In September 2020, stage IV-B germinal center diffuse large B-cell lymphoma was diagnosed in a splenectomy specimen from a 68-year-old woman. She completed first-line treatment with rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone and achieved complete remission. On June 21, 2021 (≈5 months after lymphoma treatment had ended), she experienced arthromyalgia, anorexia, night sweats, and vespertine fever. Her family physician began treatment with metamizole and cefuroxime at usual doses because of urine sediment alterations. Several days later, deep vein thrombosis developed in her right leg. Because of her previous malignancy and treatment, she was attended at her hospital’s hematology service. She was slightly anemic (hemoglobin 11.7 g/dL, reference range 12–16 g/dL) and had leukopenia (2.28 × 10³ leukocytes/µL, reference range 4–14 × 10³ leukocytes/µL) and a low neutrophil count (0.4 × 10³ neutrophils/µL, reference range 1.8–8.5 × 10³ neutrophils/µL). C-reactive protein level was elevated (62 mg/L, reference range <10 mg/L), hyponatremia was present (133 mmol Na/L, reference range 135–145 mmol Na/L), and high levels of ferritin (536 µg /L, reference range 20–200 µg/L) and β2 microglobulin (8.50 mg/L, reference range 0.8–2.4 mg/L) were observed. Other measured hematologic and biochemical parameters, including procalcitonin, were within reference ranges. Other analyses, such as antinuclear antibody testing, blood and urine cultures, and serologic assays against Coxiella burnetii, herpes virus, cytomegalovirus, and Epstein-Barr virus, did not indicate acute infection. A chest radiograph and computed tomography scan and an abdominal ultrasound did not reveal pertinent abnormalities. Recurrence of lymphoma was suspected, and a positron emission tomography/computed tomography scan showed diffuse and homogeneous bone marrow hypermetabolism without evidence of neoplastic activity at other levels.

Empirical treatment was begun with piperacillin/tazobactam and granulocyte colony stimulating factor at conventional doses; 1 week later, the patient had recovered from leukopenia, but fever persisted. A bone marrow biopsy, which did not show neoplastic infiltration or alterations in hematopoietic cells, was performed and processed for different microbiologic tests. A possible tick-related infection was suspected because the patient lived in an area endemic for Lyme disease and other tickborne diseases. The patient recalled having suffered a tick bite 20 days before onset of symptoms. A bone marrow DNA extract and serum sample collected during the acute infection phase (August 2021) were sent to the Special Pathogens Laboratory, Center for Rickettsioses and Arthropod-Borne Diseases, at San Pedro University Hospital–Center for Biomedical Research of La Rioja in Logroño, Spain, to screen for Candidatus N. mikurensis by using PCR and Anaplasma phagocytophilum by using PCR and immunofluorescence assays.

Figure

Figure. Phylogenetic analysis of groEL gene from CandidatusNeoehrlichia mikurensis infecting a patient with antecedent hematologic neoplasm, Spain. Phylogenetic tree was generated to compare 809 bp fragments of...

We performed PCR targeting the panbacterial 16S rRNA gene, fragments of 16S rRNA gene from Anaplasmataceae (designated as 16S rRNA-EHR), groEL from Candidatus N. mikurensis, and msp2 from A. phagocytophilum (Table 1). We detected PCR amplicons of the expected sizes for groEL and panbacteria and family-specific 16S rRNA in bone marrow and acute phase serum samples; nucleotide sequences corresponded to Candidatus N. mikurensis. The groEL amplicon (1,232 bp) showed the highest (99.3%) sequence similarity with that of Candidatus N. mikurensis from a wild rodent (Microtus agrestis) from Siberia in Russia (GenBank accession no. MN701626) but differed from other highly conserved sequences from Siberia and the Far East; the sequence was 98.8% identical to Candidatus N. mikurensis found in Ixodes ricinus ticks from Spain (13) (Table 2). We constructed a phylogenetic tree for groEL sequences by using the maximum likelihood method (Figure). We found no differences for the 16S rRNA-EHR sequence (306 bp). The panbacteria 16S rRNA sequence (available upon request from the authors) showed 3–27 mismatches with the 16S rRNA from Candidatus N. mikurensis. We did not detect A. phagocytophilum by PCR in the acute samples. We deposited nucleotide sequences of groEL and 16S rRNA genes generated in this study in GenBank under accession nos. OQ579033 (groEL) and OQ581737 (16S rRNA).

On the basis of PCR results, the patient was treated with doxycycline (100 mg 2×/d for 3 wk), and fever disappeared after 72 hours. Neutropenia was attributed to the intake of metamizole for symptom control. However, another case of doxycycline-treated Candidatus N. mikurensis infection associated with neutropenia has been reported (8). EDTA-anticoagulated blood and serum specimens were collected 4 (December 2021) and 6 (February 2022) months after onset of the acute infection phase, and we screened for Candidatus N. mikurensis at the Center for Rickettsioses and Arthropod-Borne Diseases, as previously described. We detected Candidatus N. mikurensis DNA in blood collected at 4 months but not in serum. The patient was healthy and blood test results did not show abnormalities at that time. Follow-up PCR of specimens collected at 6 months yielded negative results (Table 2). We did not detect IgG against A. phagocytophilum.

We report a confirmed case of Candidatus N. mikurensis infection in Spain, detected in human bone marrow aspirate, serum, and EDTA-blood samples, that was no longer detected months after completing antimicrobial drug treatment. A broad clinical spectrum of tickborne diseases is found in Spain. Human cases of Lyme borreliosis, Mediterranean spotted fever, and other tickborne rickettsioses have been described, including Dermacentor tick–borne necrosis erythema lymphadenopathy, Rickettsia sibirica mongolitimonae infection, R. massiliae infection, R. aeschlimannii infection, babesiosis, human anaplasmosis, tularemia, Borrelia hispanica relapsing fever, tick paralysis, Crimean-Congo hemorrhagic fever, and α-gal syndrome or other allergic reactions (14). Since we discovered Candidatus N. mikurensis in I. ricinus ticks in Spain (13), we have conducted surveillance of this bacterium. Candidatus N. mikurensis should be considered a potential cause of persistent fever and venous thrombosis in patients with hematologic malignancies who live in environments where ticks are prevalent. Candidatus N. mikurensis infections should be particularly suspected in patients who are immunosuppressed but also should be considered in patients with other vascular conditions who are not immunocompromised (15).