Practical Pearls for Tick-Borne Illness: Diagnosis, Treatment, Prophylaxis, and What's on the Horizon for Lyme Disease and its Co-Infections

 

NP CHRONICLES Practical Pearls for Tick-Borne Illness Diagnosis, treatment, prophylaxis, and what's on the horizon for Lyme disease and its co-infections

Clinical education for NP students and new graduates  •  Board-relevant  •  Peak tick season 2026

Summer and fall bring the seasonal wave of tick bites into primary care and urgent care visits — and with it, the perennial questions: does this bite need prophylaxis, does this rash need treatment, and which co-infection am I missing? Tick-borne illness is common (the CDC received reports of over 89,000 Lyme disease cases in 2023, with modeling suggesting the true annual treated burden may be closer to 476,000) and its presentations overlap enough that a systematic approach pays off. This post walks through the current 2020 IDSA/AAN/ACR guideline recommendations, four representative cases, and the diagnostics and treatment tables you'll want at hand.

CLINICAL BOTTOM LINE

●        Not every tick bite needs antibiotics — post-exposure prophylaxis is reserved for high-risk bites meeting all three criteria below. ●        A classic erythema migrans (EM) rash in an endemic area is a clinical diagnosis. Don't wait on serology to treat — and don't send serology at all for a textbook EM. ●        Persistent post-treatment symptoms without objective signs of relapse do not warrant additional antibiotics; guidelines recommend against it. ●        Think outside Lyme: babesiosis, anaplasmosis, ehrlichiosis, and alpha-gal syndrome share the same vector and season, but not the same treatment.

Know Your Vectors

Four tick species drive the bulk of U.S. tick-borne disease, and their geographic ranges — and the pathogens they carry — differ enough to shape your differential before the labs come back.

●        Blacklegged tick (Ixodes scapularis) — Northeast, upper Midwest, and expanding into the Southeast: Lyme disease, Borrelia miyamotoi, anaplasmosis, babesiosis, Powassan virus.

●        Lone Star tick (Amblyomma americanum) — South and lower Midwest, expanding northeast: ehrlichiosis, tularemia, STARI, and alpha-gal syndrome.

●        American dog tick (Dermacentor variabilis) — widespread east of the Rockies and on the West Coast: Rocky Mountain spotted fever, tularemia.

●        Rocky Mountain wood tick (Dermacentor andersoni) — Rocky Mountain states: Rocky Mountain spotted fever, tularemia.

Doxycycline-responsive vs. non-responsive pathogens

This distinction matters because doxycycline is the default empiric choice for a summer fever-plus-tick-exposure presentation — but it won't touch everything on the list.

Doxycycline-responsive		Not doxycycline-responsive
Lyme disease		Babesiosis
Borrelia miyamotoi		Powassan encephalitis
Anaplasmosis		Heartland virus
Ehrlichiosis		Bourbon virus
Tularemia		STARI
Rocky Mountain spotted fever (and other rickettsia)
	CASE FROM PRACTICE — Case 1
	A healthy 52-year-old woman presents to urgent care in July after her husband noticed a rash on her arm. She lives on a farm in Massachusetts — no fever, no other symptoms. The rash: an expanding, blanching, non-painful erythematous patch, roughly 5–6 cm, without a classic bullseye pattern (remember — only 60–80% of EM lesions show central clearing). Management: this is a classic presentation for early localized Lyme disease in a high-incidence state during peak season. The correct move is to treat empirically with a full course of doxycycline 100 mg BID for 10–14 days — do not wait on serology. Early Lyme serology has poor sensitivity (roughly 14–17%) in the first weeks of infection, so a negative test at this stage would be falsely reassuring, not diagnostic.

Staging Lyme Disease

Lyme disease unfolds in three overlapping clinical stages. Not every patient passes through all three in order — some present at a later stage with no recollection of an earlier rash or bite (only about a quarter of patients with EM recall the tick bite itself).

Stage	Time from bite	Cardinal features	Treatment (adult), duration
Early localized	7–28 days	Erythema migrans; fatigue, headache, neck stiffness, myalgias, arthralgias, fever	Doxycycline 100 mg BID, 10–14 d Amoxicillin 500 mg TID, 14 d Cefuroxime 500 mg BID
Early disseminated	Weeks to months	Neuro: meningitis, cranial nerve palsy, radiculopathy, peripheral neuropathy CV: Lyme carditis, AV block	Doxycycline 100 mg BID, 14–21 d Ceftriaxone 2 g IV daily, 14–28 d Cefotaxime 2 g IV q8h
Late disease	Months to years	MSK: arthritis (classically the knee), acrodermatitis chronica atrophicans Neuro: encephalopathy	Doxycycline 100 mg BID, 28 d Ceftriaxone 2 g IV daily, 28 d

 

In most adults with EM, oral therapy for 7–14 days is preferred over IV in every scenario except hospitalized or severely ill patients — efficacy is equivalent, tolerability is better, and access is easier. Azithromycin is a second-line alternative reserved for patients with contraindications to first-line agents, given its comparatively lower efficacy.

Testing: Two-Tier Serology

Serology is stage-dependent and should never be used to confirm a classic EM rash — treat that clinically. Where testing is appropriate (disseminated or late disease, or an atypical presentation), two-tier testing is standard:

●        Standard Two-Tier Test (STTT): ELISA, reflexing to Western blot if positive/equivocal (Western blot positive at ≥5 IgG bands or ≥2 IgM bands).

●        Modified Two-Tier Test (MTTT): ELISA followed by a second ELISA (C6 peptide) instead of Western blot — faster, cheaper, more objective, and now a 2020 guideline-endorsed alternative.

Stage of Lyme disease	Sensitivity	Specificity
Early localized	14–17%	>99%
Early disseminated	89.7%	>99%
Late disseminated	99.4%	>99%

 

NUANCE TO REMEMBER

Don't use serology as a test of cure. A meaningful share of successfully treated patients remain seropositive afterward — roughly 50% when treated at stage 1, and up to 80% when treated at stage 2/3. A positive antibody test after treatment reflects immune memory, not active infection, and re-infection can be genuinely difficult to distinguish serologically from a lingering antibody response.

CASE FROM PRACTICE — Case 2

A 42-year-old man with a history of splenectomy presents with fever, shaking chills, and confusion for 24 hours. Labs show pancytopenia (WBC 4.3, platelets 135) with hemolysis markers: elevated total bilirubin (3.2), elevated LDH, and low haptoglobin. A splenectomized patient with hemolytic anemia and thrombocytopenia in tick season should raise babesiosis, not Lyme disease — asplenia is a specific risk factor for severe, high-parasitemia disease. A peripheral blood smear confirmed Babesia microti at 7.2% parasitemia. Treatment for babesiosis is atovaquone plus azithromycin for 7–10 days (longer in immunocompromised patients to prevent relapse) — doxycycline has no activity against Babesia, which is why a patient who isn't improving on empiric doxycycline for a tick-borne illness deserves a second look at the diagnosis.

Co-Infections: Babesia, Anaplasma, and Ehrlichia

Babesia microti

●        Incubation: 1–4 weeks after tick bite.

●        Presentation: chills, sweats, fevers, headache, myalgias.

●        Notable labs: hemolytic anemia, thrombocytopenia.

●        More severe in immunocompromised or asplenic patients; complications include ARDS, splenic infarct, warm autoimmune hemolytic anemia, and relapse.

●        Preferred test: blood parasite smear or Babesia PCR.

●        Treatment: atovaquone + azithromycin, 7–10 days (longer if immunocompromised).

Anaplasma phagocytophilum and Ehrlichia

●        Incubation: under 1 week.

●        Presentation: fever plus non-specific symptoms; clinically indistinguishable from each other.

●        Notable labs: leukopenia, thrombocytopenia, elevated transaminases.

●        Preferred test: PCR.

●        Both respond rapidly to doxycycline.

CASE FROM PRACTICE — Case 3

A 31-year-old woman found a tick in her popliteal fossa this morning. She had been hiking two days prior and is asymptomatic, with no rash or fever. She does not meet criteria for prophylaxis, because attachment time cannot be reliably estimated as ≥36 hours and engorgement should be assessed. The correct next step is no intervention — educate her on the signs and symptoms of Lyme disease and other tick-borne illness, and have her return promptly if a rash or fever develops.

Post-Exposure Prophylaxis: The Three-Part Test

A single dose of doxycycline reduces the risk of Lyme disease after a high-risk bite — the landmark Nadelman trial found transmission in 0.4% of prophylaxed patients versus 3.2% of placebo, an 87% relative efficacy, with a number needed to treat of roughly 36. But prophylaxis is not for every bite. IDSA/AAN/ACR strongly recommend it only when all three of the following are true:

●        The bite occurred in a state or area with high Lyme disease incidence (or where >20% of local ticks are infected with B. burgdorferi).

●        The attached tick is identified as an adult or nymphal blacklegged (Ixodes) tick, and estimated attachment time is at least 36 hours, based on degree of engorgement.

●        Prophylaxis can be started within 72 hours of tick removal.

Dosing: adults receive doxycycline 200 mg orally once; children receive 4.4 mg/kg orally (max 200 mg) once, regardless of age — the single-dose regimen's risk profile is favorable even in children under 8, for whom longer courses of doxycycline carry more caution. Amoxicillin and other agents have not been adequately studied for prophylaxis and are not recommended. In pregnancy, a single prophylactic dose of doxycycline can be considered if the tick bite is high-risk and the benefit is judged to outweigh the risk — this is a shared decision with the patient.

NUANCE TO REMEMBER

Prophylaxis only covers Lyme disease. It has not been shown to prevent anaplasmosis, babesiosis, ehrlichiosis, or Rocky Mountain spotted fever — so symptom-watch counseling still applies even after a prophylactic dose is given.

Tick removal and counseling

●        Use fine-tipped tweezers, grasp as close to the skin as possible, and pull upward with steady, even pressure — don't twist or jerk.

●        Clean the bite site and hands with rubbing alcohol or soap and water afterward.

●        Save the tick (alcohol or a sealed container) for species identification and engorgement assessment — this directly informs prophylaxis eligibility.

●        General prevention: shower soon after outdoor exposure, do a tick check (including partner/buddy checks), tumble clothes in a hot dryer, and consider permethrin-treated clothing for high-exposure activities.

Alpha-Gal Syndrome

Alpha-gal is a carbohydrate found in mammalian meat and dairy. In susceptible individuals, repeated tick bites — classically from the Lone Star tick — can sensitize the immune system to this molecule, producing a delayed food allergy that can catch both patients and clinicians off guard.

●        Reactions typically develop 2–6 hours after eating red meat or dairy — the delay is the key differentiator from a typical IgE food allergy, and patients may not react to every exposure.

●        Both IgE-mediated and non-IgE-mediated mechanisms have been described.

●        Consider it in a patient with recurrent, unexplained urticaria, pruritus, or anaphylaxis-like reactions hours after meals, especially with a tick-exposure history.

●        Partner with allergy/immunology for confirmatory testing and long-term management.

CASE FROM PRACTICE — Case 4 (December)

A healthy 62-year-old physician found a tick embedded in his abdomen about 4 weeks earlier and received doxycycline 200 mg x1 for post-exposure prophylaxis. Several hours after eating a bison steak dinner, he woke from sleep with diffuse pruritus and a rash across his torso and upper extremities — sparing the palms, soles, and face. The timing (hours after eating red meat, sparing palms/soles/face, in a patient with a recent tick bite) points toward alpha-gal syndrome rather than a drug eruption from a single prophylactic dose taken weeks earlier. It's a useful reminder to ask about diet, not just medications, when a delayed rash follows a tick exposure — and that alpha-gal reactions can surface well outside the classic summer tick season, since red meat and dairy exposure happens year-round.

On the Horizon: Lyme Vaccination

The VALOR trial (Vaccine Against Lyme disease for Outdoor Recreationists) is a phase 3 study of a 6-valent OspA-targeted vaccine (LBV6), dosed at 0, 2, and 6 months, studied in Lyme-endemic areas of the U.S. and Europe. Pfizer and Valneva announced in March 2026 that the vaccine demonstrated 73.2% efficacy from 28 days post-dose 4 (season 2), with a 95% CI of 15.8–93.5. A licensed Lyme vaccine has been absent from the U.S. market for two decades — this is one to watch for patient counseling in coming seasons.

BOARD PREP

A patient in a high-incidence state finds an engorged Ixodes tick that has clearly been attached over 36 hours, and presents within 72 hours of removal. What's the appropriate management? → Single-dose doxycycline prophylaxis (200 mg adult / 4.4 mg/kg pediatric, max 200 mg) — all three high-risk criteria are met. An asplenic patient has fever, hemolytic anemia, and thrombocytopenia after a tick bite and isn't improving on doxycycline. What test and treatment should you pursue? → Peripheral blood smear or PCR for Babesia; treat with atovaquone + azithromycin, since doxycycline has no activity against Babesia. A patient successfully treated for early Lyme disease six months ago still has a positive Lyme antibody test. Does this indicate treatment failure? → No — serology is not a test of cure. Persistent seropositivity is expected in a substantial proportion of successfully treated patients.

Clinical Bottom Line, Revisited

●        Classic EM rash in an endemic area during tick season = treat empirically. Don't wait on serology.

●        Prophylaxis requires all three: high-incidence area, identified Ixodes tick attached ≥36 hours, and dosing within 72 hours of removal.

●        Not improving on doxycycline for a presumed tick-borne illness? Think Babesia — and check a smear.

●        Persistent symptoms after guideline-directed treatment, without objective signs of relapse, don't warrant more antibiotics.

●        Ask about diet as well as bites when a delayed rash follows tick season — alpha-gal syndrome is on the rise.

References

Lantos PM, Rumbaugh J, Bockenstedt LK, et al. Clinical practice guidelines by the Infectious Diseases Society of America (IDSA), American Academy of Neurology (AAN), and American College of Rheumatology (ACR): 2020 guidelines for the prevention, diagnosis and treatment of Lyme disease. Clin Infect Dis. 2021;72(1):e1-e48.

Committee on Infectious Diseases, American Academy of Pediatrics. Lyme disease. Red Book: 2024-2027 Report of the Committee on Infectious Diseases, 33rd ed. American Academy of Pediatrics; 2024.

Nadelman RB, et al. Prophylaxis with single-dose doxycycline for the prevention of Lyme disease after an Ixodes scapularis tick bite. N Engl J Med. 2001;345(2):79-84.

Centers for Disease Control and Prevention. Guidance for Clinicians: Caring for Patients after a Tick Bite. CS# 304282-B, December 14, 2021. cdc.gov/ticks/tickbornediseases/

Centers for Disease Control and Prevention. Lyme disease surveillance and data. March 13, 2025. cdc.gov/lyme/data-research/facts-stats/index.html

Branda JA, Steere AC. Laboratory diagnosis of Lyme borreliosis. Clin Microbiol Rev. 2021.

Marques AR. Laboratory diagnosis of Lyme disease. J Clin Microbiol. 2018.

Wagner L, et al. Efficacy of a six-valent OspA Lyme disease vaccine (VALOR trial). Lancet Infect Dis. 2025.

Solomon DA. Practical Pearls for Tickborne Disease. Pri-Med Institute CME, Brigham and Women's Hospital / Harvard Medical School.

Brunner R. What are the most up to date guideline recommendations for the treatment of Lyme disease? University of Illinois Chicago Drug Information Group, Monthly FAQs. July 2025.

NP Chronicles — Clinical education for NP students and new graduates. For educational purposes; always practice within your scope and consult current full-text guidelines for patient-specific decisions.