PHOENIX, Ariz. — Substances in a common plant can kill larvae of the mosquito that helps spread the viruses that cause Zika, chikungunya and dengue fever. That's the discovery of a teen from the Philippines. His research may help public health officials develop a way to slow the spread of those deadly diseases. It also may give homeowners hints about how to home-brew their own mosquito-killing cocktail.
Dengue (DEN-gay) virus is a leading cause of illness and death throughout the tropics and subtropics. The disease is spread by the Aedes aegypti (AY-dees Eh-JIP-tye) mosquito. Dengue causes high fevers, severe headaches and joint pain, among other symptoms. With no vaccine to prevent it, up to 400 million people contract dengue each year, according to the Centers for Disease Control and Prevention. More than one-third of all people on the planet live in areas at risk of this infection.
Within that big zone is The Philippines. It’s where Jerouen Paul Lumabao lives. A 10th grader at Daniel R. Aguinaldo National High School in Davao City, he wanted to look for something that would at least slow dengue’s spread. He knew that many insect-killing chemicals were first discovered in plants. So the 17-year-old decided to test new candidates that he extracted from three plants common to where he lives.
One is a thigh-high weed called tawa-tawa (Euphorbia hirta). Another is an attractive perennial called the San Francisco plant (Codiaeum variegatum). Because its leaves are colorful, people often plant it in gardens and yards, says Jerouen. (Known as the variegated croton, this plant also is grown as a houseplant in cooler, temperate zones.) The third is an herb called lemon grass (Cymbopogan citratus), which is used in cooking.
Many insect-killing extracts are isolated by soaking a plant’s leaves in alcohol. And that’s basically what Jerouen did. After picking the leaves, he dried them for one week. Then, he soaked each type in alcohol. Afterwards, he let the alcohol evaporate. What remained was a concentrated oily liquid full of plant-made chemicals.
He tested these extracts by dripping small quantities of them into water that contained mosquito eggs and larvae. Both tawa-tawa and lemon grass extracts caused the mosquito larvae to develop unusually. They would not have matured into healthy adults, Jerouen says. The San Francisco plant extract proved even more toxic to the insects. In just 24 hours, it had killed all of the mosquito eggs and larvae in the water.
Jerouen described his results here, May 12, at the Intel International Science and Engineering Fair. Created by Society for Science & the Public and sponsored by Intel, this year's competition brought together more than 1,750 students from 75 countries. (SSP also publishes Science News for Students.)
Jerouen focused his research on preventing the spread of dengue fever. But in recent months, people have become even more aware of the Zika virus. It, too, is spread by mosquito bites. It can cause fevers, rashes and eye inflammation. What’s more, if a pregnant woman gets infected, her baby might end up with birth defects. And then there’s chikungunya, a devastating disease poised to hit North America. All three viruses can be transmitted by Aedes aegypti mosquitoes. This suggests Jerouen’s plant extracts might become a powerful weapon in fighting many frightening diseases.
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Aedes aegypti A species of mosquito that can transmit the viruses responsible for several tropical diseases, including dengue fever, yellow fever, chikungunya and West Nile disease.
Centers for Disease Control and Prevention, or CDC An agency of the U.S. Department of Health and Human Services, CDC is charged with protecting public health and safety by working to control and prevent disease, injury and disabilities. It does this by investigating disease outbreaks, tracking exposures by Americans to infections and toxic chemicals, and regularly surveying diet and other habits among a representative cross-section of all Americans.
chikungunya A tropical disease that has been crippling large numbers of people in Africa and Asia. It’s caused by a virus that is spread by mosquitoes. It recently has been spreading widely throughout warm nations. More than 3 million people have suffered through its initial flu-like symptoms. A large share may also go on to develop intense pain in their muscles and joints that can last months to years. There is no cure or vaccine.
dengue fever A potentially lethal infectious disease transmitted by mosquitoes. No vaccine yet exists to prevent infection with the virus responsible for the disease, which causes high fevers, severe headache, joint pain, pain behind the eyes, rash, bone pain and sometimes mild bleeding. A more severe form of the disease, known as dengue hemorrhagic fever can cause uncontrolled bleeding if not treated right away.
extract (v.) To separate one chemical (or component of something) from a complex mix. (noun) A substance, often in concentrated form, that has been removed from its natural source. Extracts are often taken from plants (such as spearmint or lavender), flowers and buds (such as roses and cloves), fruit (such as lemons and oranges) or seeds and nuts (such as almonds and pistachios). Such extracts, sometimes used in cooking, often have very strong scents or flavors.
larva (plural: larvae) An immature life stage of an insect, which often has a distinctly different form as an adult. (Sometimes used to describe such a stage in the development of fish, frogs and other animals.)
perennial (in botany) A plant that lives for many years. Some may die back in harsh weather (extreme heat or cold), but then come back months later when conditions improve.
Society for Science and the Public (or SSP) A nonprofit organization created in 1921 and based in Washington, D.C. Since its founding, SSP has been not only promoting public engagement in scientific research but also the public understanding of science. It created and continues to run three renowned science competitions: The Intel Science Talent Search (begun in 1942), the Intel International Science and Engineering Fair (initially launched in 1950) and Broadcom MASTERS (created in 2010). SSP also publishes award-winning journalism: in Science News (launched in 1922) and Science News for Students (created in 2003). Those magazines also host a series of blogs (including Eureka! Lab).
toxic Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.
tropics The region near Earth’s equator. Temperatures here are generally warm to hot, year-round.
subtropics A geographic region that reaches to the beginning of the temperate climate zone (around 40° North and 40° South latitudes) from the edges of tropics, that band of hot climate spanning the outer belly of the planet. The tropics reach out to the Tropic of Cancer (around 23.5° north latitude) and Tropic of Capricorn (around 23.5° south latitude). The subtropics tend to be reliably warmer than temperate climates, but may experience brief periods of frost that would be unexpected in the true tropics.
temperate In geography, referring to areas that are cooler than the tropics but warmer than polar regions.
virus Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.
Zika virus A virus that can be transmitted to humans via mosquitoes. About 20 percent of infected people get sick. Symptoms include a slight fever, rash and pinkeye and usually fade quickly. A growing body of evidence suggests that the virus could also cause a devastating birth defect — microcephaly. Evidence suggests it may also cause neurological conditions such as Guillain-Barré syndrome.