Human herpesviruses exhibit diverse pathogenic outcomes and the molecular reasons are not fully understood. Human herpesvirus 6B (HHV-6B) causes exanthema subitum and encephalitis, whereas the closely related HHV-6A is typically asymptomatic. Here, we show that cellular APOBEC3 enzymes restrict HHV-6A replication but not HHV-6B. HHV-6B expresses higher levels of the U28 protein, which binds multiple APOBEC3 proteins and promotes their relocalization and degradation. In contrast, HHV-6A fails to counteract APOBEC3 activity and accumulates extensive mutations in both cell- and patient-derived viral genomes. Individual APOBEC3 gene ablation enhances HHV-6A replication and reduces the viral mutation burden. Together, our studies suggest that differential susceptibility to APOBEC3 restriction may help to shape the evolvability and clinical manifestations of HHV-6A and HHV-6B.

Blaschkitis is an acquired Blaschko-linear inflammatory dermatosis similar to classic lichen striatus. Although the pathomechanisms have not yet been fully elucidated, it has been reported that some cases were triggered by viral infections, vaccines, or drugs. We recently encountered a patient who developed multiple broad bands of erythematous papular plaques accompanied by vesicles along Blaschko lines on the left side of the trunk while taking sitagliptin, a dipeptidyl peptidase-4 inhibitor (DPP-4i) for type 2 diabetes mellitus. Histopathology showed necrotic keratinocytes in the epidermis accompanied by subepidermal blisters with infiltration of CD8-positive T cells and eosinophils in the upper dermis. Negative direct and indirect immunofluorescence ruled out DPP-4i-associated bullous pemphigoid. Within 1 week after withdrawal of DPP-4i, the skin lesions resolved, with no subsequent relapse. Furthermore, the distribution of the lesions along Blaschko lines is suggestive of cutaneous mosaicism and may be associated with immune-inflammatory responses induced by DPP-4i. Based on the clinical characteristics of this case, we speculate that DPP-4i activated T lymphocytes, which subsequently reacted to mosaic skin areas and induced blaschkitis. Accordingly, the diagnosis was DPP-4i-associated blaschkitis. We report this case together with a review of the relevant literature on drug-induced blaschkitis and lichen striatus.

Aiming at the problems of delayed early warning for severe viral exanthems and insufficient prediction accuracy based on a single data source, this study proposes a dual-branch cross-modal fusion prediction model based on TCN-TransDAF. The model adopts a Dilated-TCN branch to capture the long-term evolution law of clinical temporal indicators within 72 h after diagnosis, and a local-global attention Transformer branch to mine the variation characteristics of virulence loci in viral genomes. With the aid of a cross-modal fusion mechanism, it realizes the deep coupling of dual-dimensional information of host and pathogen, and simultaneously completes the tasks of severe risk determination, subtype identification and onset time window prediction. The experimental results show that the model achieves an AUC-ROC of 0.942 for severe case prediction and a MAE of 5.8 h for severe case onset time window prediction on the test set. Compared with the optimal baseline model, the AUC-ROC is increased by 5.79%, the MAE is reduced by 26.34%, and the recall is increased by 10.09%, which enables accurate early warning 12-18 h before the onset of severe symptoms. This study provides an efficient technical solution for the early warning of severe viral exanthems, and its cross-modal modeling idea also offers a reference for the prediction research of other infectious diseases.

A man in his early 30s presented with fever, widespread pruritic rash and deranged liver function tests shortly after returning from a religious pilgrimage. Initial assessment focused on infectious and travel-related causes given recent international travel. Investigations revealed marked eosinophilia, lymphocytosis and a mixed hepatocellular-cholestatic liver injury. Extensive viral, parasitic and autoimmune testing was negative. Despite partial symptomatic improvement following cessation of recently initiated allopurinol, the patient developed progressive eosinophilia and new lymphadenopathy. Multidisciplinary review supported a diagnosis of drug reaction with eosinophilia and systemic symptoms (DRESS), with allopurinol identified as the most likely culprit. Oral corticosteroid therapy led to rapid clinical and biochemical improvement, with normalisation of eosinophil count and liver function prior to discharge. This case highlights the diagnostic challenge of drug hypersensitivity reactions in the context of recent travel and emphasises the importance of early medication review in patients presenting with fever, rash and organ dysfunction.

Dear Editor, An otherwise healthy 24-year-old male patient presented to us with a three-day history of a diffuse, pruritic skin eruption preceded by low-grade fever and fatigue in the previous two weeks. Physical examination revealed an atypical exanthem with a polymorphic pattern characterized by diffuse erythematous macular lesions on the forehead, erythema, edema, and vesicles on the ears, erythematous papules on the forearms and trunk, and maculo-papular-petechial lesions on the pubic area and buttocks. An erythematous-purpuric enanthem and symmetrical enlargement of the cervical-axillary lymph nodes were also detected. [...].

Mpox is an emerging zoonotic infection that has shown sustained human-to-human transmission since 2022, often through sexual contact networks. We report a case of mpox in a 43-year-old Indian-origin man residing in the United Arab Emirates who presented with fever, sore throat, and a painful genital ulcer, followed by widespread vesiculo-pseudopustular lesions. Examination revealed firm, well-circumscribed, peri-umbilicated pseudopustules, distinctive lesions lacking purulent content. Laboratory investigations were unremarkable, and a polymerase chain reaction test for the Monkeypox virus, conducted on throat and skin swabs, confirmed the diagnosis. The patient was managed with supportive care and recovered uneventfully. This case highlights the characteristic pseudopustular morphology of mpox, which serves as a key diagnostic clue distinguishing it from other genital and vesicular eruptions, and underscores the need for clinicians to be aware of this condition amid evolving global epidemiology.

Human herpesvirus 6 (HHV-6) is a common cause of infection in childhood, classically presenting as exanthema subitum. Viral reactivation causing severe disease in the setting of immunosuppression is well documented in the literature. However, HHV-6 infection in immunocompetent adults has been uncommonly reported. We describe the case of an immunocompetent man in his 50s who presented with fever, headache, confusion, and a truncal maculopapular exanthema with sparse vesicular lesions. Lumbar puncture results were compatible with viral meningoencephalitis. HHV-6 DNA was identified in cerebrospinal fluid, serum, and vesicular skin lesions by polymerase chain reaction testing, supporting a diagnosis of disseminated HHV-6 infection with central nervous system and cutaneous involvement. The patient received treatment with ganciclovir followed by oral valganciclovir, with complete recovery and no sequelae. This case highlights that HHV-6 may cause severe infection even in immunocompetent adults and underscores the need for evidence-based guidance to improve diagnosis and treatment of this condition.

Background: Human parvovirus B19 causes a broad spectrum of clinical manifestations, ranging from the classic "fifth disease" to severe presentations. Clinical presentation varies considerably across age groups. In 2023-2024, a notable increase in parvovirus B19 cases was reported across Europe. Methods: We retrospectively analyzed pediatric patients with serum serology and/or plasma PCR-confirmed parvovirus B19 infection treated at the tertiary infectious diseases center (University Hospital for Infectious Diseases, Zagreb) in 2023 (January-August). Demographic, laboratory, viral load, and clinical characteristics were assessed, with emphasis on cutaneous manifestations. Results: A total of 102 patients were included (median age 10 years; 54.9% male), of whom 7.8% required hospitalization. Rash was present in 94 (92.2%) of the patients of whom 75 had erythema infectiosum and petechiae, while the rest had a combination of both. Patients with petechial rash were significantly older (p = 0.013) and exhibited lower platelet counts (p < 0.001) compared with those with erythema. A higher proportion of anti-B19V IgM (p = 0.027) and IgG (p < 0.001) antibodies was detected in patients with erythema. Petechial rash was associated with higher viral loads (p < 0.001). In univariate analysis, the presence of anti-B19V IgG antibodies was correlated with the absence of petechial rash (OR = 0.09; p < 0.001), whereas higher viral load was associated with its presence (OR = 1.7; p < 0.001). In multivariate analysis, viral load emerged as the only predictor of petechial rash (aOR = 1.4, p = 0.042). Conclusions: Parvovirus B19 remains a self-limiting illness in healthy children, despite frequent atypical presentations. Higher viremia is associated with atypical rash morphology and suggests age-related differences in immune clearance.

Urticaria is a very uncommon dermatological manifestation of infection by the dengue virus. It can hinder diagnosis since some of its features overlap with allergic conditions, such as maculopapular and petechial rashes. We present a case of a 32-year-old male, resident of a dengue-endemic area, who presented with an acute onset of generalized pruritic wheals and angioedema in the absence of any systemic symptoms, including fever. Laboratory tests showed leukopenia, thrombocytopenia, and elevated liver enzymes. Dengue serology confirmed primary infection (NS1 antigen and IgM positive). The patient responded to antihistamines and supportive care without complications. This case highlights the need to consider dengue in the differential diagnosis of acute urticaria in endemic areas, even without typical systemic symptoms.

Human herpesvirus 6 (HHV-6) is a neurotropic virus comprising two variants, HHV-6A and HHV-6B. Although HHV-6B is known to cause exanthem subitum in children, the clinical significance of HHV-6A remains poorly understood, particularly in adult and elderly populations. Here, we report a rare case of HHV-6A encephalitis in an immunosuppressed elderly patient. An 89-year-old male patient with chronic inflammatory demyelinating polyradiculoneuropathy was administered immunosuppressive therapy with prednisolone. His consciousness progressively worsened over 4 days. Brain magnetic resonance imaging with fluid-attenuated inversion recovery demonstrated a hyperintense lesion in the left medial temporal lobe. The FilmArray meningitis/encephalitis panel tested positive for HHV-6. Further testing revealed elevated HHV-6A DNA levels in both the cerebrospinal fluid and plasma, confirming the diagnosis of HHV-6A encephalitis. A moderate increase in HHV-6A DNA and a slow clinical course suggest that chromosomally integrated HHV-6 (ciHHV-6) was unlikely. The treatment consisted of tapering prednisolone and initiating foscarnet, which gradually improved the patient's level of consciousness. This case highlights the importance of HHV-6A in the differential diagnosis of encephalitis, particularly in elderly patients receiving immunosuppressive therapy. Early diagnosis using a multiplex PCR panel, combined with prompt initiation of antiviral treatment, may lead to more favorable outcomes. Further studies are required to clarify the pathogenesis, clinical spectrum, and optimal management of HHV-6A-associated central nervous system diseases.

Measles remains a leading vaccine-preventable cause of viral pneumonia worldwide. In people with advanced human immunodeficiency virus (HIV) its course is often atypical, lacking the hallmark rash and progressing rapidly to respiratory failure. We report a case of measles virus-associated acute respiratory distress syndrome in a profoundly immunosuppressed woman with HIV and chronic hepatitis B who failed to respond to ribavirin. This case underscores the diagnostic challenge of rash-less measles in acquired immunodeficiency syndrome, the narrow therapeutic window for antivirals and the urgent need to integrate adult measles screening and vaccination into HIV care.