What Is Malaria?
Malaria is a parasitic infection transmitted to humans through the bites of infected female Anopheles mosquitoes. The resulting disease in humans can be devastating. After spreading rapidly through the bloodstream to the liver, the parasite emerges again into the blood stream, finally to settle in the red blood cells, where it multiplies and emerges in bursts of new organisms. These parasites, because of their large numbers, can cause particular damage to the nervous system, liver, and kidney.
In young children and adults who have not recently been infected (and therefore have not developed natural immunity), this cycle can result in death within hours from cerebral malaria. Others die later in the infection from overwhelming anemia or liver and kidney failure. Untreated, up to 20% of persons infected with falciparum malaria will die.
Four species of malaria infect humans, though only two, falciparum and vivax cause the vast majority of clinical cases and nearly all of the deaths and serious morbidity. The disease is particularly prevalent in sub-Saharan Africa, and is common throughout tropical regions of China, India, Southeast Asia, and South and Central America.
Almost all of the serious morbidity caused by falciparum malaria occurs in children under the age of ten, and the impact is especially severe in those under the age of five. Protecting these children from malaria is a major goal of current malaria vaccine development efforts.
Malaria has a complex life cycle. Infected female mosquitoes inject malaria sporozoites when they bite, and the sporozoites are carried to the liver where they rapidly infect liver cells. Without causing symptoms, these sporozoites undergo a radical change and multiply furiously for the next 4-5 days. Tens of thousands of asexual stage merozoites are released from each infected liver cell, each of which rapidly target and invade a red blood cell. Every few days, the merozoites multiply ten-fold and burst out to infect other red blood cells. This cyclic and massive increase in parasite burden gives rise to the clinical disease we recognize as malaria.
In the absence of immunity or drug treatment, death can occur within hours of noticeable symptoms. If death does not occur and infection continues, some of the parasites further differentiate into a form that is infectious for mosquitoes, thus permitting the life cycle to continue. Strategies for developing malaria vaccines have been targeted at specific points in the parasite life cycle during which the organism appears particularly susceptible to the host's immune system.
Causes Of Malaria
Malaria is spread from the bite of a mosquito. When a mosquito bites an infected person, it ingests the malaria parasites found in that person's blood. After one week or more, the mosquito can spread the parasite to other people.
After a bite from an infected mosquito, the parasite enters the person's bloodstream and travels to the liver where it grows and multiplies. During this time when the parasite is in the liver, there are no visible symptoms and the victim doesn't feel sick.
The parasite may stay in the liver for a period as short as 8 days or as long as several months to years. After it leaves the liver, it enters red blood cells and continues to grow and multiply. The red blood cells burst, freeing the parasites to attack other red blood cells. It is during this time that symptoms of malaria may begin to surface.
Treatment of Malaria
Three main factors determine treatments: the infecting species of Plasmodium parasite, the clinical situation of the patient (for example, adult, child, or pregnant female with either mild or severe malaria), and the drug susceptibility of the infecting parasites. Drug susceptibility is determined by the geographic area where the infection was acquired. Different areas of the world have malaria types that are resistant to certain medications. The correct drugs for each type of malaria must be prescribed by a doctor who is familiar with malaria treatment protocols. Since people infected with P. falciparum malaria can die (often because of delayed treatment), immediate treatment for P. falciparum malaria is necessary.
Mild malaria can be treated with oral medication; severe malaria (one or more symptoms of either impaired consciousness/coma, severe anemia, renal failure, pulmonary edema, acute respiratory distress syndrome, shock, disseminated intravascular coagulation, spontaneous bleeding, acidosis, hemoglobinuria [hemoglobin in the urine], jaundice, repeated generalized convulsions, and/or parasitemia [parasites in the blood] of > 5%) requires intravenous (IV) drug treatment and fluids.
Drug treatment of malaria is not always easy. Chloroquine phosphate is the drug of choice for all malarial parasites except for chloroquine-resistant Plasmodium strains. Although almost all strains of P. malariae are susceptible to chloroquine, P. falciparum, P. vivax and even some P. ovale strains have been reported as resistant to chloroquine. Unfortunately, resistance is usually noted by drug-treatment failure in the individual patient. There are, however, multiple drug-treatment protocols for treatment of drug resistant Plasmodium strains (for example, quinine sulfate plus doxycycline [Vibramycin, Oracea, Adoxa, Atridox] or tetracycline [Achromycin], or clindamycin [Cleocin], or atovaquone-proguanil [Malarone]). There are specialized labs that can test the patient's parasites for resistance, but this is not done frequently. Consequently, treatment is usually based on the majority of Plasmodium species diagnosed and its general drug-resistance pattern for the country or world region where the patient became infested. For example, P. falciparum acquired in the Middle East countries is usually susceptible to chloroquine, but if acquired in sub-Sahara African countries, is usually resistant to chloroquine.