Table of Contents
Malaria is widespread throughout the tropical and subtropical zones, as well as in the temperate one. Wherever there are some conditions for the Anopheles mosquitoes, the larvae of which live in shallow freshwater ponds and swamps. Statisticians annually register 350-500 million cases of human infection with malaria; 1.3-3 million of which result into death (Campbell & Reece, 2005). Malaria control is one of the main tasks for the UN health authorities and national governments. Currently, the disease is widespread in India, many countries of Africa and South America. 85-90% of infection cases are fixed in sub-Saharan Africa. The vast majority of infected people are children under 5 years (Greenwood, Bojang, Whitty, & Targett, 2005).
The causative agents of malaria are Plasmodium protozoa. A person becomes infected with them at the moment of inoculation (injection) of the pathogen (sporozoite) into blood or a lymph system. The inoculation occurs during a bloodsucking process by a female Anopheles mosquito. After a short stay in the blood Plasmodium sporozoites enter the liver hepatocytes starting a preclinical exoerythrocytic stage of the disease. During the asexual reproduction called schizogony, one sporozoite turns into a schizont forming 2,000 to 40,000 hepatic merozoites. In most cases, these newly formed merozoites return to the blood in 1-6 weeks (Baer et al., 2007).
Symptoms of malaria include fever, chills, arthralgia (joint pain), vomiting, anemia caused by hemolysis, hemoglobinuria, and convulsions. A skin tingling sensation is also possible especially in the case of malaria caused by P. falciparum, as well as splenomegaly (enlarged spleen), unbearable headache, and cerebral ischemia (Anstey, Douglas, Poespoprodjo, & Price, 2012). Malarial infection is deadly; the especially vulnerable categories are considered to be children and pregnant women. Today, same as centuries ago, the most common medication for the treatment of malaria is quinine. For a certain period of time, it had been replaced by chloroquine, but nowadays quinine has regained its popularity again. The reason for this was the mutation of Plasmodium falciparum and emergence of its resistant to chloroquine form. Initially, the resistant form appeared in Asia and later spread to Africa and other parts of the world. There are also some other substances, which are used for the treatment and prevention of malaria. Many of them can be used for both purposes. Their application depends primarily on the parasites’ resistance to them in the area where the particular drug is used. There is currently no effective vaccine against malaria. However, active researches on its creation are conducted all over the world. Under such conditions, the methods used to prevent the spread of malaria in dangerous areas include prophylactic drugs, extermination of mosquitoes, and repellents application. The paper analyzes the problem of malaria spread in Asian and African countries, as well as existing and proposed preventive solutions.
Malaria: The Areas of Spread and Types
The geographic area of malaria spread is limited to the zone of Anopheles mosquitoes’ natural habitat and by the environment temperature ensuring the completion of sporogony in the mosquito’s organism. Within a particular geographic area, the spread of the disease is not even. It depends on the natural and socio-economic conditions. The most intense malaria foci are in the tropical and subtropical zones, first of all, in the countries of Africa, Southeast Asia, South and Central America, the Caribbean region and Oceania (World Health Organization, 2014).
The most prevalent of the malaria pathogens is P. vivax. It is common for North and East Africa, Southeast Asia, Latin America, Central Asia (Tajikistan, Uzbekistan), the Caucasus (Azerbaijan), and Dagestan. In West Africa, being populated predominantly with Negroids, this type of malaria is rare due to the genetically determined innate immunity of black Africans to P. vivax. Vivax malaria is widespread due to the P. vivax ability to develop in the mosquito’s body at lower ambient temperatures (16-17 °C). In addition, the plasmodium can be stored in a host organism in an inactive, dormant form for several months and even years.
Falciparum malaria is mainly distributed in tropical countries of West and Central Africa. Previously, its geographical area has reached 45-50° north latitude and 20° south latitude and could be found even in some parts of Central Asia. Since the middle of the 20th century, Falciparum malaria has been eliminated in Central Asia. However, in recent years, local pockets of tropical malaria have started to appear in Tajikistan. It is the only area in the WHO European Region with the local transmission of P. falciparum. Despite the relatively limited geographical area of spread P. falciparum causes a 50% incidence of malaria in the world and 98% of all deaths (World Health Organization, 2008).
Malaria caused by P. malariae is now widespread in Africa, some parts of Central and South America, the Caribbean and South-East Asia. In many centers of tropical and vivax malaria, this pathogen is absent, so the areas do not cross.
Ovale malaria (P. ovale pathogen) is registered mainly in West African countries. Sporadic cases occur in New Guinea, the Philippines, and Indochina. The limited area of P. ovale habitat is associated with long-term sporogonia taking place at high tmperatures (15 days at 25°C), as well as with low and unstable production of gametocytes, which reduces the possibility of infection. Also, the spread of infection to other areas with similar climatic conditions is limited through their lack of specific Anopheles gambiae disease vectors.
Existing Preventive Measures
Malaria control is carried out in several directions. An effective measure is drainage of waters that harbor the Anopheles larvae. Large bogs dehydration lies in draining or making a system of open channels with a constant control of water outflow. It also can be done through effluent systems, which discharge the water into a nearby river. Besides, specialists use closed drainage, i.e. porous pipes laid in the ground at a certain depth with a bias towards the surface slope of the soil. Soil drainage can be combined with artificial pumping of water from low-lying places to higher lands with the purpose of irrigation.
A popular measure against malaria spread in Asian and African countries is artificial rising of lowland localities by pouring sand and earth. Moreover, they apply the so-called colmatage, which is periodic flooding of area with water rich in sludge. Therefore, after sedimentation, it gradually increases a soil level. A careful monitoring of the irrigation systems’ condition, the prevention of water stagnation, and waterlogging plays a huge role. In rice plantations requiring a lot of water intermittent irrigation systems are used. It means that the field is filled with water for a few days; and then they stop the water inflow for 4-5 days. Due to this, the hatching larvae die. Deepening of ponds, cleaning of beaches, as well as alignment and cleaning of riverbeds make these waters inaccessible to Anopheles mosquitoes.
Small hydrotechnics also has an enormous significance. It includes the destruction and elimination of small ponds that do not have a high economic value, as well as cleaning the canals and irrigation systems. Besides, such small hydrotechnics involve shallow rivers and ponds deepening, as well as clearing them from the vegetation, installation of covers on various water containers, i.e. tanks, vats, etc. It is useful to plant broadleaf trees around the ponds that need to be kept, relying on the adverse effects of shading on the hatching of Anopheles mosquitoes. Plants like eucalyptus, willow or sunflower have a drying effect to wetland sites.
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One of the actions to destroy the larvae is petrolization. Oil spreading over the water penetrates into the breathing holes of larvae, which rise to the surface. The petrolization has direct and indirect effects. In the first case, it influences larvae and pupae directly; in the second one, it has an indirect action through destruction of places suitable for their lives. The most important means in this respect are oil and kerosene. After pouring them into the water a thin layer of oil appears on the surface. Mosquitoes’ larvae and pupae die in the water due to an inability to access fresh air. During the contact with their breathing holes, the oil layer penetrates the trachea to a certain depth resulting in the death of the larvae. Apparently, the influence of oil is important not only due to stopping the inflow of oxygen, but also because of its toxic effects.
The petrolization is a very simple procedure that does not require any special equipment. If the pond is not overgrown with plants the amount of oil or kerosene spent is 20-40 grams per 1 square meter of the water surface. Adding 1% of cresol to oil increases an effective area. This mixture has a higher ability of penetration into the plants thicket. The layer itself is more durable since cresol prevents a decomposing effect of bacteria on petroleum hydrocarbons. Sometime later, the oil slick disappears as a result of low-boiling hydrocarbons volatilization, their oxidation by atmospheric oxygen, and assimilation of the hydrocarbons by bacteria. The role of the latter ones is important; therefore, the calculation of oil for the petrolization should take into account not only the target area, but also the bacterial content of water. In some countries, local people simply scare the mosquitoes away by burning something smoky. Sometimes such measures have an effect.
The mentioned solutions have a certain preventive action against the spread of malaria, but their efficiency is low. The insufficient effectiveness of these measures is due to obsolete technologies used for them. Drainage and petrolization are the least technological methods of malaria stopping. Their popularity is determined by their cheapness since the majority of African and Asian countries do not have enough funds to apply some really effective, but more expensive solutions (Sabot et al., 2010).
Proposed Preventive Measures
The proposed measures are not new; they are quite well-known, but their application is often ignored by citizens and governments of African and Asian countries. The reason is that is occurs due to various factors such as expensiveness, lack of raw materials, absence of required equipment and educated staff, etc. Most of suggested methods are more technological than the widespread ones. That is why the countries of Africa and Asia need help for their realization. Different international organizations provide such aid to the region, but its volume is insufficient.
One of such solutions is dusting the water reservoirs with powdered insecticides from aircrafts. This method should be used very carefully, as the excessive use of poison can kill the entire populatiion of the pond. Genetic means of vector control are also effective. In this case, caught Anopheles males are exposed to radiation and X-rays. This procedure disrupts a process of meiosis. After releasing into the wild, they fertilize the females, which lay eggs unable to develop.
All of the above described measures are aimed at the destruction of mosquitoes and their habitat. However, there are also solutions directed to humans, who are at risk of contracting malaria. Simple recommendations for people attending risky areas include wearing dense, light-colored clothes when leaving the house after sunset; applying repellents to the exposed areas of the body; use of mosquito net and insecticide sprays (pyrethroids) in a sleeping room; using insecticide-treated (with permethrin or deltamethrin) canopy in the conditions of a large number of mosquitoes presence.
Except general preventive recommendations there are certain medicament measures against malaria. Depending on the area and its dominating pathogen the medications used for the disease vary. Chloroquin or proguanil are applied in the Middle East including the summer months in rural areas of Egypt and Turkey, the countries of sub-Saharan Africa, Indian Subcontinent, Afghanistan, Iran, and South America (Centers for Disease Control and Prevention, 2015). One of the chloroquin advantages is its weekly taking. This feature is preferable for people, who plan long travelling to the risk zone. Still, it has a minus, i.e. the taking should be started a week or two before the trip. Therefore, chloroquin application is not always convenient. Proguanil is a good alternative to chloroquin; it has rare side effects, but its main disadvantage is its high price. It makes its broad application hardly possible.
Mefloquine is recommended in Cameroon, Kenya, Malawi, Tanzania, Zaire, Zambia, Uganda, and Southeast Asia regions. It is a powerful medication; however, it has serious side neuropsychotropic effects. Besides, mefloquine is inappropriate for people with certain heart diseases. In Cambodia and Myanmar, physicians use doxycycline since this area has Plasmodium strains resistant to mefloquine. In contrast to chloroquin it is taken daily, so one may start using doxycycline right before the trip. Also, it has an advantage of an extended action: except malaria doxycycline prevents some other infections such as leptospirosis. Among the contraindications we can mention its inappropriateness for children and pregnant women, as well as its increasing the person’s sensitivity to sun. One more malaria preventive medicine is primaquin. It is effective against P. vivax, but has a lower efficiency against other pathogens. However, neither drug guarantees 100% protection.
Governments in many African and Asian countries, especially poor ones, pay a little attention to detecting infected people. Under such conditions international organizations must intensify their activities on identification of malaria. The detection includes two methods, i.e. active (through an organized survey of risk groups) and passive (when patients contact the hospital on their own initiative). Malaria identification is based on a blood test, indications for which are the following ones: increased temperature and complaints of malaise and chills for people living or coming from endemic areas; enlarged liver and spleen; yellowness of sclera and skin; anemia of unknown etiology; recipients of blood transfusion with increasing temperature within three months since the procedure. High-risk groups in the countries outside the endemic region are students, tourists, businessmen, refugees, seasonal workers, itinerant gypsies, demobilized soldiers, and other migrants.
The preventive measures against malaria are significant for stopping the spread of the disease across not only African and Asian countries, but also all over the world. People attending the risk area with short-time trips return infected and often seek medical help when it is already late. They may suffer from complications, which can be deadly. Besides, medics in other countries rarely face malaria and are often unable to diagnose it in time. Malaria is much easier and safer to prevent than to treat.
The most common existing measures against malaria are simple procedures with the purpose of dehumidifying the areas where Anopheles mosquitoes live and reproduce. The main actions in this sphere are drainage and petrolization of water reservoirs. They have the low cost and do not need any special equipment, materials or technology. However, these measures cannot stop the malaria spread. Scientists work on vaccine against the disease, some of the samples have passed clinical tests in African countries, but none of them is licensed yet. The World Health Organization is still checking the results, its report and possible recommendations are expected in 2015-2016. Under present conditions, possible additional solutions of the malaria problem include more technological methods of struggle against Anopheles mosquitoes such as insecticides drop from aircrafts, X-rays sterilization of the mosquitoes, local application of repellents and insecticides. Also, medical methods of prevention must become more extensively used. Chloroquin and other drugs are effective, especially for people, who come to the risk zones for a short period of time. All of these methods are not mutually exclusive. They can and must be applied simultaneously. Only concerted actions of individuals, local governments, and international organizations can stop the spread of malaria.
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