Malaria Prevention and Control
Generally speaking, the measures for prevention of malaria in individuals and for large-scale control of the disease are designed to (a) reduce man-mosquito contact, (b) reduce vector breeding habitats, (c) destroy mosquito larvae, (d) destroy adult mosquitoes, and (e) eliminate malaria parasites in human host.
Malaria vaccine. There is no malaria vaccine at the present time. While several candidate vaccines (sporozoite, merozoite and transmission blocking) are being developed. the results of clinical trials have not been encouraging. However, the most advanced one Spf 66, a synthetic peptide polymer, developed by Manual Patarroyo, has undergone large-scale phase III field trial in Columbia, Tanzania, and Thailand, but the outcome is not encouraging.
1) Personal Protection Measures. For individual protection the following measures may be employed:
Destruction of vector mosquitoes on the spot: -r- the pi—’57etion of the individuals at home. The most common formulation used is 0.1%-0.4% solution of pyrethrum 25% in kerosene. It is generally used as the main active component of commercial aerosols which are available in low- pressure spray cans. Other formulations available in the local market can also be used with care as space spraying using a hand sprayer (Flit gun). The household type of aerosol dispenser. in use now-a-days, contain pyrethrum or pyrethroid compounds or similar insecticides. Space spraying knocks down and kills any mosquitoes that may have entered the room/house. However, this knock-down effect is relatively short-lived and, therefore, frequent applications are necessary if the house is not screened.
Protection against mosquito bites: (i) Screening of house: Wherever possible, mosquito proofing of dwellings has been a very effective method for the health and comfort of the people. Fixing of screens of standard wire gauge to the’ doors, windows and other openings in, the house- provides a mechanical defense, provided the inhabitants stay indoors during the hours of vectors’ feeding activity. The screens need the regular inspection to see whether any repair or replacement is necessary. The poorly constructed house cannot be effectively screened. (ii) Use of repellents: These are products, natural or synthetic, that can be applied . to the (kin 2 clothing or bed-nets to repel mosquitoes and prevent them from biting. The • commonly used synthetic repellents are Rutgers- 612, Indalone, Dimethyl phthalate (DMP), Dibutyl phthalate (DBP), N. N. Diethyltoluamide DET. DMP provides protection for about 3 hours, DBP for about 4 hours whereas DET remains active for about 10 hours. Mosquito coils or joss sticks containing pyrethrum and DDT or synthetic pyrethroids are useful repellents. A new type .of repellent is now available This is a small semi- porous mat impregnated with synthetic pyrethroid compound, with the addition of a blue dye and perfume. When inserted into a small electric heater, the mat slowly releases insecticide. (iii) Bed net (plain) untreated: The use of bed nets (mosquito nets) is still one of the most effective measures of personal protection. A netting suitable,,,for protection against anopheles vectors is one..,of 25/26 mesh, woven of 30/S or 40/60 cotton. thread. The number of holes to the sq.. inch (6.45 cm2) would be about 150. If the nets are made up of nylon the mean size of the holes should be 1.2-1.5 mm: there should be 6.8 holes to 10 mm. (iv) Use of insecticide impregnated bednet: based on residual efficacy (decline in annual parasitic incidence) and the popularity of insecticide (synthetic pyrethroids e.g. deltamethrin) impregnated bednets are now being incorporated as personal protection method through the primary health, care system, and by other establishments. Highest mortality amongst anopheline species has been observed in nylon nettings and comparatively less in cotton nations. Bednets need to be reimpregnated every month. impregnated bednets’ are being d-is7E-ibuted by the Bangladesh Malaria Control Programme in high-risk areas.
Individual Chemoprophylaxis: Any individual who resides in the malarious area or plans to visit an area where the risk of contracting the disease exists, may protect himself by taking drugs of choice causal prophylaxis they are, however, less effective against p. vivax. Blood schizont oxides such as chloroquine and amodiaquine are good suppressive drugs.
In areas where parasite resistance against these drugs exists the combination of long-acting sulfonamides (sulphadoxine or sulpha lane) or clap serene and pyrimethamine may be used.
(2)Vector Control Measures.’ The control of mosquitoes is undoubtedly the best method of protecting a community against malaria. The measures applied for vector control are (I) Environmental management; (2) Biological control: (3) Genetic control; (4) Chemical control.
Environmental management: Before the era of large-scale application of residual insecticides. source*reduction for the prevention of breeding- of vector mosquitoes was the principal measure available. But the success of insecticide spraying after the Second World War had almost entirely replaced the source reduction or the engineering methods. The limitations of large scale residual spraying have, however, once again focused attention on the ‘environmental management measures against the aquatic stages of malaria vectors. Any long-lasting or permanent changes of land, water or vegetation aimed at the reduction of the habitat of the vector are often referred to as environmental modifications, while similar temporary or recurrent activity is called environmental_ manipulations. Environmental modifications include measures like (a) filling of small water collections, abandoned ditches, burrow pits, ponds. etc. and (b) drainage to remove u757.vanrea–water from the land surfaces (surface drains) or below the surface (sub-soil drains), whereas.ewironmental. -manipulations include changing the water levels e impounded water reservoirs, intermittent ryincc of the rice fields, stream sluicing or flushing, changing water salinity.shading of stream banks and clearing of vegetation.
Biological methods : These methods of mosqUito control are based on the introduction of the environment or various pathogens and predators of insect vectors-of disease: theses are natural predators, such as
viruses, bacteria, protozoa, fungi, etc. The larvivorous fishes that have been used in some malaria control programs are Gamhusia affinis, Lebistes rettcutatus (guppy) , annual fish (Nothobranchius), etc. Cyprin.us carpio (common carp) and a species of Tilapia have also been found useful in larvicidal operations. In recent yearsconsiderable attention has been given to two bacteria and their products; these arc Bacillus attiring fensis serotyPe 1-1-14 and Bacillus sphaericus. These have been marketed as biological larvicides.
Genetic Control : This has been the subject of research since the early 1950s. Various methods of
genetic control have been used, but the release male mosquito sterilized by irradiation or chemical compounds has received more attention. The principie is that the sterilized males sec): out and mate with the wild females in the nanire. thus preventing hatching of their eggs and lw.vering their reproduction potential.
Chemical Control: The introduction of DDT and other chemical insecticides resulted in the revolutionary concept of malaria control.
Indoor residual spraying : –Large scale application of residual insecticides has a marked effect on those species of mosquitoes which feed preferentially on man inside his dwelling and rest in the houses or in the animal sheds. Subject to epidemiological indications the treatment of premises is carried out by total, barrier or selective spraying methods. The effectiveness of these methods depends largely on the vector susceptibility to the applied insecticides and the quality of spray coverage.
External space treatment: Techniques have been developed for application of insecticides to open spaces. Although principle is the same as that of the indoor space spraying. these techniques involve sophisticated equipment. skiilcd manpower and high operational cost. As such, these methods are appropriate only for the urban centers and during emergency situations like epidemic outbreak. The methods employed are Ultra Low Volume (ULV) and Thermal Fogging techniques.
Insecticides commonly used in makiria control programme for the destruction of adult Anopheles vectors are DDT, ITCH (1311C). Malathion. Fenitrothion and Carbarnatcs. Details are given in Chapter XVI on Medical Entomology.
Larvicidal methods: The techniques of application of larvicides to wafer surfaces depend on the type of compound used and the type of breeding places. These measures of control are of particular value when employed in conjunction with environmental management method. an d arc indicated particularly in situation where the breeding areas of Anopheles well-known. The insecticides used in I:a-yielding operations are t(TET oil and otherE:roleum oilD (with the addition of a spreading agent).
Anti-parasite Measures. At present there is no ideal drug available which is effective against all t le species and all the devekopmenlid stages of malaria parasites, Moreover, treatment depends on the status of sensitivity of the parasite to antimalaria drugs, the severity of disease and Occurrence of complications.