By Rose Hoban
There are few diseases more controversial than Lyme disease.
The tick-borne virus has been the subject of debate over how many cases occur in the U.S. annually, the correct test and the correct treatment for chronic cases of the disease and whether the chronic form of the disease even exists.
But there are a couple of things that are less subject to debate: that you’re vastly more likely to get Lyme in the Northeast, where the disease was first identified, or in the upper Midwest, where it’s becoming more widespread.
Now there’s increasing evidence that Ixodes scapularis ticks bearing Borrelia burgdorferi, the bacteria that causes the disease, are becoming more common farther south, increasing the risk of contracting the disease in North Carolina.
Video showing the spread and geographical distribution of Lyme disease-bearing ticks since 2000. Maps courtesy CDC
A recent paper published by researchers from the Centers for Disease Control and Prevention mapped the geographic distribution of confirmed Lyme cases and data showing the geographic distribution of where I scapularis (commonly known as blacklegged ticks) were found to be carrying B. burgdorferi to define “high-risk” counties. The research indicated a slow, but steady, spread of increased risk areas extending down the Appalachians.
“Our results show that geographic expansion of high-risk areas is ongoing, emphasizing the need to identify broadly implementable and effective public health interventions to prevent human Lyme disease,” wrote the authors, who published their findings in the August issue of Emerging Infectious Diseases.
Spreading south
“Over the past 15 years, you can see a clear progression of the disease from the DC area along the foothills, almost to the North Carolina border,” said State Public Health Veterinarian Carl Williams. “We see cases reported in North Carolina in areas immediately south of what appears to be an emerging area in southwestern Virginia.”
Williams said he’s specifically concerned about Allegheny and Wilkes counties, and expects to start seeing the numbers of cases climb there.
“We’ve been in a position where Lyme disease cases were a much lower incidence rate here, but we’ve seen the incidence rate for Lyme really increase in Virginia,” Williams said.
“The real challenge in North Carolina is that we’re next to an endemic state,” said Duke University infectious disease researcher Paul Lantos.
Lantos said that a look at the epidemiology of Lyme in the Southeast since 2000 indicates that there are about 11,000 confirmed cases, and all but 1,000 of those are in Virginia.
“There’s been a dramatic expansion in Virginia over this time,” he said. “What we found is that northern Virginia has intensified, but there’s also been a rapid expansion down the Appalachians into Blacksburg and Roanoke possibly.”
Lantos also said ticks collected by researchers in Virginia back up the epidemiology.
Jory Brinkerhoff, a researcher at the University of Richmond, saw an increase in the number of Lyme diagnoses, and determined there were probably infected ticks in those areas.
When Brinkerhoff went looking, he found big populations of blacklegged ticks at higher elevations, and many of those were carrying B. burgdorferi.
“When you’re looking at case data, you take it with a grain of salt,” he said. “But corroborated with tick data, you can see there’s a lot of opportunity for infection because there are the ticks crawling around.”
Already here?
But some say Lyme is much more prevalent in North Carolina than this research shows. Included among them is Marcia Herman-Giddens, who advises the Tick-Borne Infections Council of North Carolina.
Herman-Giddens, who teaches at UNC-CH’s Gillings School of Global Public Health, said part of the story of underdiagnosis has to do with how Lyme is diagnosed, using a two-step series of tests for antibodies that she said is overly strict, ruling out any cases where the reading might be equivocal.
In addition, she said, those borderline cases can be misinterpreted to mean there was no disease.
“There’s not a good test, and there’s not a test of cure,” she said, while allowing that it can be difficult to prove the absence of disease for most diseases. She noted that part of the problem with Lyme is that once someone is exposed to B. burgdorferi their bodies will make antibodies for years, which will then be detected on a subsequent test.
“People do stay positive for some of the [readings] of the test, sometimes for years,” Herman-Giddens said. “So one of the areas is that if people get sick again, and you get another tick bite, then it’s really a mess. They may have antibodies from a previous infection.”
She drew some comfort from an update sent to medical providers around the state by the North Carolina state epidemiologist this April. The memo reminded doctors that testing fewer than two weeks after a rash was not enough time for the antibodies to form.
That memo also noted the presence in North Carolina of another tick-borne disease that’s been dubbed STARI, for Southern tick-associated rash illness. But STARI is caused by the bite of a different species of tick, and researchers are still unsure of what bacteria actually causes it.
“[STARI is] impossible to distinguish from early Lyme disease,” Lantos said. “So I think a lot of cases in North Carolina are diagnosed as Lyme disease because you can’t distinguish between the two.”
Everyone agrees that having around more than one tick-borne bacteria that creates similar symptoms confounds the situation and adds to the controversy over identification, diagnosis and treatment for both diseases.
This year, the Centers for Disease Control and Prevention revised their estimates for annual Lyme disease diagnoses dramatically upwards. For years, the agency counted only cases reported by state health departments, tallying about 30,000 cases per year.
But looking at lab and insurance data yielded many more diagnoses, coming in at anywhere between 288,000 and 329,000 cases per year nationally.
While Herman-Giddens pointed to this revision as evidence of overdiagnosis, Lantos argued there are a lot of false positives in the testing for Lyme, and that people who really had STARI were treated for Lyme using powerful antibiotics, potentially causing harm.
“There probably are more cases,” Lantos conceded. “The range is getting larger and we are diagnosing it more and have more sensitive surveillance to capture more patients.”
Things people can agree on
No matter the controversies over diagnosis, everyone agreed that there’s more of an issue with tick-borne diseases. And all the researchers in North Carolina bemoaned the dismantling of the state’s public health entomology unit in 2011, after it was defunded by the General Assembly. The group had been tracking the presence and spread of insect-borne diseases in the state.
Now that Lyme is poised to really take off in North Carolina, such a group would be a valuable addition to the work of TickNET, a collaboration of academics and state and federal public health entities focused on tracking, researching and preventing tick-borne diseases.
Another point of agreement was that people need to do a better job at preventing tick bites. That includes wearing long pants into the woods and gardens, tucking pants into socks and using insect repellents like DEET.
“People don’t realize you have to rub the DEET into your skin,” Herman-Giddens said. She also has found that permethrin-impregnated clothing is effective at keeping ticks off of her when she leaves her Chatham County house to go into the woods.
She also suggested saving any ticks you pull off of yourself. She tapes the tick to a card and writes the date on it, along with the place on her body where it was biting.
“If you walk into a doctor’s office with a tick on a card, that makes a difference,” she said. “And if someone is knowledgeable, they can identify the tick.”
The guidance from the state epidemiologist noted that five North Carolina counties are now defined as “endemic,” meaning that at least two lab-confirmed cases have been identified in people who did not travel outside their county of residence during the month-long disease-incubation period. Those counties are Allegheny, Guilford, Haywood, Wake and Wilkes.
“A lot more is headed in this direction, and the ticks don’t know from Virginia,” Lantos said.
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