The Olfactory Preferences of Mosquitoes: Exploring the Role of Human Body Odor

2023-07-30 07:09:00

Have you ever wondered how mosquitoes find humans at distances of up to a hundred meters? In a landmark study, a group of researchers made progress in answering this question. Experts have found that human body odor is an essential element in the long-range host-seeking behavior of mosquitoes (see image here).

Researchers have developed an outdoor test arena, the size of an ice rink, in Zambia. They then used this setup to study mosquitoes’ attraction to human body odor.

In the process, the team also identified specific airborne body odor components that might potentially explain why some people are mosquito magnets, while others are less attractive to these insects. The groundbreaking study is published in the journal Current biology.

In the past, the majority of studies focusing on mosquito preference have been conducted under controlled laboratory conditions. However, these configurations probably do not accurately represent actual mosquito experiences.

How the study was carried out

To overcome this, researchers from the Malaria Research Institute at the Johns Hopkins Bloomberg School of Public Health and the Macha Research Trust built a 1,000 cubic meter test arena in Choma District, Zambia.

“This is the largest olfactory preference rating system of any mosquito in the world,” said study co-author Diego Giraldo. He added that it presents a highly sensory environment for mosquitoes.

The unique test arena consisted of a ring of landing platforms, each heated to the average human skin temperature of 35 degrees Celsius. The researchers released 200 hungry mosquitoes into this arena each night and tracked their activity using infrared cameras.

Particular attention was paid to the frequency with which mosquitoes landed on each of the landing platforms, as this is a strong indication that they are ready to feed.

Step 1

The first step in the investigation was to compare the relative importance of heat, CO2 and human body odor in attracting mosquitoes.

Experts have found that mosquitoes show no interest in heated landing pads unless they are also baited with CO2. However, human body odor was found to be an even stronger attractant than CO2 alone.

2nd step

The researchers then tested the perceptive nature of mosquitoes. To achieve this, six volunteers slept in individual tents surrounding the arena for six consecutive nights.

Using repurposed air conditioning ducts, the team directed air from each tent – ​​with the unique aromas of each sleeping volunteer – onto the heated landing pads.

At the same time, they recorded mosquito preferences and collected night air samples from the tents to analyze and compare airborne components of body odor.

“These mosquitoes typically hunt humans in the hours before and following midnight,” said study lead author Conor McMeniman. He added that mosquitoes follow scent trails and air currents from humans and usually invade homes and bite between around 10 p.m. and 2 a.m.

Thus, the researchers sought to assess the olfactory preferences of mosquitoes during this period of maximum activity and to measure the smell of sleeping humans during the same period.

What the researchers learned

In their findings, the experts noted a consistent pattern where some people were more attractive to mosquitoes than others. Curiously, one of the volunteers, who had a noticeably different odor composition from the others, consistently drew very few mosquitoes.

The researchers detected 40 chemicals that were emitted by all of the volunteers, although at varying rates. “It’s probably a ratio-specific mix that they’re tracking,” explained study co-author Stephanie Rankin-Turner.

She expressed the team’s hope to determine exactly what in skin secretions, microbial metabolites or respiratory emissions is causing this phenomenon in the coming years.

Despite nighttime variations in each person’s olfactory profile, the researchers detected persistent patterns. Volunteers who were more attractive to mosquitoes consistently emitted higher amounts of carboxylic acids, a byproduct most likely produced by skin microbes.

In contrast, the least attractive volunteer to mosquitoes exhaled fewer carboxylic acids but regarding three times the amount of eucalyptol, a compound commonly found in many plants. The researchers hypothesize that this increase in eucalyptol levels may be associated with the individual’s diet.

The possibility of finding the perfect meal has impressed scientists

The team was surprised by the mosquitoes’ ability to locate and choose between potential human meals in the vast arena.

“When you see something moving from a small lab space where the smells are right there, and the mosquitoes are still finding them in this big open space in a field in Zambia, it really shows how powerful these mosquitoes are in as host seekers. said Rankin-Turner.

This groundbreaking study presents important insights into the host-seeking behavior of mosquitoes and the role that 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 components of body odor influence mosquito attraction. Ultimately, this information might lead to more effective mosquito control and malaria prevention measures.

Learn more regarding mosquitoes

Mosquitoes have a significant impact on humans and the environment, primarily due to their role in disease transmission.

From a human health perspective, mosquitoes are one of the deadliest animals on the planet. Indeed, they are vectors of 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 an important global health problem. According to the World Health Organization, there were around 229 million cases of malaria worldwide in 2019, resulting in around 409,000 deaths. Most of these cases and deaths have occurred in Africa, particularly in children under five.

Mosquito-borne diseases can also have other impacts, such as the economic consequences of missed work and the costs of medical treatment. They can also cause societal disruption, especially in areas where these diseases are endemic.

Environmental impact of mosquitoes

From an environmental point of view, mosquitoes play several roles. Mosquito larvae, for example, 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 species of mosquitoes also serve as pollinators, feeding on plant nectar and accidentally transferring pollen from one flower to another. However, the negative impact of mosquitoes as vectors of disease to humans and wildlife far outweighs their ecological roles.

Mosquito Population Control Strategies

Various strategies are employed to control mosquito populations and limit their impact. These include the use of insecticides, mosquito nets treated with insecticides to control malaria, habitat modification to eliminate breeding sites, and biological controls such as the introduction of natural predators . There is also considerable research into genetically modifying mosquitoes to reduce their ability to transmit disease.

Rising global temperatures due to climate change have the potential to alter mosquito distribution and disease transmission patterns, making this an important area of ​​ongoing research. Understanding mosquitoes and their behavior, like the team’s work in Zambia, is key to developing new strategies to combat these threats.

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