Background: Visceral leishmaniasis (VL) is a neglected vector-borne tropical disease caused by Leishmania donovani (L. donovani) and Leishmania infantum (L. infantum). Due to the very small dimensions of the protozoa impounded within blood cells and reticuloendothelial structure, diagnosing VL remains challenging.Case presentation: Herein, we reported a case of VL in a 17-month-old boy with acute lymphoblastic leukemia (ALL). The patient was admitted to West China Second University Hospital, Sichuan University, due to repeated fever after chemotherapy. After admission, chemotherapy-related bone marrow suppression and infection were suspected based on clinical symptoms and laboratory test results. However, there was no growth in the conventional peripheral blood culture, and the patient was unresponsive to routine antibiotics. Metagenomics next-generation sequencing (mNGS) of peripheral blood identified 196123 L. donovani reads, followed by Leishmania spp amastigotes using cytomorphology examination of the bone marrow specimen. The patient was given pentavalent antimonials as parasite-resistant therapy for 10 days. After the initial treatment, 356 L. donovani reads were still found in peripheral blood by mNGS. Subsequently, the anti-leishmanial drug amphotericin B was administrated as rescue therapy, and the patient was discharged after a clinical cure.Conclusion: Our results indicated that leishmaniasis still exists in China. Unbiased mNGS provided a clinically actionable diagnosis of a specific infectious disease from an uncommon pathogen that eluded conventional testing.

Background: Scrub typhus, caused by the Orientia tsutsugamushi (Ot), is a widespread vector-borne disease transmitted by chigger mites. Hemophagocytic lymphohistiocytosis (HLH) is considered to be one of the potentially severe complications. The diagnosis of scrub typhus-associated HLH may be overlooked due to the non-specific clinical characteristics and the absence of pathognomonic eschar.Case presentation: We obtained clinical data from two patients in the South of Sichuan, China. The first case involved a 6-year-old girl who exhibited an unexplained fever and was initially diagnosed with sepsis, HLH, and pulmonary infection. The other patient presented a more severe condition characterized by multiple organ dysfunction and was initially diagnosed with septic shock, sepsis, HLH, acute kidney injury (AKI), and pulmonary infection. At first, a specific examination for scrub typhus was not performed due to the absence of a characteristic eschar. Conventional peripheral blood cultures yielded negative results in both patients, and neither of them responded to routine antibiotics. Fortunately, the causative pathogen Orientia tsutsugamushi (Ot) was detected in the plasma samples of both patients using metagenomics next-generation sequencing (mNGS) and further confirmed by polymerase chain reaction. Subsequently, they both were treated with doxycycline and recovered quickly.Conclusion: The unbiased mNGS provided a clinically actionable diagnosis for an uncommon pathogen-associated infectious disease that had previously evaded conventional diagnostic approaches.

Background and aim: Cat scratch disease (CSD) is a zoonotic infection predominantly caused by Bartonella henselae , typically featured by regional lymphadenopathy and febrile illness. Although these classic features characterize most cases, the clinical spectrum extends to severe systemic manifestations including meningitis and neuroretinitis, leading to poor prognosis. Given this potential for diverse clinical presentations, prompt microbiological confirmation becomes essential for accurate diagnosis and appropriate management of CSD. The present study aimed to provide a comprehensive analysis of epidemiological patterns, clinical characteristics, diagnostic findings, and therapeutic outcomes in pediatric CSD cases, with the ultimate goal of optimizing early detection and enhancing the clinical understanding of this disease. Methods: This single-center retrospective study analyzed 20 pediatric cases diagnosed with CSD at West China Second University Hospital in southwestern China between September 2021 and July 2025. All diagnoses were established based on comprehensive clinical evaluation including medical history, characteristic symptoms, and imaging findings. Definitive B. henselae identification was achieved through metagenomic next-generation sequencing (mNGS). These diagnostic characteristics were systematically evaluated and discussed in detail. Results: Among the 20 patients with CSD included in the study, 18 (90.00%) reported a history of cat contact. Ten patients were male (50.00%). School-aged children (6–14 years) accounted for the majority of patients. Eleven cases (55.00%) occurred in autumn. Fever and lymphadenopathy were the primary reasons for hospitalization. B. henselae was detected in all cases using mNGS. Nine patients were diagnosed with atypical CSD, seven of whom were female. Atypical CSD was associated with higher body temperature and longer hospitalization stay. Antimicrobial agents, including azithromycin, doxycycline, and rifampin, achieved satisfactory therapeutic outcomes. Conclusion: This study elucidates the epidemiological, clinical, and laboratory characteristics of CSD in children. mNGS may serve as a powerful tool to facilitate the diagnosis of CSD, including its atypical manifestations.

Rationale: Murine typhus, caused by Rickettsia typhi , is a globally distributed flea-borne rickettsiosis. Although rarely recognized, it can trigger hemophagocytic lymphohistiocytosis (HLH), a life-threatening hyperinflammatory syndrome. Nonspecific febrile illness and atypical petechial eruptions frequently lead to delayed or missed diagnoses. This report aims to illustrate the diagnostic process and clinical implications of murine typhus-associated HLH in a pediatric patient, and to evaluate the utility of metagenomic next-generation sequencing (mNGS) as an unbiased detection tool for occult pathogens. Patient concerns: A 10-year-old child was admitted with unexplained recurrent fever and generalized petechiae, refractory to treatment at outside hospitals. Diagnoses: The patient was ultimately diagnosed with murine typhus-associated HLH caused by R typhi , based on a comprehensive diagnostic work-up. Interventions: Empirical dexamethasone was initiated promptly to control hyperinflammation. After mNGS confirmation, oral doxycycline was added for targeted anti-rickettsial therapy. Outcomes: The patient’s clinical status continued to improve, culminating in discharge. Lessons: Murine typhus-associated HLH should be considered in febrile children with unexplained cytopenias and petechiae. Early empiric HLH-directed immunosuppression followed by pathogen-specific therapy improves prognosis. mNGS provides a rapid, unbiased method to detect rare, overlooked pathogens and guide definitive treatment when conventional tests are negative.

Rationale: Bone marrow transplantation (BMT) is an established therapy for hematological malignancies. In recent years, with the advancement of medical research, evaluating the efficacy of BMT in recipients by detecting the presence or absence of chromosomes from an opposite-sex donor has been widely recognized. Numerous cases have shown that the sex hormone levels of recipients who receive BMT from the opposite sex will change significantly. However, whether such hormonal changes will impair sexual function or lead to physiological sex-related manifestations, or even cause changes in the biological sex of BMT recipients, these questions make people cannot help but think deeply. Herein, we report a case of a male patient who received allogeneic BMT from a female donor, demonstrating that transplantation only replaced the recipient’s hematopoietic stem cells and did not change the patient’s biological sex. Patient concerns: We report a 22-year-old male who was diagnosed with azoospermia during a recent physical examination and sought medical attention at our hospital. Diagnoses: Semen examination showed no sperm, and the analysis of the peripheral blood chromosome karyotype is 46,XX. The preliminary clinical diagnosis is azoospermia with sexual dysfunction. Interventions: The results of Y-chromosome microdeletion in peripheral blood could not be interpreted. After reviewing the patient’s history, we only found that he had received a BMT from an opposite-sex donor for chronic myelocytic leukemia 14 years ago, when he was only 8 years old. The peripheral blood and buccal mucosal swabs were collected for Y-chromosome microdeletion examination again. At this point, the truth has finally come to light: At this point, the etiology became clear: The patient’s peripheral blood showed chimeric DNA from both the BMT donor and recipient, while the buccal mucosal swabs—originating from embryonic development—accurately reflected his pretransplantation genetic profile. Outcomes: The patient, being only 22 years old and having no intention of getting pregnant at present, received no further medical treatment. Lessons: This case report demonstrates that while sex-mismatched BMT may alter secondary sexual characteristics, it does not fundamentally change the recipient’s genetic sex or core gender identity.