There are six major parasitic strategies of exploitation of animal hosts, namely parasitic castration, directly transmitted parasitism, trophically transmitted parasitism, vector-transmitted parasitism, parasitoidism, and micropredation.

A blood-borne disease is a disease that can be spread through contamination by blood and other body fluids. Blood can contain pathogens of various types, chief among which are microorganisms, like bacteria and parasites, and non-living infectious agents such as viruses. Three bloodborne pathogens in particular, all viruses, are cited as of primary concern to health workers by the CDC-NIOSH: HIV, hepatitis B (HVB), & hepatitis C (HVC).


Arbovirus is an informal name used to refer to any viruses that are transmitted by arthropod vectors. The word arbovirus is an acronym. The word tibovirus is sometimes used to more specifically describe viruses transmitted by ticks, a superorder within the arthropods. Arboviruses can affect both animals and plants. In humans, symptoms of arbovirus infection generally occur 3–15 days after exposure to the virus and last three or four days. The most common clinical features of infection are fever, headache, and malaise, but encephalitis and viral hemorrhagic fever may also occur.

<i>Anopheles</i> Genus of mosquito

Anopheles is a genus of mosquito first described and named by J. W. Meigen in 1818. About 460 species are recognised; while over 100 can transmit human malaria, only 30–40 commonly transmit parasites of the genus Plasmodium, which cause malaria in humans in endemic areas. Anopheles gambiae is one of the best known, because of its predominant role in the transmission of the most dangerous malaria parasite species – Plasmodium falciparum.

Tropical diseases are diseases that are prevalent in or unique to tropical and subtropical regions. The diseases are less prevalent in temperate climates, due in part to the occurrence of a cold season, which controls the insect population by forcing hibernation. However, many were present in northern Europe and northern America in the 17th and 18th centuries before modern understanding of disease causation. The initial impetus for tropical medicine was to protect the health of colonial settlers, notably in India under the British Raj. Insects such as mosquitoes and flies are by far the most common disease carrier, or vector. These insects may carry a parasite, bacterium or virus that is infectious to humans and animals. Most often disease is transmitted by an insect "bite", which causes transmission of the infectious agent through subcutaneous blood exchange. Vaccines are not available for most of the diseases listed here, and many do not have cures.

Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. They are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa. Because individual ticks can harbor more than one disease-causing agent, patients can be infected with more than one pathogen at the same time, compounding the difficulty in diagnosis and treatment. 16 tick-borne diseases of humans are known, of which four have been discovered since 2013.

Natural reservoir A living host, such as an animal or a plant, inside of which an infectious pathogen naturally lives and reproduces

In infectious disease ecology and epidemiology, a natural reservoir, also known as a disease reservoir or a reservoir of infection, is the population of organisms or the specific environment in which an infectious pathogen naturally lives and reproduces, or upon which the pathogen primarily depends for its survival. A reservoir is usually a living host of a certain species, such as an animal or a plant, inside of which a pathogen survives, often without causing disease for the reservoir itself. By some definitions a reservoir may also be an environment external to an organism, such as a volume of contaminated air or water.


The members of the Triatominae, a subfamily of the Reduviidae, are also known as conenose bugs, kissing bugs, or vampire bugs. Other local names for them used in Latin America include barbeiros, vinchucas, pitos, chipos and chinches. Most of the 130 or more species of this subfamily feed on vertebrate blood; a very few species feed on other invertebrates. They are mainly found and widespread in the Americas, with a few species present in Asia, Africa, and Australia. These bugs usually share shelter with nesting vertebrates, from which they suck blood. In areas where Chagas disease occurs, all triatomine species are potential vectors of the Chagas disease parasite Trypanosoma cruzi, but only those species that are well adapted to living with humans are considered important vectors. Proteins released from their bites have been known to induce anaphylaxis in sensitive and sensitized individuals.

Waterborne diseases diseases caused by pathogenic microorganisms transmitted in water

Waterborne diseases are conditions caused by pathogenic micro-organisms that are transmitted in water. These diseases can be spread while bathing, washing, drinking water, or by eating food exposed to contaminated water. While diarrhea and vomiting are the most commonly reported symptoms of waterborne illness, other symptoms can include skin, ear, respiratory, or eye problems. Waterborne diseases are impacted by a country's economy and also impact the economy by being costly to deal with.

<i>Culex</i> Genus of flies

Culex is a genus of mosquitoes, several species of which serve as vectors of one or more important diseases of birds, humans, and other animals. The diseases they vector include arbovirus infections such as West Nile virus, Japanese encephalitis, or St. Louis encephalitis, but also filariasis and avian malaria. They occur worldwide except for the extreme northern parts of the temperate zone, and are the most common form of mosquito encountered in some major U.S. cities, such as Los Angeles.

<i>Babesia</i> Genus of protozoan parasites

Babesia, also called Nuttallia, is an apicomplexan parasite that infects red blood cells and is transmitted by ticks. Originally discovered by the Romanian bacteriologist Victor Babeș, over 100 species of Babesia have since been identified.

A canine vector-borne disease (CVBD) is one of "a group of globally distributed and rapidly spreading illnesses that are caused by a range of pathogens transmitted by arthropods including ticks, fleas, mosquitoes and phlebotomine sandflies." CVBDs are important in the fields of veterinary medicine, animal welfare, and public health. Some CVBDs are of zoonotic concern.

Medical entomology

The discipline of medical entomology, or public health entomology, and also veterinary entomology is focused upon insects and arthropods that impact human health. Veterinary entomology is included in this category, because many animal diseases can "jump species" and become a human health threat, for example, bovine encephalitis. Medical entomology also includes scientific research on the behavior, ecology, and epidemiology of arthropod disease vectors, and involves a tremendous outreach to the public, including local and state officials and other stake holders in the interest of public safety. Medical Entomologists are employed by private and public universities, private industries, and federal, state, and local government agencies, including all three branches of the US military - who hire medical entomologists to protect the troops from infectious diseases that can be transmitted by arthropods. Historically, during wars, more people have died due to insect-transmitted diseases, than to all the battle injuries combined.

Reverse zoonosis, also known as zooanthroponosis, and sometimes anthroponosis, refers to pathogens reservoired in humans that are capable of being transmitted to non-human animals.

Mosquito-borne disease

Mosquito-borne diseases or mosquito-borne illnesses are diseases caused by bacteria, viruses or parasites transmitted by mosquitoes. Nearly 700 million people get a mosquito-borne illness each year resulting in over one million deaths.

Jamestown Canyon encephalitis is an infectious disease caused by the Jamestown Canyon virus, an orthobunyavirus of the California serogroup. It is mainly spread during the summer by different mosquito species in the United States and Canada.

Wildlife smuggling and zoonoses Health risks associated with the trade in exotic wildlife

Wildlife trafficking practices have resulted in the emergence of zoonotic diseases. Exotic wildlife trafficking is a multi-billion dollar industry that involves the removal and shipment of mammals, reptiles, amphibians, invertebrates, and fish all over the world. Traded wild animals are used for bushmeat consumption, unconventional exotic pets, animal skin clothing accessories, home trophy decorations, privately owned zoos, and for traditional medicine practices. Dating back centuries, people from Africa, Asia, Latin America, the Middle East, and Europe have used animal bones, horns, or organs for their believed healing effects on the human body. Wild tigers, rhinos, elephants, pangolins, and certain reptile species are acquired through legal and illegal trade operations in order to continue these historic cultural healing practices. Within the last decade nearly 975 different wild animal taxa groups have been legally and illegally exported out of Africa and imported into areas like China, Japan, Indonesia, the United States, Russia, Europe, and South America.


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  3. Prevention, CDC-Centers for Disease Control and (2017-03-28). "CDC - Malaria - About Malaria - History - Ross and the Discovery that Mosquitoes Transmit Malaria Parasites". Retrieved 2020-10-23.
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  7. Peter W. Price (1980). Evolutionary Biology of Parasites. Princeton University Press. pp. 61–. ISBN   0-691-08257-X.
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  12. Purlain, Ted (5 December 2012). "Lancet addresses emerging infectious vector-borne diseases". Vaccine News Daily. Chicago, Illinois. Retrieved 7 April 2014.
  13. 1 2 University of California - Santa Cruz (30 November 2012). "Emerging vector-borne diseases create new public health challenges". Science Daily. Rockville, Maryland. Retrieved 7 April 2014.