Ever wondered how mosquitoes find humans from distances of up to a hundred meters away? In a landmark study, a group of researchers have made headway into answering this question. The experts discovered that human body odor is a critical element in the long-range host-seeking behavior of mosquitoes (see image here).
The researchers developed an outdoor testing arena, the size of an ice-rink, in Zambia. They then used this setup to study the mosquito attraction to human body odor.
In the process, the team also identified specific airborne body-odor components that could potentially explain why some people are mosquito magnets, while others are less appealing to these insects. The groundbreaking study is published in the journal Current Biology.
The majority of studies in the past that focused on mosquito preference were conducted in controlled laboratory conditions. However, these setups likely don’t accurately represent the real-world experiences of mosquitoes.
To overcome this, researchers from Johns Hopkins Bloomberg School of Public Health’s Malaria Research Institute and Macha Research Trust built a testing arena spanning 1,000 cubic meters in Choma District, Zambia.
“This is the largest system to assess olfactory preference for any mosquito in the world,” said study co-author Diego Giraldo. He added that it presents a highly sensory environment for the mosquitoes.
The unique testing arena consisted of a ring of landing pads, each heated to the average human skin temperature of 35 degrees Celsius. The researchers released 200 famished mosquitoes into this arena each night and tracked their activity using infrared motion cameras.
Special attention was paid to how frequently mosquitoes landed on each of the landing pads, as it’s a strong indication that they’re ready to feed.
The first stage of the investigation involved comparing the relative importance of heat, CO2, and human body odor in attracting mosquitoes.
The experts discovered that the mosquitoes showed no interest in the heated landing pads unless they were also baited with CO2. However, human body odor proved to be an even stronger attractant than CO2 alone.
The researchers then tested the discerning nature of mosquitoes. To achieve this, six volunteers slept in single-person tents surrounding the arena over six consecutive nights.
Using repurposed air conditioner ducting, the team directed air from each tent – complete with the unique aromas of each sleeping volunteer – onto the heated landing pads.
Concurrently, they recorded the mosquitoes’ preferences and collected nightly air samples from the tents to analyze and compare the airborne components of body odor.
“These mosquitoes typically hunt humans in the hours before and after midnight,” explained study senior author Conor McMeniman. He added that the mosquitoes follow scent trails and air currents originating from humans and usually invade homes and bite between around 10 PM and 2 AM.
Thus, the researchers aimed to assess mosquito olfactory preferences during this peak activity period and gauge the odor from sleeping humans during the same timeframe.
In their findings, the experts noted a consistent pattern where some people were more attractive to mosquitoes than others. Intriguingly, one of the volunteers, who had a notably different odor composition from the rest, consistently drew very few mosquitoes.
The researchers detected 40 chemicals that were emitted by all the volunteers, albeit at varying rates. “It’s probably a ratio-specific blend that they’re following,” explained study co-author Stephanie Rankin-Turner.
She expressed the team’s hope of figuring out what exactly in skin secretions, microbial metabolites, or breath emissions are driving this phenomenon in the coming years.
Despite nightly variations in each person’s odor profile, the researchers detected some enduring patterns. The volunteers who were more attractive to mosquitoes consistently emitted higher amounts of carboxylic acids, a byproduct most likely produced by skin microbes.
Contrastingly, the volunteer least appealing to mosquitoes exhaled fewer carboxylic acids but approximately three times the amount of eucalyptol, a compound commonly found in many plants. The researchers theorize that this surge in eucalyptol levels may be associated with the individual’s diet.
The team was taken aback by the mosquitoes’ proficient ability to locate and choose between potential human meals within the expansive arena.
“When you see something moved from a tiny laboratory space where the odors are right there, and the mosquitoes are still finding them in this big open space out in a field in Zambia, it really drives home just how powerful these mosquitoes are as host seekers,” said Rankin-Turner.
This groundbreaking study presents significant insights into the host-seeking behavior of mosquitoes and the role human body odor plays in it. It also opens up potential avenues for further research on this topic.
These include a deeper understanding of how specific body odor components influence mosquito attraction. Ultimately, such insights may lead to more effective measures for mosquito control and malaria prevention.
Mosquitoes have a significant impact on both humans and the environment, largely because of their role in disease transmission.
From a human health perspective, mosquitoes are one of the deadliest animals on the planet. This is because they are vectors for a number of harmful diseases, including malaria, dengue fever, Zika virus, West Nile virus, yellow fever, and various forms of encephalitis.
Malaria, in particular, is a significant global health issue. According to the World Health Organization, there were an estimated 229 million cases of malaria worldwide in 2019, resulting in about 409,000 deaths. Most of these cases and deaths occurred in Africa, particularly among children under the age of five.
Mosquito-borne diseases can have other impacts as well, such as economic consequences from missed work and the costs of medical treatment. They can also cause societal disruption, particularly in regions where these diseases are endemic.
From an environmental perspective, mosquitoes play several roles. Mosquito larvae, for instance, serve as food for fish and other aquatic animals, and adult mosquitoes are a food source for various species of birds, bats, and spiders.
Some mosquito species also serve as pollinators, feeding on plant nectar and incidentally transferring pollen from one flower to another. However, the negative impact mosquitoes have as disease vectors for both humans and wildlife significantly outweighs their ecological roles.
Various strategies are employed to control mosquito populations and limit their impact. These include insecticide use, bed nets treated with insecticides for malaria control, habitat modification to eliminate breeding sites, and biological controls such as introducing natural predators. There’s also considerable research into genetically modifying mosquitoes to reduce their ability to transmit disease.
The increasing global temperatures due to climate change can potentially alter mosquito distributions and disease transmission patterns, making it an important ongoing area of research. Understanding mosquitoes and their behavior, like the work carried out by the team in Zambia, is vital in developing new strategies to combat these threats.