Malaria
Malaria is a group of parasitic diseases common in tropical and subtropical areas. Approximately 300 million cases occur annually worldwide, and one to nearly three million people die of malaria each year with about 90 percent of these deaths occurring in sub-Saharan Africa, with the majority being children. Malaria has been known for centuries, having been described in ancient Greek, Hebrew, and Roman writings and in Chinese and Indian medical chronicles. Efforts to eradicate malaria by draining the swamps around ancient Rome were some of the first successful public health measures recorded. Like most diseases, malaria was originally thought a result of poisonous vapors in the air, and the name of the disease comes form two Italian words, mal (meaningbad) and aria (meaning air).
One of the most predominant health problems in the world, malaria is a much-researched disease. The use of cinchona bark extracts (quinine) as treatment in the early seventeenth century by Peruvian Indians marked the first recognition of malarial fevers as a specific disease, and the clinical observations of malaria made by F. Torti and Thomas Sydenham in the later seventeenth century gave the disease a scientific basis. Malaria is caused by blood parasitesof the genus Plasmodium, which are transmitted to humans by the bite of the female Anopheles mosquito. When an Anopheles mosquito bites a human already infected with malaria, Plasmodia in the human's blood enter the mosquito's body and reproduce in her stomach. The offspring travel to her salivary glands and are transmitted to another human by her bite. In a human, the parasites travel to the liver, reproduce, and form clumps. Several days later, the clumps burst and new Plasmodia are released. Eachparasite then invades a red blood cell and reproduces again. The infected cells rupture, releasing parasites which then invade other cells.
Charles Louis Alphonse Laveran (1845-1922) first discovered parasites in a malaria patient's blood in 1880, demonstrating its parasitic origin to those doubtful scientists who expected Louis Pasteur's discovery of bacteria to explain all illnesses. Laveran's theory was validated in 1886 by the renowned histologist Camillo Golgi, who identified two distinct human malaria parasites (Plasmodium vivax and P. malariae ) by examining the blood of malaria patients. Golgi discovered the life cycle of these parasites and correctly concluded that they divide at regular intervals. Each division causes a corresponding attack of fever in the human host.
Patrick Manson (1844-1922) suggested the mosquito as the mode of transmissionamong humans in 1894, and Ronald Ross and Giovanni Grassi (1854-1925) provided an explanation of the parasite's life cycle in 1897, also confirming thatthe mosquito is the vector. Plasmodium 's life cycle was further clarified by H. E. Shortt and P. C. C. Garnham in 1948. Malaria is characterized by a 10-40 day incubation period preceding a brief stage of chills, followed by a rapid rise in body temperature ranging as high as 107° F (41.7° C) accompanied by a severe headache, and finally a sweating stage during whichthe patient begins to feel well.
When the next batch of red blood cells ruptures, the cycle begins again. Thecycle's periodicity, ranging from 48 to 72 hours, is determined by which of four species of Plasmodium ( P. vivax, P. malariae, P. falciparum or P. ovale ) is present. When more than one species of parasite ispresent, the cycles of symptoms can overlap.
The rate of death in untreated patients is greater than ten percent, and fromthe time of its introduction into Western medicine in the late seventeenth century until 1920, quinine was the only specific drug available to combat malaria's symptoms. Today, the synthetic drugs chloroquine, mefloquine, and doxycycline are commonly used in the prevention of malaria.
Because preventive drugs and vaccines are costly and Plasmodium tendsto develop resistance to them, the prevention of malaria largely depends upon the eradication of the Anopheles mosquito. In 1905, construction onthe Panama Canal was interrupted by epidemics of malaria and yellow fever. The Isthmanian Canal Commission depended on William Crawford Gorgas (1854-1920) as chief sanitary officer to eliminate the diseases. With mosquito eradication supplies and 4000 men, Gorgas eliminated yellow fever and reduced malaria to a prevalence of less than ten percent among the workers by1906 using public health measures.
During the 1950s and 1960s, the World Health Organization launched a worldwide campaign to eradicate malaria using the insecticide DDT to kill Anopheles. The disease disappeared in several countries where it had beenendemic and was greatly reduced in others, but it began to return as Anopheles developed resistance to DDT. Other areas--particularly tropical areas where mosquitos inhabit large spaces, making control by insecticide inefficient--were relatively unaffected by these measures, and research was begun into biological or genetic means of control. DDT was banned in the United States in 1972 following the publication of Rachel Carson's Silent Spring,in which she demonstrated the harmful effects of DDT in ecosystems and on vertebrates. Canada has also banned the use of DDT, but this insecticide continues to be used in Mexico, India, and the republics of the former Soviet Union.
Malaria remains a serious public health problem in Central and South America,North and Central Africa, East Asia, the Middle East, and along the bordersof the Mediterranean. In parts of Africa and South Asia, virtually the entirepopulation is infected. Resistance to attacks of malaria develops with age,making children the most vulnerable to this disease. (Every 30 seconds a child dies of malaria.)
A promising new weapon in the war on malaria is a vaccine developed by Dr. Manuel Elkin Patarroyo and his colleagues at the Immunology Institute of Colombia's National University in Bogota. While Dr. Patarroyo's vaccine is not thefirst attempt at triggering the body's natural defense system to fight the parasites, it is the first malaria vaccine to be tested and shown safe and effective in extensive field trials. (It has been tested in Brazil, Colombia, Ecuador, Venezuela, and Africa. This vaccine is only effective against parasitesof the species P. falciparum (responsible for 95 percent of malariacases worldwide), and seems to confer immunity in only two-thirds of vaccinated people. Nonetheless, scientists believe it may prove an invaluable tool ina comprehensive attack on the disease when used in conjunction with mosquitocontrol and treatment of victims with antimalarial drugs. The two other maintypes of vaccine under development are anti-sporozoite vaccines, which are designed to prevent infection, and anti-asexual blood stage vaccines, which reduce severe manifestations of the disease. Any effective vaccine against malaria will most likely have to induce a immune response to the various stages of malaria infection. In terms of prevention, the World Health Organization conducted a study which showed that bed nets impregnated with mosquito pesticides could lower childhood mortality due to malaria by 15 to 35 percent in certain situations.
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