What are the causes, signs and symptoms of malaria disease? Information about the treatment nad distribution of malaria.
MALARIA, is a tropical disease characterized by high fever, severe chills, enlargement of the spleen, and anemia. It is caused by parasites of the genus Plasmodium, which are transmitted to man through the bite of female Anopheles mosquitoes.
An attack of malaria usually begins with chills that become worse as fever begins to rise, to 103°-104° F (39.5° C) or even higher. A severe headache usually develops. The fever breaks, and profuse sweating occurs. A single infection may be characterized by repeated bouts of chills, fever, and sweating before the disease runs its course. Some forms of malaria may become chronic.
Cause and Transmission. A female Anopheles mosquito becomes infected with malarial parasites when it bites a victim of malaria, taking malaria-contaminated blood into its stomach. Some of the ingested malarial parasites, the gametocytes, are not digested in the stomach of the Anopheles mosquito but mate and produce cysts that develop on the wall of the stomach. When ripe, the cysts burst open, releasing their seeds, called sporozoites, which then move into the mosquito’s salivary glands. This development within the mosquito, from gametocyte to sporozoite, takes from 7 to 25 or more days, being faster in warmer temperatures. After this, whenever the female Anopheles mosquito bites and feeds, it injects malarial sporozoites into its victim’s bloodstream. Male Anopheles mosquitoes do not transmit the parasites.
In man, the malarial sporozoites travel through the bloodstream and invade the liver, where they develop and produce broods of young parasites. These young parasites enter the bloodstream and penetrate the erythrocytes, or red blood cells. Here the parasites grow, and most split into segments called merozoites, while a few become gametocytes. The parasitized erythrocyte disintegrates, and the merozoites attack other erythrocytes. The cycle continues until checked by immunity or treatment. Death from malaria usually results from severe anemia, from choking of the capillaries of the brain or other vital organ by masses of parasites, or from extremely high fever.
Four species of Plasmodium affect man. Plasmodium vivax, causing vivax malaria, is the most common malarial parasite. It is found in some temperate as well as tropical regions. P. falciparum, found mostly in tropical and subtropical areas, produces falciparum malaria, the most severe form of the disease. P. ovale and P. malariae less commonly produce malaria in man. Other species of Plasmodium chiefly infect birds, monkeys, and reptiles.
The periodic liberation of merozoites, metabolic products of the parasites, and erythrocyte debris into the blood plasma upsets the body’s heat-regulating mechanism, inducing the recurrent paroxyms of shivering, fever, and sweating characteristic of malaria. The attacks are timed by the development period of the infecting parasite. P. vivax, a tertian parasite, has a cycle of about 48 hours, with the patient’s chills and fever occurring typically every other day. P. ovale is also a tertian parasite. P. malariae is a quartan parasite with a 72-hour cycle. P. falciparum is the least regular.
The incubation period, from infection to first fever, averages 12 days in falciparum malaria, 14 days in vivax malaria and ovale malaria, and 20 days or more in malariae.
Since the symptoms and course of malaria are often atypical, positive diagnosis depends on microscopic identification and examination of the parasites in blood smears.
Treatment. For more than 300 years the treatment of malaria depended on quinine obtained from the bark of cinchona trees. During World War II several synthetic antimalarial drugs became available, and quinacrine hydrochloride (mepacrine hydrochloride, Atabrine) was widely used. After the war better antimalarial agents were developed. Today chloroquine (Aralen) and amodiaquin (Camoquin) hydrochloride are usually used to treat acute malaria. They are effective against erythrocytic parasites. Both these drugs often cure falciparum malaria and rapidly provide symptomatic relief for vivax malaria, though another drug generally must be used to prevent vivax relapses. Primaquine is highly effective in curing vivax malaria. It is given together with chloroquine or shortly after an acute attack that has been treated by chloroquine. Pyrimethamine (Daraprin) is another effective antimalarial agent.
Many of these drugs are also used prophylactically, and some are highly recommended for travelers to areas where malaria is still common. The particular drug, its dosage, and length of administration vary with the rate of occurrence of malaria in the region and the age and health of the individual.
History. Malaria is one of the oldest recognized diseases. Hippocrates, the ancient Greek physician, distinguished different types of malaria. Other ancient authors claimed that swamp vapors caused intermittent, fevers. In medieval Italy, people blamed bad air, or mal aria.
The germ theory of disease later led scientists to search for a malaria parasite. On Nov. 6, 1880, the French physician Charles Louis Alphonse Laveran, working in North Africa, discovered the parasite that causes malaria. Four years later a British physician, Patrick Manson, published his belief that mosquitoes transmitted malaria. The first proof of this theory came on Aug. 20-21, 1897, when Bonald Boss, an English physician in India, found malaria parasites of man growing as cysts on the stomach walls of Anopheles* mosquitoes.
Since early Boman times, observers had noted that drainage sometimes controlled intermittent fevers. The mosquito theory of malaria transmission established through the work of Boss and others provided an explanation of this observation and stimulated more widespread anti-mosquito drainage.
It soon became apparent that species of malaria mosquitoes differ greatly in habitats. For example, although the eggs, larvae, and pupae of all Anopheles mosquitoes are aquatic, not all are found in marshes. Some prefer millponds, rice fields, hill streams, wells, puddles, or springs. So malaria control became more carefully focused and included not only drainage but also killing the aquatic stages of vector anophelines with insecticidal oils and Paris green. Since Anopheles mosquitoes generally feed at night, screens and bednets to prevent their bites were introduced widely.
In the 1930’s malaria control became more often an attack on adult anophelines, through the use of pyrethrum sprays. Then, in 1939, the Swiss chemist Paul Hermann Miiller discovered the insecticidal properties of DDT.
DDT and similar insecticides have the useful property of a long-lasting killing effect after being sprayed on surfaces. One or two sprayings might be effective for a year. These residual insecticides did not need to contact mosquitoes at the time of spraying. When a susceptible insect stood on a sprayed surface, small particles of the poison would cling to its feet and be transferred to its body, with lethal effect.
Since most female anophelines take blood every other night and rest before and after feeding on walls and ceilings, there was a good chance that, if their resting places were sprayed with insecticide, no mosquito could live long enough to germinate the sporozoites. If a high proportion of malaria-carrying mosquitoes died before they could infect, then malaria transmission would be prevented. The parasites in man would thereafter gradually die out, and malaria would disappear. Observations have indicated that malaria cannot sustain itself in a community in which, for a period of three consecutive years, there has been no transmission of the disease by mosquitoes.
Distribution. In the 19th century malaria was found in North America as far north as the St. Lawrence Biver; in South America as far south as Chile and Argentina; in Europe and Asia as far north as the Dvina Biver and Lake Baikal; in Africa as far south as the Umvoti Biver; and in parts of Australia. Attempts at worldwide control have been successful, largely due to the work of the UN World Health Organization.
By the early 1970’s malaria had disappeared from many parts of the world. In large parts of Africa and southern Asia, and parts of Mexico, Central America, and northern and central South America malaria transmission occurs or might occur. Prophylactic drug use is recommended for travelers to some of these areas.