NIH Invests in Young Researcher's Disease Modeling

Holly Gaff, a mathematical ecologist for Old Dominion University's College of Health Sciences and Virginia Modeling, Analysis and Simulation Center (VMASC), is the third young ODU faculty member whose research is being promoted by a career development grant of around $500,000 from a prestigious national funding agency.

Gaff's award from the National Institutes of Health (NIH) supports her innovative research using mathematical modeling to study human monocytic ehrlichiosis (HME), an emerging tick-borne disease.

Also working currently under National Science Foundation (NSF) career development grants are Michael Nelson, assistant professor of computer science, and Min Song, assistant professor of electrical and computer engineering.

There has been a dramatic increase in tick-borne diseases throughout the United States and worldwide over the last 10 years, Gaff said.

"While many Americans are familiar with Lyme disease and Rocky Mountain Spotted Fever, other lesser known tick-borne diseases occur with increasing frequency, causing additional morbidity and mortality," she said. HME, which has been tracked only for a couple of decades, jumped from 142 reported cases in the United States in 2001 to 506 in 2005, and the geographic range of the disease also has expanded, she said.

The NIH award to Gaff was made last year, not long before she joined the ODU faculty. The university's Research Foundation announced early in April 2008 that administration of the grant had been moved to ODU.

ODU administrators and colleagues pointed out the research boost Gaff is providing both to the College of Health Sciences, where she serves as an assistant professor of community and environmental health, and to VMASC, where she is part of the medical and healthcare modeling and simulation cluster.

Mohammad Karim, ODU vice president for research, said Gaff's work is cutting edge. "Mathematical models of how diseases spread and transform over both time and space are becoming vital to our efforts to combat diseases," he explained. Andrew Balas, dean of the College of Health Sciences, agreed. "We are proud that our colleague, Dr. Gaff, is in the forefront of this exploration."

"She is an impressive young researcher," added Stacey Plichta, the chair of the School of Community and Environmental Health. "We are delighted that she has this award."

Gaff, whose NIH project is titled "Spatially-Explicit Mathematical Model of Human Monocytic Ehrlichiosis," said one of the biggest challenges to understanding tick-borne disease outbreaks is that they seem to occur unpredictably. "Given the unique and very complicated life history of ticks, it is difficult to study the disease in nature," she explained. "Many scientists have spent their lives devoted to exploring these fascinating creatures. Mathematical models provide an invaluable tool to explore the dynamics of tick-borne diseases such as HME."

The researcher began working on mathematical models of HME during her graduate work at the University of Tennessee, Knoxville, where she received her doctorate in mathematics in 1999.

Following an outbreak of HME at a retirement golf facility in Cumberland County, Tenn., Gaff worked with the Entomology Department at UTK to predict the impact of tick eradication efforts on the long-term risk of HME in the area. Although the work used a simple model, it was effective to predict that the eradication efforts would reduce the risk of HME at a greater percent reduction than even the reduction in tick population, she said.

This work led Gaff to pursue mathematical modeling of tick-borne diseases as a larger part of her career research interests. She began exploring options to obtain funding for work in that area, and was successful with NIH. Her grant, which extends until the spring of 2011, provides support for halftime academic year release as well as summer salary.

The results of her modeling work will be new insights into the spatial and temporal distribution of human tick-borne disease outbreaks, she said. Insights into the distribution patterns can be helpful for notification of medical professionals to be watchful for influxes of patients with tick-borne diseases, which otherwise may be misdiagnosed. Additionally, the analysis of the model will provide guidance for more effective control strategies aimed at reducing the numbers of HME cases, she said.

In the United States, human diseases caused by Ehrlichia bacteria have been recognized since the mid-1980s, and they have been identified mainly in south central and southeastern states. HME is caused by Ehrlichia chaffeensis and is spread by the Lone Star tick, Amblyomma americanum.

HME sometimes is deadly, but it more commonly causes damage to kidneys, lungs or other organs. It is treated with antibiotics.

Gaff's work benefits from the expertise of ODU's long-time tick researcher, Daniel Sonenshine, emeritus professor of biological sciences, who serves on her mentoring committee. Other mentors include Steve Dumler of The Johns Hopkins University School of Medicine; Abdu Azad of the University of Maryland, Baltimore; Rick Ostfeld of the Institute for Ecosystem Studies; and Denise Kirschner of the University of Michigan School of Medicine.