Tick-Borne Disease Co-Infections

Why one tick bite can transmit more than one infection – and why testing beyond Lyme matters.

50%

of chronic

Lyme patients

report co-infections

30%

report two

or more

co-infections

”>5″

different pathogens

can be carried

by one tick

 

 What are co-infections?

A co-infection is a simultaneous infection by two or more pathogens. In tick-borne illness, a single bite can transmit multiple pathogens at once. You can have any tick-borne pathogen without having Lyme. 

 

Clinical takeaway: 

Each suspected pathogen should be tested, diagnosed, and treated on its own. Treating Lyme alone won’t resolve co-infections.

Co-Infections

Overview

Black-legged ticks (Ixodes species) can transmit several pathogens in addition to Borrelia burgdorferi. Co-infections are an important consideration in patients with risk factors or persistent symptoms despite antibiotic treatment for Lyme disease.

  • Prevalence: The frequency of tick-borne co-infections in Lyme disease patients from endemic areas ranges from 4% to 45%.

  • Impact: Untreated co-infections increase morbidity and may interfere with the successful treatment of Lyme disease.

  • Testing Challenges: Laboratory tests vary in sensitivity and specificity, and often fail to account for strain differences among pathogens.

co-infection infographic

Commonly Encountered Co-Infections

  • Anaplasma

    • Intracellular white blood cell parasite

    • Symptoms: fever, headaches, body aches

    • Associated findings: leukopenia (low granulocytes), thrombocytopenia, elevated liver transaminases

  • Babesia

    • Malaria-like parasite (piroplasm) that invades red blood cells

    • Symptoms: fever, fatigue, chills, sweats, headaches, shortness of breath

    • Associated findings: anemia, elevated transaminases

  • Ehrlichia

    • White blood cell parasite, similar to Anaplasma

    • Clinical picture depends on species (different WBC types invaded)

    • Commonly associated with Lone Star ticks (Amblyomma americanum), though some strains are linked to Ixodes ticks

  • Bartonella

    • Intracellular parasite invading erythrocytes, endothelial, and other cells

    • Tick transmission: evidence increasing but not yet conclusive

    • Symptoms: fever, swollen lymph nodes, eye disorders, myocarditis, endocarditis, encephalopathy, musculoskeletal involvement

  • Powassan Virus

    • A flavivirus with two lineages; lineage II (deer tick virus) transmitted by Ixodes ticks

    • Symptoms: severe neurologic disease

    • Treatment: none currently available; fatalities documented

  • Tick-Borne Encephalitis Virus (TBEV)

    • Prominent in Europe and Asia

    • Affects the central nervous system

    • Treatment: none available

    • Prevention: vaccine used in parts of Europe (limited use in children due to adverse effects)

Selected Other Tick-Related Conditions

  • STARI (Southern Tick–Associated Rash Illness)

    • Lyme-like illness associated with Lone Star tick bites

    • Bacterial cause not yet established

    • Some evidence supports Lyme-like antibiotic treatment

    • Distribution: expanding beyond the southern and central US into the northeast

  • Alpha-Gal Allergy

    • IgE-mediated allergy to galactose-alpha-1,3-galactose (alpha-gal), a carbohydrate found in red meat

    • Triggered by Lone Star tick bites

    • Symptoms: delayed hypersensitivity reaction after eating red meat

    • Treatment: avoidance of red meat, allergy management

  • Tick Paralysis

    • Caused by neurotoxins in tick saliva during feeding

    • Symptoms: ascending paralysis

    • Treatment: removal of the tick (usually resolves symptoms)

Common co-infections (overview)

These are frequently reported alongside Lyme and other tick-borne diseases.

Babesia

Parasite • malaria-like illness
Night sweats Fatigue Air hunger
Often requires antiparasitic therapy.

Rickettsia rickettsii (RMSF)

Bacteria • Rocky Mountain Spotted Fever
High fever Rash Severe illness
Potentially deadly — urgent recognition and treatment are critical.

Bartonella

Bacteria • Cat Scratch Disease
Rashes/striae Foot pain Lymphadenopathy
May require prolonged antibiotics; presentation can be multisystemic.

Anaplasma

Bacteria • Anaplasmosis
Headache Chills Myalgia
Seen in multiple regions; consider in compatible epidemiology.

Ehrlichia

Bacteria • Ehrlichiosis
Fever Low WBC Liver involvement
Can be severe if untreated; prompt therapy is important.

Also consider

Other tick-borne pathogens
Powassan virus Borrelia miyamotoi (TBRF)
May present without Lyme; test if clinically suspected.

Why co-infections matter

Implication What it means
Separate testing Each pathogen requires its own tests; a negative Lyme test doesn’t rule out other infections.
Targeted treatment Therapies differ (e.g., antiparasitics vs. antibiotics vs. antivirals). Treating Lyme alone won’t cure co-infections.
Severity & recovery Pathogen interactions may increase symptom burden and lengthen recovery times.
Risk awareness Some infections (e.g., RMSF, Powassan) can be life-threatening if missed — timely diagnosis is essential.

Note: You can be infected with any tick-borne pathogen without Lyme. Consider local tick species and epidemiology when choosing tests.