Patterns of infection

In the field of infectious diseases, Vanessa Ezenwa (EH-zen-wa) looks at the big picture. Her interest in “community ecology”—like how an infection by one type of parasite or of one type of host can ripple across other species —has taken her from the wetlands of Louisiana to the savannahs of Kenya and South Africa. Lately, that quest has driven Ezenwa to France, for a Fulbright-backed study of the ecology of infectious diseases in humans.  

Like many students attracted to the life sciences, Ezenwa started on the pre-med track when she was an undergraduate at Rice University in Houston, Texas. However, after her first taste of ecology research in the lab, she switched gears and pursued a PhD in ecology and evolutionary biology at Princeton. “What was more interesting than pursuing medical school was asking questions about how things work,” said Ezenwa. “Or, instead of using the knowledge, discovering the knowledge.”

After teaching for five years at the University of Montana, Ezenwa was offered the chance to come to UGA in 2010. With her unique research experience, she was jointly appointed to the Odum School of Ecology and the CVM’s Department of Infectious Diseases. Such a position sounds extraordinary—but there are four other faculty with similar appointments at UGA.

Now an associate professor, Ezenwa studies parasites in wild mammals, but her research addresses major public health concerns. One of Ezenwa’s primary study subjects—parasitic worms, or helminths—infect about a third of the world’s population. In her study at Kruger National Park in South Africa, she looked at African buffalo infected with both worms and bovine tuberculosis to see how infection with each of the two pathogens would affect the host response to the other. Ezenwa treated half the buffalo for worms, and left the other half alone. As a result, the treated buffalo were nine times more likely to survive TB infection—but these survivors may continue to infect other individuals with TB within the population, potentially increasing the spread of TB. The results of the study were published in Science in January (http://tinyurl.com/nuqqtut).

Just as the interactions between two pathogens in one host can shake up the population’s overall health,  one pathogen can also behave in unexpected ways when introduced to multiple types of hosts. For her postdoctoral research, Ezenwa looked at how the West Nile Virus spread between various bird and mosquito species in the wetlands of Louisiana. In this case, the variety of hosts slowed the transmission of the virus. 

The rationale behind this is still up for debate. “One reason could be that not all hosts are equal in their ability to allow the virus to grow,” said Ezenwa. “Some species are just bad hosts. In terms of West Nile virus, bad hosts might slow the rate of transmission by keeping mosquitos from biting hosts that would provide a more favorable species for viral growth.”

Ezenwa also observes animal behaviors and how they relate to the spread of an infection. In Kenya, she’s seen how male Grant’s gazelles accumulate more parasites through their aggressive mating strategies and how—at the same time—those parasites suppress the gazelles’ ability to mate.

“All of the dynamic variability that we see—like when the male defends a territory in order to gain mates, and then  suddenly stops —might be driven, in part, by the parasites in the system,” said Ezenwa. “You can’t understand that behavior without understanding this driving force.”

Ezenwa’s research in France draws on her experiences working on wild animal systems to examine infectious diseases in people. Rather than creating new data, she gathered datasets from one species—humans—on several diseases, including tuberculosis, malaria and worm infections. 

Ezenwa first traveled to France in 2013, when a group of scientists invited her to a discussion on a familiar topic—the diversity of species and its impact on the spread of disease. “From meeting those colleagues, I thought, ‘Oh, this would be a great place to come and work with them more on this topic,’” said Ezenwa. So she applied for a Fulbright and was rewarded with the opportunity to spend six months in France on her proposed project. (Ezenwa was one of five UGA faculty members to receive a Core Fulbright Scholar Award for 2014-2015, and she is the third CVM faculty member to receive one within the last four years.)

Ezenwa is now back at UGA searching for patterns in the data she gathered while in France. “The nice thing about the Fulbright was the opportunity to really get this project started,” she said. 

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