In March 2022, a North Carolina resident sought care at an emergency room and was subsequently admitted to the hospital because of a suspected case of ehrlichiosis. The patient sought care after experiencing 48 hours of fever, chills, shortness of breath, and diarrhea. Upon admission, the patient had acute leukopenia, thrombocytopenia, anemia, acute kidney injury, transaminitis, abdominal distension with splenomegaly, and meningoencephalitis. Hospital staff discovered 2 ticks attached to the patient and identified them as lone star ticks (Amblyomma americanum). Identification by a North Carolina Division of Public Health (NCDPH) entomologist (A.M.B.) subsequently confirmed the ticks as male and nymphal lone star ticks; the ticks collected from the patient were not tested for pathogens. Although no history of travel was reported, the patient practiced multiple daily walks to the edge of their 5.6-acre property, located in rural North Carolina.

The patient was initially treated for tickborne pathogen infections and meningitis by using broad spectrum antimicrobial drugs, including doxycycline, on day 2 after admission. On day 3, the patient required increased support because of progressive encephalopathy, hypotension, lactate elevation, and concerns of gastrointestinal bleeding, along with thrombocytopenia and was transferred to the medical intensive care unit. The patient experienced continued fevers and altered mental status. Results of differential testing for other infectious etiologies were negative (Table 1). Laboratory results indicated secondary hemophagocytic lymphohistiocytosis (Appendix Table), an increasingly recognized complication of rickettsial diseases (4,5). The patient was placed on anakinra on day 8 after hospital admission to address the hemophagocytic lymphohistiocytosis, and mental status slowly improved. Although the patient experienced mild improvement after treatment with anakinra and doxycycline, it was decided that the patient should transition to home hospice care after 18 days in the hospital. The patient recovered after 4 weeks at home and was removed from hospice care.

Indirect fluorescence antibody testing of serum revealed the patient was positive for E. chaffeensis IgG on day 4 after symptom onset, indicating a history of Ehrlichia infection (Table 1). Because of limited improvement after doxycycline administration and concerns about possible arbovirus infection, staff (T.G.F.) at NCDPH coordinated specimen collection with the local county health department to send a serum sample to the Centers for Disease Control and Prevention (CDC) in Fort Collins, Colorado, USA, for testing. Quantitative reverse transcription PCR (RT-PCR) was positive for HRTV RNA (6).

In conjunction with university partners, NCDPH conducted environmental sampling. In May and June 2022, we conducted standard tick drags at the patient’s home. The habitat surrounding the home was primarily deciduous, hardwood forest that had some understory growth and heavy leaf litter. We collected ticks by passing a 1-m² cotton drag cloth over ground level vegetation. We checked the cloth every 10 m² and collected ticks for pathogen testing (7). We collected 608 ticks in May and 656 ticks in June 2022 after 5 hours of total collection time (Table 2). We sent A. americanum tick specimens collected in May 2022 to CDC in Atlanta, Georgia, USA, and in Fort Collins to test for Bourbon virus (BRBV), HRTV, E. chaffeensis, and E. ewingii. We sent A. americanum ticks collected in June 2022 to CDC in Fort Collins for BRBV and HRTV testing. E. chaffeensis and E. ewingii DNA testing consisted of real-time PCR that amplified an 82-bp fragment of the 16S rRNA gene for both species and used 2 probes specific for either E. chaffeensis or E. ewingii detection (8). CDC tested ticks for HRTV and BRBV by using real-time RT-PCR primers and probes specific for each virus, as described previously (9,10). Pathogen testing of A. americanum ticks did not detect HRTV but did detect 2 E. ewingii–positive tick pools (1 pool = 25 nymphs; 1 pool = 5 adult ticks) out of a total of 43 pools (587 total ticks), indicating a minimum infection rate (MIR) of 0.34% (2 pools/587 ticks). In addition, BRBV was also detected in 1 tick pool (n = 25 ticks), indicating an MIR of 0.08% (1 pool/1,264 total ticks).

This patient had a substantially elevated antibody titers against E. chaffeensis antigen at the time of symptom manifestation, suggesting a previous infection at some undetermined time; the lack of a rise in titer during hospitalization and the ineffectiveness of doxycycline argued against a current Ehrlichia infection. Therefore, other tickborne illnesses were considered for testing. The patient’s laboratory and clinical history were consistent with both HRTV and Ehrlichia spp. infections, but serologic and molecular testing are needed to distinguish between the 2 infections. The patient was negative for BRBV RNA by RT-PCR and negative for both HRTV and BRBV antibodies by using plaque reduction neutralization tests. However, additional testing for HRTV RNA revealed a positive RT-PCR result, indicating the patient had an active HRTV infection.

First identified in 2 farmers in Missouri, USA, in 2009, HRTV has been identified in >60 patients across the United States (11–13), including 1 previous case in North Carolina. In North Carolina, co-infection with Ehrlichia spp. and HRTV is possible because those pathogens are naturally maintained in a common tick vector. Although no evidence of co-infection existed in this case, the patient was likely exposed to both pathogens on their property. The additional findings of BRBV and E. ewingii in the collected tick pools indicate a further environmental risk for tickborne diseases at that residential site.

The MIR for E. ewingii in the collected ticks from this study is not uncommon for this region; prevalence rates for Ehrlichia spp. have been documented across the mid-Atlantic region. E. chaffeensis was detected in 2.6% and E. ewingii in 0.8% of A. americanum ticks in Tennessee (14). Virginia reported infection rates of 0%–5.08% for E. chaffeensis and 0%–8.20% for E. ewingii in A. americanum ticks (15). BRBV was identified in 1 pool of ticks collected in a North Carolina location where no BRBV in ticks has been previously reported. The presence of BRBV in A. americanum ticks indicates that citizens are at risk, albeit low, of contracting BRBV in North Carolina if bitten by lone star ticks.

Initial acute clinical features of ehrlichiosis and tickborne virus infections are similar. Therefore, healthcare providers should also consider testing patients for tickborne viruses if ehrlichiosis is suspected, especially when the infection is not responsive to doxycycline treatment. Furthermore, persons at risk for tick bites should use tick exposure prevention methods, such as applying N,N-diethyl-meta-toluamide and other US Environmental Protection Agency–approved repellants; wearing permethrin-treated clothing, long pants, and long sleeves; and performing tick checks after spending time in wooded areas.