“Cat Scratch Fever” might be best known as a catchy song, but the infection of the same name, scientifically known as Bartonella – is an easy-to-catch infection caused by a common, hard-to-detect microbe. But a test developed by N.C. State researchers could make it simpler to pinpoint the pathogen and treat the resulting symptoms.
Using a patented insect medium and a sensitive, sophisticated DNA analysis tool, N.C. State investigators have developed a Bartonella diagnostic test for humans. The goal is to identify Bartonella infections faster and more accurately, and a partnership with Research Triangle Park-based company Galaxy Diagnostics, Inc. could make the test widely available.
“This microbe is one of a handful that physicians who specialize in chronic disease look at now, but a lot of doctors don’t test for it because of the high false-negative rates. If you don’t know exactly what to look for or if you don’t have the tools, why look for it?” said Amanda Elam, Galaxy Diagnostics president. “We think we’ve found a way to identify the bacteria, and we’re helping to find it in patients with this test.”
Currently, there are more than 25 known Bartonella strains, and roughly nine have been linked to disease development in humans.
However, diagnosis is challenging because it only takes a few Bartonella particles to prompt an infection. Small amounts mean even highly sensitive tests, such as DNA analysis with the help of polymerase chain reactions (PCR), often yield false negatives.
“Locating Bartonella is like finding a needle in a haystack with the infection being the needle and the haystack being the patient,” said Ed Breitschwerdt, internal medicine professor at N.C. State’s College of Veterinary Medicine. “If the haystack is too big and there are only a few needles, PCR will miss the infection more often than not.”
How the test works
Getting a Bartonella diagnosis faster means relying on the bugs that carry it, said Breitschwerdt, who led the test’s development team.
“During our 15 years of research, it became obvious many different insects – sand flies, lice, fleas, biting flies on cattle, and ticks – were confirmed Bartonella carriers,” Breitschwerdt said. What made his research different was finding the way to grow Bartonella more quickly in a Petrie dish.
“We asked whether Bartonella would be happier in an insect-growth medium compared to mammal-growth. It’s not too sophisticated a question, but it proved important because the answer was yes.”
To identify an infection, scientists kick-start Bartonella growth by putting a small ( 4 milliliter) blood sample into an insect growth medium called Bartonella alpha Proteobacteria Growth Medium that stimulates bacteria production. Within 10 days, there are enough bacteria present in the blood for a PCR test to yield an accurate diagnosis. Through a series of up to 40 temperature changes, PCR produces multiple copies of any bacteria DNA present, allowing scientists to definitively determine whether Bartonella is present.
The entire process – from petrie dish to verified results – takes between two to three weeks, said Galaxy’s Elam. Scientists can also run the test using non-blood bodily fluids or tissue samples.
Testing teams at Galaxy Diagnostics run PCR analyses on patient samples before inserting it into the insect growth medium in order to accurately gauge the bacteria’s growth. They also determine which Bartonella strain is present by running DNA sequence verification.
According to company data, the enhanced PCR analysis is four to five times more sensitive than the traditional PCR technique used to pinpoint the bacteria in the bloodstream, Elam said. With this extra sensitivity, Breitschwerdt estimated the tests will accurately diagnose between 80 percent to 90 percent of tested individuals who have Bartonella infections.
But identifying the pathogen is only part of the battle, he said.
“Our major contribution is that we’ve gone from thinking this bacterium only occurs in immuno-compromised patients or people with cat scratch disease to knowing there are quite a few people out there in specific populations who have this bacterium in their blood,” he said. “Now, we need research to find out what it means for patients to have this bacterium in their bloodstream.”
Proceeding with caution
Terry Yamauchi, M.D., an Arkansas Children’s Hospital pediatrician with infectious disease expertise, agreed with Breitschwerdt. While the insect growth medium-enhanced PCR is a valid method of identifying Bartonella, the analysis should not be a stand-alone clinical tool.
“The test itself seems to be scientifically very sound – growing more of the organism you’re searching for to improve test sensitivity will be helpful,” he said. “However, I worry about putting all our treatment-plan bets on this test because there’s little hard-core evidence indicating Bartonella is responsible for the chronic effects attributed to these infections.”
Until additional investigations into Bartonella yield a more definitive link between the bacteria and long-term symptoms, he said, physicians should opt to pair the test with traditional clinical observation and assessment.