HSC RESEARCHERS UNMASK SECRETS TO TICK-BORNE ILLNESSES

July 1, 2003

Hiding behind the reputation of its more famous cousin Borrelia burgdorferi, the spirochete Borrelia lonestarihas escaped the notice of researchers who study tick-borne illnesses. Until recently, that is.

Scientists at UNT Health Science Center have turned their attention to B. lonestari, which infects Lone Star ticks, and are developing a test to unmask its secrets.

For years, the scientific community has focused on B. burgdorferi, the pathogen known to cause Lyme disease, and its host, the deer tick. However, B. lonestari is now thought to cause a mysterious malady with Lyme-like symptoms that does not yield positive results with current Lyme diagnostic tests. If left untreated, either infection can lead to more serious ailments, including arthritis, nerve damage, heart problems and death.

â??Nothing is known about this pathogen carried by the Lone Star tick; it hasnâ??t been cultured, has rarely had its DNA sequenced, and has never connected scientifically to the Lyme-like symptoms we suspect it of causing,â? said Phillip Williamson, PhD, a specialist in molecular genetics research and head of the Lyme Disease Laboratory at the health science center. â??Weâ??re changing all that.â?

Dr. Williamson is leading a team of researchers who are studying the Lone Star tick to find out more about the pathogen it carries, B. lonestari.

â??Under the microscope, the spirochetes look the same, but theyâ??re very different genetically,â? Dr. Williamson said. These genetic differences form the basis of the health science centerâ??s screening test for the pathogen.

In 1994, the Texas Department of Health collected more than 28,000 ticks throughout the state. They found that nearly 95 percent of them were Lone Star ticks. â??This survey and our preliminary data indicate that Lone Star ticks should be viewed as a potential health risk to Texans,â? Dr. Williamson said.

The Senate Committee on Administration, chaired by state Sen. Chris Harris, issued an interim report on the prevalence of tick-borne illnesses in Texas in 2000. This report recommended that the state develop a comprehensive diagnostic laboratory to facilitate the creation of a precise and effective diagnostic test for Lyme and other tick-borne diseases. In 2001, the Texas legislature acted on the recommendations and established the laboratory at UNT Health Science Center.

Over the past 18 months, the team has been setting up the lab, collecting specimens and establishing partnerships to further its research and help develop the diagnostic test.

Health science center researchers are collaborating with scientists at the Tick-Borne Disease Laboratory at the U.S. Army Center for Health Promotion and Preventive Medicine at Aberdeen Proving Ground in Maryland to analyze samples from any soldiers who are bitten by a tick. The Army provides the ticks, and the health science center performs DNA sequencing on the samples.

â??We need the tick in order to find the pathogen it carries,â? Dr. Williamson said. â??We now have a constant source of samples from diverse geographic locations.â?

Results are submitted to GenBank, the DNA sequence repository at the National Institutes of Health. â??GenBank contains the DNA sequences for any species,â? Dr. Williamson said. â??We use it to double-check the quality of our sequences and to identify known genetic differences within the species.â?

Since its discovery, only 17 B. lonestari sequences have been published in GenBank. These sequences offer limited insight since many of them were obtained by generating multiple sequences from a single tick sample or a group of samples collected in the same area. When Dr. Williamson and Army entomologist Ellen Stromdahl, PhD, publish their sequences later this year, they will add 67 unique sequences to the database, and they are currently preparing another 80.

â??Weâ??re not only increasing the number of sequences five-fold, but our samples come from 11 different states,â? Dr. Williamson said. â??Although some may think this species is named after the Lone Star State, weâ??re documenting that itâ??s a common parasite from the south-central United States to New England and the entire east coast. Weâ??ve also shown that the species does not vary much, so a single test should work for ticks found in other parts of the country.â?

With little intra-specie variation, researchers can focus their efforts on developing a genetic test that quickly identifies specific species of pathogens and differentiates them from their cousins.

â??Our goal is detecting Lyme disease and other tick-borne illnesses quickly and accurately,â? Dr. Williamson said. â??Weâ??ve developed a very specific test for B. lonestari that will allow us to find out how prevalent this pathogen really is in Texas.â?

In the past year, health science center researchers have demonstrated that the tick is infected with the pathogen suspected of causing Southern Tick-Associated Rash Illness, a disease with Lyme-like symptoms. Currently, they are trying to demonstrate that these ticks actually transmit the disease to humans.

â??Weâ??ve accumulated a tremendous amount of information on the organism, and weâ??ve used that information to make our test better,â? Dr. Williamson said. â??Now we need more clinical samples from recently infected people to demonstrate that the test has a clinical application and not just a scientific one.â?

Dr. Williamson, an assistant professor of pathology and anatomy, is also working with faculty from the health science centerâ??s School of Public Health and the biological sciences department at the University of North Texas in Denton to expand the scope of his research. The team is waiting to hear about possible NIH funding that would allow them to conduct a survey of the tick population in north Texas.

They plan to begin the project this winter by sending a questionnaire to physicians and veterinarians in an 11-county area surrounding Dallas and Fort Worth. Sam Atkinson, PhD, chair and professor, and Terry Gratton, DrPH, assistant professor, both of environmental and occupational health in the School of Public Health, will combine the results with a geographic information system (GIS) to pinpoint habitats where ticks infected with B. lonestari have been found.

UNT researchers will then collect samples from animals in those habitats, and Dr. Williamson would do full genetic analysis on those samples.

â??The process soon becomes a cycle where we use the samples to update the GIS model and use the GIS model to identify places to collect more samples,â? Dr. Williamson said. â??We estimate that weâ??ll analyze more than 10,000 samples over two years.â?

The team would use the information they collect to influence public health policy and develop programs to educate and inform the public about the risks associated with tick bites.

Once it develops a test for Lyme disease and other tick-borne illnesses, the lab will expand its genetics research into other areas. â??Weâ??re developing our test to be flexible so that we can quickly adapt it to identify other pathogens to help with other emerging infectious diseases,â? Dr. Williamson said.

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