SARS-CoV-2 Seroprevalence and Neutralizing Antibody Response after the First and Second COVID-19 Pandemic Wave in Croatia.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel coronavirus with a pandemic spread. So far, a total of 349,910 SARS-CoV-2 cases and 7687 deaths were reported in Croatia. We analyzed the seroprevalence and neutralizing (NT) antibody response in the Croatian general population after the first (May-July 2020) and second (December 2020-February 2021) pandemic wave. Initial serological testing was performed using a commercial ELISA, with confirmation of reactive samples by a virus neutralization test (VNT). A significant difference in the overall seroprevalence rate was found after the first (ELISA 2.2%, VNT 0.2%) and second waves (ELISA 25.1%, VNT 18.7%). Seropositive individuals were detected in all age groups, with significant differences according to age. The lowest prevalence of NT antibodies was documented in the youngest (<10 years; 16.1%) and the oldest (60-69/70+ years; 16.0% and 12.8%, respectively) age groups. However, these age groups showed the highest median NT titers (32-64). In other groups, seropositivity varied from 19.3% to 21.5%. A significant weak positive correlation between binding antibody level as detected by ELISA and VNT titer (rho = 0.439, p < 0.001) was observed. SARS-CoV-2 NT antibody titers seem to be age-related, with the highest NT activity in children under 10 years and individuals above 50 years.

Antibacterial Activity of Silver and Its Application in Dentistry, Cardiology and Dermatology.

The problem of antimicrobial resistance is increasingly present and requires the discovery of new antimicrobial agents. Although the healing features of silver have been recognized since ancient times, silver has not been used due to newly discovered antibiotics. Thanks to technology development, a significant step forward has been made in silver nanoparticles research. Nowadays, silver nanoparticles are a frequent target of researchers to find new and better drugs. Namely, there is a need for silver nanoparticles as alternative antibacterial nanobiotics. Silver nanoparticles (AgNPs), depending on their size and shape, also have different antimicrobial activity. In addition to their apparent antibacterial activity, AgNPs can serve as drug delivery systems and have anti-thrombogenic, anti-platelet, and anti-hypertensive properties. Today they are increasingly used in clinical medicine and dental medicine. This paper presents silver antimicrobial activity and its use in dentistry, cardiology, and dermatology, where it has an extensive range of effects.

Polymorphisms of Toll-like receptors 2 and 4 in chronically infected hepatitis C patients from north-east Croatia.

Chronic infection with hepatitis C virus (HCV) is caused by an inadequate immune response. Experimental data suggest that the impaired activation of Toll-like receptors (TLRs) 2 and 4 contributes to chronic infection. We assessed the distribution of three single-nucleotide polymorphisms (SNPs) in the TLR2 (Arg753Gln) and TLR4 (Asp299Gly/Thr399Ile) genes in individuals from north-east Croatia and their effect on the outcome of antiviral therapy. The study consisted of 60 chronically infected patients and 40 healthy subjects. TLR polymorphisms were determined by the PCR-based melting curve analysis. HCV genotyping was performed using the Linear Array Hepatitis C Virus Genotyping Test. Thirty-three patients were treated with standard interferon and ribavirin therapy, and their viral load was evaluated at weeks 28 and 53 after the beginning of therapy. The majority of chronic infections were caused by genotype 1 (77%), followed by genotypes 3 (15%) and 4 (7%). Patients with genotype 1 had higher viral loads than patients infected with other genotypes (P = 0.0428). Healthy individuals and patients with chronic infection had similar frequencies of TLR2-Arg753Gln and TLR4-Asp299Gly/Thr399Ile SNPs. Heterozygous and homozygous TLR4-Asp299Gly/Thr399Ile polymorphisms correlated with higher viral loads and delayed responses to antiviral therapy. We have provided the first evidence that TLR4 polymorphisms influence the success of antiviral therapy in our region. This suggests that therapeutic strategies should be adjusted not only according to HCV genotype but also to individual TLR polymorphism(s).

Distribution of Chlamydia trachomatis serotypes in clinical urogenital samples from north-eastern Croatia.

The purpose of this study was to determine prevalence of Chlamydia trachomatis (Ct) urogenital infection and its serotype distribution from clinical samples in north-eastern Croatia. During a 3-year period, 2,379 urogenital samples were analyzed by real-time polymerase chain reaction (A group), while 4,846 genital swabs were analyzed by direct fluorescent antibody test (B group). 132 Ct positive specimens were genotyped by omp1 gene sequencing. The prevalence rate of Ct was 3.2 % in A and 1 % in B group. The most prevalent chlamydial genotype was E (44 %), followed by F (33 %), K (11.5 %), G (8 %), J/UW (5.3 %), D-IC (4.4 %), D-B120 (1.8 %), and B/IU, J/IU, Ia/IU (0.9 % each) serotypes. Single-nucleotide polymorphisms (SNPs) of omp1 gene were detected in E, K, and G serotypes. Some of these SNPs (C/T at position 272 and G/A at position 813 in E strain; C/T at position 884 in D strain) might represent novel omp1 variants.

Prevalence and risk factors for herpes simplex virus type 2 infections in East Croatia.

The aim of the study was to establish the seroprevalence of herpes simplex virus type 2 (HSV-2) among sexually active adults from East Croatia and to evaluate its correlates with demographic and behavioural risk factors. This cross-sectional study was conducted from the 1st June until the 30th September 2005 at the Department of Transfusion Medicine, Osijek University Hospital Center. The study included 423 blood donors composed of 366 (86.5%) men and 57 (13.5%) women. Demographic data and data on the risky sexual behaviour during the lifetime were collected with usage of an anonymous questionnaire consisting of 15 questions. Western blot testing revealed that 3.3% (14/423) subjects were positive for the presence of IgG antibodies to herpes simplex virus 2, i.e. 10 (2.7%) men and 4 (7.0%) women. A higher HSV-2 seroprevalence was associated with female sex, older age, marital status (with single subjects been under the greater risk), irregular condom use on sexual intercourses with new partners and with higher number (five or more) of sexual partners during lifetime. Among determined risk factors in the study population, only the connection between the HSV-2 positivity and the older age was statistically significant. The study has showed that the demographic rather than the behavioural risk factors are associated with higher prevalence of HSV-2 antibodies in the observed population.

Serologically detected "new" tick-borne zoonoses in eastern Croatia.

AIM: To establish serologically a contact with causative agents of human monocytic and granulocytic ehrlichiosis, human babesiosis, recently detected rickettsioses, and Lyme disease in individuals with a history of tick bite from three counties in eastern Croatia. METHODS: Seroepidemiologic testing was performed in 102 subjects with a history of tick bite, who either requested examination for a tick bite or were suspected of having tick-borne disease. The study was carried out during the 1998-1999 period in the area of the Vukovar-Srijem, Osijek-Baranya, and Brod-Posavina counties. Serum analysis was performed by indirect immunofluorescence assay for the detection of antibodies to causative agents of human monocytic and granulocytic ehrlichiosis (Ehrlichia chaffeensis and human granulocytic ehrlichiosis agent), human babesiosis (Babesia divergens), and rickettsiosis. Enzyme-linked immunosorbent assay was used for the detection of antibodies to the spirochete Borrelia burgdorferi, the cause of Lyme disease. The assays were performed at the Department of Microbiology, Osijek Public Health Institute in Osijek, and their results were confirmed at the Department of Microbiology and Immunology, School of Medicine in Ljubljana, Slovenia. RESULTS: Ehrlichia chaffensis antibodies were detected in 5 sera, and antibodies to the causative agent of human granulocytic ehrlichiosis in 7 sera. A low titer of antibodies to the etiologic agent of babesiosis (Babesia microti) was detected only in a single serum. Eight sera that were positive for rickettsial antibodies contained rather high titers of antibodies against Rickettsia conorii, the agent of Mediterranean fever, and Rickettsia rickettsii, the agent of Rocky Mountain spotted fever. In six out of these 8 sera, antibodies to Rickettsia typhi, the cause of murine typhus, were detected possibly as a cross-reaction with some "newly detected" rickettsia circulating in this part of Europe, most likely Rickettsia slovaca. Positive titer of antibodies to Borrelia burgdorferi was detected in 15 sera. CONCLUSION: The agents of human monocytic and granulocytic ehrlichiosis and of possibly newly detected rickettsiae were indirectly demonstrated to circulate in eastern parts of Croatia. The results obtained by IFA failed to provide definite evidence for the circulation of the human babesiosis agent, because the IFA used in our study detected Babesia microti, which prevails in the USA, but not Babesia divergens, which is the predominant cause of the disease in Europe. Serologic evidence for Borrelia burgdorferi infection was demonstrated in 80% of the subjects suspected of having the skin manifestation of Lyme disease.