Lyme disease is the most common tick-borne disease in the United States, with about 30,000 cases reported annually to the Centers for Disease Control and Prevention (CDC). In August, however, the CDC indicated that the number of Americans diagnosed with Lyme disease is closer to 300,000.
"Underreporting has led to the appearance of lower disease rates in recent years. The CDC recently estimated that just 10% of actual cases were being reported," said Stephen M. Rich, PhD, professor of microbiology and director of the Laboratory of Medical Zoology at University of Massachusetts Amherst in Amherst, Mass.
"An increase in the number of cases may be related to climate change which has resulted in increased density and broader geographic distribution of the Ixodes tick population," said Jerry M. Zuckerman, MD, chief quality and patient safety officer with Einstein Healthcare Network in Philadelphia, Penn.
The steady growth of ticks and tick-borne diseases in Northeastern United States is due in large part to the rapid proliferation of deer in the region, Rich explained.
"Lyme disease is a zoonosis, meaning it is maintained in wild populations of animals (mostly white-footed mice) and spills over into humans," said Rich. "Although deer don't carry Lyme disease pathogens, they are important because ticks need to have deer around to reproduce."
The increase of Lyme disease has been reported based on various surveillance techniques that look at clinical records, laboratory reports and public surveys.
Testing and Diagnosis
The ability to diagnose a patient with Lyme disease depends on how the disease has progressed.
For patients with erythema migrans rash, the diagnosis is established by clinical evaluation. "The rash is diagnostic and there is no role for serologic testing in very early disease," explained Zuckerman. "Serologic tests will be negative for antibodies for the first 2 to 3 weeks."
For patients presenting with later manifestions of Lyme disease, the current recommended approach is a two-tier testing method, Zuckerman told ADVANCE. According to the CDC, the same blood sample can be used in both tests for evidence of antibodies against the Lyme disease bacteria, Borrelia burgdorferi.
First, an enzyme-linked immuno assay, or ELISA, should be performed to detect and measure antibodies in the blood. A negative result requires no further testing. If the test is positive, Zuckerman said, then a confirmatory immunoblot test commonly called the Western blot test, should be performed. The diagnosis is confirmed if 5 of the 10 bands are positive on the Western blot.
"Patients who are asymptomatic or have no objective symptoms or findings that may be suggestive of Lyme should not be tested," Zuckerman shared. "Seropositivity alone is not sufficient to make the diagnosis of Lyme disease."
According to Zuckerman, the FDA-approved VLsE C6 ELISA test may have increased sensitivity for certain subtypes of the spirochete that causes Lyme. "It also may detect infection earlier compared with current ELISA," he said. "PCR can also be used on synovial fluid or CSF samples to detect Lyme. False positives are common and sensitivity is low for CSF fluid."
Measuring Exposure Risk
"Debate surrounds the means and interpretation of clinical Lyme testing," said Rich. "This is due to the nature of the infection itself but also hinges upon the need for clearly defining the association between disease and infection status."
To clarify the necessity of his work, he likened it to radon testing. Radon testing is used to measure the risk of exposure to cancer causing agents, not to determine a diagnosis of human disease. "The tests we conduct in our lab are not intended to provide a clinical diagnosis, but rather serve as a measure of exposure risk," Rich explained. "Having information about exposure history, whether radon, second-hand smoke or tick bites, can be relevant to a circumspect clinical diagnosis," he explained.
Because people don't get infected with Lyme by other people, standard epidemiological approaches such as those used to measure incidence of cancer or flu are of limited use for Lyme disease, Rich observed. "Two distinct kinds of surveillance, the epidemiological and the entomological, reveal different aspects of risk assessment for humans," Rich said.
The medical zoology lab at UMass provides the missing link to these two aspects. "We test ticks that are on human patients for Lyme and a variety of other pathogens," Rich explained. "This process lets us determine who is being bitten (age, location, etc.), when they are they are being bitten (month/season), and what the biting tick is carrying around (pathogens)."
According to Rich, although the epidemiological-entomological combination approach is a powerful tool for assessing risk, it should not be confused with clinical diagnosis. "The infection status of a given tick is just one factor in determining whether the individual will develop disease," he explained. "But knowledge of the tick's infection status (particularly for rare pathogens such as Anaplasma or the tularemia bacterium) can change the dialogue between patient and doctor and may facilitate diagnoses that would otherwise be overlooked."
The lab at UMass collects ticks to be tested for Lyme and nearly a dozen other pathogens. For more information on how you can be a part of this important research, please visit: www.tickdiseases.org
Rebecca Knutsen is on staff at ADVANCE. Contact: firstname.lastname@example.org.