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, [1] 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, Chagas disease, and various forms of encephalitis, including the West Nile virus. [2]
To be effective, the mesh of a mosquito net must be fine enough to exclude such insects without obscuring visibility or ventilation to unacceptable levels. The netting should be made of stiff cotton or synthetic thread to allow the movement of air. A white net allows the user to see mosquitoes against the background. Netting with 285 holes per square inch is ideal because it is very breathable but will prevent even the smallest mosquito from entering. [3] It is possible to increase the effectiveness of a mosquito net greatly by treating it with an appropriate insecticide or insect repellent. Research has shown mosquito nets to be an extremely effective method of malaria prevention, averting approximately 663 million cases of malaria over the period 2000–2015. [4]
Mosquito netting is mainly used for the protection against the malaria transmitting vector, Anopheles gambiae . The first record of malaria-like symptoms occurred as early as 2700 BCE from China. The vector for this disease, specifically avian malaria, was not identified until 1897 when Sir Ronald Ross identified mosquitoes as a vector for malaria. [5]
Conopeum or Conopium (Ancient Greek : κωνώπιον or κωνόπιον or κωνωπεῖον) was a mosquito-curtain. It was made to keep away mosquitos and other flying insects. It took its name from κώνωψ, which means mosquito in Greek, and is the origin of the English word canopy. These curtains were especially used in Egypt because of the mosquitoes which infest the Nile. The Scholiast on Juvenal mention that at Rome they were called cubiculare. They are still used in Greece and other countries surrounding the Mediterranean. [6] [7] [8] [9]
Mosquito netting has a long history. Though use of the term dates from the mid-18th century, [1] Indian literature from the late medieval period has references to the usage of mosquito nets in ritual Hindu worship. Poetry composed by Annamayya, the earliest known Telugu musician and poet, references domatera, which means "mosquito net" in Telugu. [10] Use of mosquito nets has been dated to prehistoric times. It is said that Cleopatra, the last active pharaoh of Ancient Egypt, also slept under a mosquito net. [11] Mosquito nets were used during the malaria-plagued construction of the Suez Canal. [11]
Mosquito netting can be made from cotton, polyethylene, polyester, polypropylene, or nylon. [12] A mesh size of 1.2 millimetres (0.047 in) stops mosquitoes, and smaller, such as 0.6 millimetres (0.024 in), stops other biting insects such as biting midges/no-see-ums. [13]
A mosquito bar is an alternate form of a mosquito net. It is constructed of a fine see-through mesh fabric mounted on and draped over a box-shaped frame. It is designed to fit over an area or item such as a sleeping bag to provide protection from insects. A mosquito bar could be used to protect oneself from mosquitoes and other insects while sleeping in jungle areas. [14] The mesh is woven tightly enough to stop insects from entering but loosely enough to not interfere with ventilation. The frame is usually self-supporting or freestanding although it can be designed to be attached from the top to an alternative support such as tree limbs. [14]
Mosquito nets are often used where malaria or other insect-borne diseases are common, especially as a tent-like covering over a bed. For effectiveness, it is important that the netting not have holes or gaps large enough to allow insects to enter. It is also important to 'seal' the net properly because mosquitoes are able to 'squeeze' through improperly secured nets. Because an insect can bite a person through the net, the net must not rest directly on the skin. [15]
Mosquito netting can be hung over beds from the ceiling or a frame, built into tents, or installed in windows and doors. When hung over beds, rectangular nets provide more room for sleeping without the danger of netting contacting skin, at which point mosquitoes may bite through untreated netting. Some newer mosquito nets are designed to be both easy to deploy and foldable after use. [16] [17]
Where mosquito nets are freely or cheaply distributed, local residents sometimes opportunistically use them inappropriately, for example as fishing nets. When used for fishing, mosquito nets have harmful ecological consequences because the fine mesh of a mosquito net retains almost all fish, including bycatch such as immature or small fish and fish species that are not suitable for consumption. [18] [19] [20] [21] In addition, insecticides with which the mesh has been treated, such as permethrin, may be harmful to the fish and other aquatic fauna. [19]
Mosquito nets treated with insecticides—known as insecticide-treated nets (ITNs) or bednets—were developed and tested in the 1980s for malaria prevention by P. Carnevale and his team in Bobo-Dioulasso, Burkina Faso. ITNs are estimated to be twice as effective as untreated nets, [22] and offer greater than 70% protection compared with no net. [23] These nets are dip-treated using a synthetic pyrethroid insecticide such as deltamethrin or permethrin which will double the protection over a non-treated net by killing and repelling mosquitoes. For maximum effectiveness, ITNs should be re-impregnated with insecticide every six months. This process poses a significant logistical problem in rural areas. Newer, long-lasting insecticidal nets (LLINs) have now replaced ITNs in most countries and dual agent nets, typically using alpha-cypermethrin and chlorfenapyr, are starting to be used in response to reports of mosquito resistance. [24] [25]
The distribution of mosquito nets or bednets treated with insecticides such as permethrin or deltamethrin has been shown to be an extremely effective method of malaria prevention. [4] According to a 2015 Nature study, mosquito nets averted 68% of an estimated 663 million averted cases of malaria infection since 2000. [4] It is also one of the most cost-effective methods of prevention. These nets can often be obtained for around $2.50–$3.50 (2–3 euros) from the United Nations, the World Health Organization (WHO), and others. ITNs have been shown to be the most cost-effective prevention method against malaria and are part of WHO's Millennium Development Goals (MDGs). [26] Generally LLINs are purchased by donor groups and delivered through in-country distribution networks.
ITNs protect people sleeping under them and simultaneously kill mosquitoes that contact the nets. Some protection is provided to others by this method, including people sleeping in the same room but not under the net. However, mathematical modeling has suggested that disease transmission may be exacerbated after bed nets have lost their insecticidal properties under certain circumstances. [27] Although ITN users are still protected by the physical barrier of the netting, non-users could experience an increased bite rate as mosquitoes are deflected away from the non-lethal bed net users. [27] The modeling suggests that this could increase transmission when the human population density is high or at lower human densities when mosquitoes are more adept at locating their blood meals. [27]
In December 2019 it was reported that West African populations of Anopheles gambiae include mutants with higher levels of sensory appendage protein 2 (a type of chemosensory protein in the legs), which binds to pyrethroids, sequestering them and so preventing them from functioning, thus making the mosquitoes with this mutation more likely to survive contact with bednets. [28]
While some experts argue that international organizations should distribute ITNs and LLINs to people for free to maximize coverage (since such a policy would reduce price barriers), others insist that cost-sharing between the international organization and recipients would lead to greater use of the net (arguing that people will value a good more if they pay for it). Additionally, proponents of cost-sharing argue that such a policy ensures that nets are efficiently allocated to the people who most need them (or are most vulnerable to infection). Through a "selection effect", they argue, the people who most need the bed nets will choose to purchase them, while those less in need will opt out.
However, a randomized controlled trial study of ITNs uptake among pregnant women in Kenya, conducted by economists Pascaline Dupas and Jessica Cohen, found that cost-sharing does not necessarily increase the usage intensity of ITNs nor does it induce uptake by those most vulnerable to infection, as compared to a policy of free distribution. [29] [30] In some cases, cost-sharing can decrease demand for mosquito nets by erecting a price barrier. Dupas and Cohen's findings support the argument that free distribution of ITNs can be more effective than cost-sharing in increasing coverage and saving lives. In a cost-effectiveness analysis, Dupas and Cohen note that "cost-sharing is at best marginally more cost-effective than free distribution, but free distribution leads to many more lives saved." [29]
The researchers base their conclusions about the cost-effectiveness of free distribution on the proven spillover benefits of increased ITN usage. [31] ITNs protect the individuals or households that use them, and they protect people in the surrounding community in one of two ways. [32]
When a large number of nets are distributed in one residential area, their chemical additives help reduce the number of mosquitoes in the environment. With fewer mosquitoes, the chances of malaria infection for recipients and non-recipients are significantly reduced. (In other words, the importance of the physical barrier effect of ITNs decreases relative to the positive externality effect[ clarification needed ] of the nets in creating a mosquito-free environment when ITNs are highly concentrated in one residential cluster or community.)
Standard ITNs must be replaced or re-treated with insecticide after six washes and, therefore, are not seen as a convenient, effective long-term solution to the malaria problem. [36] [37] [38]
As a result, the mosquito netting and pesticide industries developed so-called long-lasting insecticidal mosquito nets, which also use pyrethroid insecticides. There are three types of LLINs — polyester netting which has insecticide bound to the external surface of the netting fibre using a resin; polyethylene which has insecticide incorporated into the fibre and polypropylene which has insecticide incorporated into the fibre. All types can be washed at least 20 times, but physical durability will vary. A survey carried out in Tanzania concluded that effective life of polyester nets was 2 to 3 years; [39] with polyethylene LLINs there are data to support over 5 years of life with trials in showing nets which were still effective after 7 years. [40]
A review of 22 randomized controlled trials of ITNs [41] found (for Plasmodium falciparum malaria) that ITNs can reduce deaths in children by one fifth and episodes of malaria by half.
More specifically, in areas of stable malaria "ITNs reduced the incidence of uncomplicated malarial episodes by 50% compared to no nets, and 39% compared to untreated nets" and in areas of unstable malaria "by 62% compared to no nets and 43% compared to untreated nets". As such the review calculated that for every 1000 children protected by ITNs, 5.5 lives would be saved each year.
Through the years 1999 and 2010 the abundance of female anopheles gambiae densities in houses throughout western Kenya were recorded. This data set was paired with the spatial data of bed net usage in order to determine correlation. Results showed that from 2008 to 2010 the relative population density of the female anopheles gambiae decreased from 90.6% to 60.7%. [42] The conclusion of this study showed that as the number of houses which used insecticide treated bed nets increased the population density of female anopheles gambiae decreased. This result did however vary from region to region based on the local environment.
A 2019 study in PLoS ONE found that a campaign to distribute mosquito bednets in the Democratic Republic of Congo led to a 41% decline mortality for children under five who lived in areas with a high malaria risk. [43]
Malaria and other arboviruses are known to contribute to economic disparity within that country and vice versa. This opens the stage for corruption associated to the distribution of self-protection aides. [44] The least wealthy members of society are both more likely to be in closer proximity to the vectors' prime habitat and less likely to be protected from the vectors. [45] This increase in probability of being infected increases the demand for self-protection which therefore allows for higher pricing and uneven distribution of self-protection means. A decrease in per capita income exaggerates a high demand for resources such as water and food resulting in civil unrest among communities. Protecting resources as well as attempting to obtain resources are both a cause for conflict.
Mosquito nets have been observed to be used in fisheries across the world, where their strength, light weight and free or cheap accessibility make them an attractive tool for fishing. People who use them for fishing catch vast numbers of juvenile fish. [46]
Mosquito nets do reduce air flow to an extent and sleeping under a net is hotter than sleeping without one, which can be uncomfortable in tropical areas without air-conditioning.
Some alternatives are:
Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, 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 limit the spread of the insect-borne diseases 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". The WHO's anti-malaria campaign of the 1950s and 1960s relied heavily on DDT and the results were promising, though there was a resurgence in developing countries afterwards.
Malaria is a mosquito-borne infectious disease that affects vertebrates. Human malaria causes symptoms that typically include fever, fatigue, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. Symptoms usually begin 10 to 15 days after being bitten by an infected Anopheles 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.
Anopheles is a genus of mosquito first described by the German entomologist J. W. Meigen in 1818, and are known as nail mosquitoes and marsh mosquitoes. Many such mosquitoes are vectors of the parasite Plasmodium, a genus of protozoans that cause malaria in birds, reptiles, and mammals, including humans. The Anopheles gambiae mosquito is the best-known species of marsh mosquito that transmits the Plasmodium falciparum, which is a malarial parasite deadly to human beings; no other mosquito genus is a vector of human malaria.
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.
Vector control is any method to limit or eradicate the mammals, birds, insects or other arthropods 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.
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.
Deltamethrin is a pyrethroid ester insecticide. Deltamethrin plays a key role in controlling malaria vectors, and is used in the manufacture of long-lasting insecticidal mosquito nets; however, resistance of mosquitos and bed bugs to deltamethrin has seen a widespread increase.
The Anopheles gambiae complex consists of at least seven morphologically indistinguishable species of mosquitoes in the genus Anopheles. The complex was recognised in the 1960s and includes the most important vectors of malaria in sub-Saharan Africa, particularly of the most dangerous malaria parasite, Plasmodium falciparum. It is one of the most efficient malaria vectors known. The An. gambiae mosquito additionally transmits Wuchereria bancrofti which causes lymphatic filariasis, a symptom of which is elephantiasis.
Paratransgenesis is a technique that attempts to eliminate a pathogen from vector populations through transgenesis of a symbiont of the vector. The goal of this technique is to control vector-borne diseases. The first step is to identify proteins that prevent the vector species from transmitting the pathogen. The genes coding for these proteins are then introduced into the symbiont, so that they can be expressed in the vector. The final step in the strategy is to introduce these transgenic symbionts into vector populations in the wild. One use of this technique is to prevent mortality for humans from insect-borne diseases. Preventive methods and current controls against vector-borne diseases depend on insecticides, even though some mosquito breeds may be resistant to them. There are other ways to fully eliminate them. “Paratransgenesis focuses on utilizing genetically modified insect symbionts to express molecules within the vector that are deleterious to pathogens they transmit.” The acidic bacteria Asaia symbionts are beneficial in the normal development of mosquito larvae; however, it is unknown what Asais symbionts do to adult mosquitoes.
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 diseases or mosquito-borne illnesses are diseases caused by bacteria, viruses or parasites transmitted by mosquitoes. Nearly 700 million people contract mosquito-borne illnesses each year, resulting in more than a million deaths.
VectorBase is one of the five Bioinformatics Resource Centers (BRC) funded by the National Institute of Allergy and Infectious Diseases (NIAID), a component of the National Institutes of Health (NIH), which is an agency of the United States Department of Health and Human Services. VectorBase is focused on invertebrate vectors of human pathogens working with the sequencing centers and the research community to curate vector genomes.
Anopheles stephensi is a primary mosquito vector of malaria in urban India and is included in the same subgenus as Anopheles gambiae, the primary malaria vector in Africa. A. gambiae consists of a complex of morphologically identical species of mosquitoes, along with all other major malaria vectors; however, A. stephensi has not yet been included in any of these complexes. Nevertheless, two races of A. stephensi exist based on differences in egg dimensions and the number of ridges on the eggs; A. s. stephensisensu stricto, the type form, is a competent malaria vector that is found in urban areas, and A. s. mysorensis, the variety form, exists in rural areas and exhibits considerable zoophilic behaviour, making it a poor malaria vector. However, A. s. mysorensis is a detrimental vector in Iran. An intermediate form also exists in rural communities and peri-urban areas, though its vector status is unknown. About 12% of malaria cases in India are due to A. stephensi.
Attractive toxic sugar baits (ATSBs) are oral insecticides designed to reduce malaria infections by killing the host vector – the mosquito – rather than the parasite itself.
Janet Hemingway is a British infectious diseases specialist. She is the former Director of Liverpool School of Tropical Medicine (LSTM) and founding Director of Infection Innovation Consortium and Professor of Tropical Medicine at LSTM. She is currently the President of the Royal Society of Tropical Medicine and Hygiene.
Thioester containing protein 1, often called TEP1 is a key component of the arthropod innate immune system. TEP1 was first identified as a key immunity gene in 2001 through functional studies on Anopheles gambiae mosquitoes.
Thorselliaceae is a family of bacteria belonging to the class Gammaproteobacteria and it was first described in February 2015. It is not assigned to an order. The family consists of four species in two genera. The bacteria are Gram-negative and rod shaped, approximately 1 μm wide and 2 μm long. They are facultative anaerobes and motile. Thorselliaceae bacteria have been found around the world associated with vector mosquitoes, mainly with vectors of malaria.
Quartan fever is one of the four types of malaria which can be contracted by humans.
Flaminia Catteruccia is an Italian professor of immunology and infectious disease at the Harvard T.H. Chan School of Public Health, studying the interactions between malaria and the Anopheles mosquitoes that transmit the parasites.
Abdoulaye Diabaté is an African parasitologist, Professor and Head of the Medical Entomology and Parasitology Department at the Health Sciences Research Institute. His research considers the use of gene drive to eliminate malaria, and he leads Target Malaria Burkina Faso. He delivered the first genetically modified mosquitoes in Africa, marking a historic moment for science. He was awarded the 2023 Falling Walls Science Prize for Science and Innovation Management. In April 2024, he spoke at the TED 2024: The Brave and The Brilliant conference in Vancouver.