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Malaria and Natural Selection

  • Malaria4-1728x800_cMalaria poses a great threat to 2.4 billion people—over one third of the world’s population—living in more than 90 countries, most of them in the tropics. Symptoms of malaria include fever, headache, and vomiting, and usually appear between 10 and 15 days after the mosquito bite. If not treated, malaria can quickly become life-threatening by disrupting the blood supply to vital organs. Relatively unknown initially, it went on to become the most deadly parasite and certainly most well-known. India, in 2003, experienced a small but serious malaria outbreak, and of particular concern is that the malaria was the result of bites from local mosquitoes, not brought in by travellers from nations where malaria is a continual problem.

    The massive effects of Malaria have been neglected over the years, but the situation seems to become more and worse. Worldwide, an estimated 300–400 million people are infected each year, and 1.1 million of them die. It is the fourth largest cause of death of children in developing nations— in Africa alone, more than 3,000 children die daily from this disease. Once thought to be caused by filth or bad air (hence the name malaria, from the Latin for “bad air”), malaria is actually caused by parasitic microbes four species of the protozoon Plasmodium. These microbes affect and are carried by Anopheles mosquitoes, which then transfer the protozoa to people. One solution to the malaria problem, then, would be the eradication of Anopheles mosquitoes.

    World Wars have always been a focal point in course of world development but the discoveries that have been associated cannot be forgotten. The threat of Malaria outbreaks in army camps were raised as sanitary conditions began to worsen in such areas. That made the bright minds back home to develop a treatment. By the end of World War II, scientists had discovered that the pesticide DDT was extremely effective against Anopheles mosquitoes. Though later coming under scrutiny for its effect on the environment it was considered the saviour. They had also found chloroquine highly effective in killing Plasmodium parasites. Chloroquine is an artificial derivative of quinine, a chemical from the bark of the quinine tree that was an early treatment for malaria. In 1957 the World Health Organization (WHO) began a $6 billion campaign to rid the world of malaria using a combination of DDT and chloroquine. The initiative has so far reaped benefits; however complementary programmes need to be undertaken.

    At first, the strategy seemed successful. By large the Malaria outbreaks were history. By the mid-1960s, malaria was nearly gone or had been eliminated from 80% of the target areas. The nature however had other plans as this success was short-lived. The mosquitoes began to develop a resistance to DDT, and the protozoa became resistant to chloroquine. In many tropical areas, the incidence of malaria worsened. For example, the WHO program had reduced the number of cases in Sri Lanka from 1 million to only 17 by 1963, but by 1975, 600,000 cases had been reported, and the actual number is believed to be four times higher. Worldwide, in 2006 there were 247 million cases of malaria, resulting in 881,000 deaths. There were an approximately 207 million cases of malaria in 2012 and an estimated 627 000 deaths. 90% of all malaria deaths occur in sub-Saharan Africa, and 77% occur in children under five. Between 2000 and 2012, an estimated 3.3 million lives were saved as a result of a scale-up of malaria interventions. 90%, or 3 million, of these lives saved are in the under-five age group, in sub-Saharan Africa.

    However the current progress looks bleak and seemed to have lost steam over the years. The mosquitoes’ resistance to DDT became ubiquitous, and resistance of the protozoa to chloroquine was found in 80% of the 92 countries where malaria was a major killer. The mosquitoes and the protozoa developed this resistance through natural selection. Meaning the survival of the most resistive among all. When they were exposed to DDT and chloroquine, the susceptible individuals died; they left few or no offspring, and any offspring they left were susceptible. The most resistant survived and passed their resistant genes on to their offspring. Thus, a change in the environment—the human introduction of DDT and chloroquine—caused a particular genotype to become dominant in the populations.
    However such cases are not new to us with numerous disease outbreaks having gripped the lives of millions. A practical lesson from this experience is that if we set out to eliminate a disease-causing species, we must attack it completely at the outset and destroy all the individuals before natural selection leads to resistance. But sometimes this is impossible, in part because of the natural genetic variation in the target species. Since the drug chloroquine is generally ineffective now, new drugs have been developed to treat malaria. However, these second- and third-line drugs will eventually become unsuccessful, too, as a result of the same process of biological evolution by natural selection. This process is speeded up by the ability of the Plasmodium to rapidly mutate.

    But the question arises- How to do we counter such a scenario? Especially such a deadly one. An alternative is to develop a vaccine against the Plasmodium protozoa. Biotechnology has made it possible to map the genetic structure of these malaria-causing organisms. Scientists are currently mapping the genetic structure of P. falciparum, the most deadly of the malaria protozoa, and expect to finish within several years. With this information, they expect to create a vaccine containing variety of the species that is benign in human beings but produces an immune reaction. In addition, scientists are mapping the genetic structure of Anopheles gambiae, the carrier mosquito. This project could provide insight into genes, which could prevent development of the malaria parasite within the mosquito. In addition, it could identify genes associated with insecticide resistance and provide clues to developing a new pesticide.


    In short, Until and unless some serious and meticulous advancement is done, we can never be assured of a a malaria free environment. Governments and UN alike along with WHO have taken such significant steps leaving no stone unturned. If we contribute individually Malaria might soon be a thing of the past.


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