Ognjen Ležakov

Dr. Ognjen Ležakov

Institut za zdravstvenu zaštitu dece i omladine Vojvodine, Novi Sad, Serbia
orcid

Research Focus & Metrics

Academic Career Length

8Years (2019-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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18 November 2024 in Pathogens
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VSVerica Simin
Verica Simin
Ognjen LežakovOgnjen Ležakov
Ognjen Ležakov
IBIvana Bogdan
Ivana Bogdan
DMDragana Mijatović
Dragana Mijatović
DGDragana Gazibara
Dragana Gazibara
Pavle BanovicPavle Banovic
Pavle Banovic
Tick-borne encephalitis (TBE) is a vaccine-preventable viral infection that poses significant public health challenges, particularly in regions where tick-borne diseases are endemic. This case report describes a 2-year-old boy with confirmed abortive TBEV infection following a tick bite during travel to Switzerland. The patient developed fever and mild symptoms but did not exhibit central nervous system involvement. The case underscores the importance of raising awareness among healthcare providers and travelers from non-endemic areas, such as Serbia, about TBE risk and the potential benefits of preventive vaccination. Strategic immunization campaigns could mitigate the public health impact of travel-related TBE.

4 October 2025 in Children
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MSMirjana Vladimir STOJSIC
Mirjana Vladimir STOJSIC
Ognjen LežakovOgnjen Ležakov
Ognjen Ležakov
SĆSanja Ćeranić
Sanja Ćeranić
NSNikola Stojšić
Nikola Stojšić
MRMarko Rajković
Marko Rajković
NBNina Brkić
Nina Brkić
Background/Objectives: Pharmacogenetics examines genome variability and its influence on drug efficacy and toxicity, forming the foundation for personalized medicine. Patients with inflammatory bowel disease (IBD) treated with azathioprine with thiopurine S-methyltransferase (TPMT) deficiency are at an increased risk of drug-related toxic effects. Variability in the HLA-DQA1 and DQB1 alleles may lead to an inadequate therapeutic response. This study aimed to determine the significance of TPMT and HLA-DQ Allelic Variants in therapy optimization planning. Methods: A retrospective study was conducted to determine TPMT gene polymorphism and the presence of HLA-DQA1 and HLA-DQB1 alleles in children diagnosed with IBD and treated at the Institute for Child and Youth Health Care of Vojvodina in May 2023. Results: The study included 104 children with a mean age of 13.71 ± 3.1 years, with a balanced gender distribution. A TPMT mutation was identified in only one child. The most common HLA-DQA1 alleles were *01 (49%) and *05 (28.8%), while the most frequent allele at the HLA-DQB1 locus was 03 (15.4%). The presence of the HLA-DQA105 allele was associated with the development of anti-drug antibodies against anti-TNF therapy (RR: 1.23; 95% CI: 1.03–1.50), while the presence of HLA-DQA101 was significantly more frequent in children on optimized therapeutic regimens (RR: 1.63; 95% CI: 1.13–2.10). Conclusions: Prior to the initiation of azathioprine therapy, TPMT genotyping should be performed to prevent adverse effects and ensure optimal drug dosing. Identification of the HLA-DQA105 and HLA-DQA101 alleles plays an important role in the planning of biological therapy regimens, including decisions on dose escalation or interval shortening.

5 January 2024 in Iranian Journal of Pediatrics
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GVGordana Milorad Velisavljev-Filipović
Gordana Milorad Velisavljev-Filipović
Ognjen LežakovOgnjen Ležakov
Ognjen Ležakov
Introduction: Elizabethkingia meningoseptica (EM) is a gram-negative aerobic organism that can cause severe infections. Although the incidence is higher in developing countries, human infections associated with this organism are seldom described in Serbia. This bacterium is usually resistant to most antibiotics, making the treatment challenging. We present a single twin born as a late-preterm newborn who developed sepsis and meningitis caused by EM. Case Presentation: This case report aims to show that this rare bacterium is present in our country and the clinical presentation of the resulting disease and bacterial resistance to antibiotics. In addition, we assessed if a more thorough diagnosis, including the immunological status of the newborn, is needed. Conclusions: Considering the high mortality and morbidity rates of EM and its multiresistance, early identification of the infection cause and determining the patient’s immunological status are vital for treatment and improved patient outcomes.

23 May 2025 in Children
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BMBorko Milanovic
Borko Milanovic
GVGordana Vijatov-Đurić
Gordana Vijatov-Đurić
ADAndrea Djuretic
Andrea Djuretic
JKJelena Kesic
Jelena Kesic
VSVesna Stojanović
Vesna Stojanović
Ognjen LežakovOgnjen Ležakov
Ognjen Ležakov
Ataxia-telangiectasia is a rare autosomal recessive disorder that is difficult to diagnose due to its unpredictable presentation. It is characterized by cerebellar degeneration, telangiectasias, immunodeficiency, frequent pulmonary infections, and tumors. Immune system abnormalities manifest as disruptions in both cellular and humoral immunity. The most common findings include decreased levels of immunoglobulin classes (IgA, IgM, IgG, and IgG subclasses) and a reduced number of T and B lymphocytes. A four-year-old girl was initially evaluated and treated for skin lesions that presented as crusts spreading across her body. She was monitored by a pulmonologist due to frequent bronchial obstructions. Over time, she developed bilateral scleral telangiectasia, saccadic eye movements, and impaired convergence. Her gait was wide-based and unstable, with truncal ataxia and a positive Romberg sign. Laboratory tests revealed decreased immunoglobulin G levels, subclass IgG4 levels, elevated alpha-fetoprotein, and a reduced number of T and B lymphocytes. Brain magnetic resonance imaging showed cerebellar atrophy. Whole-exome sequencing identified heterozygous variants c.1564-165del, p.(Glu5221lefsTer43), and c.7630-2A>C in the serine/threonine-protein kinase ATM (ataxia-telangiectasia mutated) gene, confirming the diagnosis of ataxia-telangiectasia. Following diagnosis, treatment with intravenous immunoglobulin replacement was initiated along with infection prevention and management. The goal of this case report is to raise awareness of the atypical initial presentation that may lead to a diagnostic delay. We emphasize the importance of considering ataxia-telangiectasia in the differential diagnosis, even when classical neurological signs are not yet evident.

6 November 2024 in Journal of Clinical Medicine
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GVGordana Vijatov-Đurić
Gordana Vijatov-Đurić
BMBorko Milanović
Borko Milanović
NBNenad Barišić
Nenad Barišić
JIJelena Ivetic
Jelena Ivetic
AĐAndrea Đuretić
Andrea Đuretić
VSVesna Stojanović
Vesna Stojanović
Background/Objectives: To investigate if the severity and presentation of multisystem inflammatory syndrome in children (MIS-C) vary between different severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. Methods: This retrospective study included 59 patients aged 0–18 years, diagnosed with COVID-19 and MIS-C, treated and monitored over a one-year period after discharge from hospital. The patients were grouped according to the predominant SARS-CoV-2 variant. The predominant variant of SARS-CoV-2 was assumed by the date of hospitalization. The following patient data were collected: demographic data (age, sex), information on comorbidities, body mass index, clinical data (fever and duration of febrile periods, symptoms of Kawasaki-like phenotypes, and presence of respiratory, cardiovascular, gastrointestinal, neurological and other symptoms), and laboratory and imaging findings. Results: In total, 24 (41%), 19 (32%), and 15 (25%) patients were diagnosed with MIS-C during the Alpha, Delta, and Omicron periods, respectively (63.8% were males; 36.2% were females). Comorbidities were present in 49% of patients. Respiratory symptoms were the most common during the Delta period (73%, p = 0.028). There was no statistically significant difference in the occurrence of other symptoms, laboratory findings, treatment, complications, and long-term outcomes between groups. Conclusions: No significant correlation was found between hospitalization date (used to estimate COVID-19 variant) and presentation/severity of MIS-C.

1 January 2019 in Medicinski podmladak
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Ognjen LežakovOgnjen Ležakov
Ognjen Ležakov
IVIvana Vorgučin
Ivana Vorgučin
Introduction: Cryptorchidism is a disorder of the testicles, when during a physical exam, testicles, one or both of them, are not found in the scrotum, but are found either along the inguinal canal or in the abdomen. Two main modalities of treatment are hormonal and surgical treatment. Aim: The aim of this paper was to determine the success rate of hormonal therapy with human chorionic gonadotropin (hCG) in undescended testicle treatment in patients treated at the Institute for Child and Youth Health Care in Vojvodina, from January 1, 2010, to December 31, 2017. Material and methods: This research included the patients from the Institute for Child and Youth Health Care in Vojvodina ages 0-18, treated from January 1, 2010, to December 31, 2017. Medical documentation has been analyzed and interpreted using methods of descriptive statistic. The research included boys with undescended testicles, to whom the hormonal therapy was indicated. Patients were divided into 3 groups (6 years). The therapy was applied twice a week, in the course of 5 weeks (hCG 250-1000 IJ/dose). The position 12 months after therapy was used as a final position. Results: The hormonal descend was achieved in 63 patients (62.4%) of the total number of patients. Тhe highest success rate was achieved in oldest of our patients (80%). Conclusion: Hormonal therapy with hCG leads to descent in a high percentage, with very little transitory adverse effects, and it is an important modality in undescended testicles treatment.