Wolbachia, a genus of bacteria that infects insects and other arthropods, has been used in the past to control mosquitoes and to hinder their ability to spread diseases such as dengue virus.
However, researchers who wanted to know whether the bacteria could be used as a tool against West Nile virus have found that Wolbachia can instead make certain mosquitoes even more likely to become infected with the virus — not less — which also makes them more likely to transmit West Nile to humans.
Expecting to find that Wolbachia would block infection by West Nile virus in the same way that it blocks dengue virus, Jason Rasgon, an associate professor of entomology at Penn State University, and his colleagues injected the Wolbachia bacteria into adult female Culex tarsalis mosquitoes. They then allowed the Wolbachia to replicate inside the mosquitoes and fed the mosquitoes a meal of blood that was infected with West Nile virus.
“We were surprised to find that Wolbachia infection did not block West Nile virus in this mosquito,” Rasgon said. “Instead, these mosquitoes had significantly higher West Nile virus infection rates seven days after we fed them the infected blood. In other words, Wolbachia infection allowed the mosquitoes to become infected with West Nile virus faster than our controls.”
Their results are published in the journal PLOS Neglected Tropical Diseases.
“Our results point to a previously unforeseen complication — the possibility that mosquitoes rendered resistant to one pathogen by Wolbachia infection might become better vectors of an alternative pathogen,” Rasgon said.
According to Rasgon, the team suspected that Wolbachia could enhance some pathogens within mosquitoes.
“Multiple studies suggest that Wolbachia may enhance some Plasmodium parasites in mosquitoes, thus increasing the frequency of malaria transmission to rodents and birds,” he said. “We recently published a paper in the journal PLOS Pathogens in which we summarized the current literature of Wolbachia-mediated pathogen enhancement with particular focus on Plasmodium parasites.”
But, he added, the team did not suspect that Wolbachia would enhance mosquito infection with the human pathogen West Nile virus.
“In this study, we were surprised to find that Wolbachia infection enhances, rather than suppresses, mosquito infection by West Nile virus,” Rasgon said.
The team also found that West Nile virus enhancement in the Wolbachia-infected mosquitoes occurred in conjunction with the suppression of genes associated with the mosquitoes’ anti-viral immune response. According to Rasgon, the researchers plan to conduct additional experiments to determine the exact mechanism of Wolbachia-based West Nile virus enhancement in Culex tarsalis.
“This is the first study to demonstrate that Wolbachia can enhance a human pathogen in a mosquito,” Rasgon said. “The results suggest that caution should be used when releasing Wolbachia-infected mosquitoes into nature to control vector-borne diseases of humans.”
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