Using Bark to Cure the Bite

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February, 2000: Peru

Ague, swamp fever, night chills . . . . Although not referred to by its modern name, symptoms recorded in the earliest written literature document that malaria has been a health problem for thousands of years. The name mal'aria was coined in the sixteenth century and literally means "foul or bad air." The disease is characterized by bouts of fever, muscle stiffness, shaking, pain in joints, sweating, and extreme thirst. For more than 100 years, the most effective treatment for the symptoms of malaria has been a drug derived from the bark of a tree native to Peru.

 

Distribution of malaria, 1997. (Courtesy of WHO, Geneva.)

Malaria continues to be a source of concern even today. On a global level, over 300 million people are infected with the disease. About one-third to one-half of those infected each year die; most of them are under 5 years of age. The disease is endemic to more than 94 countries, with regions of prevalence including tropical areas of Central and South America, India, Sri Lanka, China, Madagascar, and Indonesia. Countries within Africa account for more than 90% of the global level of infection.

Malaria is caused by Plasmodium, a parasitic protozoan discovered in 1880. Four species of Plasmodium cause varying degrees of malaria: P. falciparum, P. malaria, P. ovale, and P. vivax. The most deadly is P. falciparum. Plasmodium sp. are microparasites, which use a vector to transmit infection from host to host. While some microparasites use abiotic (nonliving) vectors such as the air, Plasmodium relies on a living or biotic vector. Since 1897, this vector has been known to be the female Anopheles mosquito. The protozoan develops initially in the mosquito's gut and then moves to the salivary glands. Each time an infected Anopheles feeds on blood, the microparasite is passed to the new host via the mosquito's saliva. The parasites are then carried by the victim's blood to the liver, where they complete the balance of their life cycle and multiply. Female Anopheles typically feed at night and require a meal of blood in order to promote egg maturation. They lay their eggs on or near stagnant water, where the larvae develop. Male mosquitoes usually feed exclusively on flower nectar, as do female mosquitoes when they are not promoting egg maturation.

Cinchona tree. (Photo © 1999 Erica Kipp.)

Quinine.

In 1640, Spanish colonists in the Incan Empire noticed Peruvian Indians using the bark of the cinchona tree to treat malaria. This was an important discovery because Europeans entering these new areas brought new diseases like malaria back home. But it was not until 1820 that quinine, the active agent within the bark extract, was isolated. In the 1860s, the Dutch government began cultivating cinchona trees on the island of Java in an attempt to monopolize the world production of quinine. Even though the trees are now cultivated worldwide, the bark is still sometimes referred to as "Peruvian" bark.

Cinchona is a genus in the Rubiaceae family, dicots that usually have secondary growth and tend to produce a wide range of chemicals that are insect and herbivore repellents. Quinine is an alkaloid, a major class of natural products that have a physiological effect on other organisms. They characteristically contain carbon, hydrogen, nitrogen, and in many cases, oxygen. Because of their potent pharmacological effects, alkaloids are the basis for many drugs.

 

Quinine sulfate.

In 1944, advances in organic chemistry enabled quinine to be produced synthetically. The alkaloid quinine is the active substance in an oral prescription drug called quinine sulfate, which is available in capsule or tablet form. Quinine suppresses trophozoites (parasitic microorganisms such as Plasmodium) and acts as an analgesic, or pain medication. Suppressing parasites and relieving pain are two major benefits of naturally derived quinine, benefits not surpassed by the synthetic versions. Therefore, cinchona tree bark is still the major source of quinine for treating the bite of malaria, especially in developing countries where the bark is readily available--or more readily available than in the pharmacy!

References, Websites, and Further Reading

World Health Organization: Division of Control of Tropical Disease

Life cycle of a mosquito

Malaria, the disease

Stern, Introductory Plant Biology, 8th Edition

Chapter 2: The Nature of Life
Elements, molecules, and compounds, pp. 15-18

Chapter 4: Tissues
Secondary growth, pp. 52-53

Chapter 8: Flowers, Fruits, and Seeds
Monocots and dicots compared, pp. 129-30

Chapter 24: Flowering Plants and Civilization
South American Center, pp. 437-38

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