Malaria parasites have been with us since the beginning of time, andfossils of mosquitoes up to thirty million years old show that malarias vectorhas existed for just as long. The parasites causing malaria are highly specific,with man as the only host and mosquitoes as the only vector. Every year,300,000,000 people are affected by malaria, and while less than one percent ofthese people die, there are still an estimated 1,500,000 deaths per year. WhileMalaria was one of the first infectious diseases to be treated successfully witha drug, scientist are still looking for a cure or at least a vaccination today(Cann, 1996). Though many people are aware that malaria is a disease, they areunaware that it is life threatening, kills over a million people each year, andis a very elusive target for antimalarial drugs (Treatment of Malaria, 1996).
Being a very specific disease, malaria is caused by only four protozoalparasites: Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, andPlasmodium malariae. Not only is the disease specific, but the parasites aretoo, with only 60 of 380 species of female Anopheles mosquitoes as vectors.
With the exception of Plasmodia Malariae which may affect other primates, allparasites of malaria have only one host, Homo sapiens. Because some mosquitoescontain substances toxic to Plasmodium in their cells, not all species ofmosquitoes are vectors of Plasmodium. Although very specific, malaria stillcauses disruption of over three hundred million people worldwide each year (Cann,1996).
The life cycle of the parasite causing malaria exists between twoorganisms, humans and the Anopheles mosquito. When a female mosquito bites ahuman, she injects an anticoagulant saliva which keeps the human bleeding andensures an even flowing meal for her. When the vector injects her saliva intothe human, it also injects ten percent of her sporozoite load. Once in thebloodstream, the Plasmodium travel to the liver and reproduce by asexualreproduction. These liver cells then burst releasing the parasites back intothe bloodstream where they then enter red blood cells. Here, the Plasmodiumfeed on hemoglobin and reproduce again by asexual reproduction. Afterwards, thered blood cells burst and release the parasites. Some of the parasites releasedfrom red blood cells may be able to replicate by sexual reproduction. When thehost has been bitten by a mosquito again, infected blood inters the mosquito.
Here, sexual forms of the parasite develop in the stomach of the Anophelesmosquito completing the parasites life cycle (Herman, 1996).
People infected malaria have several symptoms including fever, chills,headaches, weakness, and an enlarged spleen (Herman, 1996). The amount of timefor symptoms to appear differs depending on the form of the parasite. Thoseinfected with Plasmodium falciparum experience symptoms after about twenty-fourhours, those infected with Plasmodium vivax and Plasmodium ovale producesymptoms after a forty-eight hour interval, and after seventy-two hoursPlasmodium malariae begin causing fever and chills (Cann, 1996).
Most malaria cases seem to cluster in the tropical climate areasextending into the subtropics, and malaria is especially endemic in Africa. In1990 eighty percent of all reported cases were in Africa, while the remainder ofmost cases came from nine countries: India, Brazil, Afghanistan, Sri-Lanka,Thailand, Indonesia, Vietnam, Cambodia, and China. Globally, the diseasecirculates in almost one hundred countries causing up to 1,500,000 deathsannually (Cann, 1996).
Because there is no definite cure for malaria, scientists are tryingtheir hardest to contain the parasite to where it now exists. The range of avector from a suitable habitat is fortunately limited to a maximum of two miles(Cann, 1996). If this were the only factor, scientist would have no problemcontaining the disease. Humans migrate, however, and over time the disease hasslowly spread throughout the tropics. Major problems also exist when ignoranttourists to Africa transfer the parasite to non malarious areas (Graham, 1996).
Biologists are also using control measures, such as spraying DDT to killmosquitoes, draining stagnant water, and using the widespread use of nets tocontain the mosquito itself (Herman, 1996). Because of the worsening situation,the World Health Organization (WHO) declared malaria control to be a globalpriority (Limited Imagination, 1996).
Although limiting the spread of malaria is not easy, finding a cure haspresented several problems in recent years. One main reason finding a cure formalaria is so hard is that different strains in different parts of the worldrequire different drugs, all of which soon lose their effectiveness as theparasite evolves resistance to them (Limited Imagination, 1996). Secondly, oncethe parasite enters the human bloodstream, it changes form several times insidethe body, making it an elusive target for the immune system (Cann, 1996). Last,while research and development is very expensive, Africas third world countriesdont have the money to support such research (Graham, 1996).
Research in the field of malarias microbiology enables a search forbetter vaccines and a possible cure for malaria (Atovaquone, 1996). In the pastseveral decades, scientists have developed many drugs that have all fallenvictim to the resistance of the Plasmodium parasites. Such drugs includechloroquine, pyrimethamine, chloroguanide, desipramine, halofantrine, mefloquine,and arteether (Herman, 1996). Scientists too often find their drugseffectiveness wearing off as malarial parasites build tolerance to them (Graham,1996).
Several drugs used to treat the disease have been around for centuries.
One such drug is quinine, a compound extracted from the bark of the cinchonatree. This drug was a secret of the locals of the Amazon jungle for centuriesuntil European missionaries learned of its use. The trouble remains thatquinine is expensive to harvest, is extremely hard to synthesize, and fails toprevent relapses (Limited Imagination, 1996). Another unique treatment ofmalaria is the use of the herb Artemisia annua. This herb has been used forcenturies in traditional Chinese medicine to treat malaria and fever. Neitherof these drugs are one hundred percent effective (Herman, 1996).
While the need for malarial vaccines grows urgent, so does the number ofpeople affected each year. Although it is caused by a highly specific parasite,malaria still seems to kill off between one to two million people annually. Asthe Plasmodium parasites mutate more and more to resist the effect ofantimalarials, it becomes harder for scientist to find a cure (Treatment ofMalaria, 1996). Over forty percent of the worlds population still at risk fromthis deadly disease, is yearning for a cheap, effective vaccine (Cann, 1996).
BibliographyDr. Cann, Alan J. PhD., “The Walter and Eliza Hall Institute Malaria Database”,1996, http://www.wehi.edu.au/biology/malaria/who.html.
Graham, David, “Malaria-Proof Mosquitoes,” Technology Review, October 1996, Vol.
99, Issue 7, p20-22, MAS FullTEXT ELITE, Nancy Guinn Library.
Herman, Robert, “Malaria,” New Groliers Multimedia Encyclopedia, Copywrite 1996.
“Atovaquone and Proguanil for Plasmodium Falciparum Malaria,” Lancet, June 1,1996, Vol. 347, Issue 9014, p1511-1515, MAS FullTEXT ELITE, Nancy Guinn Library.
“Limited Imagination,” Economist, September 28, 1996, Vol. 340, Issue 7985, p80-82, MAS FullTEXT ELITE, Nance Guinn Library.
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335, Issue 11, p800-807, MAS FullTEXT ELITE, Nancy Guinn Library. Category: Science