Frequently Asked Questions
What is malaria?
Malaria is a vector-borne disease caused by single celled parasites, the Plasmodium protozoa, and transmitted by female Anopheles mosquitoes. A vector is something that carries a disease from one living thing to another. In malaria's case, the vector is the female Anopheles mosquito. Malaria can also be transmitted from mother to fetus or by blood to blood contact from sharing needles or blood transfusions. About sixty species of the Anopheles mosquito are major transmitters of the disease. Four distinct species of Plasmodium cause malaria: P. falciparum (the deadliest); P. malariae ; P. ovale ; P. vivax. Within each species there are variant strains.
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How does a mosquito transmit malaria?
The complex story of a malaria infection begins with the female Anopheles mosquito taking a blood meal from a human. The benign Anopheles males feed on nectar. While feeding, the female mosquito injects a small stream of parasites in the form of sporozoites, or tiny, thread like creatures that dwell in the mosquito's salivary glands, into the blood stream. These sporozoites make their way to the liver where they each enter a liver cell and develop into round spores or merozoites. For a period of approximately 2 weeks, they multiply greatly, destroying their host cell.
Until this stage, the human host of these parasites will not have experienced any symptoms of disease. That all changes when the spores burst out of their now destroyed liver cells and enter the blood stream. At this point, the unfortunate human will experience a clinical attack of malaria with high fevers and sweating. Each spore ( merozoite ) enters a red blood cell and devours the hemoglobin, and the parasite grows and grows until it fills more than half of the blood cell. This is known as the trophozoite phase. The next stage of the life cycle is the asexual multiplication of the parasites within the blood cell. A parasite's nucleus breaks into individual parts, and each part forms into a spore (or merozoite ). These newly formed merozoites then burst out of the blood cell, ready to infect another blood cell and repeat the multiplication process.
Each of these stages occurs at the same time for all of the parasites within the body. Each new stage brings with it a new bout of fevers, hence the 48-hour intervals of P. falciparum and P. vivax and the 72-hour intervals of P. malariae.
After several asexual reproductions, some of the merozoites become either male of female gametocytes, and, as the other merozoites do, they invade a red blood cell. These sexual spores however do not multiply like their asexual relations; rather they increase in size, almost filling the blood cell, and circulate within the host's body, waiting to be ingested by the next female Anopheles mosquito that feeds on the unfortunate person.
The sexual cycle of the Plasmodium parasite then takes place in the gut of the mosquito. The male gametocyte transforms itself and develops many peculiar filaments that lash about as they make their way to the female gamete in order to complete fertilization. The fertilized egg then rests on the wall of the mosquito's stomach for two to three weeks, after which the sporozoites burst out and travel to the salivary glands, ready to infect another human host.
Click here for an illustration of the malaria parasite's life cycle.
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Do all mosquitoes transmit malaria?
No. So far, entomologists have identified over 2000 species of mosquito, but only the Anopheles mosquito actually transmits malaria. In Africa, the major vectors for malaria are An. gambiae sl complex and An. funestus, and there are many members of both groups of mosquito. Most Anopheles mosquitoes do not feed during the day but rather do so at dusk or during the night. An. funestus for example feeds most actively between 2am and 4am.
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What are the symptoms of malaria?
Plasmodium falciparum malaria cases, the most common in Africa, can be diagnosed as either uncomplicated or severe, and the treatment regimen varies accordingly. Uncomplicated malaria usually results in mild fevers, minimal vomiting and does not cause delusions or other mental problems. For people that have had frequent bouts of malaria and have built a certain amount of resistance, uncomplicated malaria does not normally require hospitalization, and affected patients usually remain ambulatory.
Severe malaria usually occurs in people that are either immuno-suppressed or have no immunity at all. Young children and pregnant women are particularly at risk as well as people that travel to malarial areas and have no prior immunity.
The symptoms of complicated malaria include convulsions, impaired consciousness and respiratory distress that may take the form of acidosis1, ARDS2 or pulmonary edema3. Patients can also become jaundiced, start hemorrhaging, experience renal failure and go into circulatory shock.
1 Acidosis is a condition characterized by excessive acid in the bodily fluids. This can be caused by breathing difficulties when there are excessive amounts of CO2 (which is acidic) in the body.
2 ARDS, or acute respiratory distress syndrome, occurs when the lungs become inflamed and fluid accumulates in the air sacks or alveoli.
3 Pulmonary edema refers to swelling of the lungs and the accumulation of fluid in the lungs.
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Is malaria a big problem?
Though the disease has been wiped out in most of the developed world, it is still a leading cause of illness and death in Africa, Latin America and Southern Asia. The World Health Organisation estimates up to 500 million cases of malaria annually around the world. Other scientists suggest as many as 660 million cases. The disease kills at least one million of those infected each year, which amounts to someone dying every 30 seconds. About 90% of these deaths are in sub-Saharan Africa, where P. falciparum accounts for over 90% of all malaria infections. Malaria primarily affects young children and pregnant women, whose reduced immunity makes them especially vulnerable. Due to, among other things, increased resistance to cheap anti-malarial drugs, malaria has become the leading killer of children under age five in Africa. Malaria also impedes economic development. Economists have estimated that malaria costs endemic countries 1.3% of GDP annually in lost productivity. This translates to an annual loss of $12 billion for the entire African continent.
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Why are malaria cases increasing?
Many factors have contributed to the increasing trend of malaria cases. One factor is that malaria parasites have developed resistance to many of the drugs used to fight malaria, such as chloroquine and SP. In addition, in many parts of Africa, increased movement of people displaced by war and other events introduces new strains of the parasite to different areas and can add to the number of cases.
Climate can play a part in increasing malaria transmission as, depending on the type of vector, increased rainfall can result in more breeding pools and larger numbers of the disease carrying vectors. The relationship between malaria and climate, however, is highly complex. Increased rainfall and higher temperatures do not necessarily result in increased malaria rates. In some cases, higher rainfall can flush out breeding pools and reduce malaria transmission. We know that the eventual eradication of malaria from North America and Europe had nothing to do with climate, and more to do with wealth and development and human intervention to halt the spread of the disease4.
Another important factor that has contributed to the rise in cases in recent years in some countries is the discontinuation of vector control programs that spray insecticides on the inside walls of houses. According to Prof. Donald R. Roberts, MD, of the U.S. Uniformed Services University of the Health Sciences, "Although many factors contribute to increasing malaria, the strongest correlation is with decreasing number of houses sprayed with DDT."5 The research of Roberts and his colleagues demonstrates a causal link between DDT spraying and malaria rates. The study notes that other factors also appear to play a role, but not to the extent of reduced spraying6.
4 For a more detailed explanation of the relationship between climate change and mosquito borne diseases, see P. Reiter "Climate Change and Mosquito-Borne Disease", Environmental Health Perspectives 2001, 109:1 February 2001. See also S. Hay et al. "Climate change and the resurgence of malaria in the East African Highlands", Nature 41: 21, February 2002, and" Dangers of Disinformation ", Paul Reiter, International Herald Tribune, January 11, 2007.
5 D. R. Roberts, S. Manguin, J. Mouchet, "DDT house spraying and re-emerging malaria", Lancet, 2000, 356: 330 - 332.
6 D. Roberts, L. Laughlin, P. Hsheih and L. Legters, "DDT, Global Strategies and a Malaria Control Crisis in South America", Emerging Infectious Diseases , Vol 3. No 3 July-Sept 1997.
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How do we fight malaria?
Malaria is preventable and curable. A variety of strategies exist to prevent the transmission of malaria. The World Health Organisation (WHO) endorses a strategy of integrated vector management that considers local factors, such as types of parasites and vectors, climate and seasonal peaks of transmission. By far the most effective preventive strategies are indoor residual spraying (IRS) and sleeping under insecticide-treated mosquito nets (ITNs), preferably the long-lasting insecticidal nets (LLINs), which can remain effective for more than 5 years.
IRS involves spraying tiny amounts of approved insecticides on the inside walls of homes and dwellings. The number of times a home must be sprayed through the year depends on the type of insecticide used, and the length of the transmission season. In some parts of Africa where malaria is not transmitted throughout the year and DDT, for example, is used, spraying need only take place once a year. This is because DDT has a longer-lasting residual effect. It is also among the cheapest approved insecticides, making it one of the most cost-effective options where resistance is not a significant problem.
Sleeping under an ITN or LLIN provides effective protection against malaria-carrying mosquitoes. However a person must remain under the net all night to avoid being bitten by mosquitoes. He or she must also take care not to tear the net, and make sure that if it is not an LLIN, it is treated regularly with insecticide. The recent development of long-lasting insecticidal nets has made this less a problem, as they remain effective for up to five years. Ensuring that enough people have access to ITNs or LLINs has proven a significant challenge. The debate over whether a net should be free or sold at subsidized prices continues. Some donors and development partners are successfully distributing nets in conjunction with other services, such as vaccination programs or antenatal clinic visits for expecting mothers.
A variety of drugs also exist to treat malaria. In much of sub-Saharan Africa, however, malaria parasites have grown resistant to cheap and historically effective drugs like chloroquine and Sulphadoxine-pyrimethamine (SP), and treatment failure rates in many countries are above the WHO's accepted levels. This is why the WHO recommends that all countries revise their national malaria treatment policies when current treatment failure rates exceed 10 percent, preferably to Artemisinin-based combination therapies (ACTs). Combination therapies, as opposed to monotherapies, refer to the use of more than one drug in a single treatment to ensure that malaria parasites resistant to one drug are killed by another drug. Even Artemisinin, which has been used as an effective anti-malarial drug in Asia for centuries, has begun to fail in critical numbers, primarily along the southeastern border between Cambodia and Thailand. For this reason, the WHO has insisted that drug companies stop producing Artemisinin monotherapies. It is working with African governments to prepare for the potential import of these resistant strains of malaria into sub-Saharan Africa.
Because parasitic resistance as well as insecticide resistance are increasingly problematic for malaria control, research into new insecticides and drugs is crucial. After decades of failed vaccine efforts, a recently developed candidate was successful in a limited number of cases in preventing malaria. It is currently being tested more widely. Even if it is effective, however, a deployable vaccine won't be available until 2010 at the earliest.
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What is vector control?
In 1898, Dr. Ronald Ross, a physician in the British Army based in India, discovered that that female Anopheles mosquito was responsible for transmitting the malaria parasite. This discovery gave public health officials a new target to attack for disease control: the Anopheles mosquito. This discovery revolutionized malaria control, which had historically been haphazard or based purely on treating the patient and thereby killing the malaria parasites.
There are various methods of vector control and they are not necessarily mutually exclusive. Because the Anopheles mosquito normally bites in the early evening and through the night, not during the day, many of these methods focus on protecting dwellings and their inhabitants. One of the most effective methods of vector control is indoor residual spraying (IRS). IRS involves the application of small amounts of insecticide on the inside walls of dwellings. The insecticide is applied by a sprayer using a hand held pump, usually a Hudson pump. When mosquitoes rest on the walls, they absorb the insecticide through their feet. The pesticide either kills them immediately or soon afterward. In another method of control, a person sleeps under insecticide-treated nets (ITNs) or preferably one of the long-lasting ITNs. The ITN works not only by creating a barrier between the mosquito and its intended meal, but also by killing the mosquito if it lands on the net.
Countries around the world use other methods of vector control with varying degrees of success. These methods include larviciding, or killing with insecticides the mosquito larvae before they hatch, the removal of breeding grounds, drying up wetlands or ensuring that pools of standing water are dried up, and using biological controls such as fish that eat mosquito larvae. The success of these controls depends highly on the type of vector and its breeding habits, the geography of the area and the socio-economic status of the population at risk.
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What is integrated vector management?
Integrated Vector Management is the targeted use of different vector control methods so as to reduce the contact between humans and malaria vectors in a cost-effective and sustainable manner. As malaria control is highly complex and there are many different factors that can influence the spread of the disease, it makes sense to use different vector control strategies to control the mosquito.
IVM comprises primarily indoor residual spraying and distributing insecticide-treated nets. Other methods are less universally applicable, but can be very effective in some cases. These include larvicides, such as the natural larvicide, Baccillus thuringensis (Bt), the draining of mosquito breeding sites and changing irrigation practices to create fewer breeding sites, among other things.
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What is DDT?
DDT, or dichlorodiphenyltrichloroethane, is an organochlorine pesticide. DDT became widely used in pest control after scientist Paul Herman Muller discovered its insecticidal properties in 1939. Hailed as a major public health achievement, Muller's discovery earned him a Nobel Prize in 1948 because it provided an affordable way to manage major public health risks carried by mosquitoes, lice, and other vectors. DDT helped cleanse World War II victims of disease-ridden lice, protected allied troops against vermin and typhus, and became a key tool in fighting malaria around the world, saving millions of lives. In 1972, the U.S. Environmental Protection Agency banned DDT for agricultural use in the United States, based largely on concerns that it posed a threat to wildlife. After this decision, indoor residual spraying programs grew less popular among donors and many were discontinued.
However, some nations still effectively used DDT for malaria control. For example, Ecuador has increased its use of DDT since 1993 and has experienced the largest reduction of malaria rates in the world7. When South Africa removed DDT from its malaria control program in 1996, one of the worst malaria epidemics in the country's history followed. Only when South Africa reintroduced DDT in 2000 did it manage to bring the epidemic under control.
In 1999, the Stockholm Treaty on Persistent Organic Pollutants gave DDT an exemption for public health use. In light of malaria's persistent burden on sub-Saharan Africa, USAID and the World Health Organisation both reversed longstanding policy in 2006 to actively support DDT for indoor residual spraying. The first USAID-financed shipment of DDT in over a decade arrived in Zambia on September 11, 2006. The World Health Organisation held a press conference on September 15, 2006 to publicize its new indoor residual spraying guidelines and give DDT a clean bill of health for malaria control.
To read more about DDT, please visit: http://www.who.int/malaria/ddtandmalariavectorcontrol.html and http://junkscience.com/ddtfaq.htm
You can also download AFM's DDT FAQ .
7 D. Roberts et al. (1997)
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Is indoor residual spraying (IRS) bad for the environment?
IRS involves the spraying of tiny quantities of residual insecticides on the inside walls of houses and under the eaves. When synthetic pyrethroids are used, for example, as little as 0.02 grams of active ingredient per meter squared is used. The spray teams return the unused insecticides to marked containers and do not dispose of insecticides irresponsibly. The total amount of insecticide used in malaria control programs is a fraction of that once used in agriculture, which was sprayed over far wider areas and contaminated ecosystems when used irresponsibly.
Some commentators and activists have raised concerns about DDT contaminating the environment if it is used in vector control. As with the other insecticides used in IRS, DDT causes minimal or zero contamination of the wider environment. Because DDT does not escape into the wider environment, it poses little or no threat to wildlife. Recognizing that malaria and poverty are worse for the environment than any trace amounts of DDT, the Endangered Wildlife Trust of Southern Africa along with the Sierra Club and numerous other environmentalist groups now fully support the responsible use of DDT in malaria control.
In most malarial areas, the poverty and lack of development that result from high rates of malaria are far worse for the environment than any insecticide used in malaria control. IRS programs ensure healthy and productive populations that are less reliant on the natural environment for shelter, heat and nutrition; this is highly beneficial for the natural environment.
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Does DDT in indoor residual spraying programs affect human health?
DDT is one of the most, if not the most, studied chemical known to man. DDT has been used in public health programs since the 1940s and for several decades was used very widely in agriculture. In all the years of use and after thousands of studies, no scientific study has been able to pinpoint actual human harm from DDT. The World Health Organisation conducts regular assessments of chemical risks in a program known as the International Programme on Chemical Safety (IPCS). The IPCS provides the most comprehensive review of the scientific literature on DDT. According to the IPCS:
"A 2000 Joint WHO/FAO international assessment is the latest WHO risk assessment of DDT and its metabolites. This assessment documents the wide spectrum of toxicological findings which have been observed in animal studies, including reproductive, developmental and neurotoxicological effects and recommends a provisional tolerable daily intake for human exposure. While biologically plausible, this wide spectrum of toxicological effects have so far not been confirmed by human epidemiological studies. An updated WHO report of the scientific literature relevant to an assessment of human risks will be available for peer review at the end of 2006. In conclusion, and in the meantime there is no reason to change the current WHO position regarding use of DDT for vector control."
This is why WHO renewed DDT's bill of health for malaria control in September, 2006.
Furthermore, according to A.G. Smith of the Lancet, "The early toxicological information on DDT was reassuring; it seemed that acute risks to health were small. If the huge amounts of DDT used are taken into account, the safety record for human beings is extremely good. In the 1940s many people were deliberately exposed to high concentrations of DDT through dusting programs or impregnation of clothes, without any apparent ill effect. In summary, DDT can cause toxicological effects but the effects on human beings at likely exposure are very slight."8
The Allies first used DDT in disease prevention. During World War II, they dusted it on troops and civilians to control the body lice that transmit typhus. They never recorded any adverse human health effects from this use of DDT; on the contrary, the use of DDT quickly controlled the typhus epidemics, and mortality and morbidity dropped dramatically. Indeed wherever public health programs have used DDT, disease incidence has dropped dramatically and people have enjoyed longer, healthier lives.
The International Agency for Research on Cancer classifies DDT as a possible carcinogen. It shares this classification with coffee, vegetables pickled in the Asian style and carageenan, a seaweed extract that is used as a thickener in ice cream, yogurt and puddings. Even during the years of widespread DDT use in agriculture, the carcinogenic risk to which you would have been exposed was 50 times lower than the risk from the known carcinogens in coffee. The average consumption of wine, beer, lettuce, apples, orange juice and potatoes all expose humans to higher carcinogenic risks than exposure to DDT9. During the 60 years of widespread DDT use, researchers have conducted hundreds of scientific studies on its human health effects. In all that time, not once has a researcher been able to affirmatively replicate a case-control study of DDT's human carcinogenicity10.
Some commentators and scientists express concern that DDT acts as an endocrine disruptor, affecting the reproductive capacity of humans and other mammals. While there is the potential for endocrine disruption, there is little evidence of actual human health harm as a result of this disruption. It is important, when discussing endocrine disruption, to link levels of potentially endocrine disrupting compounds with adverse human health effects because the human diet contains naturally occurring endocrine disruptors in fruits and vegetables. Indeed, the effect of naturally occurring endocrine disruptors in foodstuffs such as potatoes, carrots, peas, beans, apples, garlic and coffee is far stronger than the hormonal effect of synthetic chemicals. As Stephen Safe, Distinguished Professor of Toxicology at Texas A&M University and Director of the National Institute of Environmental Health Sciences, explains, "the amount of estrogenic compounds found in a single glass of cabernet wine is 1000 times greater than the estimated daily intake of estrogenic organochlorine pesticide residues."11
Claims also persist that chemicals such as DDT cause declining male reproductive capacity and breast cancer12,13. There is no evidence supporting a link between DDT and human cancers. Pressure against the use of organochlorines (among them DDT) persist because of the claim that they are linked to a fall in sperm quality. In 1992, Danish scientists of the Copenhagen University Hospital published a paper showing that the number of sperm cells in men's semen had fallen over the past 50 years14. Among the numerous reasons posited for the decline was the possible exposure to synthetic estrogens.
The media widely disseminated this study, and environmentalist groups such as Greenpeace used it very effectively in their campaign against synthetic chemicals. The study has sparked a great deal of debate in the scientific community and many investigations around the world into sperm quality. Subsequent studies conducted in Europe and the US found that in some cases sperm quality deteriorated and in some cases not; overall, scientists cannot find any meaningful decline in sperm quality. Part of the problem with these studies is that we do not have reliable pre-1970 data and so time series comparisons of sperm quality are inherently unreliable. According to Prof. Stephen Safe, "researchers have found no correlation between chemical exposures and measures of decreased male reproductive capacity. Demographic differences are more likely to account for the differences seen in the initial studies."15 Science simply does not support the assertion that DDT and other organochlorines are responsible for human health harms by disrupting the endocrine system.
Most recently, Eskenazi et al.16 published evidence linking DDT exposure to human harm. Like the innumerable studies before it, the study was roundly criticized by technical experts, and the authors' spurious recommendation to keep DDT out of malaria control was challenged by Africa Fighting Malaria.
The hypothetical risks to human health from the use of DDT in malaria control must be weighed against the very real benefits that it brings in malaria control. Even if a child survives a bout of malaria, the disease can severely damage his or her cognitive development, leaving him or her debilitated for life. The benefits of using DDT far outweigh any potential harm.
8 A. G. Smith, "How Toxic is DDT?" Lancet , Vol 356, No. 9226, July 22, 2000.
9 B. Ames & L. Gold, "Pollution, pesticides and cancer misconceptions," in What Risk? , ed. R. Bate, Butterworth Heineman, London (1997).
10 A. Attaran, D. Roberts, C. Curtis, W. Kilama, "Balancing risks on the backs of the poor", Nature Medicine, Vol 6 No 7 July 2000.
11 S. Safe, "Endocrine Disruptors. New Toxic Menace" in Earth Report 2000 , R. Bailey (ed), Washington DC: Competitive Enterprise Institute (2000) p. 190-191.
12 Liroff, R. "Reduction and elimination of DDT should proceed slowly" British Medical Journal , Vol 321. 2 December 2000, pp 1404-1405.
13 World Wildlife Fund, Resolving the DDT Dilemma , World Wildlife Fund (1998).
14 Carlsen, E, Giwercman A, Keiding, N, Skakkebaek, N "Evidence for decreasing quality of semen during the past 50 years" British Medical Journal Vol 305, pp 609-613.
15 Safe (2000) p 190. For instance, we know that the shorter the time since an ejaculation, the lower a man's sperm count is. During the time period chosen for a 1992 Danish study, statistics have shown that the frequency of masturbation has doubled for unmarried men (from 30 times a year to 60) and it also rose for married men (from 6 times a year to 24). At the same time the frequency of marital coitus also increased from around 1.9 times a week to 3 times a week (for married 30-year olds). So the sexual revolution of the 1960s could contribute greatly to the any observed decrease in sperm quality. Lomborg, B. The Skeptical Enironmentalist , Cambridge University Press (2001). p 240.
16 Brenda Eskenazi PhD et al. "In Utero Exposure to Dichlorodiphenyltrichloroethane (DDT) and Dichlorodiphenyldicholorethylene (DDE) and Neurodevelopment Among Young Mexican American Children" Pediatrics Vol 118, No. 1, July 2006.
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Will DDT use in malaria control affect agricultural exports?
This concern was originally expressed by the European Union (EU) in regard to Uganda re-introducing DDT for malaria control and the potential ban on contaminated exports. After much confusion and debate, it was laid to rest by the EU in a statement to the New Vision newspaper in Uganda on December 7, 2006, explicitly clarifying that no exports to the EU have ever been banned because of DDT contamination, nor would its use automatically result in an export ban. It went on to say it was "confident that appropriate controls can be put in place to ensure DDT is used without risk to food safety."
The fact is that at least 10 African countries use DDT, and they have not suffered any export bans - quite the contrary. In Zambia, South Africa, Swaziland and Mozambique, businesses have found that supporting malaria control programs that use DDT reduces malaria effectively, increases productivity and is beneficial to their bottom line.
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Will mosquitoes develop resistance to DDT?
As parasites inevitably grow resistant to drugs, so too do mosquitoes develop resistance to insecticides. Resistance to DDT has been reported in Western and in scattered parts of Southern and Eastern Africa, as has resistance to synthetic pyrethroids and most other insecticides. However, Sharma et al.17 demonstrated that DDT was effective against malaria even in the presence of resistance.
The fact is that the limited use of DDT for public health has continued to be effective in areas where it is used inside homes. As DDT's chief property is repellency, mosquitoes often avoid the DDT treated homes altogether. In so doing, they avoid the exposure that promotes resistance as well. Other insecticides, such as synthetic pyrethroids, tend to be used with insecticide-treated nets and in agricultural spraying as well, increasing mosquito exposure to the insecticide and with it the potential for resistance. Pyrethroid resistance in South Africa in the late 1990s18 led to one of its worst regional epidemics ever.
DDT is permitted strictly for public health application. Its controversial nature and Stockholm Convention status ensure that its use is closely monitored whenever it is used for malaria control. Additionally, health ministries and donors, such as the President's Malaria Initiative, increasingly monitor vector resistance trends and will rotate insecticides when a critical level of resistance is reached.
17 S.N. Sharmaa, R.P. Shuklaa, K. Raghavendrab & Sarala K. Subbarao, "Impact of DDT spraying on malaria transmission in Bareilly District, Uttar Pradesh, India" J Vect Borne Dis 42, June 2005, pp 54-60.
18 K. Hargreaves, L. Koekemoer, B. Brooke, R. Hunt, J. Mthembu, M. Coetzee, " Anopheles funestus resistant to pyrethroid insecticides in South Africa", 14 Medical and Veterinary Entomology (2000) 181-9.
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Does the Stockholm Convention on POPs affect the use of DDT?
The Stockholm Convention on Persistent Organic Pollutants (POPs) gives a specific exemption for the use of DDT in public health programs. This exemption is important, and many malaria researchers and activists fought environmental groups to ensure that they could still use the insecticide.
Rules and regulations regarding the trade, storage and use of DDT under the Stockholm Convention could however make its use more difficult and expensive. In developing rules and regulations, UN organizations should take into consideration the burden of these regulations on poor countries where there are competing uses for scarce funds. AFM believes that if the regulations prove too burdensome and result in procurement delays, they should be revisited and revised. The status of DDT in the Stockholm Convention is reviewed every three years.
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Why not use alternatives to DDT?
DDT is not only highly effective in malaria control, but it is also significantly cheaper than the other insecticides that are suitable for indoor residual spraying (IRS). It is easy to use and safe for both the residents of houses sprayed and the sprayers themselves. That said, alternative insecticides can and should be used for a number of reasons:
1) DDT leaves white marks on walls, which is often unsightly, and residents sometimes plaster over the insecticide, rendering it useless;
2) Bedbugs are resistant to DDT, but are irritated by it, making them more active. This is unpopular with residents of DDT sprayed houses, and so health departments may need to use alternative insecticides to control the bed bugs;
3) DDT is only suitable on traditional mud structures. As people build more western style houses with painted and plastered walls, malaria control programs will need suitable alternatives;
4) In order to control for the development of insecticide resistance, malaria control programs should use alternative insecticides either on an annual rotational basis or sprayed in a mosaic pattern. DDT will kill the mosquitoes resistant to pyrethroid insecticides and vice versa. Rotational and mosaic spraying has proved effective at controlling insecticide resistance in various parts of the world.
Good malaria control programs should always be seeking alternative insecticides for use in IRS. DDT is still much needed because it forms part of resistance management strategies. Because of the limited number of suitable insecticides that can be used in IRS, malaria control will likely require DDT to curb the disease for many years to come. The dearth of investment in finding new insecticides has also limited options in this respect
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Are synthetic pyrethroids environmentally friendlier than DDT?
Pyrethrum is a natural insecticide derived from the chrysanthemum flower that people have used for many hundreds of years in various parts of the world. Synthetic pyrethroids are a synthetic version of this insecticide and are considered to be more environmentally friendly as they are not as persistent as organochlorines, such as DDT. The shorter half life of these insecticides means that they will break down faster than the alternatives and could pose less of a threat to wildlife. However, in water, synthetic pyrethroids can have severe negative effects on fish and crustaceans in the short term. Synthetic pyrethroids cannot be used on water bodies for malaria control but they are effective when impregnated into bed nets. People in malarial areas frequently wash these nets in rivers or use malaria nets as fishing nets, which then release synthetic pyrethroids into water bodies. Synthetic pyrethroids therefore are potentially harmful to aquatic life and so their environmental "friendliness" depends on whether or not they get into water bodies.
It should be noted however that agriculture widely uses synthetic pyrethroids so they are likely to be found in fairly high concentrations around agricultural land. It is also important to remember that indoor residual spraying for malaria control uses very small quantities of any insecticides - be they pyrethroids, organochlorines or carbamates - inside houses and under the eves. Because indoor residual spraying uses such small quantities in such a targeted way, the environmental contamination is minimal.
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If indoor residual spraying works, why doesn't every malarial country use it?
Simply put, recipient countries are not free to do whatever they want with donor funding. Although indoor residual spraying (IRS) is highly effective and many countries have wanted to use it over the past few decades, most donor agencies have been reluctant to sanction its use. Pressure from environmentalist groups has doubtlessly influenced these policies, framing IRS as unsustainable or unsafe for humans and the environment. These notions have been proven false as more countries have adopted IRS programs and cut malaria rates without harming people or the environment.
In 2006 the US Agency for International Development significantly increased funding and logistical support for IRS in Angola, Uganda and Zanzibar as part of the President's Malaria Initiative (PMI). This is a very welcome change to years of anti-IRS policies. Most Roll Back Malaria partners have shied away from supporting IRS in the past, however under the leadership of Dr Arata Kochi, the World Health Organisation's Global Malaria Program is attempting to redress these policies and support countries that wish to include IRS as part of their anti-malaria strategy. The PMI is financing IRS in FY2007 countries now as well, including Rwanda, Senegal, Malawi and Mozambique.
For some years the Global Fund for AIDS, TB and Malaria has supported IRS in some African countries, such as Mozambique, Swaziland and South Africa as well as in Zambia. More countries require funding for malaria control that gives them the independence to determine the best possible set of policies for their circumstances and not to simply adopt the policies that donors and their contractors wish to foist on them. AFM welcomes the fact that IRS is once again a policy option for malaria control programs, however, IRS will not be applicable in every situation; malarial control programs in each country must conduct research to determine the appropriate mix of policies that are best for their circumstances. Countries and their development partners must ensure that they have the technical capacity to run IRS programs and use this intervention in the most appropriate settings.
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Why not just use insecticide-treated nets to control malaria?
Insecticide-treated nets (ITNs) or long-lasting insecticidal nets (LLINs) are nets impregnated with synthetic pyrethroid insecticides that cover a person in bed, and are an effective tool for vector control. People have used bed nets as protection from various pests for decades, but they have only recently been employed as a strategy for malaria control. The World Health Organisation (WHO) encourages pregnant women and young children, who are most at risk from malaria to use ITNs. Several studies have confirmed their efficacy at reducing mortality and morbidity in these two population groups.
Relatively high prices continue to act as a barrier to ITN use, but donors and governments are subsidizing or giving away freely an increasingly large proportion of ITNs. While ITNs do provide good personal protection, they require very high usage rates (above 80%) within a community to act as an effective public health tool. There are other problems that detract from their effectiveness as well. Although long-lasting ITNs (LLINs) are now being manufactured and distributed or sold to replace older ITNs, these nets also need to be retreated periodically (after 4-5 years as opposed to 1-2 years with earlier generations of ITNs) to ensure that the insecticide is still effective. Should the nets tear, they are useless as protection against malaria. In some areas there is cultural resistance to using ITNs because people are not used to them or aware of their benefits. In warm climates ITNs can also be uncomfortably hot to sleep under. Both Africa and India have reported that people frequently use as ITNs as fishing nets, which not only washes the insecticide off, making them ineffective in vector control, but also contaminates rivers and lakes with insecticide.
Overall, ITNs are an effective tool against malaria control, but they ultimately rely upon the correct and consistent use of individuals and communities at risk of malaria. ITN programs must be combined with good education programs to ensure that people know why they use ITNs, and their use should be monitored and evaluated. Overall, one intervention should not be used to the exclusion of another - malaria is a complex disease requiring all effective interventions as recommended by the WHO.
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Are insecticide-treated nets a more sustainable strategy?
Many commentators have argued that insecticide-treated nets (ITNs) offer a more "sustainable" malaria control strategy because they do not rely on vertical malaria control programs. Communities can manage them on a horizontal basis. Yet to date, the use of solely ITNs has not demonstrated a significant reduction in the burden of malaria. In contrast, many countries in southern Africa have managed to sustain well managed indoor residual spraying (IRS) programs for many decades and have kept malaria cases well under control.
It is wrong to suggest that ITNs are either environmentally or socially more sustainable than IRS. IRS programs often use sprayers and staff from the local communities, a practice that helps to sustain the programs. The residents whose houses are being sprayed often know the sprayers, and the sprayers earn money, which they then spend in the community. As with other services, governments need to make the decision to make programs sustainable and ensure they are financed. One could argue that garbage collection in cities is unsustainable, yet city authorities decide to sustain them and use public funds to do so. This should be the same philosophy with IRS.
A recent World Bank study on malaria control in the Solomon Islands concluded that both IRS with DDT and ITN use had their place, but that ITNs alone could not replace DDT use without an increase in the number of malaria cases19.
19 Bernard Bakote'e, et al. "Impregnated Nets Cannot Fully Substitute for DDT: The Field Effectiveness of Alternative Methods of Malaria Prevention in Solomon Islands, 1993-99" , Washington DC: World Bank (2003).
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What drugs are used to treat malaria patients?
Some 400 years after quinine was first discovered in Peru, doctors still use it to treat severe malaria patients. The problem of drug resistance is very real and has contributed to the rise in malaria cases around the world. Many parts of Africa use sulphadoxine-pyrimethamine, and some countries still use chloroquine even though treatment failure rates associated with this treatment are often unacceptably high.
The most promising and efficacious malaria treatment available to date derives from an ancient Chinese herbal remedy, Artemesia annua. When used in combination with other drugs, Artemisinin-based Combination Therapies are very effective at clearing malaria parasites from a patient's bloodstream.
The most important factor for people suffering from malaria is rapid diagnosis and treatment. In a few days, the disease can progress to cerebral malaria, rapidly resulting in coma and death. The need for early diagnosis and treatment highlights the importance of education about the disease for people living in malarial areas and for medical staff around the world. For travelers that have flu-like symptoms, the first question any physician should ask is, "Have you been to a malarial area?"
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What does co-infection mean?
Co-infection refers to one individual contracting and hosting multiple diseases at once. In recent years, scientists have come to understand that malaria co-infection with HIV/AIDS exacerbates the effects of both diseases on the individual. For example, a person with HIV/AIDS will have diminished immunity, and is more likely to contract and die from an episode of malaria than a healthy person. Pregnant women infected with both HIV/AIDS and malaria are likely to suffer from anemia, pre-term birth and intrauterine growth retardation.
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Are new malaria drugs being developed?
Several drug companies, such as GlaxoSmithKline, Novartis and Sanofi-Aventis, are actively researching new malaria therapies. In addition, many academic researchers are constantly researching new compounds and molecules that can target the various stages of the malaria parasite's development. Perhaps the most promising source for new malaria drugs is a public private partnership between the World Health Organisation and the drug industry called the Medicines for Malaria Venture. This venture has already isolated a number of different potential therapies that should produce new effective medicines in the years to come.
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Do malaria prophylactics mask the symptoms of malaria?
No. This is a myth. It is important to take prophylactics if you are going to a malaria area, especially if you have no immunity to the disease. If you take prophylactics and still get infected with the malaria parasites, it may ensure that the initial stages of the disease are less severe and that complications will be slower to arise. This can buy you important time in which to seek medical help that could save your life.
Mefloquine (Lariam®) is a highly effective weekly dosage prophylactic, but it does require a doctor's prescription because it has some contraindications. Malarone® (atovaquone and proguanil HCI) is another highly effective fixed-dose treatment, and also requires a prescription and has mild side-effects. Doxycycline, an antibiotic, is also effective and should be used when other prophylactics are unsuitable. Another prophylaxis is the combination of Proguanil and Chloroquine; however resistance to these drugs is widespread in southern Africa.
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Is there a vaccine for malaria?
Developing a vaccine against the complex P. falciparum parasite has proven extremely difficult. As such, experts estimate that an effective vaccine against malaria will not be available for at least another five years. Even when an effective vaccine is discovered, public health programs will inevitably face problems in deploying it. Anti-malarial drugs and preventive tools will still be necessary, as will effective policies designed to ensure they reach those at risk of malaria.
The creation of the Malaria Vaccine Initiative (MVI) has enabled considerable progress towards finding an effective malaria vaccine. A recent vaccine candidate trial in Mozambique reduced childhood infection by a third and outbreaks of severe malaria by half. MVI in conjunction with GlaxoSmithKline and other partners is coordinating the next round of testing in Ghana.
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Can Plasmodium falciparum malaria relapse?
P. falciparum malaria does not relapse. Other types of malaria, such as P. ovale and P. vivax can relapse due to a reactivation of some of the parasites in the liver. However if a patient suffers a "relapse" from P. falciparum, it is most likely to be a re-infection or recrudescence of the parasite because of a failure in the malaria treatment.
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Do mosquitoes transmit HIV/AIDS?
No. Although this is a common fear, there is no evidence to support the theory that mosquitoes can transmit the Human-Immunodeficiency Virus (HIV). Studies by the US Centers for Disease Control and others can find no evidence that mosquitoes, or any other blood-sucking insect, can transmit HIV. In countries where both high HIV prevalence and high malaria rates exist, such as Uganda, HIV mainly affects the sexually active population. If mosquitoes could transmit HIV, one would expect to find a far more even distribution of HIV infection throughout the population.
Understanding the way in which a mosquito bites is important to understanding why they cannot transmit HIV. When a mosquito feeds on a human, it injects a small amount of saliva, which acts as a lubricant, so the mosquito can feed smoothly. It does not inject another person's blood into the person it is feeding on. Also, after a mosquito has fed, it usually rests and digests the meal before it feeds again. Even if there were small amounts of blood on the mosquito's mouth parts, these would have dried or disappeared before the mosquito's next meal.
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Why is treatment important for pregnant women?
Malaria is particularly dangerous for pregnant women. Pregnancy often weakens their immune systems, and the mother can transmit the malaria parasite to the unborn child. Contracting malaria while pregnant greatly increases the chances of maternal anemia, abortion, preterm birth or stillbirth, intrauterine growth retardation and low infant birth weight. The World Health Organisation (WHO) estimates that malaria causes between 8% and 14% of all low birth weight babies and between 3% and 8% of all infant deaths in Africa. According to the WHO, malarial anemia alone causes around 10,000 deaths every year in Africa20. It is therefore essential that pregnant women seek treatment early in order to protect their lives and those of their unborn children.
In order to reduce the risks of malaria to pregnant women, malaria experts recommend intermittent preventive treatment. This involves giving at least two preventive treatments of an effective anti-malarial drug to pregnant women. The WHO also recommends the use of insecticide-treated nets as a means of reducing the risk of malaria. However, as described above, some serious obstacles hamper the widespread introduction of ITNs in southern Africa.
20 Roll Back Malaria "Malaria in pregnancy" WHO, Geneva http://www.sahims.net/doclibrary/malaria/Malaria&Pregnancy.pdf
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Does sickle cell anaemia confer malaria immunity?
A gene coded for the manufacture of abnormal hemoglobin, the "working" constituent of red blood cells, causes sickle cell anemia. It is thought that aboriginal Vendoids, who left their native India and came to Africa, introduced sickle cell to Africa around 4000 years ago21. When a child inherits sickle cell genes from both parents, the resulting anemia can cause eventual death. However if only one parent passes on the abnormal gene and the other contributes a normal hemoglobin gene, the resultant "diluted" sickle cell anemia protects against the effects of P. falciparum malaria.
Although sickle cell children are just as likely to contract malaria as non-sickle cell children, the effects of the disease are less severe, and the duration of the malaria attack is likely to be shorter. As sickle cell children grow up, they will have greater acquired immunity to the disease and are more likely to survive the disease than non-sickle cell people.
A recent study in the Lancet22 found that the sickle cell gene, "...provides significant protection against all-cause mortality, severe malarial anemia and high density parasitemia. This significant reduction in mortality was detected between the ages of 2 and 16 months, the highest risk period for severe malarial anemia in this area. These data are important in understanding the role of malaria in the selection and maintenance of the sickle cell gene."
21 See Robert Desowitz, The Malaria Capers, New York: Norton, 1991, p 147.
22 Aidoo, M. et al "Protective effects of the sickle cell gene against malaria morbidity and mortality," Lancet 359 (9314)Apr 13, 2002: 1311-2.
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Centers for Disease Control and Prevention
Global Fund to Fight AIDS, TB and Malaria
Global Health Advocates
Innovative Vector Control Consortium
Lubombo Spatial Development Initiative
Malaria Foundation International
Malaria Vaccine Initiative
Medical Research Council
Medicines for Malaria Venture
Multilateral Initiative on Malaria
Nature Medicine (Malaria)
President's Malaria Initiative
Roll Back Malaria Partnership
South Africa Department of Health (Malaria)
East and Southern African Malaria Control
World Health Organisation
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Selected References and Further Reading
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- D. R. Roberts, S. Manguin, J. Mouchet, "DDT house spraying and re-emerging malaria", Lancet, 2000, 356: 330 - 332
- D. Roberts, L. Laughlin, P. Hsheih and L. Legters, "DDT, Global Strategies and a Malaria Control Crisis in South America", Emerging Infectious Diseases, Vol. No 3 July-Sept 1997
- A. G. Smith, "How Toxic is DDT?" Lancet , Vol. 356, No. 9226, July 22, 2000.
- B. Ames & L. Gold, "Pollution, pesticides and cancer misconceptions," in What Risk? , ed. R. Bate, Butterworth Heineman, London (1997)
- A. Attaran, D. Roberts, C. Curtis, W. Kilama, "Balancing risks on the backs of the poor", Nature Medicine, Vol. 6 No 7 July 2000.
- S. Safe, "Endocrine Disruptors. New Toxic Menace" in Earth Report 2000, R. Bailey (ed), Washington DC: Competitive Enterprise Institute (2000) p. 190 - 191.
- K. Hargreaves, L. Koekemoer, B. Brooke, R. Hunt, J. Mthembu, M. Coetzee, " Anopheles funestus resistant to pyrethroid insecticides in South Africa", 14 Medical and Veterinary Entomology (2000) 181-9.