Malaria parasites have been with us since the beginning of time, and fossils of
mosquitoes up to thirty million years old show that malaria's vector has 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 of these people die, there are still an
estimated 1,500,000 deaths per year. While Malaria was one of the first infectious
diseases to be treated successfully with a 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 are unaware that it is life threatening, kills over a million people
each year, and is a very elusive target for antimalarial drugs (Treatment of Malaria,
1996).
Being a very specific disease, malaria is caused by only four protozoal parasites:
Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae. Not
only is the disease specific, but the parasites are too, with only 60 of 380 species of
female Anopheles mosquitoes as vectors. With the exception of Plasmodia Malariae which
may affect other primates, all parasites of malaria have only one host, Homo sapiens.
Because some mosquitoes contain substances toxic to Plasmodium in their cells, not all
species of mosquitoes are vectors of Plasmodium. Although very specific, malaria still
causes disruption of over three hundred million people worldwide each year (Cann, 1996).
The life cycle of the parasite causing malaria exists between two organisms, humans and
the Anopheles mosquito. When a female mosquito bites a human, she injects an
anticoagulant saliva which keeps the human bleeding and ensures an even flowing meal for
her. When the vector injects her saliva into the human, it also injects ten percent of
her sporozoite load. Once in the bloodstream, the Plasmodium travel to the liver and
reproduce by asexual reproduction. These liver cells then burst releasing the parasites
back into the bloodstream where they then enter red blood cells. Here, the Plasmodium
feed on hemoglobin and reproduce again by asexual reproduction. Afterwards, the red
blood cells burst and release the parasites. Some of the parasites released from red
blood cells may be able to replicate by sexual reproduction. When the host has been
bitten by a mosquito again, infected blood inters the mosquito. Here, sexual forms of
the parasite develop in the stomach of the Anopheles mosquito 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 time for symptoms to
appear differs depending on the form of the parasite. Those infected with Plasmodium
falciparum experience symptoms after about twenty-four hours, those infected with
Plasmodium vivax and Plasmodium ovale produce symptoms after a forty-eight hour interval,
and after seventy-two hours Plasmodium malariae begin causing fever and chills (Cann,
1996).
Most malaria cases seem to cluster in the tropical climate areas extending into the
subtropics, and malaria is especially endemic in Africa. In 1990 eighty percent of all
reported cases were in Africa, while the remainder of most cases came from nine
countries: India, Brazil, Afghanistan, Sri-Lanka, Thailand, Indonesia, Vietnam,
Cambodia, and China. Globally, the disease circulates in almost one hundred countries
causing up to 1,500,000 deaths annually (Cann, 1996).
Because there is no definite cure for malaria, scientists are trying their hardest to
contain the parasite to where it now exists. The range of a vector 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 problem containing the disease. Humans migrate,
however, and over time the disease has slowly spread throughout the tropics. Major
problems also exist when ignorant tourists to Africa transfer the parasite to non
malarious areas (Graham, 1996). Biologists are also using control measures, such as
spraying DDT to kill mosquitoes, draining stagnant water, and using the widespread use of
nets to contain the mosquito itself (Herman, 1996). Because of the worsening situation,
the World Health Organization (WHO) declared malaria control to be a global priority
(Limited Imagination, 1996).
Although limiting the spread of malaria is not easy, finding a cure has presented
several problems in recent years. One main reason finding a cure for malaria is so hard
is that different strains in different parts of the world require different drugs, all of
which soon lose their effectiveness as the parasite evolves resistance to them (Limited
Imagination, 1996). Secondly, once the parasite enters the human bloodstream, it changes
form several times inside the body, making it an elusive target for the immune system
(Cann, 1996). Last, while research and development is very expensive, Africa's third
world countries don't have the money to support such research (Graham, 1996).
Research in the field of malaria's microbiology enables a search for better vaccines and
a possible cure for malaria (Atovaquone, 1996). In the past several decades, scientists
have developed many drugs that have all fallen victim to the resistance of the
Plasmodium parasites. Such drugs include chloroquine, pyrimethamine, chloroguanide,
desipramine, halofantrine, mefloquine, and arteether (Herman, 1996). Scientists too
often find their drugs effectiveness 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 cinchona tree. This drug was a
secret of the locals of the Amazon jungle for centuries until European missionaries
learned of its use. The trouble remains that quinine is expensive to harvest, is
extremely hard to synthesize, and fails to prevent relapses (Limited Imagination, 1996).
Another unique treatment of malaria is the use of the herb Artemisia annua. This herb
has been used for centuries in traditional Chinese medicine to treat malaria and fever.
Neither of these drugs are one hundred percent effective (Herman, 1996).
While the need for malarial vaccines grows urgent, so does the number of people 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. As the Plasmodium parasites mutate
more and more to resist the effect of antimalarials, it becomes harder for scientist to
find a cure (Treatment of Malaria, 1996). Over forty percent of the world's population
still at risk from this deadly disease, is yearning for a cheap, effective vaccine (Cann,
1996).
Bibliography
Dr. 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.
"Treatment of Malaria," New England Journal of Medicine, September 12, 1996, Vol. 335,
Issue 11, p800-807, MAS FullTEXT ELITE, Nancy Guinn Library.
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