Transgene

From Wikipedia, the free encyclopedia

 

A transgene is a gene or genetic material that has been transferred naturally, or by any of a number of genetic engineering techniques from one organism to another. The introduction of a transgene (called "transgenesis") has the potential to change the phenotype of an organism. 

In its most precise usage, the term transgene describes a segment of DNA containing a gene sequence that has been isolated from one organism and is introduced into a different organism. This non-native segment of DNA may either retain the ability to produce RNA or protein in the transgenic organism or alter the normal function of the transgenic organism's genetic code. In general, the DNA is incorporated into the organism's germ line. For example, in higher vertebrates this can be accomplished by injecting the foreign DNA into the nucleus of a fertilized ovum. This technique is routinely used to introduce human disease genes or other genes of interest into strains of laboratory mice to study the function or pathology involved with that particular gene.

The construction of a transgene requires the assembly of a few main parts. The transgene must contain a promoter, which is a regulatory sequence that will determine where and when the transgene is active, an exon, a protein coding sequence (usually derived from the cDNA for the protein of interest), and a stop sequence. These are typically combined in a bacterial plasmid and the coding sequences are typically chosen from transgenes with previously known functions.

Transgenic or genetically modified organisms, be they bacteria, viruses or fungi, serve all kinds of research purposes. Transgenic plants, insects, fish and mammals have been bred. Transgenic plants such as corn and soybean have replaced wild strains in agriculture in some countries (e.g. the United States). Transgene escape has been documented for GMO crops since 2001 with persistence and invasiveness. Transgenetic organisms pose ethical questions and may cause biosafety problems.

History

The idea of shaping an organism to fit a specific need isn't a new science; selective breeding of animals and plants started before recorded history. However, until the late 1900s farmers and scientist could breed new strains of a plant or organism only from closely related species, because the DNA had to be compatible for offspring to be able to reproduce another generation.

In the 1970 and 1980s, scientists passed this hurdle by inventing procedures for combining the DNA of two vastly different species with genetic engineering. The organisms produced by these procedures were termed transgenic. Transgenesis is the same as gene therapy in the sense that they both transform cells for a specific purpose. However, they are completely different in their purposes, as gene therapy aims to cure a defect in cells, and transgenesis seeks to produce a genetically modified organism by incorporating the specific transgene into every cell and changing the genome. Transgenesis will therefore change the germ cells, not only the somatic cells, in order to ensure that the transgenes are passed down to the offspring when the organisms reproduce. Transgenes alter the genome by blocking the function of a host gene; they can either replace the host gene with one that codes for a different protein, or introduce an additional gene.

The first transgenic organism was created in 1974 when Annie Chang and Stanley Cohen expressed Staphylococcus aureus genes in Escherichia coli. In 1978, yeast cells were the first eukaryotic organisms to undergo gene transfer. Mouse cells were first transformed in 1979, followed by mouse embryos in 1980. Most of the very first transmutations were performed by microinjection of DNA directly into cells. Scientists were able to develop other methods to perform the transformations, such as incorporating transgenes into retroviruses and then infecting cells, using electroinfusion which takes advantage of an electric current to pass foreign DNA through the cell wall, biolistics which is the procedure of shooting DNA bullets into cells, and also delivering DNA into the egg that has just been fertilized.

The first transgenic animals were only intended for genetic research to study the specific function of a gene, and by 2003, thousands of genes had been studied.

Use in plants

A variety of transgenic plants have been designed for agriculture to produce genetically modified crops, such as corn, soybean, rapeseed oil, cotton, rice and more. As of 2012, these GMO crops were planted on 170 million hectares globally.

Golden rice

One example of a transgenic plant species is golden rice. In 1997,^{[citation needed]} five million children developed xerophthalmia, a medical condition caused by vitamin A deficiency, in Southeast Asia alone. Of those children, a quarter million went blind. To combat this, scientists used biolistics to insert the daffodil phytoene synthase gene into Asia indigenous rice cultivars. The daffodil insertion increased the production of ß-carotene. The product was a transgenic rice species rich in vitamin A, called golden rice. Little is known about the impact of golden rice on xerophthalmia because anti-GMO campaigns have prevented the full commercial release of golden rice into agricultural systems in need.

Transgene escape

The escape of genetically-engineered plant genes via hybridization with wild relatives was first discussed and examined in Mexico and Europe in the mid-1990s. There is agreement that escape of transgenes is inevitable, even "some proof that it is happening". Up until 2008 there were few documented cases.

Corn

Corn sampled in 2000 from the Sierra Juarez, Oaxaca, Mexico contained a transgenic 35S promoter, while a large sample taken by a different method from the same region in 2003 and 2004 did not. A sample from another region from 2002 also did not, but directed samples taken in 2004 did, suggesting transgene persistence or re-introduction. A 2009 study found recombinant proteins in 3.1% and 1.8% of samples, most commonly in southeast Mexico. Seed and grain import from the United States could explain the frequency and distribution of transgenes in west-central Mexico, but not in the southeast. Also, 5.0% of corn seed lots in Mexican corn stocks expressed recombinant proteins despite the moratorium on GM crops.

Cotton

In 2011, transgenic cotton was found in Mexico among wild cotton, after 15 years of GMO cotton cultivation.

Rapeseed (canola)

Transgenic rapeseed Brassicus napus, hybridized with a native Japanese species Brassica rapa, was found in Japan in 2011 after they had been identified 2006 in Québec, Canada. They were persistent over a 6-year study period, without herbicide selection pressure and despite hybridization with the wild form. This was the first report of the introgression—the stable incorporation of genes from one gene pool into another—of an herbicide resistance transgene from Brassica napus into the wild form gene pool.

Creeping bentgrass

Transgenic creeping bentgrass, engineered to be glyphosate-tolerant as "one of the first wind-pollinated, perennial, and highly outcrossing transgenic crops", was planted in 2003 as part of a large (about 160 ha) field trial in central Oregon near Madras, Oregon. In 2004, its pollen was found to have reached wild growing bentgrass populations up to 14 kilometres away. Cross-pollinating Agrostis gigantea was even found at a distance of 21 kilometres. The grower, Scotts Company could not remove all genetically engineered plants, and in 2007, the U.S. Department of Agriculture fined Scotts $500,000 for noncompliance with regulations.

Risk assessment

The long-term monitoring and controlling of a particular transgene has been shown not to be feasible. The European Food Safety Authority published a guidance for risk assessment in 2010.

Use in mice

Genetically modified mice are the most common animal model for transgenic research. Transgenic mice are currently being used to study a variety of diseases including cancer, obesity, heart disease, arthritis, anxiety, and Parkinson’s disease. The two most common types of genetically modified mice are knockout mice and oncomice. Knockout mice are a type of mouse model that uses transgenic insertion to disrupt an existing gene’s expression. In order to create knockout mice, a transgene with the desired sequence is inserted into an isolated mouse blastocyst using electroporation. Then, homologous recombination occurs naturally within some cells, replacing the gene of interest with the designed transgene. Through this process, researchers were able to demonstrate that a transgene can be integrated into the genome of an animal, serve a specific function within the cell, and be passed down to future generations.

Oncomice are another genetically modified mouse species created by inserting transgenes that increase the animal’s vulnerability to cancer. Cancer researchers utilize oncomice to study the profiles of different cancers in order to apply this knowledge to human studies.

Use in Drosophila

Multiple studies have been conducted concerning transgenesis in Drosophila melanogaster, the fruit fly. This organism has been a helpful genetic model for over 100 years, due to its well-understood developmental pattern. The transfer of transgenes into the Drosophila genome has been performed using various techniques, including P element, Cre-loxP, and ΦC31 insertion. The most practiced method used thus far to insert transgenes into the Drosophila genome utilizes P elements. The transposable P elements, also known as transposons, are segments of bacterial DNA that are translocated into the genome, without the presence of a complementary sequence in the host’s genome. P elements are administered in pairs of two, which flank the DNA insertion region of interest. Additionally, P elements often consist of two plasmid components, one known as the P element transposase and the other, the P transposon backbone. The transposase plasmid portion drives the transposition of the P transposon backbone, containing the transgene of interest and often a marker, between the two terminal sites of the transposon. Success of this insertion results in the nonreversible addition of the transgene of interest into the genome. While this method has been proven effective, the insertion sites of the P elements are often uncontrollable, resulting in an unfavorable, random insertion of the transgene into the Drosophila genome.

To improve the location and precision of the transgenic process, an enzyme known as Cre has been introduced. Cre has proven to be a key element in a process known as recombination-mediated cassette exchange (RMCE). While it has shown to have a lower efficiency of transgenic transformation than the P element transposases, Cre greatly lessens the labor-intensive abundance of balancing random P insertions. Cre aids in the targeted transgenesis of the DNA gene segment of interest, as it supports the mapping of the transgene insertion sites, known as loxP sites. These sites, unlike P elements, can be specifically inserted to flank a chromosomal segment of interest, aiding in targeted transgenesis. The Cre transposase is important in the catalytic cleavage of the base pairs present at the carefully positioned loxP sites, permitting more specific insertions of the transgenic donor plasmid of interest.

To overcome the limitations and low yields that transposon-mediated and Cre-loxP transformation methods produce, the bacteriophage ΦC31 has recently been utilized. Recent breakthrough studies involve the microinjection of the bacteriophage ΦC31 integrase, which shows improved transgene insertion of large DNA fragments that are unable to be transposed by P elements alone. This method involves the recombination between an attachment (attP) site in the phage and an attachment site in the bacterial host genome (attB). Compared to usual P element transgene insertion methods, ΦC31 integrates the entire transgene vector, including bacterial sequences and antibiotic resistance genes. Unfortunately, the presence of these additional insertions has been found to affect the level and reproducibility of transgene expression.

Future potential

The study of application of transgenes is a rapidly growing area of molecular biology. In fact, it is predicted that in the next two decades, 300 000 lines of transgenic mice will be generated. Researchers have identified many applications for transgenes, particularly in the medical field. Scientists are focusing on the use of transgenes to study the function of the human genome in order to better understand disease, adapting animal organs for transplantation into humans, and the production of pharmaceutical products such as insulin, growth hormone, and blood anti-clotting factors from the milk of transgenic cows.

There are currently five thousand known genetic diseases, and the potential to treat these diseases using transgenic animals is, perhaps, one of the most promising applications of transgenes. There is a potential to use human gene therapy to replace a mutated gene with an unmutated copy of a transgene in order to treat the genetic disorder. This can be done through the use of Cre-Lox or knockout. Moreover, genetic disorders are being studied through the use of transgenic mice, pigs, rabbits, and rats. More recently, scientists have also begun using transgenic goats to study genetic disorders related to fertility.

Transgenes may soon be used for xenotransplantation from pig organs. Through the study of xeno-organ rejection, it was found that an acute rejection of the transplanted organ occurs upon the organ's contact with blood from the recipient due to the recognition of foreign antibodies on endothelial cells of the transplanted organ. Scientists have identified the antigen in pigs that causes this reaction, and therefore are able to transplant the organ without immediate rejection by removal of the antigen. However, the antigen begins to be expressed later on, and rejection occurs. Therefore, further research is being conducted.

Transgenes are being used by manufactures to produce goods such as milk with high levels of proteins, silk from the milk of goats, and microorganisms that are capable of producing proteins that contain enzymes that increase the rate of industrial reactions. Agricultural applications aim to selectively breed animals for particular traits and animals that are resistant to diseases.

Ethical controversy

Transgene use in humans is currently fraught with issues. Transformation of genes into human cells has not been perfected yet. The most famous example of this involved certain patients developing T-cell leukemia after being treated for X-linked severe combined immunodeficiency (X-SCID). This was attributed to the close proximity of the inserted gene to the LMO2 promoter, which controls the transcription of the LMO2 proto-oncogene. In common with most forms of genetic engineering, the use of transgenes for purposes other than to correct life-threatening genetic abnormalities is a major bioethical issue.

Pest control

From Wikipedia, the free encyclopedia

An agricultural aircraft applies low-insecticide bait against western corn rootworm.

 

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. 

In agriculture, pests are kept at bay by cultural, chemical and biological means. Ploughing and cultivation of the soil before sowing reduces the pest burden and there is a modern trend to limit the use of pesticides as far as possible. This can be achieved by monitoring the crop, only applying insecticides when necessary, and by growing varieties and crops which are resistant to pests. Where possible, biological means are used, encouraging the natural enemies of the pests and introducing suitable predators or parasites. 

In homes and urban environments, the pests are the rodents, birds, insects and other organisms that share the habitat with humans, and that feed on and spoil possessions. Control of these pests is attempted through exclusion, repulsion, physical removal or chemical means. Alternatively, various methods of biological control can be used including sterilisation programmes.

History

Bronze cat, Ancient Egypt. (664–525 BC)

 

Pest control is at least as old as agriculture, as there has always been a need to keep crops free from pests. As long ago as 3000 BC in Egypt, cats were used to control pests of grain stores such as rodents. Ferrets were domesticated by 500 AD in Europe for use as mousers. Mongooses were introduced into homes to control rodents and snakes, probably by the ancient Egyptians.

The conventional approach was probably the first to be employed, since it is comparatively easy to destroy weeds by burning them or ploughing them under, and to kill larger competing herbivores. Techniques such as crop rotation, companion planting (also known as intercropping or mixed cropping), and the selective breeding of pest-resistant cultivars have a long history.

Red weaver ants, here feeding on a snail, have been used to control pests in China, Southeast Asia and Africa for many centuries.

 

Chemical pesticides were first used around 2500 BC, when the Sumerians used sulphur compounds as insecticides. Modern pest control was stimulated by the spread across the United States of the Colorado potato beetle. After much discussion, arsenical compounds were used to control the beetle and the predicted poisoning of the human population did not occur. This led the way to a widespread acceptance of insecticides across the continent. With the industrialisation and mechanization of agriculture in the 18th and 19th centuries, and the introduction of the insecticides pyrethrum and derris, chemical pest control became widespread. In the 20th century, the discovery of several synthetic insecticides, such as DDT, and herbicides boosted this development.

Biological control is first recorded around 300 AD in China, when colonies of weaver ants, Oecophylla smaragdina, were intentionally placed in citrus plantations to control beetles and caterpillars. Also in China, ducks were used in paddy fields to consume pests, as illustrated in ancient cave art. In 1762, an Indian mynah was brought to Mauritius to control locusts, and about the same time, citrus trees in Burma were connected by bamboos to allow ants to pass between them and help control caterpillars. In the 1880s, ladybirds were used in citrus plantations in California to control scale insects, and other biological control experiments followed. The introduction of DDT, a cheap and effective compound, put an effective stop to biological control experiments. By the 1960s, problems of resistance to chemicals and damage to the environment began to emerge, and biological control had a renaissance. Chemical pest control is still the predominant type of pest control today, although a renewed interest in traditional and biological pest control developed towards the end of the 20th century and continues to this day.

In agriculture, horticulture and forestry

Control methods

Biological pest control

Biological pest control: parasitoid wasp (Cotesia congregata) adult with pupal cocoons on its host, a tobacco hornworm Manduca sexta (green background)

 

Biological pest control is a method of controlling pests such as insects and mites by using other organisms. It relies on predation, parasitism, herbivory or other natural mechanisms, but typically also involves an active human management role. Classical biological control involves the introduction of natural enemies of the pest that are bred in the laboratory and released into the environment. An alternative approach is to augment the natural enemies that occur in a particular area by releasing more, either in small, repeated batches, or in a single large-scale release. Ideally, the released organism will breed and survive, and provide long-term control. Biological control can be an important component of an integrated pest management programme. 

For example: mosquitoes are often controlled by putting Bt Bacillus thuringiensis ssp. israelensis, a bacterium that infects and kills mosquito larvae, in local water sources.

Cultural control

Cultivation by ploughing exposes insect pests to predators such as black-headed gulls.

 

Mechanical pest control is the use of hands-on techniques as well as simple equipment and devices, that provides a protective barrier between plants and insects. This is referred to as tillage and is one of the oldest methods of weed control as well as being useful for pest control; wireworms, the larvae of the common click beetle, are very destructive pests of newly ploughed grassland, and repeated cultivation exposes them to the birds and other predators that feed on them.

Crop rotation can help to control pests by depriving them of their host plants. It is a major tactic in the control of corn rootworm, and has reduced early season incidence of Colorado potato beetle by as much as 95%.

Trap cropping

A trap crop is a crop of a plant that attracts pests, diverting them from nearby crops. Pests aggregated on the trap crop can be more easily controlled using pesticides or other methods. However, trap-cropping, on its own, has often failed to cost effectively reduce pest densities on large commercial scales, without the use of pesticides, possibly due to the pests' ability to disperse back into the main field.

Pesticides

Spraying pine logs with insecticide against Ips sexdentatus, a pine engraver beetle

 

Pesticides are applied to crops by agricultural aircraft, tractor-mounted crop sprayers or as seed dressings to control pests. However, successful control by pesticides is not easy; the right formulation must be chosen, the timing is often critical, the method of application is important, adequate coverage and retention on the crop are necessary. The killing of natural enemies of the target pest should be minimised. This is particularly important in countries where there are natural reservoirs of pests and their enemies in the countryside surrounding plantation crops, and these co-exist in a delicate balance. Often in less-developed countries, the crops are well adapted to the local situation and no pesticides are needed. Where progressive farmers are using fertilisers to grow improved crop varieties, these are often more susceptible to pest damage, but the indiscriminate application of pesticides may be detrimental in the longer term.

The efficacy of chemical pesticides tends to diminish over time. This is because any organism that manages to survive the initial application will pass on its genes to its offspring and a resistant strain will be developed. In this way, some of the most serious pests have developed resistance and are no longer killed by pesticides that used to kill their ancestors. This necessitates higher concentrations of chemical, more frequent applications and a movement to more expensive formulations.

Pesticides are formulated to kill pests, but many have detrimental effects on non-target species; of particular concern is the damage done to honey-bees, solitary bees and other pollinating insects and in this regard, the time of day when the spray is applied can be important. The widely used neonicotinoids have been banned on flowering crops in some countries because of their effects on bees. Some pesticides may cause cancer and other health problems in humans, as well as being harmful to wildlife. There can be acute effects immediately after exposure or chronic effects after continuous low-level, or occasional exposure. Maximum residue limits for pesticides in foodstuffs and animal feed are set by many nations.

Spruce budworm (adult and pupa shown), a serious pest of forests, can be monitored using pheromone traps.

Forestry

Forest pests present a significant problem because it is not easy to access the canopy and monitor pest populations. In addition, forestry pests such as bark beetles, kept under control by natural enemies in their native range, may be transported large distances in cut timber to places where they have no natural predators, enabling them to cause extensive economic damage. Pheromone traps have been used to monitor pest populations in the canopy. These release volatile chemicals that attract males. Pheromone traps can detect the arrival of pests or alert foresters to outbreaks. For example, the spruce budworm, a destructive pest of spruce and balsam fir, has been monitored using pheromone traps in Canadian forests for several decades. In some regions, such as New Brunswick, areas of forest are sprayed with pesticide to control the budworm population and prevent the damage caused during outbreaks.

In homes and cities

Many unwelcome animals visit or make their home in residential buildings, industrial sites and urban areas. Some contaminate foodstuffs, damage structural timbers, chew through fabrics or infest stored dry goods. Some inflict great economic loss, others carry diseases or cause fire hazards, and some are just a nuisance. Control of these pests has been attempted by improving sanitation and garbage control, modifying the habitat, and using repellents, growth regulators, traps, baits and pesticides.

General methods

Physical pest control

Dog control van, Rekong Peo, Himachal Pradesh, India

 

Physical pest control involves trapping or killing pests such as insects and rodents. Historically, local people or paid rat-catchers caught and killed rodents using dogs and traps. On a domestic scale, sticky flypapers are used to trap flies. In larger buildings, insects may be trapped using such means as pheromones, synthetic volatile chemicals or ultraviolet light to attract the insects; some have a sticky base or an electrically charged grid to kill them. Glueboards are sometimes used for monitoring cockroaches and to catch rodents. Rodents can be killed by suitably baited spring traps and can be caught in cage traps for relocation. Talcum powder or "tracking powder" can be used to establish routes used by rodents inside buildings and acoustic devices can be used for detecting beetles in structural timbers.

Historically, firearms have been one of the primary methods used for pest control. "Garden Guns" are smooth bore shotguns specifically made to fire .22 caliber snake shot or 9mm Flobert, and are commonly used by gardeners and farmers for snakes, rodents, birds, and other pest. Garden Guns are short range weapons that can do little harm past 15 to 20 yards, and they're relatively quiet when fired with snake shot, compared to a standard ammunition. These guns are especially effective inside of barns and sheds, as the snake shot will not shoot holes in the roof or walls, or more importantly injure livestock with a ricochet. They are also used for pest control at airports, warehouses, stockyards, etc.

The most common shot cartridge is .22 Long Rifle loaded with #12 shot. At a distance of about 10 feet (3 m), which is about the maximum effective range, the pattern is about 8 inches (20 cm) in diameter from a standard rifle. Special smoothbore shotguns, such as the Marlin Model 25MG can produce effective patterns out to 15 or 20 yards using .22 WMR shotshells, which hold 1/8 oz. of #12 shot contained in a plastic capsule.

Poisoned bait

Rodent bait station, Chennai, India

 

Poisoned bait is a common method for controlling rats, mice, birds, slugs, snails, ants, cockroaches and other pests. The basic granules, or other formulation, contains a food attractant for the target species and a suitable poison. For ants, a slow-acting toxin is needed so that the workers have time to carry the substance back to the colony, and for flies, a quick-acting substance to prevent further egg-laying and nuisance. Baits for slugs and snails often contain the molluscide metaldehyde, dangerous to children and household pets.

Warfarin has traditionally been used to kill rodents, but many populations have developed resistance to this anticoagulant, and difenacoum is often substituted. These are cumulative poisons, requiring bait stations to be topped up regularly. Poisoned meat has been used for centuries to kill animals such as wolves and birds of prey. Poisoned carcasses however kill a wide range of carrion feeders, not only the targeted species. Raptors in Israel were nearly wiped out following a period of intense poisoning of rats and other crop pests.

Fumigation

Tent fumigation of a house in America

 

Fumigation is the treatment of a structure to kill pests such as wood-boring beetles by sealing it or surrounding it with an airtight cover such as a tent, and fogging with liquid insecticide for an extended period, typically of 24–72 hours. This is costly and inconvenient as the structure cannot be used during the treatment, but it targets all life stages of pests.

An alternative, space treatment, is fogging or misting to disperse a liquid insecticide in the atmosphere within a building without evacuation or airtight sealing, allowing most work within the building to continue, at the cost of reduced penetration. Contact insecticides are generally used to minimise long lasting residual effects.

Sterilization

Populations of pest insects can sometimes be dramatically reduced by the release of sterile individuals. This involves the mass rearing of a pest, sterilising it by means of X-rays or some other means, and releasing it into a wild population. It is particularly useful where a female only mates once and where the insect does not disperse widely. This technique has been successfully used against the New World screw-worm fly, some species of tsetse fly, tropical fruit flies, the pink bollworm and the codling moth, among others.

Laboratory studies conducted with U-5897 (3-chloro-1,2-propanediol) were attempted in the early 1970s for rat control, although these proved unsuccessful. In 2013, New York City tested sterilization traps, demonstrating a 43% reduction in rat populations. The product ContraPest was approved for the sterilization of rodents by the United States Environmental Protection Agency in August 2016.

Methods for specific pests

Natural rodent control

Brown rat infestation

 

Several wildlife rehabilitation organizations encourage natural form of rodent control through exclusion and predator support and preventing secondary poisoning altogether. The United States Environmental Protection Agency notes in its Proposed Risk Mitigation Decision for Nine Rodenticides that "without habitat modification to make areas less attractive to commensal rodents, even eradication will not prevent new populations from recolonizing the habitat." The United States Environmental Protection Agency has prescribed guidelines for natural rodent control and for safe trapping in residential areas with subsequent release to the wild. People sometimes attempt to limit rodent damage using repellents. Balsam fir oil from the tree Abies balsamea is an EPA approved non-toxic rodent repellent. Acacia polyacantha subsp. campylacantha root emits chemical compounds that repel animals including rats.

Pantry pests

The red flour beetle, Tribolium castaneum, attacks stored grain products worldwide.

 

Insect pests including the Mediterranean flour moth, the Indian mealmoth, the cigarette beetle, the drugstore beetle, the confused flour beetle, the red flour beetle, the merchant grain beetle, the sawtoothed grain beetle, the wheat weevil, the maize weevil and the rice weevil infest stored dry foods such as flour, cereals and pasta.

In the home, foodstuffs found to be infested are usually discarded, and storing such products in sealed containers should prevent the problem from reoccurring. The eggs of these insects are likely to go unnoticed, with the larvae being the destructive life stage, and the adult the most noticeable stage. Since pesticides are not safe to use near food, alternative treatments such as freezing for four days at 0 °F (−18 °C) or baking for half an hour at 130 °F (54 °C) should kill any insects present.

Clothes moths

Larva, pupa and adult clothes moth Tineola bisselliella with characteristic damage to fabric

 

The larvae of clothes moths (mainly Tineola bisselliella and Tinea pellionella) feed on fabrics and carpets, particularly those that are stored or soiled. The adult females lay batches of eggs on natural fibres, including wool, silk and fur, as well as cotton and linen in blends. The developing larvae spin protective webbing and chew into the fabric, creating holes and specks of excrement. Damage is often concentrated in concealed locations, under collars and near seams of clothing, in folds and crevices in upholstery and round the edges of carpets as well as under furniture. Methods of control include using airtight containers for storage, periodic laundering of garments, trapping, freezing, heating and the use of chemicals; mothballs contain volatile insect repellents such as 1,4-Dichlorobenzene which deter adults, but to kill the larvae, permethrin, pyrethroids or other insecticides may need to be used.

Carpet beetles

Carpet beetles are members of the family Dermestidae, and while the adult beetles feed on nectar and pollen, the larvae are destructive pests in homes, warehouses and museums. They feed on animal products including wool, silk, leather, fur, the bristles of hair brushes, pet hair, feathers and museum specimens. They tend to infest hidden locations and may feed on larger areas of fabrics than do clothes moths, leaving behind specks of excrement and brown, hollow, bristly-looking cast skins. Management of infestations is difficult and is based on exclusion and sanitation where possible, resorting to pesticides when necessary. The beetles can fly in from outdoors and the larvae can survive on lint fragments, dust and inside the bags of vacuum cleaners. In warehouses and museums, sticky traps baited with suitable pheromones can be used to identify problems, and heating, freezing, spraying the surface with insecticide and fumigation will kill the insects when suitably applied. Susceptible items can be protected from attack by keeping them in clean airtight containers.

Bookworms

Books are sometimes attacked by cockroaches, silverfish, book mites, booklice, and various beetles which feed on the covers, paper, bindings and glue. They leave behind physical damage in the form of tiny holes as well as staining from their faeces. Book pests include the larder beetle, and the larvae of the black carpet beetle and the drugstore beetle which attack leather-bound books, while the common clothes moth and the brown house moth attack cloth bindings. These attacks are largely a problem with historic books, because modern bookbinding materials are less susceptible to this type of damage.

Evidence of attack may be found in the form of tiny piles of book-dust and specks of frass. Damage may be concentrated in the spine, the projecting edges of pages and the cover. Prevention of attack relies on keeping books in cool, clean, dry positions with low humidity, and occasional inspections should be made. Treatment can be by freezing for lengthy periods, but some insect eggs are very resistant and can survive for long periods at low temperatures.

Beetles

House timber split open to reveal larvae of the house longhorn beetle, Hylotrupes bajulus, in their burrows, which are partially filled with frass

 

Various beetles in the Bostrichoidea superfamily attack the dry, seasoned wood used as structural timber in houses and to make furniture. In most cases, it is the larvae that do the damage; these are invisible from the outside of the timber, but are chewing away at the wood in the interior of the item. Examples of these are the powderpost beetles, which attack the sapwood of hardwoods, and the furniture beetles, which attacks softwoods, including plywood. The damage has already been done by the time the adult beetles bore their way out, leaving neat round holes behind them. The first that a householder knows about the beetle damage is often when a chair leg breaks off or a piece of structural timber caves in. Prevention is through chemical treatment of the timber prior to its use in construction or in furniture manufacture.

Termites

Termites with colonies in close proximity to houses can extend their galleries underground and make mud tubes to enter homes. The insects keep out of sight and chew their way through structural and decorative timbers, leaving the surface layers intact, as well as through cardboard, plastic and insulation materials. Their presence may become apparent when winged insects appear and swarm in the home in spring. Regular inspection of structures by a trained professional may help detect termite activity before damage becomes substantial. Inspection and monitoring of termites is important because termite alates (winged reproductives) may not always swarm inside a structure. Control and extermination is a professional job involving trying to exclude the insects from the building and trying to kill those already present. Soil-applied liquid termiticides provide a chemical barrier that prevents termites from entering buildings, and lethal baits can be used; these are eaten by foraging insects, and carried back to the nest and shared with other members of the colony, which goes into slow decline.

Mosquitoes

Mosquito (Aedes aegypti) biting a human

 

Mosquitoes are midge-like flies in the family Culicidae. Females of most species feed on blood and some act as vectors for malaria and other diseases. Historically they have been controlled by use of DDT and other chemical means, but since the adverse environmental effects of these insecticides has been realised, other means of control have been attempted. The insects rely on water in which to breed and the first line of control is to reduce possible breeding locations by draining marshes and reducing accumulations of standing water. Other approaches include biological control of larvae by the use of fish or other predators, genetic control, the introduction of pathogens, growth-regulating hormones, the release of pheromones and mosquito trapping.

On airfields

Jet engine fan blades damaged by bird strike

 

Birds are a significant hazard to aircraft, but it is difficult to keep them away from airfields. Several methods have been explored. Stunning birds by feeding them a bait containing stupefying substances has been tried, and it may be possible to reduce their numbers on airfields by reducing the number of earthworms and other invertebrates by soil treatment. Leaving the grass long on airfields rather than mowing it is also a deterrent to birds. Sonic nets are being trialled; these produce sounds that birds find distracting and seem effective at keeping birds away from affected areas.

Guidelines & Legislation

Guidelines and legislation regarding the usage, permitted methods of application and the storage conditions of pesticides and chemicals vary from country to country, often being legislated by each state of territory.

Australia

Australian Capital Territory (ACT)

Environment Protection Act 1997 ACT 

New South Wales

"Occupational Heath and Safety Regulation 2001 NSW pursuant to the Occupational Health & Safety Act 2000. Part 9.1" . 17 July 2005.

South Australia

Pesticides Regulations 2003 SA Pursuant to Controlled Substances Act 1984 SA 

Victoria

Health (Pest Control) Regulations 2002 Vic pursuant to the Health Act 1958 Vic 

Western Australia

Health (Pesticide) Regulations 1956 WA pursuant to Health Act 1911 WA 

India

The Insecticides Act 1968 

Malaysia

Pesticide Act 1974 

Singapore

Control of Vectors and Pesticides Act 

United Kingdom

Prevention of Damage by Pests Act 1949 

Pesticide poisoning

From Wikipedia, the free encyclopedia

Pesticide toxicity
A sign warning about potential pesticide exposure.
Specialty	Emergency medicine, toxicology

A pesticide poisoning occurs when chemicals intended to control a pest affect non-target organisms such as humans, wildlife, or bees. There are three types of pesticide poisoning. The first of the three is a single and short-term very high level of exposure which can be experienced by individuals who commit suicide, as well as pesticide formulators. The second type of poisoning is long-term high-level exposure, which can occur in pesticide formulators and manufacturers. The third type of poisoning is a long-term low-level exposure, which individuals are exposed to from sources such as pesticide residues in food as well as contact with pesticide residues in the air, water, soil, sediment, food materials, plants and animals.

In developing countries, such as Sri Lanka, pesticide poisonings from short-term very high level of exposure (acute poisoning) is the most worrisome type of poisoning. However, in developed countries, such as Canada, it is the complete opposite: acute pesticide poisoning is controlled, thus making the main issue long-term low-level exposure of pesticides.

Cause

The most common exposure scenarios for pesticide-poisoning cases are accidental or suicidal poisonings, occupational exposure, by-stander exposure to off-target drift, and the general public who are exposed through environmental contamination.

Accidental or suicidal

Self-poisoning with agricultural pesticides represents a major hidden public health problem accounting for approximately one-third of all suicides worldwide. It is one of the most common forms of self-injury in the Global South. The World Health Organization estimates that 300,000 people die from self-harm each year in the Asia-Pacific region alone. Most cases of intentional pesticide poisoning appear to be impulsive acts undertaken during stressful events, and the availability of pesticides strongly influences the incidence of self poisoning. Pesticides are the agents most frequently used by farmers and students in India to commit suicide.

Occupational

Pesticide poisoning is an important occupational health issue because pesticides are used in a large number of industries, which puts many different categories of workers at risk. Extensive use puts agricultural workers in particular at increased risk for pesticide illnesses. Exposure can occur through inhalation of pesticide fumes, and often occurs in settings including greenhouse spraying operations and other closed environments like tractor cabs or while operating rotary fan mist sprayers in facilities or locations with poor ventilation systems. Workers in other industries are at risk for exposure as well. For example, commercial availability of pesticides in stores puts retail workers at risk for exposure and illness when they handle pesticide products. The ubiquity of pesticides puts emergency responders such as fire-fighters and police officers at risk, because they are often the first responders to emergency events and may be unaware of the presence of a poisoning hazard. The process of aircraft disinsection, in which pesticides are used on inbound international flights for insect and disease control, can also make flight attendants sick.

Different job functions can lead to different levels of exposure. Most occupational exposures are caused by absorption through exposed skin such as the face, hands, forearms, neck, and chest. This exposure is sometimes enhanced by inhalation in settings including spraying operations in greenhouses and other closed environments, tractor cabs, and the operation of rotary fan mist sprayers.

Residential

When thinking of pesticide poisoning, one does not take into consideration the contribution that is made of their own household. The majority of households in Canada use pesticides while taking part in activities such as gardening. In Canada 96 percent of households report having a lawn or a garden. 56 percent of the households who have a lawn or a garden utilize fertilizer or pesticide. This form of pesticide use may contribute to the third type of poisoning, which is caused by long-term low-level exposure. As mentioned before, long-term low-level exposure affects individuals from sources such as pesticide residues in food as well as contact with pesticide residues in the air, water, soil, sediment, food materials, plants and animals.

Pathophysiology

Organochlorines

DDT, an organochlorine

 

The organochlorine pesticides, like DDT, aldrin, and dieldrin, are extremely persistent and accumulate in fatty tissue. Through the process of bioaccumulation (lower amounts in the environment get magnified sequentially up the food chain), large amounts of organochlorines can accumulate in top species like humans. There is substantial evidence to suggest that DDT, and its metabolite DDE, act as endocrine disruptors, interfering with hormonal function of estrogen, testosterone, and other steroid hormones.

Anticholinesterase compounds

Malathion, an organophosphate anticholinesterase

 

Cholinesterase-inhibiting pesticides, also known as organophosphates, carbamates, and anticholinesterases, are most commonly reported in occupationally related pesticide poisonings globally. Besides acute symptoms including cholinergic crisis, certain organophosphates have long been known to cause a delayed-onset toxicity to nerve cells, which is often irreversible. Several studies have shown persistent deficits in cognitive function in workers chronically exposed to pesticides.

Diagnosis

Most pesticide-related illnesses have signs and symptoms that are similar to common medical conditions, so a complete and detailed environmental and occupational history is essential for correctly diagnosing a pesticide poisoning. A few additional screening questions about the patient's work and home environment, in addition to a typical health questionnaire, can indicate whether there was a potential pesticide poisoning.

If one is regularly using carbamate and organophosphate pesticides, it is important to obtain a baseline cholinesterase test. Cholinesterase is an important enzyme of the nervous system, and these chemical groups kill pests and potentially injure or kill humans by inhibiting cholinesterase. If one has had a baseline test and later suspects a poisoning, one can identify the extent of the problem by comparison of the current cholinesterase level with the baseline level.

Prevention

Accidental poisonings can be avoided by proper labeling and storage of containers. When handling or applying pesticides, exposure can be significantly reduced by protecting certain parts of the body where the skin shows increased absorption, such as the scrotal region, underarms, face, scalp, and hands. Safety protocols to reduce exposure include the use of personal protective equipment, washing hands and exposed skin during as well as after work, changing clothes between work shifts, and having first aid trainings and protocols in place for workers.

Personal protective equipment for preventing pesticide exposure includes the use of a respirator, goggles, and protective clothing, which have all have been shown to reduce risk of developing pesticide-induced diseases when handling pesticides. A study found the risk of acute pesticide poisoning was reduced by 55% in farmers who adopted extra personal protective measures and were educated about both protective equipment and pesticide exposure risk. Exposure can be significantly reduced when handling or applying pesticides by protecting certain parts of the body where the skin shows increased absorption, such as the scrotal region, underarms, face, scalp, and hands. Using chemical-resistant gloves has been shown to reduce contamination by 33–86%.

Treatment

Specific treatments for acute pesticide poisoning are often dependent on the pesticide or class of pesticide responsible for the poisoning. However, there are basic management techniques that are applicable to most acute poisonings, including skin decontamination, airway protection, gastrointestinal decontamination, and seizure treatment.

Decontamination of the skin is performed while other life-saving measures are taking place. Clothing is removed, the patient is showered with soap and water, and the hair is shampooed to remove chemicals from the skin and hair. The eyes are flushed with water for 10–15 minutes. The patient is intubated and oxygen administered, if necessary. In more severe cases, pulmonary ventilation must sometimes be supported mechanically. Seizures are typically managed with lorazepam, phenytoin and phenobarbitol, or diazepam (particularly for organochlorine poisonings).

Gastric lavage is not recommended to be used routinely in pesticide poisoning management, as clinical benefit has not been confirmed in controlled studies; it is indicated only when the patient has ingested a potentially life-threatening amount of poison and presents within 60 minutes of ingestion. An orogastric tube is inserted and the stomach is flushed with saline to try to remove the poison. If the patient is neurologically impaired, a cuffed endotracheal tube inserted beforehand for airway protection. Studies of poison recovery at 60 minutes have shown recovery of 8%–32%. However, there is also evidence that lavage may flush the material into the small intestine, increasing absorption. Lavage is contra-indicated in cases of hydrocarbon ingestion.

Activated charcoal is sometimes administered as it has been shown to be successful with some pesticides. Studies have shown that it can reduce the amount absorbed if given within 60 minutes, though there is not enough data to determine if it is effective if time from ingestion is prolonged. Syrup of ipecac is not recommended for most pesticide poisonings because of potential interference with other antidotes and regurgitation increasing exposure of the esophagus and oral area to the pesticide.

Urinary alkalinisation has been used in acute poisonings from chlorophenoxy herbicides (such as 2,4-D, MCPA, 2,4,5-T and mecoprop); however, evidence to support its use is poor.

Epidemiology

Acute pesticide poisoning is a large-scale problem, especially in developing countries. 

"Most estimates concerning the extent of acute pesticide poisoning have been based on data from hospital admissions which would include only the more serious cases. The latest estimate by a WHO task group indicates that there may be 1 million serious unintentional poisonings each year and in addition 2 million people hospitalized for suicide attempts with pesticides. This necessarily reflects only a fraction of the real problem. On the basis of a survey of self-reported minor poisoning carried out in the Asian region, it is estimated that there could be as many as 25 million agricultural workers in the developing world suffering an episode of poisoning each year." In Canada in 2007 more than 6000 cases of acute pesticide poisoning occurred.

Estimating the numbers of chronic poisonings worldwide is more difficult.

Society and culture

Rachel Carson's Silent Spring brought about the first major wave of public concern over the chronic effects of pesticides.

In other animals

An obvious side effect of using a chemical meant to kill is that one is likely to kill more than just the desired organism. Contact with a sprayed plant or "weed" can have an effect upon local wildlife, most notably insects. A cause for concern is how pests, the reason for pesticide use, are building up a resistance. Phytophagous insects are able to build up this resistance because they are easily capable of evolutionary diversification and adaptation. The problem this presents is that in order to obtain the same desired effect of the pesticides they have to be made increasingly stronger as time goes on. Repercussions of the use of stronger pesticides on vegetation has a negative result on the surrounding environment, but also would contribute to consumers' long-term low-level exposure.