The Immune Response To A Tick Bite: The Role of Blood Testing
Tick-borne infections are a significant contributor to chronic disease and illness. Daily steps to prevent a tick bite should be an integral part of self-care. Just like you eat well and exercise to protect your health, engaging in habits that reduce your risk of a tick-borne illness is essential.
However, even the best efforts can fail. And many people are unaware of the risk of tick bites until too late.
While prevention is the gold standard, a close second is prompt, aggressive action after experiencing a bite. Different doctors recommend different regimens to address the risk of tick-borne infection after a tick is found. Unfortunately, not all of these regimens are backed by good science.
In my practice, after treating hundreds of patients with Lyme and other tick-borne infections, a few things have become clear. There are steps that can help, and some that do more harm than good.
Blood testing for Lyme disease is common practice after a tick bite. But let’s take a step back and question why? What benefit does an immediate blood test provide? And more importantly, what limitations?
Today I want to look at:
The pathology of a tick bite
How the immune system responds to a tick-borne illness
Limitations of testing for Lyme disease after a tick bite
When a blood test may help
What Happens When A Tick Bites
To understand why a blood test may or may not be useful, you have to know how tick bites work.
Ticks are parasites that feed on the blood of hosts for survival. Unlike a mosquito that lands, feeds, and quickly flies away, ticks require a long period of time to feed. As a result, they have developed sophisticated mechanisms to allow them the time they need.
When a tick bites a host, it uses several methods to lodge itself in place firmly. The first is its uniquely shaped “mouth,” which has backward-facing spines. Once the tick inserts its mouth, those spines provide a lot of staying power. Secondly, some ticks secrete a cement-like substance that helps hold them in place.
Anyone with experience removing a tick can attest to how stubborn they can be. For this reason, care should be taken when removing one to prevent it from breaking apart or becoming embedded.
Once a tick is attached, it inserts a long rod with grooves that draw the host's blood into itself. The grooves also allow some of the tick's saliva to enter the host. If the tick is a carrier of any pathogens, for example, from previously feeding off an infected host, they may be transmitted to the host through the saliva.
Exposure to tick saliva is where the danger lies.
Timeline Of A Tick Bite
Immediately after a tick bite, you are unlikely to notice any symptoms or concerns. During this time, it’s possible the tick may still be attached and feeding. Some ticks stay attached for upwards of 2 weeks, especially in hard-to-reach areas such as the groin or scalp, where they may go unnoticed.
During this time, any pathogen passed from the tick saliva to the host is gaining a foothold.
Your body has finely tuned mechanisms to identify and neutralize foreign invaders such as bacteria or viruses from tick bites. We’ll talk more about how the body coordinates an immune response in a bit.
Here is where things begin to get tricky. In some people, symptoms of an infection from a tick bite may appear during this time frame. Early symptoms can include:
However, not everyone experiences pronounced symptoms at this stage. Don’t assume just because you are symptom-free you are in the clear.
One interesting adaptation ticks have developed is the ability to blunt the body's immune response. This means you may not see robust immune activation to effectively neutralize pathogens. Components of tick saliva may also cause dysregulation between the innate and adaptive immune systems. More on that later.
30 days +
If left untreated, tick-borne infections cause a range of symptoms, some of which may present themselves early and others that may not appear until much later. For some people, the onset of symptoms may be so delayed that they do not connect their experience with a tick bite.
Common symptoms patients may experience at this time include:
Insomnia or sleep disturbances
Joint pain with or without joint swelling
Decreased short-term memory
Difficulty with concentration
Numbness and tingling
Dizziness or vertigo
Chronic abdominal pain
Another possibility is that individuals treated with a short, prophylactic round of antibiotics after a tick bite may have lingering, resistant pathogens still circulating. Chronic Lyme disease is one example of what can happen when tick-borne infections go unnoticed or are treated incorrectly.
Aside from infections transmitted by ticks, there is another condition to be aware of that could present around 4-6 weeks after a tick bite, particularly if it’s the Lone Star tick. Alpha-gal Syndrome (AGS) is not caused by an infection but can be serious and life threatening. The Lone Star tick can carry Alpha-gal (galactose-alpha-1,3-galactose), a carbohydrate found in most mammals which can cause a person bitten by this tick to develop allergic reactions to things that contain alpha-gal, like red meat, meat products and even some medications. It is worth noting that there is a simple blood test for this that looks at IgE levels to glactose-alpha-1,3 galactose.
Where Does Testing for Tick-Borne Infections Come In?
It’s tempting to assume that a blood test will definitively answer the question of whether you’ve become infected from a tick bite. But, in reality, the timing of a blood test determines its usefulness, and even then, blood tests are not 100% accurate.
Not all blood tests for tick-borne illnesses are the same, and not all labs follow procedures that provide reliable results.
In my experience, testing for tick-borne illness is much more complex than it appears. It takes a skilled, experienced practitioner to know not only what tests to order but also what labs deliver reliable results and how to sort through any conflict between a patient's history, symptoms, and blood results.
What Do Blood Tests Look For?
The results of most blood tests for tick-borne infections, especially for Lyme, don’t tell you whether you have the bacteria or virus in your bloodstream. Instead, the tests look for antibodies. Antibodies are specific cells the immune system produces to target a pathogen.
But here’s the thing, antibodies are produced by the adaptive immune system. The adaptive immune system is just one part of your body’s immune response, and it’s not the quickest. The two parts of your immune system work together to protect you from a foreign invader. Here’s how that works.
The Innate Immune System
Your innate immune system responds immediately to any threat with a preprogrammed set of responses. When your immune system detects a foreign invader, it immediately releases inflammatory mediators to begin the process of stimulating immune cells to neutralize the threat. Mast cell degranulation is a good example of the innate immune system in action.
While the innate immune system is an essential first responder to a bacteria or virus, its actions are non-specific. Kind of like using a sledgehammer to pound in a nail. After that initial protective surge, it’s time for the adaptive immune system to take over.
The Adaptive Immune System
While the innate immune system responds immediately, the adaptive immune system takes longer to ramp up. Just like its name implies, this aspect of your immune system adapts itself to target the specific cells of the bacteria or virus. As is true for most forms of adaptation, there is a certain amount of time involved.
One of the jobs of the innate immune system is to gather information on the structural make-up of the pathogen and pass that information along to the adaptive immune system. The adaptive system then begins the production of antibodies to specifically target the invading cells. But antibodies aren’t ready right away. The adaptive immune system may not start releasing antibodies for days or even weeks after infection.
With this understanding, you can see how a blood test may not be a useful tool in the early identification of a tick-borne infection. Until the adaptive immune system has time to develop effective antibodies against the tick-borne pathogen, a blood test cannot provide the necessary information.
Currently, most doctors who order blood tests rely on a screening ELISA test that measures antibodies to the Lyme bacteria. If this is positive, another test called the western blot is done to confirm it truly is Lyme disease. But, the sad truth is there is about a 50% false-negative rate on the ELISA test. The result can be an infection that flies under the radar for much too long, leading to a chronic condition.
Doctors and patients may feel a false sense of security after a negative blood test. An early negative test will likely hinder the diagnosis of a tick-borne infection later if one is there hiding all along. I’ve worked with many patients who’ve struggled with symptoms for years and have been unable to get the answers they desperately need.
Testing too early doesn’t make sense in the context of what we know about Lyme disease. It’s very good at hiding.
The Big Downfall Of Testing
While premature testing is a common downfall of blood tests for tick-borne illness, another problem is how narrowly most doctors test.
If a patient experiences a tick bite, most people (including doctors) are concerned about a Lyme infection. It makes sense. Lyme gets the most press by far.
Yet, while Lyme disease is the most common tick-borne infection in the US, it is by no means the only one. In spite of this, most lab panels that test for tick-borne infections focus almost exclusively on Lyme antibodies. This does a grave disservice to patients.
Ticks can carry many other pathogens, including:
Rocky Mountain spotted fever
Tick-borne relapsing fever
For a blood test to be useful, it must test for more than just Lyme disease. Even in cases where Lyme disease is present, there is always the possibility of multiple infections. It is not uncommon for me to see patients with Lyme disease and a coinfection such as Bartonella, causing a wide range of symptoms that have mystified their doctors.
Diagnosing and treating both conditions is essential to return the patient to health.
Narrow testing panels are more likely to miss critical information and send patients and doctors down the wrong path looking for answers. When I order blood tests for a patient, it is comprehensive, checking for even obscure tick-borne (and other vector-borne) illnesses we wouldn’t want to leave undiagnosed and untreated.
When Testing Can Help
It’s easy to talk about the pitfalls of blood tests for tick-borne illnesses, but that doesn’t mean they are never useful. For the right patient, a blood test may provide information to guide treatment or reveal a clearer picture of their medical history. The key is discernment, and a comprehensive understanding of the tricky diseases that ticks carry.
In my practice, I use blood tests in two ways.
To determine if a patient has been exposed in the past or is currently infected. Remember the adaptive immune system? One of its superpowers is its ability to remember how to fight pathogens it has seen before. A blood test for antibodies may reveal if the body has ever battled Lyme disease or other infection in the past or is currently battling it. This can provide a clue as to where else to look to explain a patient's symptoms. But this might not reveal enough information so there are other tests available like PCR and FISH that can help determine if an active infection is present and these could be positive sooner than antibody tests.
To create a baseline. For patients who were recently exposed to a tick bite or undergoing treatment, it may be helpful to catch a snapshot of their immune response for baseline purposes. In these cases, the plan is always to retest in four to five weeks and compare.
Even in the presence of reliable blood test results, the patient always comes first. There are limitations to what a blood test can tell us, and tick-borne infections are remarkably good at hiding. When my patient's symptoms and history are suspicious for tick-borne infection, we do a range of testing to rule out or confirm any confounding conditions.
In my years of working with Lyme disease patients, it has become clear that diagnosing tick-borne infections requires a blend of modern medicine, traditional medicine, and finely honed diagnostic instincts.
To Test Or Not To Test
If this information leaves you wondering where to go from here, you are not alone. Tick-borne diseases are high on the list of mysterious illnesses that often stump mainstream practitioners.
Lyme disease and other tick-borne and more generally, vector-borne illnesses are not like other infections where a quick blood test and a round of antibiotics are a sure thing. Knowing when to test, how to test, and perhaps most importantly, WHY you are testing is crucial for a good outcome.
I know how frustrating it can be to navigate the medical system after a tick bite. My goal for every patient I see is to clear away the confusion and follow the best practices to get them a diagnosis, treatment, and ultimately, a full recovery.
Testing for tick-borne illness may have a role to play in that process. But the answer is unique to each patient, which is why medical care that is individualized, not formulaic, is the best guide.