Vector control

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Vector control taking place in the Southern United States during the 1920s. Vector Control.jpg
Vector control taking place in the Southern United States during the 1920s.

Vector control is any method to limit or eradicate the mammals, birds, insects or other arthropods (here collectively called "vectors") which transmit disease pathogens. The most frequent type of vector control is mosquito control using a variety of strategies. Several of the "neglected tropical diseases" are spread by such vectors.

Mammal Animals with milk-producing glands

Mammals are vertebrate animals constituting the class Mammalia, and characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex, fur or hair, and three middle ear bones. These characteristics distinguish them from reptiles and birds, from which they diverged in the late Triassic, 201–227 million years ago. There are around 5,450 species of mammals. The largest orders are the rodents, bats and Soricomorpha. The next three are the Primates, the Cetartiodactyla, and the Carnivora.

Bird Warm-blooded, egg-laying vertebrates with wings, feathers and beaks

Birds, also known as Aves or avian dinosaurs, are a group of endothermic vertebrates, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5 cm (2 in) bee hummingbird to the 2.75 m (9 ft) ostrich. They rank as the world's most numerically successful class of tetrapods, with approximately ten thousand living species, more than half of these being passerine, or "perching" birds. Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds. Wings, which evolved from forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in some birds, including ratites, penguins, and diverse endemic island species of birds. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have further evolved for swimming.

Insect Class of invertebrates

Insects or Insecta are hexapod invertebrates and the largest group within the arthropod phylum. Definitions and circumscriptions vary; usually, insects comprise a class within the Arthropoda. As used here, the term Insecta is synonymous with Ectognatha. Insects have a chitinous exoskeleton, a three-part body, three pairs of jointed legs, compound eyes and one pair of antennae. Insects are the most diverse group of animals; they include more than a million described species and represent more than half of all known living organisms. The total number of extant species is estimated at between six and ten million; potentially over 90% of the animal life forms on Earth are insects. Insects may be found in nearly all environments, although only a small number of species reside in the oceans, which are dominated by another arthropod group, crustaceans.

Contents

Importance

For diseases where there is no effective cure, such as Zika virus, West Nile fever and Dengue fever, vector control remains the only way to protect human populations.

<i>Zika virus</i> Species of virus

Zika virus (ZIKV) is a member of the virus family Flaviviridae. It is spread by daytime-active Aedes mosquitoes, such as A. aegypti and A. albopictus. Its name comes from the Ziika Forest of Uganda, where the virus was first isolated in 1947. Zika virus is related to the dengue, yellow fever, Japanese encephalitis, and West Nile viruses. Since the 1950s, it has been known to occur within a narrow equatorial belt from Africa to Asia. From 2007 to 2016, the virus spread eastward, across the Pacific Ocean to the Americas, leading to the 2015–16 Zika virus epidemic.

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%.

Dengue fever tropical disease caused by the dengue virus, transmitted by mosquito

Dengue fever is a mosquito-borne tropical disease caused by the dengue virus. Symptoms typically begin three to fourteen days after infection. This may include a high fever, headache, vomiting, muscle and joint pains, and a characteristic skin rash. Recovery generally takes two to seven days. In a small proportion of cases, the disease develops into severe dengue, also known as dengue hemorrhagic fever, resulting in bleeding, low levels of blood platelets and blood plasma leakage, or into dengue shock syndrome, where dangerously low blood pressure occurs.

However, even for vector-borne diseases with effective treatments the high cost of treatment remains a huge barrier to large amounts of developing world populations. Despite being treatable, malaria has by far the greatest impact on human health from vectors. In Africa, a child dies every minute of malaria; this is a reduction of more than 50% since 2000 due to vector control. [1] In countries where malaria is well established the World Health Organization estimates countries lose 1.3% annual economic income due to the disease. [2] Both prevention through vector control and treatment are needed to protect populations.

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.

As the impacts of disease and virus are devastating, the need to control the vectors in which they carried is prioritized. Vector control in many developing countries can have tremendous impacts as it increases mortality rates, especially among infants. [3] Because of the high movement of the population, disease spread is also a greater issue in these areas. [4]

As many vector control methods are effective against multiple diseases, they can be integrated together to combat multiple diseases at once. [5] The World Health Organization therefore recommends "Integrated Vector Management" as the process for developing and implementing strategies for vector control. [6]

World Health Organization Specialized agency of the United Nations

The World Health Organization (WHO) is a specialized agency of the United Nations that is concerned with international public health. It was established on 7 April 1948, and is headquartered in Geneva, Switzerland. The WHO is a member of the United Nations Development Group. Its predecessor, the Health Organization, was an agency of the League of Nations.

Methods

Vector control focuses on utilizing preventative methods to control or eliminate vector populations. Common preventative measures are:

Habitat and environmental control

Removing or reducing areas where vectors can easily breed can help limit their growth. For example, stagnant water removal, destruction of old tires and cans which serve as mosquito breeding environments, and good management of used water can reduce areas of excessive vector incidence.

Further examples of environmental control is by reducing the prevalence of open defecation or improving the designs and maintenance of pit latrines. This can reduce the incidence of flies acting as vectors to spread diseases via their contact with feces of infected people.

Open defecation is the human practice of defecating outside rather than into a toilet. People may choose fields, bushes, forests, ditches, streets, canals or other open space for defecation. They do so because either they do not have a toilet readily accessible or due to traditional cultural practices. The practice is common where sanitation infrastructure and services are not available. Even if toilets are available, behavior change efforts may still be needed to promote the use of toilets. The term "open defecation free" (ODF) is used to describe communities that have shifted to using a toilet instead of open defecation. This can happen for example after community-led total sanitation programs have been implemented.

Pit latrine Toilet that collects human feces in a hole in the ground

A pit latrine, also known as pit toilet or long drop, is a type of toilet that collects human feces in a hole in the ground. Urine and feces enter the pit through a drop hole in the floor, which might be connected to a toilet seat or squatting pan for user comfort. Pit latrines can be built to function without water or they can have a water seal. When properly built and maintained, pit latrines can decrease the spread of disease by reducing the amount of human feces in the environment from open defecation. This decreases the transfer of pathogens between feces and food by flies. These pathogens are major causes of infectious diarrhea and intestinal worm infections. Infectious diarrhea resulted in about 700,000 deaths in children under five years old in 2011 and 250 million lost school days. Pit latrines are a low cost method of separating feces from people.

Human feces Solid or semisolid remains of the food that could not be digested or absorbed in the small intestine of humans

Human feces are the solid or semisolid remains of the food that could not be digested or absorbed in the small intestine of humans, but has been rotted down by bacteria in the large intestine. It also contains bacteria and a relatively small amount of metabolic waste products such as bacterially altered bilirubin, and the dead epithelial cells from the lining of the gut. It is discharged through the anus during a process called defecation.

Reducing contact

Limiting exposure to insects or animals that are known disease vectors can reduce infection risks significantly. For example, bed nets, window screens on homes, or protective clothing can help reduce the likelihood of contact with vectors. To be effective this requires education and promotion of methods among the population to raise the awareness of vector threats.

Chemical control

Insecticides, larvicides, rodenticides, Lethal ovitraps and repellents can be used to control vectors. For example, larvicides can be used in mosquito breeding zones; insecticides can be applied to house walls or bed nets, and use of personal repellents can reduce incidence of insect bites and thus infection. The use of pesticides for vector control is promoted by the World Health Organization (WHO) and has proven to be highly effective. [7]

Biological control

The use of natural vector predators, such as bacterial toxins or botanical compounds, can help control vector populations. Using fish that eat mosquito larvae, the use cat fish to eat up mosquito larve in pond can eradicate the mosquito population, or reducing breeding rates by introducing sterilized male tsetse flies [8] have been shown to control vector populations and reduce infection risks. [9]

Legislation

United States

In the United States, cities or special districts are responsible for vector control. For example, in California, the Greater Los Angeles County Vector Control District is a special district set up by the state to oversee vector control in multiple cities. [10]

See also

Related Research Articles

DDT Organochloride known for its insecticidal properties

Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochlorine. It was originally developed as an insecticide, then it became infamous for its environmental impacts. DDT was first synthesized in 1874 by the Austrian chemist Othmar Zeidler. DDT's insecticidal action was discovered by the Swiss chemist Paul Hermann Müller in 1939. DDT was used in the second half of World War II to control malaria and typhus among civilians and troops. Müller was awarded the Nobel Prize in Physiology or Medicine in 1948 "for his discovery of the high efficiency of DDT as a contact poison against several arthropods".

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 increased.

Pesticide substance used to destroy pests

Pesticides are substances that are meant to control pests, including weeds. The term pesticide includes all of the following: herbicide, insecticides nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, antimicrobial, and fungicide. The most common of these are herbicides which account for approximately 80% of all pesticide use. Most pesticides are intended to serve as plant protection products, which in general, protect plants from weeds, fungi, or insects.

Insecticide pesticide used against insects

Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to be a major factor behind the increase in the 20th-century's agricultural productivity. Nearly all insecticides have the potential to significantly alter ecosystems; many are toxic to humans and/or animals; some become concentrated as they spread along the food chain.

<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.

Pest control Control of species that are harmful to health, economy or ecology

Pest control is the regulation or management of a species defined as a pest, a member of the animal kingdom that impacts adversely on human activities. The human response depends on the importance of the damage done, and will range from tolerance, through deterrence and management, to attempts to completely eradicate the pest. Pest control measures may be performed as part of an integrated pest management strategy.

Sterile insect technique Method of biological control

The sterile insect technique (SIT) is a method of biological insect control, whereby overwhelming numbers of sterile insects are released into the wild. The released insects are preferably male, as this is more cost-effective and the females may in some situations cause damage by laying eggs in the crop, or, in the case of mosquitoes, taking blood from humans. The sterile males compete with wild males to mate with the females. Females that mate with a sterile male produce no offspring, thus reducing the next generation's population. Sterile insects are not self-replicating and, therefore, cannot become established in the environment. Repeated release of sterile males over low population densities can further reduce and in cases of isolation eliminate pest populations, although cost-effective control with dense target populations is subjected to population suppression prior to the release of the sterile males.

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.

Mosquito net fine net used to exclude mosquitos and other biting insects

A mosquito net is a type of meshed curtain that is circumferentially draped over a bed or a sleeping area, to offer the sleeper barrier protection against bites and stings from mosquitos, flies, and other pest insects, and thus against the diseases they may carry. Examples of such preventable insect-borne diseases include malaria, dengue fever, yellow fever, zika virus and various forms of encephalitis, including the West Nile virus.

Mosquito control

Mosquito control manages the population of mosquitoes to reduce their damage to human health, economies, and enjoyment. Mosquito control is a vital public-health practice throughout the world and especially in the tropics because mosquitoes spread many diseases, such as malaria and the Zika virus.

Methoprene chemical compound

Methoprene is a juvenile hormone (JH) analog which acts as a growth regulator when used as an insecticide. It is an amber-colored liquid with a faint fruity odor. According to the MSDS, methoprene is a material that may be irritating to the mucous membranes and upper respiratory tract, may be harmful by inhalation, ingestion, or skin absorption, may cause eye, skin, or respiratory system irritation and is very toxic to aquatic life. The GHS signal word is "Warning," with notes such as P273 Avoid release into the environment and P391 collect spillage. It is used in drinking water cisterns to control mosquitoes which spread dengue fever and malaria.

Pyriproxyfen chemical compound

Pyriproxyfen is a pesticide which is found to be effective against a variety of insects. It was introduced to the US in 1996, to protect cotton crops against whitefly. It has also been found useful for protecting other crops. It is also used as a prevention for flea control on household pets, for killing indoor and outdoor ants and roaches. Methods of application include aerosols, bait, carpet powders, foggers, shampoos and pet collars.

Bendiocarb insecticide

Bendiocarb is an acutely toxic carbamate insecticide used in public health and agriculture and is effective against a wide range of nuisance and disease vector insects. Many bendiocarb products are or were sold under the tradenames "Ficam" and "Turcam."

Vector (epidemiology) agent that carries and transmits an infectious pathogen into another living organism

In epidemiology, a disease vector is any agent which carries and transmits an infectious pathogen into another living organism; 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.

Indoor residual spraying or IRS is the process of spraying the inside of dwellings with an insecticide to kill mosquitoes that spread malaria. A dilute solution of insecticide is sprayed on the inside walls of certain types of dwellings—those with walls made from porous materials such as mud or wood but not plaster as in city dwellings. Mosquitoes are killed or repelled by the spray, preventing the transmission of the disease. In 2008, 44 countries employed IRS as a malaria control strategy. Several pesticides have historically been used for IRS, the first and most well-known being DDT.

Mosquito-borne disease diseases caused by bacteria, viruses or parasites transmitted by mosquitoes

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.

Rajpal Singh Yadav is an Indian scientist in the field of vector ecology and management at World Health Organization headquarters, Geneva, Switzerland. He has been working with various countries and international organizations to formulate and promote policies for public health pesticide management and vector control.

Metofluthrin chemical compound

Metofluthrin is a pyrethroid used as an insect repellent. The vapors of metofluthrin are highly effective and capable of repelling up to 97% of mosquitoes in field tests. Metofluthrin is used in a variety of consumer products, called emanators, for indoor and outdoor use. These products produce a vapor that protects an individual or area. Effectiveness is reduced by air movement. Metofluthrin is neurotoxic, and is not meant to be applied directly to human skin.

Quartan fever

Quartan fever is one of the four types of malaria which can be contracted by humans.

References

  1. "WHO Malaria". World Health Organization. 2015.
  2. Gallup, John Luke; Sachs, Jeffrey D. (October 1998). "The Economic Burden of Malaria" (PDF). Center for International Development at Harvard.
  3. "10 Facts on Malaria". World Health Organization. 2009.
  4. Walsh, Julia A.; Kenneth S. Warren (1980). "Selective primary health care: An interim strategy for disease control in developing countries". Social Science & Medicine. Part C: Medical Economics. 14 (2): 145–63. doi:10.1016/0160-7995(80)90034-9. PMID   7403901.
  5. Golding, Nick; Wilson, Anne L.; Moyes, Catherine L.; Cano, Jorge; Pigott, David M.; Velayudhan, Raman; Brooker, Simon J.; Smith, David L.; Hay, Simon I.; Lindsay, Steve W. (October 2015). "Integrating vector control across diseases". BMC Medicine. 13 (1): 249. doi:10.1186/s12916-015-0491-4. PMC   4590270 . PMID   26423147.
  6. "Handbook for Integrated Vector Management" (PDF). World Health Organization . Retrieved 3 December 2015.
  7. "Pesticides and their application for the control of vectors and pests of public health importance" (PDF). World Health Organization. 2006.
  8. Vreysen, MJ; et al. (2000). "Glossina austeni (Diptera: Glossinidae) eradicated on the island of Unguja, Zanzibar, using the sterile insect technique". Journal of Economic Entomology. 93 (1): 123–135. doi:10.1603/0022-0493-93.1.123. PMID   14658522.
  9. "HEALTH AND SAFETY CODE SECTION 2010-2014". California Health and Safety Code. California. Retrieved 18 December 2013.