Those infected with the dengue or Zika virus secrete a substance that attracts mosquitoes. However, it is not produced by the cells themselves, but by special bacteria on the skin, which multiply better because of the infection, reports a working group led by Gong Cheng from Tsinghua University in Beijing. As she explains in “Cell,” flaviviruses suppress the skin protein RELMα, which keeps bacteria in check. This multiplies bacteria that produce the substance acetophenone – in experiments, the molecule proved to be a strong attractant for mosquitoes that spread the virus. The team also writes that the effect can be reversed by mixing the acne drug isotretinoin into food, which stimulates the production of RELMα.
The study is based on the working group’s finding that mosquitoes prefer to bite mice infected with dengue or Zika. Both viruses spread by being transmitted from host to host by mosquitoes, so it makes sense for them to make an infected organism more attractive to mosquitoes. To find out how this works, Cheng’s experts analyzed the body odor of infected mice and humans for molecules that attract mosquitoes. They found that the hosts secreted unusually large amounts of acetophenone – about ten times as much as uninfected organisms.
The working group then examined which genes were suppressed the most in infected cells. They came across the gene Retnla, which was very strongly suppressed in skin cells; this gene produces the protein RELMα (resistin-like molecule α) in mice and the closely related protein RETN in humans. While the group only demonstrated that RELMα is less common in infected mice, the same is likely true of RETN in humans. In experiments on bacterial cultures, both molecules suppressed the growth of various skin bacteria. Conversely, acetophenone-producing organisms preferentially colonized the skin of infected mice.