It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Saturday, August 31, 2024
Study reveals spread of malaria-carrying anopheles stephensi mosquitoes in Yemen
Findings emphasize urgent need for continued vector surveillance and control measures to mitigate the spread of malaria in previously unaffected regions
Malaria remains a significant global health issue, with around 249 million cases reported in 2022 by the World Health Organization. The malaria-carrying mosquito, Anopheles stephensi, has recently spread to Africa and has now been detected in Yemen, according to new Baylor University research.
Baylor mosquito researcher Tamar Carter, Ph.D., assistant professor of biology and a tropical disease biologist, and the Ministry of Health in Yemen’s capital of Sana’a have published a significant study in the journal Emerging Infectious Diseases, in which they detail the spread of the invasive mosquito in Yemen and their connection to East Africa.
The research highlights the ongoing threat of malaria in regions previously unaffected by the Anopheles stephensi mosquito species.
“Concerns are growing about the status and spread of the Anopheles stephensi mosquito species in the Mediterranean region,” Carter said. “We are seeing growing evidence of thismosquito’s resistance to multiple classes of insecticides, its association with a recent malaria outbreak and genomic evidence that outbreak sites may also be central locations for this invasive mosquito to travel to new areas.”
Carter along with Dr. Methaq Assada, lead investigator and manager of the Yemen National Malaria Control Program, analyzed immature mosquitoes collected from two semiurban locations in Yemen: in the Ad Dahi district in December 2021 while conducting Aedes aegypti mosquito surveillance during a dengue fever outbreak, and in the Zabid district during monthlong Anopheles surveillance in March 2022. The specimens morphologically identified as Anopheles stephensi mosquitoes were preserved and sent to Carter’s lab at Baylor University for molecular analysis.
Key findings
The study, Carter said, provides critical insights into the genetic diversity of Anophelesstephensi mosquitoes in Yemen.
The researchers’ key findings include:
Detection and confirmation:Anopheles stephensi mosquitoes were first detected in Aden, Yemen, in 2021 and confirmed by molecular analysis in 2023. Subsequent surveillance revealed their presence in the Ad Dahi and Zabid districts of Al Hudaydah.
Genetic insights: Through DNA sequencing, two haplotypes of the mosquito's cytochrome c oxidase subunit I (COI) gene were identified. One haplotype matches those found in East Africa, while the other is newly discovered, providing crucial insights into the genetic diversity and spread of these mosquitoes.
Implications for malaria control: The findings emphasize the urgent need for continued vector surveillance and control measures to mitigate the spread of malaria in Yemen and potentially other regions of the Arabian Peninsula.
Recommendations and future directions
Carter has previously discovered critical insights into the spread of the invasive Anopheles stephensi mosquito in the Horn of Africa, posing a significant public health threat in those new regions.
With her latest new research detecting the mosquito in Yemen, Carter advocates for extensive genomic analysis and increased surveillance efforts across Yemen and neighboring regions to better understand and control the spread of Anopheles stephensi. These steps, she said, are vital to addressing the public health impact of malaria, particularly in high-prevalence areas.
Funding and acknowledgments
This study was made possible through funding from the NIH Research Enhancement Award (1R15AI151766) and the support of the Yamaan Foundation for Health and Social Development.
Tamar Carter, Ph.D., Researcher at Baylor University
ABOUT THE AUTHOR
Tamar Carter earned her Ph.D., in genetic and genomics and Master of Public Health at the University of Florida, where she studied genetic variation associated with parasite antimalarial resistance and host genetic red blood cell disorders in Haiti. Her interest in bridging research and public health led her to complete an internship at the UF Public Health Laboratory in Gressier, Haiti, and serve as a James A. Ferguson Emerging Infectious Diseases fellow at the Centers for Disease Control and Prevention in Atlanta.
During her postdoctoral fellowship at the University of North Carolina at Charlotte, her interests grew to include malaria vector surveillance through collaborations with Jigjiga University in east Ethiopia. Now at Baylor, Carter’s research program applies both molecular and data science approaches to investigate vector and parasite evolution, coevolution, and ecology to inform strategies for malaria control.
ABOUT THE COLLEGE OF ARTS & SCIENCES AT BAYLOR UNIVERSITY
The College of Arts & Sciences is Baylor University’s largest academic division, consisting of 25 academic departments in the sciences, humanities, fine arts and social sciences, as well as 11 academic centers and institutes. The more than 5,000 courses taught in the College span topics from art and theatre to religion, philosophy, sociology and the natural sciences. The College’s undergraduate Unified Core Curriculum, which routinely receives top grades in national assessments, emphasizes a liberal education characterized by critical thinking, communication, civic engagement and Christian commitment. Arts & Sciences faculty conduct research around the world, and research on the undergraduate and graduate level is prevalent throughout all disciplines. Visit the College of Arts & Sciences website.
ABOUT BAYLOR UNIVERSITY
Baylor University is a private Christian University and a nationally ranked Research 1 institution. The University provides a vibrant campus community for more than 20,000 students by blending interdisciplinary research with an international reputation for educational excellence and a faculty commitment to teaching and scholarship. Chartered in 1845 by the Republic of Texas through the efforts of Baptist pioneers, Baylor is the oldest continually operating University in Texas. Located in Waco, Baylor welcomes students from all 50 states and more than 100 countries to study a broad range of degrees among its 12 nationally recognized academic divisions.
A high-pitched buzzing sound in your ear is an unmistakable sign that a female mosquito is out on the hunt — for they, not males, drink blood. Hearing that tone might make you turn to try to swat the pest. But for a male mosquito, that tone means it’s time to mate.
An international team led by researchers at the University of Washington has uncovered surprising details about mosquito mating, which could lead to improved malaria control techniques and even help develop precision drone flight. In a paper published Aug. 30 in the journal Current Biology, the team revealed that when a male Anopheles coluzzii mosquito hears the sound of female-specific wingbeats, his vision becomes active.
Many mosquito species have relatively poor vision, and Anopheles coluzzii — a major spreader of malaria in Africa — is no exception. But the team found that when a male hears the telltale buzz of female flight, his eyes “activate” and he visually scans the immediate vicinity for a potential mate. Even in a busy, crowded swarm of amorous mosquitoes, which is how A. coluzzii mates, the researchers found that the male can visually lock on to his target. He then speeds up and zooms deftly through the swarm — and avoids colliding with others.
“We have discovered this incredibly strong association in male mosquitoes when they are seeking out a mate: They hear the sound of wingbeats at a specific frequency — the kind that females make — and that stimulus engages the visual system,” said lead author Saumya Gupta, a UW postdoctoral researcher in biology. “It shows the complex interplay at work between different mosquito sensory systems.”
This strong link between males hearing the female-like buzz and moving toward an object in their field of vision may open up a new route for mosquito control: a new generation of traps specific to the Anopheles mosquitoes that spread malaria.
“This sound is so attractive to males that it causes them to steer toward what they think might be the source, be it an actual female or, perhaps, a mosquito trap,” said senior author Jeffrey Riffell, a UW professor of biology.
Like most Anopheles species, Anopheles coluzzii mate in large swarms at sunset. The bulk of the bugs in these swarms are males, with only a few females. To human eyes, the swarms may appear chaotic. Mosquitoes of both sexes rapidly zip past each other. Males must use their senses to both avoid collision and find a rare female.
Gupta, Riffell and their colleagues — including scientists from Wageningen University in the Netherlands, the Health Sciences Research Institute in Burkina Faso, and the University of Montpelier in France — wanted to understand the interplay between mosquitoes’ senses and how they work together in these swarms. To test the flight behavior of individual male mosquitoes, they built a miniature arena that uses a curved, pixelated screen to mimic the visual chaos of a swarm. The arena is essentially a mosquito flight simulator. In it, the mosquito test subject, which is tethered and cannot freely move, can still see, smell and hear, and also beat its wings as if it is in flight.
In arena tests with dozens of male Anopheles coluzzii mosquitoes, the researchers discovered that males responded differently to an object in their field of vision based on what sound the researchers broadcast into the arena. If they played to a tone at 450 hertz — the frequency at which female mosquito wings beat in these swarms — males steered toward the object. But males did not try to turn toward the object if the researchers played a tone at 700 hertz, which is closer to the frequency at which their fellow males beat their wings.
The mosquito’s perceived distance to the object also mattered. If the simulated object appeared more than three body lengths away, he would not turn toward it, even in the presence of female-like flight tones.
“The resolving power of the mosquito eye is about 1,000-fold less than the resolving power of the human eye,” said Riffell. “Mosquitoes tend to use vision for more passive behaviors, like avoiding other objects and controlling their position.”
In addition to their dramatic response to objects when hearing female flight tones, arena experiments revealed that males made a different set of subtle flight adjustments to other objects. They modified their wingbeat amplitude and frequency in response to an object in their field of view, even with no wingbeat sounds piped in through the speaker. The team hypothesized that these visually driven responses may be preparatory maneuvers to avoid an object. To learn more, they filmed male-only swarms in the laboratory. Analyses of those movements showed that males accelerated away when they neared another male.
“We believe our results indicate that males use close-range visual cues for collision avoidance within swarms,” said Gupta. “However, hearing female flight tones appears to dramatically alter their behavior, suggesting the importance of integrating sound and visual information.”
This research may demonstrate a new method for mosquito control by targeting how mosquitoes integrate auditory and visual cues. The males’ strong and consistent attraction to visual cues when they hear the female buzz may be a vulnerability that researchers can utilize while designing the next generation of mosquito traps —particularly traps for the Anopheles species, which are a major spreader of malaria pathogens.
“Mosquito swarms are a popular target for mosquito control efforts, because it really leads to a strong reduction in biting overall,” said Riffell. “But today’s measures, like insecticides, are increasingly less effective as mosquitoes evolve resistance. We need new approaches, like lures or traps, which will draw in mosquitoes with high fidelity.”
Co-authors are Antoine Cribellier, Serge Poda and Florian Muijres of Wageningen University of Wageningen University in the Netherlands and Olivier Roux of the University of Montpelier in France. Roux and Poda are also with the Health Sciences Research Institute in Burkina Faso. The research was funded by the Human Frontiers Science Program, the National Institutes of Health, the Air Force Office of Scientific Research and the French National Research Agency.
An image of a male Anopheles coluzzii.
Credit
Adam Blake
An image of swarming Anopheles coluzzii mosquitoes.
Credit
Simon Sawadogo
The flight simulator arena used to test an individual mosquito. The lights within it appear as different visual objects to a tethered individual.
The flight simulator arena used to test an individual mosquito. The lights within it appear as different visual objects to a tethered individual.
Human Frontiers Science Program: HFSP-RGP0044/2021
National Institutes of Health: R01AI148300, R01AI175152
Air Force Office of Scientific Research: FA9550-21-1-0101, AWD-004055-G4
French National Research Agency: ANR-15-CE35-0001-01
Reference:
Gupta S, Cribellier A, Poda SB, Roux O, Muijres FT, Riffell JA. “Mosquitoes integrate visual and acoustic cues to mediate conspecific interactions in swarms.” Current Biology. 2024. 10.1016/j.cub.2024.07.043
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