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In 1992 W.H.O. Ministerial Conference was held to evolve a Global Strategy for Malaria Control which highlighted the importance of vector control and emphasis on treatment. Control strategies are used to contain malaria epidemics, prevent death and disability (mortality and morbidity), and to reduce socioeconomic loss. The control of malaria involves control of human (host), mosquito (vector), parasite (agent), and their environment. Currently, a number of control measures are used against the human malaria parasites and their mosquito vectors, such measures include:
the early diagnosis and treatment of malaria with antimalarial drugs to vulnerable population such as infants and pregnant women, who receive intermittent preventive treatment (IPT);
reducing the number of people being infected through personal protection measures such as insecticide-treated bed nets;
prevention of infection through vector control.
Early diagnosis and treatment
Early diagnosis and treatment is a very significant aspect of malaria control. Making early detection and effective and timely treatment can cure the disease by controlling malaria in its early stages and reduce the spread of parasitic resistance to drugs. In this way, the parasite load in the population is decreased, thus reducing the transmission of malaria.
When adequatly and promptly treated, a person with malaria can expect a complete recovery. However, severe malaria can develop from uncomplicated disease within hours and most malaria mortality take place in rural regions where people have low access to health care facilities. For chronic infection, which is not as serious as severe malaria, treatment is also essential because it can result in anaemia.
correct and prompt treatment can also reduce the development of drug resistance, and in regions of low transmission can disrupt malaria transmission by lowering the amount of gametocytes which can be transmitted to the mosquito host. Though, in regions of high transmission, in most people carrying the malaria parasite disease symptoms don not appear and so they do not receive prompt treatment. Hence, in this manner, the number of gametocytes circulating in the inhabitants cannot be reduced.
Clinical Diagnosis is based on the patient's symptoms and on physical findings at examination. The first symptoms of malaria, such as fever, chills, headaches, muscle pains, nausea and vomiting, are often not specific and are also found in other diseases. Similarly, the physical findings are often not specific (elevated temperature, perspiration, tiredness). Clinical findings in severe malaria, such as confusion, coma, neurologic focal signs, anaemia, respiratory problems, are more prominent and may increase the suspicion index for malaria. As a result, generally the early clinical findings in malaria are not characteristic and a laboratory test is required for confirmation.
Presumptive treatment of all cases of fever is very important. Tests for malarial parasite should be done in all cases of fever, and presumptive treatment with first full dose of chloroquine should be administered. Chloroquine is highly effective as schizonticidal against all species of malaria and is also gametocytocidal against all except P. falciparum. Thus, by administering chloroquine to all cases of fever, it is possible to sterilize the gametocytes and thus prevent the spread to mosquitoes. Whenever resistance to chloroquine is known or suspected, second line anti malarials should be used to treat P. falciparum malaria.
Microscopic Diagnosis involves identifying malaria parasites by examining using a microscop, where a drop of the patient's blood is spread out as a "blood smear" on a microscope slide. This method is typically used for laboratory confirmation of malaria.
Other methods include:
Antigen Detection involves detection of antigens derived from malaria parasites by using the available test kits. Such immunologic tests most often use a dipstick or cassette format, and provide results within 15 minutes. in situations where effective microscopic diagnosis is not accessible, These "Rapid Diagnostic Tests" (RDTs) provide a reliable alternative.
Molecular Diagnosis involves the detection of Parasite nucleic acids using polymerase chain reaction (PCR). This technique is more accurate than microscopy, but more expensive and requires a specialized laboratory.
When malaria is caused by Plasmodium falciparum, can be fatal and devastating, and treatment should be initiated at the earliest possible time. Treatment eliminates an important component of the cycle (the parasite) and therefore interrupts the transmission cycle. The WHO recommends that treatment should be started with an effective antimalarial drug within 24 hours once the first symptoms develop. patients with uncomplicated malaria can be treated on an ambulatory basis, i.e. without hospitalization, but patients with severe malaria should be hospitalized if possible. Patients who have severe malaria (caused by P. Falciparum) or who cannot take oral medications should be treated by giving continuous intravenous infusion. Several drugs are available to prevent malaria in malaria-endemic countries (prophylaxis). These prophylactic drugs are active against the parasite forms in blood and include:
artemisin derivatives (this drug is not licensed for use in the US, but is frequently sold abroad)
treatment of P. falciparum infections in endemic countries In the last 5 years has transformed by the use of combinations of drugs containing an artemisinin derivative. The combination of multiple drugs increases clinical efficacy and may delay the resistance of parasites from developing (12). However, these drugs are not always affordable and not widely available. Chloroquine resistant P. falciparum, and severe and cerebral phases of malaria can be treated with intravenous or intramuscular quinine or the artemisinin derivative artesunate.additionally, primaquine is active against hypnozoites (which are the dormant parasite liver forms) and causes prevention of relapses. pregnant women or people who are deficient in glucose-6-phosphate dehydrogenase (G6PD) should not take primaquine. Thus patients are not given primaquine for treatment until a screening test has excluded deficiency of G6PD.
A community trial in Ethiopia in an area of low malaria transmission demonstrated that under-5 mortality was decreased by 40% as a result of educating mothers to provide chloroquine treatment at home promptly for fevers (9) (Figure 3.1). thogh this high level of effect may be due to the broad improvement in child care. Other indirect evidence in Brazzaville revealed that due to the extensive use of chloroquine as self-treatment (10) there was reduced malaria-specific mortality. during the 1990s a 15% dcerase in infant and child mortality rate was recrded Demographic and Health Surveys in Malawi, conversely with increasing infant and child mortality rates in Rwanda, Zimbabwe the United Republic of Tanzania, Uganda, Kenya and Zambia. This outstanding mortality reduction in Malawi may be as a result of the drug policy change from chloroquine to SP in 1993.
Drug resistance has become one of the greatest challenges in malaria treatment. Unfortunately, resistance has developed to several antimalarial drugs, particularly to chloroquine which is the most widely accessible and affordable antimalarial drug.
The figure shows how Chloroquine has lost its clinical effectiveness in certain most parts of Africa (Figure 3.3). Resistance of P. falciparum to other cheap drugs, such as SP, is also an emerging problem in southern and eastern Africa (Figure 3.4).
Self-diagnosis and treatment in endemic regions also include strategies such as using herbal remedies, e.g. Artemisia annua tea, traditional healers, and antimalarials bought over the counter. Most individuals do not seek help from primary health care facilities unless these methods are unsuccessful and facilities are nearby, hence, reliable and efficient treatment is delayed as a result. Educating parents, carers and shopkeepers about providing suitable drug doses and information on other care aspects would promote prompt and effective treatment.
Administration of antimalarial drugs cannot prevent infection in vulnerable population groups, which happens through mosquito bites. However, antimalarial drugs can prevent disease by getting rid of the disease causing parasites that are in the blood. Vulnerable groups such as Pregnant women are most often targeted, and so they may receive intermittent preventive treatment (IPT) with antimalarial drugs which are given most frequently at antenatal consultations throughout the second and third trimesters of pregnancy.
Evidence: Currently, SP given at a therapeutic dose is the antimalarial with the best overall effectiveness for preventing malaria in pregnancy in regions of high transmission, and low resistance to SP.
Studies carried out in Kenya (6,7) and Malawi (8) have revealed that IPT with minimum of two treatment doses of SP has been very effective in lowering the percentage of women with anaemia and placental malaria infection at delivery. Advantages of IPT for both maternal and infant health have been evident in a variety of different surroundings of malaria transmission (Figures 4.2-4.4).
Intermittent preventive treatment for malaria in infants (IPTi) is a possible approach of using existing malaria drugs to protect infants from the worst effects of the disease. In this approach, infants are given an antimalarial drug three times during the first year of life, whether or not they have malaria, in combination with their routine childhood immunisations in the frame of the Expanded Pro- gramme on Immunisation (EPI) (an organisation of regular health contact with young African children). Evidence has demonstarted that IPTi-SP is safe, effective and there should be little concern about the return of malaria after termnation of IPTi.Â in eastern Africa, approxiamtely three quarters of preschool children suffer from anemia. Two studies in Tanzania have shown that an antimalarial drug (SP) could be administered to children at 2,3, and 9 months of age attending vaccination visits, resulting in an almost 60% reduction in rates of clinical malaria and a 50% reduction in the rate of severe anemia compared to those receiving placebo (Schellenberg et al Lancet 2001).The project recognised the cost-effectiveness of IPTi when applied within routine health services together with EPI and the potential for rapid scaling up.
Reducing the number of people being infected
Preventing malaria-carrying mosquitoes from biting humans can prevent infection. Such strategies include applying effective preventative interventions such as prophylaxis and insect repellents. In order to avoid infection, Non-immune adults entering endemic regions should take antimalarials prophylactically. Most malaria carrying mosquitoes bite at night, thus, an alternative is to provide an insecticide-treated bed net (ITN) which provides a physical barrier that helps prevent exposure to infected mosquito bites and reduces the number of mosquitoes in a room. ITN combines vector control and personal protection. Because of the insecticide in the net, it can reduce the lifespan of the mosquitoes that come into contact with it and as a result lower the mosquito population and malaria transmission.
Evidence: It has been estimated that ITNs are twice as much effective than untreated nets and provide 70% more protection compared with no net.. Even though ITNs have been shown to be very effective in controlling and preventing malaria, only about 2% of children in Sub-Saharan Africa urban regions are protected by ITNs. ITNs have been proven to be the most cost-effective prevention method against malaria and are part of WHO's Millennium Development Goals (MDGs).
various studies have demostrated that the use of these ITNs results in a 20% reduction in all-cause mortality and 40-60% reduction in infection and their use have shown to lower the number of cases of severe malaria in children under five years old. African Randomized controlled trials have shown that ITNs can lower under-5 deaths by approximately one-fifth (5), i.e. about 6 out of every 1000 children aged 1-59 months are protected every year (Figure 2.1). The incidence of clinical episodes of P. falciparum infection is reduced by 50% on average. ITNs have also been shown to be very successful in reducing low birth weight, placental infection and maternal anaemia in pregnant women (6).
Nevertheless, in high transmission regions where immunity develops over time, fewer infected bites can result in delay in immunity and lead to an increase in the number of cases of severe disease in older children. The use of Bed nets are encouraged in malarious regions, but nets can be unaffordable in developing countries and require regular re-treatment.
The aim of Vector control is to reduce contacts between mosquitoes and humans. Vector control measures reduce the numbers of mosquitoes and hence reduce malaria parasite transmission. These include insecticide spraying, environmental management and biological control. Environmental management measures, such as covering wells and filling in ditches, and keeping irrigation channels fast flowing, reduces the number of mosquito breeding sites.
Insecticide spraying Reduces malaria transmission by reducing the survival of malaria vectors entering houses or sleeping units. three types of spraying are used against mosquito vectors; 1) residual spraying, 2) space spraying (which are used against the adult mosquito) and 3) larviciding (which is used against mosquito larvae).
In Indoor Residual spraying (IRS) the insecticide is mixed with solvent and the internal surfaces of houses are sprayed with it. This spray is an effective way of controlling mosquito numbers. The understanding of the resting and breeding habits of the mosquito species in question is required for appropriate areas to be treated. After the water has evaporated, the insecticide residue is active for months and kills mosquitoes when they land on treated surfaces. incidence of malaria can be lowered by reducing the life span of the female mosquito, reducing the mosquito population and reducing human-mosquito contact.
IRS is fairly expensive and there may be a likelihood of mosquitoes becoming resistant to the insecticide sprays, or walls being re-plastered after spraying.
during malaria epidemics Space spraying is frequently used as a control measure, where a 'fog' of insecticide is sprayed into the air. In order to be effective This technique requires huge supply of insecticide and specialist equipment and has only a short-term effect.
Larviciding involves chemical spraying of water sources to reduce mosquito breeding sites. However, non-toxic methods and environmentally friendly are favoured. Thus, bacteria such as Bacillus thuringiensis can be sprayed into water, where the mosquito larvae eats the bacteria and dies since the bacteria acts as a gut poison. Guppy fish eat mosquito larvae and can be used as a form of biological control against mosquitoes in wells and irrigation channels.
Evidence: in conjunction with the observation and treatment of infected humans, Vector control programs have successfully and efficiently eradicated malaria from United States and southern Europe. In the early 1990's, malaria was eradicated from the northern parts of the USA by employing such control methods, and the use of the pesticide DDT eliminated it from the Southern parts of USA by 1951. In 2002, 1,059 cases of malaria were reported in the US, including eight deaths, but only five of those cases contracted malaria in the USA.
Figure: Malaria Morbidity and Mortality Rates in All USA States Reporting Cases and Deaths During 1920-1946 Inclusive
in Africa, These control methods have seen little function for more than 50 years. there was a major public health effort In the 1950s and 1960s to eliminate malaria worldwide by selectively targeting mosquitoes in regions where malaria was widespread. yet these efforts have so far been unsessuful in eradicating malaria in many areas of the developing world, particularly in Africa.
Other alternative methods
in some parts of the developing world, Education in understanding the symptoms of malaria has lowered the number of cases by almost 20%. Identifying the early stages of malaria can also stop the disease from being fatal. People can be educated to cover over areas of still water, for example water tanks which are often the perfect parasite and mosquito breeding grounds. This will reduce the risk of transmission between people in urban areas where there are large number of population living in a confined space.
Despite ambitious goals such as those of the Roll Back Malaria Initiative to halve malaria deaths by 2010, mortality from the disease has actually risen halfway through the program . Clearly the tools we have to control malaria, or the ways in which we are using them, are not working.
The failure of existing methods for malaria control has sparked interest in several new approaches. These include better and cheaper antimalarial drugs , the development of genetically modified mosquitoes (GMMs) and renewed efforts to find a vaccine  either to reduce population sizes or to replace existing populations with vectors unable to transmit the disease.
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Malaria vector control: current and future strategies
References and further reading may be available for this article. To view references and further reading you must purchase this article.
Willem Takkena, and Bart G.J. Knolsa. Trends in Parasitology
Volume 25, Issue 3, March 2009, Pages 101-104