Testing for tick-borne diseases is far from simple. Several factors impact the accuracy of a patient’s test results, from the timing of the test to how the test is designed and processed. The reliability of tick-borne disease lab tests has serious consequences not only for patients’ health and finances, but also for public health.
This is especially true when it comes to the ability of lab tests to detect infections at the species level. Detecting a bacterial infection – which most tick-borne diseases are – means detecting pathogens or, more often, antibodies produced in response to those pathogens. But many of the bacteria that cause the most common tick-borne diseases have several species and strains that cause the same disease.
While knowing the particular species responsible for infection is not necessarily required for diagnostic purposes, it is valuable for clinical and surveillance purposes. In this article, learn about how testing for bacterial infections at the species level can contribute to public health education and ultimately lead to better patient outcomes.
Understanding tests for bacterial infection
Before learning about the difference between genus-level and species-level testing, it’s important to understand some basic facts about how tests for bacterial infection work.
Note: While it is possible to test urine, saliva, and other samples for some tick-borne diseases, most tests for tick-borne bacterial infections are blood tests.
Direct vs. indirect testing
First, the vast majority of tick-borne disease lab tests are indirect tests. This means that rather than detecting the antigens (disease-causing agents) themselves, the test detects the antibodies that the patient’s immune system produced in response to the infection.
This is part of the reason why the timing of testing is important. As with tests for COVID-19, indirect tests for bacterial infection are typically only capable of detecting the infection once enough antibodies have been produced, which can take several days to weeks, depending on the disease. Testing too early may result in negative results despite infection.
What’s more, the body produces different types of antibodies at different stages of disease: IgM antibodies appear early and become undetectable over time while IgG antibodies appear later and stay around longer. Some tests detect one type of antibody better than the other, a factor to consider when deciding on how soon after exposure to get tested.
This is not to say that direct testing is not valuable. In fact, the diagnosis of any tick-borne disease should not be based solely on the detection of antibodies to a bacteria. Some people are immunosuppressed or their immune system does not react to bacteria. In those cases, a direct test such as PCR or FISH would be a better choice. This is why we always recommend a panel, which combines direct and indirect testing methods.
Sensitivity vs. specificity
Tests for bacterial infection are typically evaluated by sensitivity and specificity. These criteria often have an inverse relationship. So, a test that is highly sensitive will not be very specific, leading to the possibility of false positives, since the test might pick up something that looks a lot like the target antibody but isn’t.
By contrast, a test that is highly specific will only produce a positive result when a certain amount of a very specific type of antibody is present. This means a positive result from a highly specific test is very reliable (accurate), but a negative test result may be false, as it could mean there simply isn’t enough of the right kind of antibody present in the patient’s body yet.
For this reason, it is often recommended that patients take multiple types of tests to confirm test results.
Bacteria genus vs. species
Disease-causing bacteria are typically discussed using their genus and species names. For example, the bacteria that causes Bartonellosis – a group of diseases associated with fleas, lice, and sometimes ticks, including Cat Scratch Disease – is referred to by the genus name, Bartonella. But within the genus Bartonella, there are several different disease-causing species, which are referred to first by the genus name (“B.” for short) and then by the species name.
These species are associated with different hosts and disease vectors – for example, B. henselae is a species most commonly carried by fleas and ticks, while B. quintana is most often carried by lice. There are at least nine species and subspecies of Bartonella known to cause disease in humans or animals.
Blood tests for bacterial infection can be designed to detect infection at the genus level, species level, or both. As an example, see the five different test types offered in IGeneX’s Bartonella test panel:
- Bartonella ImmunoBlot: The ImmunoBlot is a species-level test, able to detect species and strains from North America, Europe, and Australia, including B. henselae, B. quintana, B. elizabethae, and B. vinsonii. Because it is species-level and not genus-level, it should be used in conjunction with other lab tests (and clinical symptoms) for patients already suspected of having a Bartonella infection.
- Bartonella IFA: The Bartonella IFA is also a species-level test. However, it can detect antibodies to one species at a time, e.g., the species B. henselae. Like the ImmunoBlot, it should also be used in conjunction with other lab tests, clinical symptoms, and other evidence known to the diagnosing practitioner.
- Bartonella PCR: This highly sensitive and highly specific test can detect infection at both the genus level and the species level.
- Bartonella FISH: While the Bartonella FISH can detect multiple species of Bartonella, it only reports results at the genus level. This means that the test is sensitive – i.e., unlikely to produce a false negative because of the species responsible for infection – but patients will not know exactly what species is responsible for their infection with a FISH test alone.
- Bartonella IgXSpot: This test is used to measure the patient’s T-cell response to the infection, and it does so at the genus level. After an infection the body first has a T-cell response followed by a B-cell (IgM and IgG), therefore, this test works best early in an infection.
Because of the different capabilities of each test, it is best to get tested with a full panel. Learn more about the advantages and characteristics of each Bartonella test from IGeneX.
The benefits of testing at the species level
If you look up how tick-borne diseases are treated, you will find a fair amount of commonality in the types of antibiotics used and the lengths of treatment no matter what species has caused the patient’s infection. So, what is the advantage of being able to detect infection at the species level?
For starters, being able to report disease cases at the species level is immensely helpful for surveillance purposes. It helps public health officials and health practitioners understand which bacteria species are most common where and in what types of ticks, and whether there are any changes in the prevalence of certain species. This in turn increases the public’s awareness about which diseases to worry about and what activities or risk factors are associated with each.
Reporting at the species level also increases clinical knowledge about the presentation and required treatment for different tick-borne diseases. Different species of a single genus may cause slightly different symptoms and/or require different treatments. With awareness of these differences, doctors can make more accurate diagnoses. A certain symptom that may have otherwise been ignored may alert doctors to test a patient for tick-borne disease, or to choose a certain type of test over another.
A useful analogy can be made to COVID-19. It is now understood that the symptoms of the Omicron variant differ in some significant ways from previous variants. Knowing the symptoms of infection caused by Omicron is crucial for diagnostic purposes. People who would not previously have believed they could have COVID-19 may now pursue testing, which can then give them a better picture of their health, allowing them to pursue treatment if necessary and make better decisions that protect those around them.
In sum, testing at the species level is useful for surveillance and disease research, which in turn should lead to better patient outcomes over time.
Get tested with IGeneX
Testing for bacterial infections can be complex and challenging, but IGeneX is always working to create better, more accurate tests for tick-borne diseases including Lyme, Tick-Borne Relapsing Fever, Rocky Mountain Spotted Fever, Bartonellosis, and more. Learn more about what makes our tests different.