Hello, and welcome to Part 2 of this “Hot
Topic” series on tick-borne diseases. I’m Dr. Bobbi Pritt, and I co-direct the
Vector-Borne Diseases Laboratory Services area along with my colleague, Dr. Elli Theel. Before I begin, I’d like to say that I have
no disclosures to make. Before we discuss our first case, I’d like
to introduce the algorithm that I will be subsequently referring to. This algorithm for acute tick-borne disease
testing is freely available on the Mayo Medical Laboratories website and it contains links
to most of the tests that I will be discussing today. Now, let’s move on to our cases. Case #1 is a seven-year-old boy living in
Connecticut who presents with several days of fever, fatigue, and body aches. He had been camping with his family at a local
state park two weeks prior to presentation, and his mother reports multiple mosquito bites
but doesn’t recall any tick bites. Also, no rash was noted. If we go to our algorithm, we can determine
our next steps. The algorithm starts with the clinical scenario—in
this case, a scenario where there is a clinical suspicion of tick-borne disease based on patient
characteristics. The boy has an illness during tick season
with fever, fatigue, and body aches. He also has a recent environmental exposure
to ticks, even though his mother doesn’t recall any tick bites. In this situation, the next step is to consider
a number of tick-borne pathogens based on his geographic exposure. This map from the Centers for Disease Control
and Prevention (CDC) shows the distribution of key tick-borne diseases reported in 2015. I like this map because it nicely demonstrates
where the main clusters of disease are, as well as the overlap of many tick-borne diseases. It also shows how there are a smattering of
cases outside of the main clusters of disease. Although our focus will be on the main areas
of tick-borne disease, it’s important to keep in mind that cases can occur outside
of these areas. The next step in our algorithm is to determine
if the patient is at risk for Rocky Mountain spotted fever, as shown on the left in the
green box, or the other tick-borne diseases shown on the right. Depending on the patient’s residence and
exposure history, he or she may be at risk for both groups of diseases. In this case, our patient’s potential tick
exposure is in Connecticut, and he is therefore at risk for Lyme disease, anaplasmosis, babesiosis,
and Borrelia miyamotoi disease. We will therefore be following the arm of
the algorithm shown in the red box. The next question in the algorithm is whether
a classic erythema migrans rash is present. If yes, then no testing is indicated for Lyme
disease since the presence of the classic erythema migrans rash is consistent with Lyme
disease. Thus, presumptive therapy for Lyme disease
is indicated. If the answer is no, as it is with this patient,
then one or more of the tests listed should be considered. Also, therapy for anaplasmosis should be considered
while waiting for the test results since this disease can be potentially fatal. In this case, the Lyme disease serology was
ordered to further evaluate for Lyme disease, and because the patient had systemic symptoms,
a PCR panel for tick-borne pathogens was also ordered. The Lyme disease serology was performed and
was negative. However, the tick panel, which is comprised
of PCR tests for Ehrlichia species and Anaplasma phagocytophilum, Borrelia miyamotoi, and Babesia
species, was positive for Babesia microti. Let’s briefly discuss babesiosis. It’s an interesting tick-borne disease,
since unlike the other diseases in this algorithm, it is a parasitic infection. It is primarily due to Babesia microti in
the United States, and it’s highly endemic in the northeast and upper Midwest. It is primarily transmitted through the bite
of Ixodes scapularis, the black-legged or “deer” tick. Less commonly, babesiosis is due to Babesia
duncani—primarily on the west coast, and the Babesia MO-1 strain. Babesia duncani is transmitted through the
bite of Ixodes pacificus, the western black-legged tick whereas Babesia MO-1 is possibly transmitted
by Amblyomma americanum, the lone star tick. Babesia divergens is another important pathogen
and is the most common cause of babesiosis in Europe and Asia. Of note, all of the species listed on this
slide can be detected by the Mayo Clinic PCR test, which is particularly helpful for patients
who have travelled throughout the United States or overseas. Babesiosis is often asymptomatic or causes
only mild disease. However, elderly, immunocompromised, and asplenic
patients are at risk for severe disease. Treatment is with a combination of agents. The standard therapy for most patients is
atovaquone plus azithromycin, whereas clindamycin plus quinine is usually reserved for severely
ill patients. Babesiosis is traditionally diagnosed using
microscopic examination of thick and thin blood films. This method also allows for calculation of
percent parasitemia, which is important for guiding therapy and determining the patient’s
prognosis. However, the Mayo Clinic Babesia PCR is more
sensitive than blood films and is therefore the initial recommended test for detection
of babesiosis. In looking back at the patient’s case, you
may wonder if it makes sense that no one recalled a tick bite. Well, in fact, it’s not uncommon that patients
with tick-borne illnesses don’t recall getting a tick bite. Therefore, the absence of a recalled tick
bite cannot be used to exclude a tick-borne illness. Another question to be considered is why testing
for so many pathogens at once is recommended. That is because multiple organisms can be
transmitted through a single tick bite, and clinical features are not usually sufficient
to differentiate them. Now, let’s move on to our second case. The patent is a 42-year-old man living in
Minnesota who found an embedded tick on his back. He had initially mistaken it as a skin tag
and only later discovered that it was an engorged tick. He had been hiking in northern Minnesota during
the past weekend and estimates that the tick had been attached for at least two days. After removing the tick, the patient’s physician
submitted it to the laboratory. This is the specimen that was received in
the laboratory. It is clearly alive and obviously engorged. You can see that it’s having some difficulty
walking across this petri dish. The test that the physician ordered is the
parasite identification. This broad-ranging test is used for the identification
of worms, bugs, and anything that looks like these objects (the ticks). If the object is an arthropod, it is identified
to the medically appropriate level, which, where appropriate, includes the genus and
species name. For ticks specifically, the information that
we provide is the degree of engorgement, the gender and life-cycle stage, and the presence
or absence of mouth parts. This information can then be used to guide
preventative therapy in certain situations. For Lyme disease, the CDC and Infectious Diseases
Society of America (IDSA) recommend prophylactic treatment when all of the circumstances shown
on this slide in the red box are met. Note that the second circumstance is that
the attached tick needs to be identified as an adult or nymphal Ixodes scapularis tick. By providing this identification service,
a laboratory can help health care professionals decide if Lyme disease prophylaxis is appropriate
for their patients. Another important take-away message from this
slide is that antibiotic treatment following a tick bite is not recommended as a means
to prevent tick-borne illness other than Lyme disease, including anaplasmosis, babesiosis,
ehrlichiosis, and Rocky Mountain spotted fever. Now, going back to our case, the patient’s
tick was identified as a Dermacentor variabilis female tick. It was fully engorged, and its mouth parts
were intact. Given this identification, the patient was
reassured that he was not at risk of acquiring Lyme disease from this tick and that no prophylactic
antibiotics were indicated. He was, however, advised to watch for signs
of tick-borne illness and see his health care provider if they appeared. One request that we occasionally receive is
to test ticks by PCR to see what they are carrying. However, this is not a test that we offer
through Mayo Medical Laboratories. Why is this? Well, it is because finding a tick on your
body does not mean that it bit you or transmitted a pathogen. Instead, the identification, gender, and degree
of engorgement of the tick are better indicators for risk of disease, and those are all aspects
of the identification that we provide. In summary:
There are multiple tick-borne diseases, many of which are clinically indistinguishable. The preferred test varies by the time that
the patient presents in the course of illness. Therefore, an algorithmic approach is useful
for optimizing laboratory testing, ensuring that all of the necessary tests are ordered
without performing unneeded tests. Thank you for joining me today in this second
part of our Hot Topic series on tick-borne diseases.