Exploring how ticks carrying the Bourbon virus move through wildlife and humans

On a cold spring morning, virologist Jacco Boon, PhD, of Washington University in St. Louis, and wildlife ecologist Solny Adalsteinsson, PhD, wave and drag a large white flag through a wooded area in the western end of St. Louis County. Boon, an associate professor of infectious disease medicine at Washington University School of Medicine in St. Louis, and Adalsteinsson, a principal investigator at the university’s Tyson Research Center, are looking for lone ticks carrying the potentially deadly Bourbon virus.

Earlier this year, the two – along with David Wang, PhD, Robert C. Packman Professor of Molecular Microbiology in the School of Medicine – published a paper in the journal Tick and Tick-borne Diseases showing that about one in 150 lone star ticks in the Saint-Louis area carry the virus. By scouring the woods for the tiny but potentially dangerous arachnids, researchers hope to learn more about the location of ticks carrying the Bourbon virus to better understand how the virus spreads through wildlife and humans.

The technique – known as tick flagging – sounds weird, but it works. After about 15 minutes of beating and sweeping through the university’s Woodsy Tyson Research Center, an environmental field station for faculty, staff, and students, Adalsteinsson stops and carefully plucks a single blackhead from the fabric with a pair of pliers. It’s a lone star tick, so small it’s barely visible between the delicate metal spikes. They take him inside Adalsteinsson’s research lab for further study.

“Tick-borne diseases are becoming more common. There are several reasons for this,” Boon said. Since he began studying the Bourbon virus, Boon has received more than $4 million in grants from the National Institutes of Health (NIH). He is principal investigator on two NIH grants and co-investigator on two other grants to study the virus.

Matt MillerJacco Boon holds a solitary tick collected at the University of Washington’s Tyson Research Center. Solitary ticks can carry the potentially deadly Bourbon virus. Boon and his colleagues are studying this virus and how it spreads through wildlife and humans.

With climate change, winters are warmer and more ticks are surviving the winter. Urban areas are greening up, which is a good thing, but all these new green spaces are attracting white-tailed deer and coyotes, and with them ticks. My expertise is in virology, but since I started working on the Bourbon virus, I’ve realized that the only way to understand and solve the problem of tick-borne viruses is to also understand what’s going on. in the environment and among wild animals carrying ticks.”

Jacco Boon, PhD, virologist, Washington University in St. Louis

The virus was named after where it originated: Bourbon County, Kansas. The first case was discovered there in 2014, in a man who died of the disease. Since then, there have been only four other documented cases, including one further death – statistics that make the Bourbon virus seem rare but deadly. However, a Boon study published last year in the journal mSphere showed that a surprisingly high percentage of people in the St. Louis area have antibodies to the Bourbon virus, suggesting many people may have been infected. and never knew it.

To understand how the newly identified virus is affecting residents of the St. Louis area, Boon is collaborating with Adalsteinsson and Sharon L. Deem, DVM, PhD, wildlife veterinarian and epidemiologist at the St. Louis Zoo. This triad of researchers represents a commitment to One Health, or the framework that human health is intertwined with animal and environmental health.

The first evidence of the Bourbon virus in the St. Louis area came in 2017, when a woman was admitted to Barnes-Jewish Hospital with a fever, rash and body aches that turned out to be be caused by the Bourbon virus. There is no specific treatment for the Bourbon virus infection – finding an effective therapy is something Boon is still working on – and she eventually died of the disease. Boon and his team cultured the virus from the St. Louis patient and used it to develop a mouse model of infection, which allowed them to study how the virus behaves in the body. The mouse model has also helped lead to potential drug therapy, although the drug in question has not progressed to clinical trials. Researchers have also developed a way to test anti-Bourbon virus antibodies in the blood.

“We have now tested blood samples from 1,500 people in the St. Louis area,” Boon said, referring to the mSphere study. “Of these 1,500 randomly selected individuals, five have antibodies against the Bourbon virus. This is a very small number, but it is still a very important number, because it means that the Bourbon virus infection is much more common than we previously thought.” The fact that it was so easy to find five other infections suggests that many people were likely infected without becoming seriously ill, Boon said.

People become infected with Bourbon virus when they are bitten by a lone star tick that has acquired the virus from an infected animal. Deem’s part of the project is focused on understanding how local wildlife may be affected by the virus and how it may play a role in the epidemiology of the virus.

“Our work reveals information that is critical to understanding the epidemiology of emerging pathogens that may threaten wildlife conservation and human health,” Deem said. “We can achieve this by understanding how pathogens move among wildlife in the region and how animals can serve as hosts for ticks and viral pathogens.”

Deem leads a collaborative initiative based at the Tyson Research Center that includes the zoo, the University of Washington, and the Endangered Wolf Center, a wolf conservation nonprofit located on property owned by the Tyson Research Center. The initiative is dedicated to studying the movements of local carnivores such as foxes, coyotes and bobcats, as well as the diseases they carry. During the colder months, Deem’s team traps the animals and examines them, including taking blood samples to test for various infections. Then they tag and sometimes place a tracking device on the animals before releasing them unharmed. Antibodies against the Bourbon virus have been found in most of the animal species trapped. The team also collects ticks directly from the trapped animals, and the presence of the Bourbon virus is also studied within these ticks.

Matt MillerJacco Boon, left, and Solny Adalsteinsson examine a lone star tick under a microscope at the Tyson Research Center.

During this time, Adalsteinsson collects ticks in the environment along with detailed data on nearby habitat characteristics and wildlife community, and coordinates blood and tick collections from deer shot by hunters. She sends the ticks she collected to Boon’s lab to be tested for the Bourbon virus. With Boon’s help, Adalsteinsson was able to identify hotspots in Tyson, or geographic areas with a high proportion of Bourbon-positive ticks. By identifying the environments most conducive to the proliferation of tick species or the Bourbon virus, she hopes to learn more about the drivers of transmission.

“I’m interested in linking the concepts of ecology and conservation to human health,” Adalsteinsson said. “There are many aspects of tick biology and tick-borne diseases that explicitly show how how humans interact with and manage their environment can impact their own health.”

There is still a lot of work to do. Boon is working to learn more about the basic biology of the virus, like how it enters cells, as a first step toward developing drugs and vaccines. Going forward, the interdisciplinary One Health team aims to better understand how the virus spreads through wild animals, and where and how animals and people become infected. One of the objectives is to identify so-called reservoir species, the animal species that harbor the virus and keep it circulating. This information is crucial for designing effective intervention strategies. Another goal is to find out how long it takes for a tick to transmit the virus to a person, which will indicate how often people should check themselves for ticks.

“There’s still so much we don’t know,” Adalsteinsson said. “We know the species of ticks that transmit the virus, but we don’t know which wild hosts might be involved in maintaining them. We don’t know the full extent of the range where they might occur. We have a lot basic information questions, and by bringing together our complementary expertise, we are making progress towards finding answers.”

Stay safe during tick season

Solitary ticks are most common in the St. Louis area from March through October, although other ticks can be found year-round. To protect yourself from tick-borne infections, experts recommend that you:

• Wear long pants, long sleeves, and insect repellent when outdoors in grassy, ​​brushy, or wooded areas.
• Perform a full body check for ticks after spending time outdoors. If you find a tick, carefully remove it with tweezers as recommended by the CDC.
• See a doctor if you develop a rash or fever within weeks of removing a tick.