A new study examining the associations between mosquito species and the germs they carry finds just 9.3 percent of species transmit human disease-causing pathogens—but those associations are strong and likely resilient to the removal of individual species from the vector network. Within that network, the southern house mosquito (Culex quinquefasciatus) was the “most connected” species, capable of transmitting many pathogens that may also be transmitted by many other mosquitoes. (Photo by Jim Gathany, CDC Public Health Image Library)

Don Yee, Ph.D., BCE

Of all the species of mosquitoes on Earth, the exact number of species relevant to human health is unknown. This poses challenges in understanding the scope and breadth of vector–pathogen relationships and how resilient mosquito vector–pathogen networks are to targeted eradication of vectors.

To try to solve this problem, Don Yee, Ph.D., BCE, and students in his lab in the School of Biological, Environmental and Earth Sciences at the University of Southern Mississippi embarked on an extensive literature survey to document medically important mosquitoes. Their findings, reported in June in Parasites & Vectors, estimate for the first time how many mosquitoes are medically important across the world.

“To date no scientific investigation has been made to count the mosquito species involved in the spread of human pathogens that cause disease,” says Yee. “We performed an extensive literature survey to determine the associations between mosquito species and their associated pathogens of human medical importance.”

A new study examining the associations between mosquito species and the germs they carry finds just 9.3 percent of species transmit human disease-causing pathogens—but those associations are strong and likely resilient to the removal of individual species from the vector network. Researchers at the University of Southern Mississippi diagrammed the networks of connections between mosquito species (circles) and pathogens (squares). While 331 species were found to have some relationship with at least one of 78 pathogens, their analysis identified 894 mosquito-pathogen pairs (lines). (Image originally published in Yee et al 2022, Parasites & Vectors)

As Yee’s team performed this survey, for each vector–pathogen association, they determined the strength of the associations (e.g., natural infection, lab infection, lab dissemination, lab transmission, known vector). A network analysis was used to identify relationships among all pathogens and vectors. Finally, they examined how elimination of either random or targeted species affected the extinction of pathogens.

In their results they found that 88 of 3,578 mosquito species (2.5 percent) are known vectors for 78 human disease-causing pathogens; however, an additional 243 species (6.8 percent) were identified as potential or likely vectors, bringing the total of all mosquito species implicated in human disease to 331 (9.3 percent).

Catherine Dean Bermond (left) and Limarie Reyes (right) are students in the Yee Mosquito Lab at the University of Southern Mississippi and co-authored a new study examining the associations between mosquito species and the germs they carry finds. (Photo courtesy of Don Yee, Ph.D.)

Nicole Fijman, Nicole Scavo, and Joe Nelsen (left to right) are students in the Yee Mosquito Lab at the University of Southern Mississippi and co-authored a new study examining the associations between mosquito species and the germs they carry finds. (Photo courtesy of Don Yee, Ph.D.)

Network analysis revealed that known vectors and pathogens were compartmentalized, with the removal of six vectors being enough to break the network (i.e., cause a pathogen to have no vector). However, the presence of potential or likely vectors greatly increased redundancies in the network, requiring more than 41 vectors to be eliminated before breaking the network.

“For the first time we determined how many mosquito species are important for human health and also the strength of associations between pathogens and mosquitoes,” says Yee. “We found that less than 10 percent of all mosquito species are important in human disease. However, the associations between mosquitoes and pathogens are strong, making elimination of pathogens exceedingly difficult through just mosquito control. This work also suggests we still have a long way to go to fully understand all the mosquito species that are relevant to human health.”

Adapted from a news article published June 28, 2022, by the University of Southern Mississippi.