Tuesday, October 4, 2016
Cambodia - A New Weapon to Fight Mosquito-Borne Diseases: Tiny Fish
Scientists hope the simple solution can help slow the spread of dengue, malaria, Zika, and other illnesses.
Kampong Cham, Cambodia—In a backyard lush with mango and papaya trees, an addition to Touch Sophea’s family was stirring excitement: Several tadpole-size guppies were doing laps in a large barrel of water.
“They’re pretty to look at, with so many colors,” said the farmer. The 33-year-old gathered around the container with her three children, her husband, and her niece at their home in Kampong Cham province, about 80 miles from Cambodia’s capital, Phnom Penh.
Fish often have a spiritual significance in Asian cultures, and in Cambodia, they are seen as lucky. But these little swimmers, which at about half an inch long would be tough to spot if they weren’t so active, are not just pets, as Sophea’s children think of them.
They are part of a promising one-year trial testing a low-tech innovation against dengue and other diseases spread by mosquitoes.
The nonprofit Malaria Consortium is nearing the end of an experiment in Cambodia that pits a low-tech innovation against a modern problem:
As climate change has worsened, new regions are seeing more cases of dangerous illnesses spread by mosquitoes, such as dengue, which is responsible for an estimated 400 million infections annually, according to the World Health Organization.
Though deaths from dengue are on the decline, the illness racks the body with symptoms including a mild fever, headaches, rashes, and sore muscles and joints—devastating livelihoods. In deadly cases, dengue causes severe bleeding and organ impairment.
Infection numbers have risen, and in 2015 there were more than 3.2 million known dengue cases across the Americas, Southeast Asia, and Western Pacific, according to the World Health Organization.
About 70 percent of infections occur in Asia, according to the journal Nature.
Touch Sophea and her children gather around a barrel containing guppies. (Photo: Amy Fallon)
That high percentage is why scientists here are exploring simple solutions to some of medicine’s toughest problems—even as the search continues for cures to dengue and other mosquito-borne illnesses, such as Zika, malaria, and West Nile.
“There is an urgent need to find an effective low-cost and home-grown solution,” Jeffrey Hii, a senior vector-control specialist for Malaria Consortium, told TakePart.
What can a guppy do? The aim of the pilot, which is funded by the U.K. and German governments, is for the fish to eat the mosquito larvae that are typically laid in natural water sources—which are abundant in the tropics—before the insects grow into adults and spread the disease.
The guppies, which are indigenous to rice paddies and other of the region’s natural water sources, are kept in rain barrels that Cambodians have long relied on to hold water for cooking and cleaning. The barrels are situated near homes and attract the majority of mosquitoes that carry dengue nearer to humans.
In Kampong Cham, which has one of the highest dengue incidence rates in Cambodia, thousands of guppies have been given to about 3,000 households by Malaria Consortium Cambodia, the organization's local branch, which began its pilot last October. Each villager is given two guppies, doled out from a school kept at the local health center, to breed at home. If these swimmers die, villagers can get more, though guppies typically reproduce within a month.
Dr. Jeffrey Hii. (Photo: Vanney Keo for Malaria Consortium)
Scores of community health volunteers, trained by Malaria Consortium Cambodia, are responsible for distributing the guppies and informing residents about prevention, including mosquito nets.
Traditionally, the best ways to reduce dengue have included properly throwing out trash, using insecticide sprays, coils, vaporizers, window screens, and bed nets, and wearing long-sleeved clothes.
But chemical insecticides are costly and require funding, and there is resistance to them, among other concerns.
Recently, pesticide sprays targeting Zika mosquitos in South Carolina were blamed for a massive bee die-off.
While Malaria Consortium supports some use of pesticides in times of outbreak, finding natural alternatives is a priority.
Sophea learned about the trial when a volunteer visited her province, which is home to nearly 1 million people. The trial’s social mobilization and communication strategy involved a tuk-tuk, a motorized rickshaw, driving through villages handing out fliers and informing residents through songs with informative lyrics.
“This was an effective and culturally appropriate method to reinforce message using songs. The songs were liked the most,” Hii said.
For Sophea, adopting a couple of fish didn’t take much convincing.
“One of my neighbors had dengue,” said Sophea. “I’m very concerned about my children contracting it. If they get it, my baby can die in one week.”
With about three-quarters of those infected with dengue not showing signs, some health experts have labeled it a silent disease. In July, Cambodia’s government warned of a rise in dengue—it typically occurs in outbreaks every three to five years—with more than 1,000 additional cases in the country in about a year.
Officially there were more than 15,000 cases and 38 deaths in 2015 across the country of about 15 million people, but Malaria Consortium Cambodia says the real figures are much higher.
As she watched the barrel’s waters on an August day, peeping at the guppies darting back and forth, Sophea said she couldn’t wait to see them hatch even more hungry fish.
“Before there were many mosquitoes, during the day and night, but now there’s less, and the kids can play around the house,” she said. Sophea also knows to watch for early symptoms of dengue, because she was told by health volunteers to be alert to a high fever, headaches, vomiting, and rashes.
The pilot ends in November, after which the government could include it in its health policy. In November the consortium plans to prepare policy recommendations, which could include expansion to more provinces. With government approval, the nonprofit would continue the work.
One local government official is impressed with one facet. Dr. Hay Ra, Kampong Cham dengue supervisor, praised the guppy program for being inexpensive.
But, Ra said, “we don’t know yet if the community will accept the guppy fish forever, if they will keep them for a long time. If it’s successful, the program can be applied in the whole country.”
He said weather patterns had affected the spread of dengue in Cambodia.
“Climate change is a big problem,” said Ra. “The number of larvae can increase, and the mosquitoes can increase. If we don’t prevent dengue, many people will die. Prevention is very important.”
While the guppies are being used in the first-of-its-kind trial in Asia, scientists thousands of miles away on another continent have come up with a surprising possible protection against malaria.
Sleeping with a chicken next to one’s bed, or suspending a live chicken in a cage, could guard against the disease, researchers at the Swedish University of Agricultural Sciences and Addis Ababa University in Ethiopia have discovered, according to a trial published in Malaria Journal in July.
The study was conducted in Ethiopian villages and found that Anopheles arabiensis, one of the main mosquito species spreading malaria in sub-Saharan Africa, according to the World Health Organization, was repelled by chicken odor. The mosquito accounts for nearly 90 percent of malaria cases. Although it’s early days, the research could pave the way for a chicken-scent repellent being introduced on the market.
“In terms of really low-tech innovations, keeping a chicken indoors shouldn’t be very expensive,” lead researcher Rickard Ignell, from the Swedish University of Agricultural Sciences, told TakePart. “It’s a matter of persuading people to do it.”
Ignell said in several villages across Africa that his team worked in and visited, many households kept their livestock inside but usually in a separate room next door.
(Photo: Vanney Keo for Malaria Consortium)
He stressed it was still important that households use bed nets and sprays to decrease the presence of mosquitoes indoors.
“This could potentially be used all around the world where there’s malaria. Now we’ve only done it for one species of malaria mosquitoes. We still need to check if other mosquitoes will behave the same,” Ignell said.
Beyond using animals to police mosquito populations, the plant world may offer another solution to decreasing malaria transmission, researchers in West Africa have found.
The Anopheles mosquito’s fondness for natural sources of plant sugar, such as nectar, fruits, and tree sap, can be used to reduce its ability to transmit malaria via certain plants, researchers in Burkina Faso found.
Their study, published in the PLOS Pathogens medical journal in August, showed that a mosquito’s ability to transmit malaria decreased if it fed from the plant Thevetia neriifolia, known as yellow oleander. Other plants increased the insect’s ability to transmit illness.
“What we are really aiming for now is testing a wider range of plant species, trying to find one or two that are attractive to mosquito vectors, that completely stop transmission,” researcher Thierry Lefèvre told TakePart. “Then what we imagine is to foster the planting of such species.”
Some existing malaria control methods, such as bed nets and indoor spraying, have faced resistance, so both low- and high-cost solutions were needed, said Ignell.
“To introduce new control methods, especially low-tech technologies, it is important that researchers working with mosquitoes work closely with social scientists, who have better tools and are more skilled to interact with villagers in the affected communities,” he said.
In Asia, Malaria Consortium hopes the current focus on Zika can be used to improve dengue control.
“We hope that the global attention can draw more attention to the urgent need to control one of the fastest-growing infectious diseases in the world that has been largely overlooked by the international community, a potentially fatal disease infecting millions per year,” Hii said.