Vector (epidemiology)

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A mosquito shortly after obtaining blood from a human (note the droplet of blood being expelled as a surplus). Mosquitos are a vector for several diseases, most notably malaria. Anopheles stephensi.jpeg
A mosquito shortly after obtaining blood from a human (note the droplet of blood being expelled as a surplus). Mosquitos are a vector for several diseases, most notably malaria.

In epidemiology, a disease vector is any agent who carries and transmits an infectious pathogen into another living organism; [1] [2] most agents regarded as vectors are organisms, such as intermediate parasites or microbes, but it could be an inanimate medium of infection such as dust particles. [3]

Epidemiology is the study and analysis of the distribution and determinants of health and disease conditions in defined populations.

In biology, a pathogen, in the oldest and broadest sense, is anything that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.

Parasitism Interaction between two organisms living together in more or less intimate association in a relationship in which association is disadvantageous or destructive to one of the organisms

In evolutionary biology, parasitism is a relationship between species, where one organism, the parasite, lives on or in 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 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.

Contents

Arthropods

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]

Arthropod phylum of animals

An arthropod is an invertebrate animal having an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda, which includes insects, arachnids, myriapods, and crustaceans. The term Arthropoda as originally proposed refers to a proposed grouping of Euarthropods and the phylum Onychophora. Arthropods are characterized by their jointed limbs and cuticle made of chitin, often mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages. The rigid cuticle inhibits growth, so arthropods replace it periodically by moulting. Arthopods are bilaterally symmetrical and their body possesses an external skeleton. Some species have wings.

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.

<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.

Malaria Mosquito-borne infectious disease

Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases it can cause yellow skin, seizures, coma, or death. Symptoms usually begin ten to fifteen days after being bitten by an infected mosquito. If not properly treated, people may have recurrences of the disease months later. In those who have recently survived an infection, reinfection usually causes milder symptoms. This partial resistance disappears over months to years if the person has no continuing exposure to malaria.

Filariasis Parasitic disease caused by a family of nematode worms

Filariasis is a parasitic disease caused by an infection with roundworms of the Filarioidea type. These are spread by blood-feeding diptera as black flies and mosquitoes. This disease belongs to the group of diseases called helminthiases.

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.

Triatominae subfamily of insects

The members of the Triatominae, a subfamily of the Reduviidae, are also known as conenose bugs, kissing bugs, assassin bugs, or vampire bugs. Other local names for them used in the Latin Americas 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.

<i>Trypanosoma</i> genus of Kinetoplastea

Trypanosoma is a genus of kinetoplastids, a monophyletic group of unicellular parasitic flagellate protozoa. Trypanosoma is part of the phylum Sacromastigophora. The name is derived from the Greek trypano- (borer) and soma (body) because of their corkscrew-like motion. Most trypanosomes are heteroxenous and most are transmitted via a vector. The majority of species are transmitted by blood-feeding invertebrates, but there are different mechanisms among the varying species. Some, such as Trypanosoma equiperdum, are spread by direct contact. In an invertebrate host they are generally found in the intestine, but normally occupy the bloodstream or an intracellular environment in the mammalian host.

<i>Trypanosoma cruzi</i> species of Kinetoplastea

Trypanosoma cruzi is a species of parasitic euglenoids. Amongst the protozoa, the trypanosomes characteristically bore tissue in another organism and feed on blood (primarily) and also lymph. This behaviour causes disease or the likelihood of disease that varies with the organism: for example, trypanosomiasis in humans, dourine and surra in horses, and a brucellosis-like disease in cattle. Parasites need a host body and the haematophagous insect triatomine is the major vector in accord with a mechanism of infection. The triatomine likes the nests of vertebrate animals for shelter, where it bites and sucks blood for food. Individual triatomines infected with protozoa from other contact with animals transmit trypanosomes when the triatomine deposits its faeces on the host's skin surface and then bites. Penetration of the infected faeces is further facilitated by the scratching of the bite area by the human or animal host.

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]

Chytridiomycota division of fungi

Chytridiomycota are a division of zoosporic organisms in the kingdom Fungi, informally known as chytrids. The name is derived from the Greek χυτρίδιον chytridium, meaning "little pot", describing the structure containing unreleased zoospores. Chytrids are one of the early diverging fungal lineages, and their membership in kingdom Fungi is demonstrated with chitin cell walls, a posterior whiplash flagellum, absorptive nutrition, use of glycogen as an energy storage compound, and synthesis of lysine by the α-amino adipic acid (AAA) pathway.

Olpidium brassicae is a plant pathogen, it is a fungal obligate parasite. In 1983, the Alsike, Alberta area's clover was struck by a fungus epidemic of Olpidium brassicae, previously not seen in Canada.

Zoospore

A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria and fungi to propagate themselves.

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]

Stem rust species of fungus

The stem, black, and cereal rusts are caused by the fungus Puccinia graminis and are a significant disease affecting cereal crops. Crop species that are affected by the disease include bread wheat, durum wheat, barley and triticale. These diseases have affected cereal farming throughout history. Since the 1950s, wheat strains bred to be resistant to stem rust have become available. Fungicides effective against stem rust are available as well.

<i>Berberis</i> A genus of flowering plants representing the barberry family

Berberis, commonly known as barberry, is a large genus of deciduous and evergreen shrubs from 1–5 m (3.3–16.4 ft) tall, found throughout temperate and subtropical regions of the world. Species diversity is greatest in South America and Asia; Europe, Africa and North America have native species as well. The best-known Berberis species is the European barberry, Berberis vulgaris, which is common in Europe, North Africa, the Middle East, and central Asia, and has been widely introduced in North America. Many of the species have spines on the shoots and along the margins of the leaves.

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

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]

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.

See also

Notes

  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

Yellow fever viral disease

Yellow fever is a viral disease of typically short duration. In most cases, symptoms include fever, chills, loss of appetite, nausea, muscle pains particularly in the back, and headaches. Symptoms typically improve within five days. In about 15% of people, within a day of improving the fever comes back, abdominal pain occurs, and liver damage begins causing yellow skin. If this occurs, the risk of bleeding and kidney problems is also increased.

Zoonosis infectious disease that is transmitted between species (sometimes by a vector) from animals other than humans to humans or from humans to other animals

Zoonoses are infectious diseases caused by bacteria, viruses and parasites that spread between animals and humans.

Mosquito family of insects

Mosquitoes are a group of about 3500 species of small insects that are a type of fly. Within that order they constitute the family Culicidae. The word "mosquito" is Spanish for "little fly". Mosquitoes have a slender segmented body, a pair of wings, three pairs of long hair-like legs, feathery antennae, and elongated mouthparts.

West Nile fever human disease

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%.

Arbovirus

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, including humans, 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 hemorrhagic fever may also occur.

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. Tick-borne illnesses 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. As of 2016, 16 tick-borne diseases of humans are known.

Natural reservoir long-term host of the pathogen of an infectious disease

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.

Waterborne diseases diseases caused by pathogenic microorganisms transmitted in water

Waterborne diseases are conditions caused by pathogenic micro-organisms that are transmitted in water. Disease can be spread while bathing, washing or 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.

<i>Culex</i> genus of insects

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 US 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, 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, finally in current situation related to one health approach mostly health policy makers recommends to widely applicability of medical entomology for disease control efficient and best fit on achieving development goal and to tackle the newly budding zoonotic diseases. Thoughtful to have and acquaint with best practice of Med. Entomologist to tackle the animal and public health issues together with controlling arthropods born diseases by having Medical Entomologists’ the right hand for bringing the healthy world [Yon w].

Mosquito-borne disease

Mosquito-borne diseases or mosquito-borne illnesses are diseases caused by bacteria, viruses or parasites transmitted by mosquitoes. They can transmit disease without being affected themselves. Nearly 700 million people get a mosquito-borne illness each year resulting in over one million deaths.

Dirofilaria repens is a filarial nematode that affects dogs and other carnivores such as cats, wolves, coyotes, foxes, and sea lions, as well as muskrats. It is transmitted by mosquitoes. Although humans may become infected as aberrant hosts, the worms fail to reach adulthood while infecting a human body.

Kunjin virus (KUNV) is a zoonotic virus of the family Flaviviridae and the genus Flavivirus. It is a subtype of West Nile Virus endemic to Oceania.

<i>Trypanosoma antiquus</i> species of Kinetoplastea

Trypanosoma antiquus is an extinct species of kinetoplastid, a monophyletic group of unicellular parasitic flagellate protozoa.

<i>Culex quinquefasciatus</i> species of insect

Culex quinquefasciatus Say, 1823, commonly known as the southern house mosquito, is a medium-sized mosquito found in tropical and subtropical regions of the world. It is the vector of Wuchereria bancrofti, avian malaria, and arboviruses including St. Louis encephalitis virus, Western equine encephalitis virus, zika virus and West Nile virus. It is taxonomically regarded as a member of the Culex pipiens species complex. Its genome was sequenced in 2010, and was shown to have 18,883 protein-coding genes.

Patricia (Pat) Anne Nuttall, OBE is a British virologist and acarologist known for her research on tick-borne diseases. Her discoveries include the fact that pathogens can be transmitted between vectors feeding on a host without being detectable in the host's blood. She is also a science administrator who served as the director of the Natural Environment Research Council (NERC) Centre for Ecology & Hydrology (2001–11). As of 2015, she is professor of arbovirology in the Department of Zoology of the University of Oxford.

Jamestown Canyon encephalitis is an infectious disease cause 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.

References

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  3. Roberts, Larry S.; John, Janovy; Gerald D., Schmidt (2008). Foundations of Parasitology. McGraw Hill. ISBN   978-0-07-302827-9. OCLC   226356765.
  4. "Classification of Animal Parasites". plpnemweb.ucdavis.edu.
  5. https://cid.oxfordjournals.org/content/29/4/734.full.pdf
  6. 1 2 R. S. Mehrotra (2013). Fundamentals of Plant Pathology. Tata McGraw-Hill Education. pp. 342–. ISBN   978-1-259-02955-4.
  7. Peter W. Price (1980). Evolutionary Biology of Parasites. Princeton University Press. pp. 61–. ISBN   0-691-08257-X.
  8. Haynes, A R. et al. Comparison of two parasitic vines: Dodder (Cuscuta) and Woe vine(Cassytha). Florida Dept Agric & Consumer Services. Division of Plant Industry. Botany Circular No. 30. January/February 1996
  9. "Handbook for Integrated Vector Management" (PDF). World Health Organization . Retrieved 3 December 2015.
  10. 1 2 "Vector-borne disease". The Health and Environment Linkages Initiative (HELI). Geneva, Switzerland: World Health Organization. Retrieved 7 April 2014.
  11. Parrish, Ryan (7 April 2014). "WHO focuses on vector-borne diseases for World Health Day 2014". Vaccine News Daily. Chicago, Illinois. Retrieved 7 April 2014.
  12. 1 2 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.

Bibliography