Detecting tick-borne diseases (TBDs) can be tricky, but increased awareness and better diagnostics can help reduce false negatives.

By Ann H. Carlson

Tick-borne diseases (TBDs) are notoriously difficult to diagnose. In the first few days and weeks after infection, patients may experience flu-like symptoms, such as fever, headache, and nausea, that mimic a variety of more common illnesses. If patients are unaware they’ve been bitten by a tick—especially if they live in a region where tick bites are less common—their physicians may not order tests to diagnose or rule out TBDs.

“There’s a lot of misdiagnosis; there’s a lot of missed diagnosis,” says Timothy J. Sellati, PhD, chief scientific officer for the Global Lyme Alliance, Stamford, Conn.

Months or even years after the initial bite, untreated TBDs such as Lyme disease can produce severe late-stage symptoms, including partial facial paralysis, inflammation of the joints and heart, and cognitive impairment. Left untreated, TBDs can even lead to fatal complications. Unfortunately, severe symptoms, too, can easily be mistaken for other illnesses.

It’s no wonder, then, that it is difficult to determine the exact number of active TBD cases in the United States. The Centers for Disease Control and Prevention (CDC) received reports of 50,865 TBD cases in 2019 – a slight increase from 47,743 cases in 2018.1

However, the CDC acknowledges that cases are significantly underreported. For example, only about 35,000 cases of Lyme disease, by far the most common TBD, are reported to the CDC annually. This likely represents less than 10% of actual cases. To account for this discrepancy, the CDC recently upped its estimate of diagnosed and treated Lyme disease cases from 300,000 to 476,000 annually, based on insurance data from 2010 to 2018.2

“While the absolute numbers of emerging tick-borne illnesses remain low, it is certainly the case that they are increasing,” says Andy Lane, PhD, an Independent Consultant, previously commercial director at The Native Antigen Company, a U.K.-based manufacturer of antigens and antibodies for infectious diseases. “Of course, this might be due to increased awareness, but it is also due to increasing exposure of people to ticks with higher levels of outdoor activity, and also due to climate change, which has the potential to increase the geographical range of ticks.”

Tick-Borne Diseases Detection Deficits

Even when patients know that they have been bitten by a tick, diagnosing TBDs is tricky. False negatives are very common, particularly when patients are tested in the early stages.

“Direct detection of some pathogens that cause tickborne diseases can be challenging because many of these agents reside only briefly in the bloodstream or are present in very low concentrations,” says Kate Fowlie, public affairs for the National Center for Emerging and Zoonotic Infectious Diseases at the CDC. “Also, unlike with some diagnostics, such as bacterial blood cultures that can be used broadly to identify a number of potential pathogens, most tick-borne disease testing is pathogen-specific. This means that clinicians must suspect either a specific pathogen or group of pathogens and order either a specific test(s) or tick-borne test panels that bundle together multiple tests.”

For example, Lyme disease can be very difficult to detect because of the lack of bacteria present in a given patient’s blood sample. “The problem with Lyme disease is that the bacteria hides really well,” says Gerrit Mueller, director of project management for Gold Standard Diagnostics, Davis, Calif., which specializes in Lyme disease diagnostics. “So, you might get infected, you might have some symptoms for a couple of weeks, but then it goes away, and you might have nothing for a whole year.”

Further complicating the issue, no single testing method successfully detects every tick-borne pathogen equally well.

“In my opinion, molecular-based assays, e.g., PCR, are generally the most sensitive for pathogens that infect blood elements, such as Anaplasma and Ehrlichia,” says Franklin Moore, MD, director of molecular pathology at Baystate Health, Springfield, Mass. “However, for pathogens such as Borrelia [the bacteria that causes Lyme disease], blood may not always be the most sensitive specimen type. In these cases, antibody testing, while taking longer to become positive, may still be the best assay, which is why serology is still the gold standard for diagnosing Lyme disease.”

New Testing Methodologies

Until recently, that gold standard, a two-tiered testing system put in place by the CDC in 1994, was traditionally defined as an ELISA (enzyme-linked immunoassay) test followed by a Western blot test. Still practiced today, if the ELISA results are positive or equivocal, the more specific Western blot test is run to help identify the pathogen.

Since then, notable diagnostic improvements have been made in ELISA testing. “A number of companies, such as Quidel, have dramatically improved the sensitivity of serological diagnosis so that fewer early Lyme disease cases are being missed,” Sellati says. “This is of critical importance, as the earlier Lyme disease can be diagnosed and treatment initiated, the better the prognosis for the patient.”

In 2019, the CDC revised its guidelines to acknowledge testing advances like these that make it possible to detect more antibodies—and, therefore, the presence of disease—earlier.

“More recently, a newer algorithm has been accepted, and it’s called the modified two-tiered algorithm,” says Jennifer Roth, vice president of business development for Gold Standard Diagnostics. “In that case, you can use two different types of ELISA tests, and the blot testing is not required.”

This can be good news for laboratories looking for a way to streamline the very time-consuming process involved in blot testing.

“Where the traditional testing method is a very manual, hands-on process, the ELISA testing can be run on instruments that help automate the process, so it makes it more widely accessible,” says Sean Hoesterey, vice president of sales and marketing at Gold Standard Diagnostics. “We’re in the transition period. A lot of places still run both [tests]; some have switched to the new algorithm. We have both available to our customers. It depends on the situation.”

However, according to Sellati, even the CDC’s “gold standard” diagnostic system for Lyme disease is more accurate the longer the patient has been carrying the disease. In some cases, a new blood sample should be drawn from the patient two to four weeks later and tested for the presence of antibodies that may have been produced since the first test.

“Serological testing for Lyme disease is more effective at diagnosing late-stage disease than it is early disease,” he says. “This is particularly true for the gold standard CDC two-tiered test. This is because, oftentimes, the longer the disease progresses, the higher the level of antibodies in the blood.”

Of course, there are other limitations for this approach, as well.

“The problem is that these tests look at a limited number of Borrelia species that cause the illness and therefore miss many patients,” says Jyotsna Shah, PhD, president and laboratory director of IGeneX, Milpitas, Calif., a reference laboratory specializing in clinical and research testing for Lyme disease and associated tick-borne diseases. “Borrelia, the pathogen that causes Lyme, consists of many species, and a test that looks for only one or two is destined to be inaccurate.”

To bridge this gap, IGeneX offers a test that can detect eight different species of Borrelia.

“The most effective way to diagnose TBDs is to use advanced testing called immunoblotting,” Shah says. “This method is more specific, more sensitive, and far more inclusive than the standard type of testing that had been in common use. This is important because ticks can contain and transmit multiple infections to the person—patients can become ‘co-infected.’ Immunoblots offer the broadest range of pathogen detection of any currently available serological test, and this lessens the risk of missing an important pathogen.”

Lane notes that some progress has been made in PCR testing as well.

“There are certainly more new tests in development,” he says. “A group from the University of Leicester in the UK has developed a more sensitive PCR test for Lyme disease, targeting a novel marker, and another European group is working on morphological tests to confirm Lyme diagnosis.”

PCR tests are also effective for other TBDs. “PCR assays are available for Ehrlichia, Anaplasma, and Rickettsia species,” Fowlie says. “These tests are sensitive, specific, and can be used when patients are symptomatic. Real-time Rickettsia RNA assays have also been developed. These tests have improved limits of detection for diagnosis in symptomatic patients.”

According to Sellati, an emerging direct diagnostic method from Ionica Sciences, funded by the Global Lyme Alliance, may make it possible to detect the presence of Borrelia in the blood more accurately and earlier than ever before. “Even though the spirochetes are relatively few and far between, they do spend time in the blood, and they do shed parts of themselves into the bloodstream, including outer surface proteins (OSP),” he says. “[Ionica Sciences] applied a technology that allows you to capture OSP-A out of the bloodstream and actually detect and quantify its presence in a patient’s sample.” He expects this technology to become widely available in the next five years.

Slow Progress

Why do technology leaps in TBD testing seem so few and far between?

“One key point is that the total number of cases is relatively small,” Lane notes. “That means that funding to develop new tests is relatively limited. From a commercial perspective, the relatively small number of cases equates to fewer sales, hence less investment. Figures from the National Institutes of Health show that research funding for Lyme disease is around 1% of that for HIV/AIDS, although there are probably 10 to 15 times the number of cases of Lyme disease annually. Perhaps related to the funding issues is the fact that the infections occur in relatively discrete geographical locations, so the ‘problem’ isn’t countrywide and doesn’t attract so much attention.”

Moore agrees that lack of public awareness may be a factor. “One possibility is that tick-borne diseases have not received a lot of attention in the popular media nor become a bigger part of the public consciousness despite their prevalence and medical/economic burden,” he says.

Another issue is the COVID-19 pandemic, which has impacted diagnostic development and testing across all medical disciplines by diverting resources and attention away from all other diseases.

“The heavy burden COVID-19 placed on state and local laboratories impacted the ability to keep up with routine TBD testing,” Fowlie says. “To fill this gap, CDC has offered to help perform additional diagnostic testing for tick and mosquito-borne diseases as needed.”

On the flip side, the progression of COVID-19 itself, particularly its manifestation as long-COVID, could actually provide much needed insight into chronic TBDs, such as late-stage Lyme disease.

“Interestingly, symptoms of long COVID, also called post-COVID, can mimic those of late stage, chronic TBDs,” Shah says. “This is helpful in that it shines much-needed light on the reality of chronic Lyme, an entity whose existence has long been denied by many. In addition, the apparent immune suppression associated with COVID may allow latent infections, including TBDs, to re-emerge. This has been observed by many clinicians and once again emphasizes the importance of accurate testing. Some cases of what were thought to be long COVID actually turned out to be [a TBD] reactivation. This results in the possibility for effective treatments for these patients.”

Despite the slow-seeming progress in TBD diagnostics, advancements are being made. Fowlie notes that some improvements, such as 16S metagenomics to detect tick-borne bacteria from whole blood,3  may not be widely available to support routine diagnostics at this time. However, these advancements offer a window into future possibilities.

“Incremental advances in tickborne disease diagnostics occur regularly, but giant leaps have been less common,” she says. “The CDC’s Division of Vector-Borne Diseases diagnostic laboratories work to facilitate advances in diagnosis of tickborne diseases via development of innovative diagnostic approaches, provision of critical samples or reagents for external development, and validation of new diagnostic assays and through the discovery of new tickborne pathogens, for example, Heartland and Bourbon viruses.”

A much-needed advance would be to offer more commercially viable panels that test for multiple TBDs simultaneously. A tick can transfer a variety of pathogens in a single bite, making TBD co-infections distressingly common and difficult to diagnose.

“Multiplexed syndromic panels are becoming more popular in the lab, which is especially useful since many tick-borne pathogens cause non-specific symptoms, such as malaise, fever, etc., and there is not always a history of a tick bite,” Moore says.

According to Sellati, there will likely be more multiplexed options in the near future. “Global Lyme Alliance is working with a number of investigators at top academic research and medical institutions in the country to develop a blood-based diagnostic test that’s serological but at least it looks for all the major tick-borne pathogens that can cause disease in humans,” he says. “We’re hoping that within the next five years or so, there may be more accurate, more economical ways of diagnosing multiple tick-borne diseases.”

In the meantime, laboratories can help play a role in educating the local medical community about TBDs.

“Laboratories can work with state and local health departments to help healthcare providers understand which tickborne diseases agents are present in their area,” Fowlie says. “Laboratories can clearly list the assays that are available at their facilities, specimen type required, timing of specimen collection, shipping instructions, and the limitations of each assay.”

Laboratorians can even recommend additional testing. “It is possible for a patient to have more than one tick-borne infection at a time, and labs may be able to advise clinicians on additional tests that can be run either at the same time, or if negative results are obtained with the first set of tests that are completed,” Lane notes.

Sellati recommends providing more targeted TBD education in medical schools to reinforce an understanding of TBD coinfections in budding clinicians. “You have to do it in the medical schools because it’s too difficult to catch everybody once they’ve already graduated,” he says.

Shah agrees that practitioner education is key. “Tick-borne diseases have spread across the country, but the mindset for many physicians and patients is that these diseases are still contained to the Northeast and Upper Midwest,” she says. “Therefore, many patients with tick-borne disease symptoms are thought to have the flu or a cold, and are never properly diagnosed.”

TBDs in the USA

A single tick bite has the ability to transmit a variety of pathogens simultaneously, which means patients may need to be screened for more than just one tick-borne disease (TBD) when they present with symptoms. Many of these pathogens are regional, which means it is important to know which diseases could be endemic to the region where the patient was bitten when ruling out co-infections. While TBDs are generally rare, these are some notable diseases transmitted by ticks in the United States:

DiseasePathogen*Region*Annual cases*
Lyme disease                     Borrelia burgdorferi, B. mayoniiIn most states; mostly prevalent in the Northeastern states30,000 reported (estimated 476,000 actual)
AnaplasmosisAnaplasma phagocytophilum. Northeast, upper Midwest, West Coast 5,000
Rocky Mountain Spotted FeverRickettsia rickettsiiThroughout the United States, but most commonly reported in North Carolina, Tennessee, Missouri, Arkansas, and Oklahoma 5,000
EhrlichiosisEhrlichia chaffeensis, E. ewingii, or E. muris eauclairensis South-central and Eastern United States, including Minnesota and Wisconsin3,000
BabesiosisBabesia microti, B. duncani Northwest and upper Midwest states2,500
TularemiaFrancisella tularensisThroughout the United States275
Tick-borne relapsing feverBorrelia hermsii, B. parkeri, and B. turicatae Reported in 15 states: Arizona, California, Colorado, Idaho, Kansas, Montana, Nevada, New Mexico, Ohio, Oklahoma, Oregon, Texas, Utah, Washington, and Wyoming 493 cases reported between 1990 and 2011
Southern Tick-Associated Rash IllnessUnknownCentral Texas and Oklahoma, southern states, Atlantic coast Unreported

Other less common diseases include Heartland and Bourbon viruses, Powassan encephalitis, and Q fever.



Ann H. Carlson is a regular contributor to CLP.


1. “Tickborne Disease Surveillance Data Summary.” Centers for Disease Control and Prevention. October 6, 2021.

2. “How many people get Lyme disease?” Centers for Disease Control and Prevention. January 13, 2021.

3. Rodino KG, Wolf MJ, Sheldon S, Kingry LC, Petersen JM, Patel R, Pritt BS. Detection of Tick-Borne Bacteria from Whole Blood Using 16S Ribosomal RNA Gene PCR Followed by Next-Generation Sequencing. J Clin Microbiol. 2021 Apr 20;59(5):e03129-20. doi: 10.1128/JCM.03129-20. PMID: 33627320; PMCID: PMC8091845.