A relatively new mosquito-borne virus known as Zika has rapidly spread to more than two dozen countries.
Transmitted by the aggressive Aedes aegypti mosquito, the virus has been linked to a heart wrenching neurological disorder that results in babies being born with abnormally small heads.
The disorder, microcephaly, causes severe developmental issues and sometimes death.
World Health Organization Director-General Margaret Chan has described the virus’s spread as “a public health emergency of international concern,” with the potential to infect an estimated 3 million to 4 million people across the Americas in the next year.
With no treatment or vaccine available, the controversial pesticide DDT — illegal in the United States for more than 40 years — has been mentioned in some circles as a way to combat the Zika virus.
Dr. Lyle Petersen, director of the division of vector-borne diseases at the Centers for Disease Control and Prevention, told The New York Times last week that concerns about DDT have to be “reconsidered in the public health context.”
Still, experts say, don’t count on a comeback in the United States, which banned DDT in 1972.
“The fact is that DDT was widely used 50 years ago and virtually eliminated this mosquito from the Americas, but DDT was also widely used in agriculture, got into the environment and had serious problems in the environment for many species,” CDC Director Dr. Tom Frieden, told CNN this week. “It remains in the body for a long time. We’re looking at safer, more effective ways to kill mosquitoes.”
Here are five important things to know about DDT.
What is DDT?
Dichlorodiphenyltrichloroethane (DDT) was the first of the modern synthetic insecticides created in the 1940s, according to the U.S. Environmental Protection Agency.
The insecticide was effective in battling malaria, typhus and the other insect-borne diseases in military and civilian settings.
It became a common weapon in the control of insects in crop and livestock production. DDT also was sprayed in institutions, homes and gardens.
DDT was at one time the most widely used pesticide “in practically every part of the world,” according to the EPA.
A 1940s marketing film shows a housewife drenching her home with the potent bug killer, using a simple spray pump.
“It almost seemed like a parody,” Michael Schulder, a former senior executive producer for CNN, wrote in 2010.
In the 30 years before the ban, more than 1.3 million tons of what became known as the “miracle” pesticide was used domestically, the EPA said.
It peaked in 1959, when nearly 80 million pounds were sprayed across America.
What led to the DDT ban?
Before the federal EPA was formed in 1970, the U.S. Department of Agriculture regulated pesticides.
In the 1950s and 1960s, as evidence of DDT’s environmental and toxicological effects began to mount, agricultural officials restricted its use.
A characteristic of DDT’s popularity — its persistence — would eventually contribute to its demise.
“Once in someone’s body, it can take decades to eliminate it,” Jonathan Chevrier, a professor of epidemiology at McGill University in Canada, said via email. “DDT also crosses the placenta and is found in breast milk, so developing fetuses and children will be exposed if their mothers are exposed.”
While scientists had warned of the hazards of pesticides as early as the 1940s, it was the 1962 publication of naturalist Rachel Carson’s landmark book, “Silent Spring,” that spurred widespread public concern. The book is credited with launching the environmental movement in the United States.
The book predicted that spring mornings would be silent and devoid of wildlife if something was not done about the dangers of unbridled pesticide use. In addition, it suggested that DDT could be responsible for the thinning of Bald Eagles egg shells and could lead to their potential extinction.
Over the next decade, groups on both sides of the DDT debate squared off in court and regulatory proceedings.
In 1971, DDT’s use had declined to about 13 million pounds, applied mostly to cotton. The reasons for the decline included “increased insect resistance, development of more effective alternative pesticides, growing public and user concern over adverse environmental side effects — and governmental restriction on DDT use since 1969,” the EPA said.
On December 31, 1972, the EPA announced: “The general use of the pesticide DDT will no longer be legal in the United States after today, ending nearly three decades of application during which time the once-popular chemical was used to control insect pests on crop and forest lands, around homes and gardens, and for industrial and commercial purposes.”
The cancellation order cited the “adverse environmental effects, such as those to wildlife, as well as its potential human health risks” of DDT.
Is DDT an option against the Zika virus?
The use of DDT for public health emergencies is an option in the U.S., said Lynn Goldman, an epidemiologist and pediatrician who is dean of Milken Institute School of Public Health at the George Washington University.
But Goldman said spraying DDT now to control Zika would be “misguided and reckless.”
“There are many pest control measures that potentially can be used, many of which are far more effective, now and in the long term, than DDT,” she said via email.
DDT is used around the world to combat malaria.
Goldman said the pesticide is effective against the Anopheles mosquito, a night-biter that spreads malaria indoors while people are sleeping.
In many developing countries, DDT has proven effective when sprayed on the indoor walls of buildings.
“Basically the anopheles likes to rest on a wall surface between feedings and thus is poisoned by the DDT that is on the walls,” Goldman said.
“Also there are insecticide impregnated bed nets — usually with pyrethroids, and, infrequently, with DDT — to guard against malaria transmission while sleeping. Bed nets also are very effective.”
But the mosquito that transmits Zika is not the anopheles but another genus known as the Aedes, which also transmits dengue and chikungunya viruses, according to Goldman.
Aedes mosquitos bite outdoors, during the day, she said. Spraying walls with DDT won’t help.
The best way to deal with aedes is by controlling its breeding and using products such as the popular insect repellent DEET, Goldman said.
Aedes mosquitos are difficult to control. They breed in the tiniest amount of water — the cup formed by a large leaf, water in used tires or plant saucers, said Goldman.
Aedes also like urban, not rural areas, Goldman said. Successful control efforts have involved door-to-door campaigns to eliminate breeding areas.
The use of pesticides, especially DDT, to combat Zika must be considered with extreme care, Chevrier said.
“Using DDT now would result in exposure to local populations for decades,” he said.
“In fact, DDE, a breakdown product from DDT, is still detected in the blood of a majority of Americans even though DDT was banned in the U.S. about 40 years ago.”
Jeffrey Scott, a professor of entomology at Cornell University, said that while DDT has “unquestionably saved millions and millions” of lives around the world, he doubts it will ever make a comeback in the U.S.
“I don’t think anybody would survive the political fallout of trying to bring this back,” he said in an interview. “It’s got religious zeal to it some camps.”
Jay Feldman, executive director of Beyond Pesticides, told CNN, “The concern we have is that in combating an immediate public health threat [with DDT], we create a greater long term public health problem.”
Is DDT used elsewhere?
DDT is banned internationally by the Stockholm Convention on Persistent Organic Pollutants, an agreement ratified by more than 170 countries.
But an exception is allowed for malaria control — a disease that still kills millions of people worldwide.
Several countries, mostly in Africa, currently use DDT to combat malaria.
In September 2006, the World Health Organization declared its support for the indoor use of DDT in African countries where malaria remains a major health problem. The WHO said the benefits of the pesticide outweighed the health and environmental risks.
DDT is one of a dozen pesticides the WHO recommends for indoor spraying programs. Individual countries decide whether or not to use DDT.
Are dangers of DDT real?
DDT is classified as a probable human carcinogen by U.S. and international authorities.
The insecticide has been linked to a number of health issues including affects on the brain development of children and breast cancer.
“It is unclear whether DDT does cause these issues but current evidence raises concerns,” Chevrier said.
In addition to its known persistence in the environment, DDT accumulates in fatty tissues and can travel long distances in the upper atmosphere, according to the EPA.
Another drawback involves harm to other species.
Using DDT to control the Aedes mosquito by spraying the yards around people’s homes — which is where Aedes breed — would have adverse affects on birds and, possibly, aquatic ecosystems, Goldman said.
Human health effects from DDT at low environmental doses are unknown, according to the CDC. After exposure to high doses, human symptoms include vomiting, tremors or shakiness and seizures.
Laboratory animal studies have shown effects on the liver and reproduction.
“Although there is some uncertainty, the potential impacts of DDT on human health, wildlife and the ecology are real,” Chevrier said.
