SARS-CoV-2 specific antibody response after an mRNA vaccine as the third dose: Homologous versus heterologous boost

The aim of this study was to evaluate immunogenicity and longevity of the humoral immune response within six months after the homologous (BNT162b2/BNT162b2) or heterologous (BBIBP-CorV/BNT162b2) third dose, and to assess breakthrough infections among vaccinees during the Omicron wave in Serbia. Serum samples were analyzed at four timepoints: five months after the primary series; three weeks, three months, and six months after the boost. IgG antibodies against the receptor-binding domain of the spike protein were detected using enzyme-linked fluorescence assay. Both homologous (n = 55) and heterologous group (n = 36) showed a highly significant increase in antibody concentrations (p < 0.001) three weeks after the boost. A moderate inverse correlation between the age of recipients and the antibody levels at three weeks post-boost was observed in the homologous group (p = 0.02, r = -0.37), while the same correlation was not significant for heterologous group (p = 0.55, r = -0.15). Heterologous group had significantly higher antibody concentrations than homologous group at three weeks (Median 851.4(IQR 766.6-894.1); 784.3(676.9-847.4); p = 0.03) and three months post-boost (766.6(534.8-798.9); 496.8(361.6-664.0); p < 0.001). However, a significant decline in antibody response over time was noted for both strategies. The overall incidence of breakthrough cases was estimated at 36.36% (20/55) for homologous, and 16.67% (6/36) for heterologous group, but none of them required hospitalization. Although observed incidence in the homologous group was more than double when compared to the heterologous group, this difference was not statistically significant, most likely due to the small sample size. In conclusion, waning immunity after inactivated vaccine can be recovered by BNT162b2 heterologous boost regardless of the age of recipients, and both boost strategies induced potent humoral immune response and protection against severe COVID-19 during the Omicron wave. However, as the observed incidence of breakthrough infections was higher in the homologous group, although non-significant, this finding could indicate an advantage of heterologous approach.

New Iron Twist to Chloroquine─Upgrading Antimalarials with Immunomodulatory and Antimicrobial Features

Herein, upgraded chloroquine (CQ) derivatives capable of overcoming Plasmodium resistance and, at the same time, suppressing excessive immune response and risk of concurrent bacteremia were developed. Twelve new ferrocene-CQ hybrids tethered with a small azathia heterocycle (1,3-thiazolidin-4-one, 1,3-thiazinan-4-one, or 5-methyl-1,3-thiazolidin-4-one) were synthesized and fully characterized. All hybrids were evaluated for their in vitro antiplasmodial, antimicrobial, and immunomodulatory activities. Additional assays were performed on selected hybrids to gain insights into their mode of action. Although only hybrid 4a was more potent than the parent drug toward CQ-resistant Dd2 Plasmodium falciparum strain, several other hybrids (such as 6b, 6c, and 6d) manifested substantially improved antimicrobial and immunomodulatory properties. Interesting structure-activity relationship data were obtained, hinting at future research for the development of new multitarget chemotherapies for malaria and other infectious diseases complicated by drug resistance, bacterial co-infection, and immune-driven pathology issues.

Toxoplasma gondii Genotypes Circulating in Serbia-Insight into the Population Structure and Diversity of the Species in Southeastern Europe, a Region of Intercontinental Strain Exchange

In Europe, Toxoplasma gondii lineage II is dominant, and ToxoDB#1 the most frequently occurring genotype. The abundance of lineage III genotypes varies geographically and lineage I are rare, yet present in several regions of the continent. Data on the T. gondii population structure in southeastern Europe (SEE) are scarce, yet necessary to appreciate the diversity of the species in Europe. To help fill this gap, we genotyped 67 strains from nine species of intermediate hosts in Serbia by MnPCR-RFLP, determined the population structure, and identified the genotypes using ToxoDB. A neighbor-joining tree was also constructed from the isolates genotyped on nine loci. While 42% of the total genotype population consisted of ToxoDB#1 and ToxoDB#2, variant genotypes of both lineages comprised 46% of the population in wildlife and 28% in domestic animals and humans. One genotype of Africa 4 lineage was detected in a human sample. Interestingly, the findings include one lineage III variant and one II/III recombinant isolate with intercontinental distribution, which appear to be moderately related to South American genotypes. Based on these findings, SEE is a region of underappreciated T. gondii genetic diversity and possible strain exchange between Europe and Africa.

Postnatal ocular toxoplasmosis in immunocompetent patients

INTRODUCTION

Ocular toxoplasmosis is the most common cause of infectious posterior uveitis worldwide. It can be prenatal or postnatal in origin. Despite estimations that postnatal ocular toxoplasmosis is more prevalent, only several cases of proven postnatal ocular toxoplasmosis have been reported in non-epidemic settings. Here, the clinical evolution of ocular toxoplasmosis of conclusively proven postnatal origin in immunocompetent patients is reported.

METHODOLOGY

Postnatal ocular toxoplasmosis was diagnosed based on clinical diagnosis supported by the longitudinal detection of Toxoplasma gondii-specific IgG, IgM and IgA antibodies in the serum as well as by direct detection of the parasite (bioassay) and/or its DNA (real-time PCR) in aqueous humor.

RESULTS

Three cases involved adults in whom ocular toxoplasmosis developed during primary T. gondii infection, as part of the clinical presentation in two and as the sole manifestation in one patient. The fourth patient was a case of inactive ocular toxoplasmosis in a 14-year-old boy, where postnatal infection was confirmed by exclusion of maternal infection. The causative parasite strain was genotyped in only one case and it belonged to genotype II, the dominant type in Europe. One patient acquired the infection in Africa, suggesting an atypical strain.

CONCLUSIONS

The distinction between prenatal and postnatal ocular toxoplasmosis is only possible in particular clinical situations, and requires extensive laboratory investigation. Genotyping of the parasite strain involved may be important, particularly if atypical strains are suspected, requiring tailored treatment approaches.

Risk of reactivated toxoplasmosis in haematopoietic stem cell transplant recipients: a prospective cohort study in a setting withholding prophylaxis

OBJECTIVES

Reactivation of latent toxoplasmosis may be life-threatening in haematopoietic stem cell transplant (HSCT) recipients. We conducted an 8-year-long prospective study on the diagnosis and monitoring of reactivated toxoplasmosis in paediatric HSCT recipients. The primary objective was to determine the incidence of reactivated toxoplasmosis in a setting that withholds prophylaxis until engraftment. The second objective was to identify the subgroups of HSCT recipients particularly prone to reactivation who may benefit the most from regular PCR follow-up.

METHODS

Serological and qPCR screening targeting the Toxoplasma 529 bp gene was performed before HSCT, and continued by weekly monitoring after HSCT for a median time of 104 days.

RESULTS

Reactivated toxoplasmosis was diagnosed in 21/104 (20.2%), predominantly in allo- (19/75) and rarely in auto-HSCT (2/29) recipients. Over 50% (14/21) of cases were diagnosed during the first month after HSCT, while awaiting engraftment without prophylaxis. Toxoplasma disease evolved in only three (14.3%, 3/21) patients, all treated by allo-HSCT. Reactivation was more frequent in patients treated for acute lymphoblastic leukaemia (3/27, p 0.03) and especially, in recipients of haploidentical stem cells (10/20, p 0.005). Seronegative status of the donor (where was known) contributed to 75% (12/16) cases of reactivated toxoplasmosis after allo-HSCT.

DISCUSSION

The presented results show that peripheral blood-based qPCR, both before and after HSCT, is a valuable asset for the diagnosis of reactivated toxoplasmosis, whereas the results of serology in recipients should be interpreted with caution. Weekly qPCR monitoring, at least until successful engraftment and administration of prophylaxis, allows for prompt introduction of specific treatment.

Prospective Cohort Study of the Kinetics of Specific Antibodies to SARS-CoV-2 Infection and to Four SARS-CoV-2 Vaccines Available in Serbia, and Vaccine Effectiveness: A 3-Month Interim Report

Real-life data on the performance of vaccines against SARS-CoV-2 are still limited. We here present the rates of detection and levels of antibodies specific for the SARS-CoV-2 spike protein RBD (receptor binding domain) elicited by four vaccines available in Serbia, including BNT-162b2 (BioNTech/Pfizer), BBIBP-CorV (Sinopharm), Gam-COVID-Vac (Gamaleya Research Institute) and ChAdOx1-S (AstraZeneca), compared with those after documented COVID-19, at 6 weeks and 3 months post first vaccine dose or post-infection. Six weeks post first vaccine dose, specific IgG antibodies were detected in 100% of individuals fully vaccinated with BNT-162b2 (n = 100) and Gam-COVID-Vac (n = 12) and in 81.7% of BBIBP-CorV recipients (n = 148), while one dose of ChAdOx1-S (n = 24) induced specific antibodies in 75%. Antibody levels elicited by BNT-162b2 were higher, while those elicited by BBIBP-CorV were lower, than after SARS-CoV-2 infection. By 3 months post-vaccination, antibody levels decreased but remained ≥20-fold above the cut-off in BNT-162b2 but not in BBIBP-CorV recipients, when an additional 30% were seronegative. For all vaccines, antibody levels were higher in individuals with past COVID-19 than in naïve individuals. A total of twelve new infections occurred within the first 3 months post-vaccination, eight after the first dose of BNT-162b2 and ChAdOx1-S (one each) and BBIBP-CorV (six), and four after full vaccination with BBIBP-CorV, but none required hospitalization.

Aminoquinolines afford resistance to cerebral malaria in susceptible mice

OBJECTIVES

Malaria treatment is impeded by increasing resistance to conventional antimalarial drugs. Here we explored the activity of ten novel benzothiophene, thiophene and benzene aminoquinolines.

METHODS

In vitro testing was performed by the lactate dehydrogenase assay in chloroquine (CQ)-sensitive Plasmodium falciparum strain 3D7 and CQ-resistant (CQ^R) P. falciparum strain Dd2. In vivo activity was evaluated by a modified Thompson test using C57BL/6 mice infected with Plasmodium berghei ANKA strain.

RESULTS

Nine of the ten compounds had a lower 50% inhibitory concentration (IC₅₀) than CQ against the CQ^R strain Dd2. Five of these compounds that were available for in vivo evaluation were shown to be non-toxic. All five compounds administered at a dose of 160mg/kg/day for 3 days prolonged the survival of treated compared with untreated mice. Untreated control mice died by Day 7 with a mean parasitaemia of 15%. Among treated mice, a dichotomous outcome was observed, with a two-third majority of treated mice dying by Day 17 with a low mean parasitaemia of 5%, whilst one-third survived longer with a mean hyperparasitaemia of 70%; specifically, five of these mice survived a mean of 25 days, whilst two even survived past Day 31.

CONCLUSIONS

The significant antimalarial potential of this aminoquinoline series is illustrated by its excellent in vitro activity against the CQ^RP. falciparum strain and significant in vivo activity. Interestingly, compounds ClAQ7, ClAQ9 and ClAQ11 were able to confer resistance to cerebral malaria and afford a switch to hyperparasitaemia to mice prone to the neurological syndrome.

Taeniosis and cysticercosis in Serbia, 1990-2018: Significance of standard of living

OBJECTIVES

As is the case for all of Southeast Europe, Serbia is an area traditionally endemic for Taenia saginata and Taenia solium infections. This study was performed to analyse the epidemiological data on taeniosis and cysticercosis in Serbia for the period 1990-2018.

METHODS

Data on cases of T. saginata and T. solium infection were collected via a systematic search of published articles, the grey literature, and official reports, as well as by performing clinical observational studies of patients treated in the departments for infectious diseases of hospitals and university clinics in Serbia.

RESULTS

A total of 212 cases of taeniosis were reported, all between 1997 and 2004 when taeniosis was notifiable (incidence range 0.04-0.9/100 000 population/year). From 1990 to 2018, 170 cases of cysticercosis (all but one of neurocysticercosis), were registered (incidence range 0-0.29/100 000 population/year), with a strong decrease since 2000 and a single case in the last 9 years. The annual number of cases of both taeniosis (Pearson's r = 0.914, p =  0.001) and cysticercosis (Pearson's r = 0.582, p = 0.014) correlated with the consumer price index.

CONCLUSIONS

In Serbia, T. saginata and T. solium infections are autochthonous but occur only sporadically. However, the potential for re-emergence exists, depending on the socio-economic state of the country.

Examination of the antimalarial potential of experimental aminoquinolines: poor in vitro effect does not preclude in vivo efficacy

Malaria remains a major disease in the developing world and globally is the most important parasitic disease causing significant morbidity and mortality. Because of widespread resistance to conventional antimalarials, including chloroquine (CQ), new drugs are urgently needed. Here we report on the antimalarial efficacy, both in vitro and in vivo, of a series of aminoquinoline derivatives with adamantane or benzothiophene as a carrier. In vitro efficacy was evaluated by a lactate dehydrogenase (LDH) assay in cultures of a CQ-sensitive (3D7) and CQ-resistant (Dd2) strain of Plasmodium falciparum. Of a series of 26 screened compounds, 12 that exerted a growth inhibition rate of ≥50% were further examined in vitro to determine the 50% inhibitory concentration (IC₅₀) values. Nine compounds shown in preliminary experiments to be non-toxic in vivo were evaluated in C57BL/6 mice infected with Plasmodium berghei ANKA strain using a modified Thompson test. All nine compounds examined in vivo prolonged the survival of treated versus untreated mice, four of which afforded ≥60% survival. Most notably, two of these compounds, both with the adamantane carrier, afforded complete cure (100% survival and parasite clearance). Interestingly, one of these compounds had no in vitro effect against the CQ-resistant P. falciparum strain. Better in vivo compared with in vitro results suggest a role for compound metabolites rather than the compounds themselves. The results presented here point to adamantane as a carrier that enhances the antimalarial potential of aminoquinolines.

Reinvestigating Old Pharmacophores: Are 4-Aminoquinolines and Tetraoxanes Potential Two-Stage Antimalarials?

The syntheses and antiplasmodial activities of various substituted aminoquinolines coupled to an adamantane carrier are described. The compounds exhibited pronounced in vitro and in vivo activity against Plasmodium berghei in the Thompson test. Tethering a fluorine atom to the aminoquinoline C(3) position afforded fluoroaminoquinolines that act as intrahepatocytic parasite inhibitors, with compound 25 having an IC50 = 0.31 μM and reducing the liver load in mice by up to 92% at 80 mg/kg dose. Screening our peroxides as inhibitors of liver stage infection revealed that the tetraoxane pharmacophore itself is also an excellent liver stage P. berghei inhibitor (78: IC50 = 0.33 μM). Up to 91% reduction of the parasite liver load in mice was achieved at 100 mg/kg. Examination of tetraoxane 78 against the transgenic 3D7 strain expressing luciferase under a gametocyte-specific promoter revealed its activity against stage IV-V Plasmodium falciparum gametocytes (IC50 = 1.16 ± 0.37 μM). To the best of our knowledge, compounds 25 and 78 are the first examples of either an 4-aminoquinoline or a tetraoxane liver stage inhibitors.