Malaria : Treatment and Biology

by CDC

(Page 3 of 14)

Treatment

Malaria can be a severe, potentially fatal disease (especially when caused by Plasmodium falciparum) and treatment should be initiated as soon as possible.

In endemic areas, the World Health Organization recommends that treatment be started within 24 hours after the first symptoms appear. Treatment of patients with uncomplicated malaria can be conducted on an ambulatory basis (without hospitalization) but patients with severe malaria should be hospitalized if possible.

In areas where malaria is not endemic, all patients with malaria (uncomplicated or severe) should be kept under clinical observation if possible.

Patients who have severe P. falciparum malaria or who cannot take oral medications should be given the treatment by continuous intravenous infusion.

In some countries (but not the United States) some antimalarial drugs are found in suppository form.

Several antimalarial drugs are available for treatment by continuous intravenous infusion.

Most drugs used in treatment are active against the parasite forms in the blood (the form that causes disease) and include:

• chloroquine
• sulfadoxine-pyrimethamine (Fansidar®)
• mefloquine (Lariam®)
• atovaquone-proguanil (Malarone®)
• quinine
• doxycycline
• artemisin derivatives (not licensed for use in the United States, but often found overseas)

In addition, primaquine is active against the dormant parasite liver forms (hypnozoites) and prevents relapses. Primaquine should not be taken by pregnant women or by people who are deficient in G6PD (glucose-6-phosphate dehydrogenase). Patients should not take primaquine until a screening test has excluded G6PD deficiency.

How to treat a patient with malaria depends on:

• The type (species) of the infecting parasite
• The area where the infection was acquired and its drug-resistance status
• The clinical status of the patient
• Any accompanying illness or condition
• Pregnancy
• Drug allergies, or other medications taken by the patient

Report a serious drug side effect

If you have had a serious side effect while taking a drug, you or your health care provider can report that side effect to the federal Food and Drug Administration (FDA). MedWatch is the FDA Safety Information and Adverse Event Reporting Program.

The advantage to having your health care provider file the report is that he/she can provide clinical information based on your medical record that can help the FDA evaluate the report.

However, for a variety of reasons, you may not wish to have the form completed by your provider, or the provider may not wish to complete the form. Your health care provider is not required to report to the FDA.

Biology

Life Cycle of Malaria

In nature, malaria parasites spread by infecting successively two types of hosts: humans and female Anopheles mosquitoes. In humans, the parasites grow and multiply first in the liver cells and then in the red cells of the blood. In the blood, successive broods of parasites grow inside the red cells and destroy them, releasing daughter parasites ("merozoites") that continue the cycle by invading other red cells.

The blood stage parasites are those that cause the symptoms of malaria. When certain forms of blood stage parasites ("gametocytes") are picked up by a female Anopheles mosquito during a blood meal, they start another, different cycle of growth and multiplication in the mosquito.

After 10-18 days, the parasites are found (as "sporozoites") in the mosquito's salivary glands. When the Anopheles mosquito takes a blood meal on another human, the sporozoites are injected with the mosquito's saliva and start another human infection when they parasitize the liver cells.

Thus the mosquito carries the disease from one human to another (acting as a "vector"). Differently from the human host, the mosquito vector does not suffer from the presence of the parasites.

Human Hosts

Humans infected with malaria parasites can develop a wide range of symptoms. These vary from asymptomatic infections (no apparent illness), to the classic symptoms of malaria (fever, chills, sweating, headaches, muscle pains), to severe complications (cerebral malaria, anemia, kidney failure) that can result in death. The severity of the symptoms depends on several factors, such as the species (type) of infecting parasite and the human's acquired immunity and genetic background.

Malaria Parasites

Four species of malaria parasites can infect humans under natural conditions: Plasmodium falciparum, P. vivax, P. ovale and P. malariae. The first two species cause the most infections worldwide. Plasmodium falciparum is the agent of severe, potentially fatal malaria, causing an estimated 700,000 - 2.7 million deaths annually, most of them in young children in Africa. Plasmodium vivax and P. ovale have dormant liver stage parasites ("hypnozoites") which can reactivate ("relapse") and cause malaria several months or years after the infecting mosquito bite. Plasmodium malariae produces long-lasting infections and if left untreated can persist asymptomatically in the human host for years, even a lifetime.

Anopheles Mosquitoes

Malaria is transmitted among humans by female mosquitoes of the genus Anopheles. Female mosquitoes take blood meals to carry out egg production, and such blood meals are the link between the human and the mosquito hosts in the parasite life cycle. Of the approximately 430 known species of Anopheles, only 30-50 transmit malaria in nature. The successful development of the malaria parasite in the mosquito (from the "gametocyte" stage to the "sporozoite" stage) depends on several factors. The most important is ambient temperature and humidity (higher temperatures accelerate the parasite growth in the mosquito) and whether the Anopheles survives long enough to allow the parasite to complete its cycle in the mosquito host ("sporogonic" or "extrinsic" cycle, duration 10 to 18 days). Differently from the human host, the mosquito host does not suffer noticeably from the presence of the parasites.

About the Author

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