A new study found that a weapon against mosquitoes could be forged from the unlikeliest of sources: the humble chicken. The findings suggest that these insects find fowl smell quite foul, a potential starting point for new repellents to be used against them.
Want to ward off malaria, or the Zika outbreak? Sleep with a chicken over your head.
By this point some of you are no doubt skeptical — and I can’t blame you. That sounds more like the ramblings of a witch in a medieval village than sound medial advice. But surprisingly enough, a study by Swedish and Ethiopian scientists found that mosquitoes avoid homes which contained a live chicken suspended in a cage. Interestingly enough, they don’t even have to see the chicken — one whiff of the birds’ smell is enough to make them turn tail and run.
“We were surprised to find that malaria mosquitoes are repelled by the odors emitted by chickens,” said Professor Richard Ignell, of the Swedish University of Agricultural Sciences.
“This study shows for the first time that malaria mosquitoes actively avoid feeding on certain animal species, and that this behavior is regulated through odor cues.”
The researchers suspect that mosquitoes have evolved to avoid chickens because these birds pray on them, and their blood isn’t nutritious enough to justify the risk of biting them. They instinctively avoid the fowl’s “odor bubble,” no matter how hungry. The researchers found that most mosquitoes won’t even enter a house with a chicken in it, let alone a single room. Just in case sleeping with chickens caged above your face isn’t your thing (but let’s be honest, how could it not?) they’ve isolated the chemical compounds that scare off the mosquitoes and are now planning to develop them into a repellent.
“The difference between this repellent and ones on the market is it acts on a very large scale. Most repellents only work after a mosquito lands on you but we know that this can cut populations by up to 95 per cent throughout an entire house, so it’s very efficient,” Ignell added.
“[The repellent] really creates an odour bubble which stops the mosquitos coming near, so it can stop the spread of malaria.”
This has the potential to be huge. Mosquitoes are responsible for spreading terrible diseases such as malaria and the Zika virus, which causes mothers to give births to children with drastic abnormalities, such as microcephaly. Zika was declared a global emergency by the World Health Organisation earlier this year and more than 50 countries have confirmed outbreaks. Finding an efficient way to protect people from mosquito bites and the spread of these diseases could save some of the 3.2 billion people at risk of malaria.
“People in sub-Saharan Africa have suffered considerably under the burden of malaria over an extended period of time and mosquitoes are becoming increasingly physiologically resistant to pesticides, while also changing their feeding habits for example by moving from indoors to outdoors.
“For this reason there is a need to develop novel control methods. In our study, we have been able to identify a number of natural odour compounds which could repel host-seeking malaria mosquitoes and prevent them from getting in contact with people.”
For the study, the researchers collected data on the population of human and domestic animals in three Ethiopian villages, with help from Addis Ababa University in Ethiopia. In these areas, people still share their living space with livestock, and the researchers found that Anopheles arabiensis, one of the prime transmitters of malaria in sub-Saharan Africa, avoids chickens both inside and outdoors.
The team determined which chemical compounds were present only in chicken feathers and then tested them by placing samples in traps in 11 homesteads. A single volunteer aged between 27 and 36 years slept in each of the houses under an untreated bed net – and traps were positioned in the room to count the number of mosquitoes that flew in. Significantly fewer mosquitoes were caught in traps baited with chicken compounds than in control traps. Volunteers also slept in mosquito-net covered beds (just to make sure they weren’t bit) but found that suspending a chicken outside the bed sent the insects running.
The main mosquito species that transmits Zika is Aedes aegypti and laboratory tests have shown that it much prefers feeding on humans and dogs, although will occasionally bite chickens if they are restrained. Asked if the repellent could work to prevent Zika, Ignell said:
“I think it should. We haven’t tested it on other mosquitos but there are lots of varieties which won’t feed on chickens and so would be repelled.”
The full paper, titled “Chicken volatiles repel host-seeking malaria mosquitoes” has been published online in the Malaria Journal.