In the early days of the COVID-19 pandemic, questions like "How long after being infected will I be symptomatic?" and "How quickly will I clear the virus?" were important to answer for scientists working round the clock to model the virus and help save lives.

A new journal article by Kathryn Hanley, a New Mexico State University biology professor with more than 20 years' experience tracking viruses that spillover from animals into human populations, is providing answers to some of these questions regarding dengue and Zika virus.

Hanley's most recent research on the transmission of these infectious diseases is published in the journal "Nature Communications" in April. Link here.

"I have been extremely interested in spillover of pathogens from wildlife, particularly monkeys, into humans," Hanley said. "And once those viruses have spilled over from monkeys into humans, humans have the capacity to move them worldwide."

Hanley's postdoctoral fellow Helene Cecilia is the co-first author of the paper. Ben Althouse, an affiliate faculty member at NMSU, is also part of the research team along with several undergraduates working in Hanley's lab as well as collaborators at the University of Texas Medical Branch. 

Hanley's team took two species of monkey, an old world primate and a new world primate, and infected both with either dengue virus or Zika virus. Zika virus was very prominent in 2016, causing microcephaly in the developing human fetus. Currently, Brazil is experiencing a historic outbreak of dengue with no end in sight, and the virus has spread across the Caribbean, causing what's called "break bone fever" as well as dengue hemorrhagic fever.

"The monkeys were infected by mosquitoes, which is how viral infections happen naturally," Hanley said. "So, when an organism is infected by a mosquito, it doesn't just get injected with the virus, it gets injected with mosquito saliva proteins, whose make up is very complex cocktail of proteins, which changes the whole immune response to the virus."

The monkey samples and the mosquito samples were all shipped to Hanley's lab, where members of her team performed quantification and statistical analysis of the data. During the process of monitoring transmission from monkeys back to uninfected mosquitoes over the course of 28 days, Hanley's team identified a detailed picture of transmission for both Zika and dengue.

"We discovered that Zika virus infected the new world monkey extremely well and was transmitted extremely efficiently," Hanley said. "That's important because Zika virus is circulating among people in the Americas. Our results suggest it very likely to spill back into monkeys and establish a forest cycle of transmission. The other discovery we made is that dengue virus, although we had a hard time even detecting it in the monkeys, can be transmitted even at very low levels of virus back to mosquitoes."

Currently, there is no cure for either dengue or Zika virus so everything scientists can learn about how those viruses are regulated gives them a window to find a cure. While monitoring immune responses to the virus, Hanley's team recognized something unusual.

"We found that natural killer cells, which are a kind of immune cell, were highly correlated with patterns of replication," Hanley explained. "This suggests that these cells are very important in shaping the dynamics of infection. Once we know the dynamics of the infection, maybe we can intervene."

During the next steps of Hanley's research, her team will take the data they have acquired and put it into their mathematical models to answer other significant questions.

"We'd like to know whether Zika virus can be sustained in a cycle in American monkeys," Hanley said. "It looks like it can, but that's a good question to use a model to answer. The other thing we'd like to know is how is it that dengue is being transmitted at these very, very low viral load levels not typical of other viruses. We need to investigate with more experiments."

The full article can be seen at https://newsroom.nmsu.edu/news/nmsu-professor-s-research-links-monkeys--mosquitoes-and-natural-virus-killers/s/8e9e6876-d15d-41ae-aa4e-274bd5f117b8