The Development of Diagnostic and Vaccine Strategies for Early Detection and Control of Human Brucellosis, Particularly in Endemic Areas

Investigation of genomic island 2 deciphers the evolution of a genus Brucella

HGT acquisition of genomic island 2 (GI-2) into the Brucella genome endowed these organisms with two transglycosylases which function in the final steps of the O-polysaccharide (OPS) polymerization. Here, the investigation of the brucellaphage Pr genome revealed sequence similarities to GI-2 in two DNA regions, the Chelativorans sp. BNC1 and the Ochrobactrum anthropi ATCC 49188 DNAs, respectively. This led the investigation of the published GI-2 elements, using the phage attB and attP sequences as hallmarks of the integration site. The study identified a Mesorhizobium loti integrative, conjugative element (ICE) into which GI-2 integrated. A similar ICE, which nevertheless lacks GI-2, and shows characteristic chromosomal architectural differences between the taxa, was found in the genomes of the Ochrobactrum sister clade and the alphaproteobacterial Chelativorans sp. BNC1 strains. This proves that Brucella and Ochrobactrum diverged at the genus level while being in the state of a monopartite genome bearing organism.

Hepatic and extra-hepatic hydatid cysts: A case series of radiological and clinical insights

Hydatid disease, caused by Echinococcus granulosus, is a parasitic infection that primarily affects the liver but can also involve other organs, including the spleen, kidney, and peritoneum. This case series examined 9 patients with hydatid cysts, highlighting their clinical presentations, radiological findings, and management strategies. This study analyzed 9 patients diagnosed with hepatic and extrahepatic hydatid cysts. Comprehensive evaluations were performed for all patients, including clinical history and contrast-enhanced computed tomography (CT) imaging. The cases included cystic lesions in the liver (7 patients), spleen (3 patients), kidney (2 patients), and peritoneum (1 patient). Typical radiological features, such as the "double-wall sign," daughter cysts, and peripheral calcifications, were observed. The management strategies varied from surgical excision to medical therapy with albendazole. Hydatid disease presents diverse clinical and radiological features. Early diagnosis using advanced imaging techniques and a multidisciplinary approach is critical for effective management and prevention of complications.

Advances in biosensors: A breakthrough in rapid and precise brucellosis detection

Brucellosis, a significant zoonotic disease, poses a threat to both livestock and human health. Infections in livestock lead to abortion, infertility, and substantial economic losses in the industry. In humans, acute brucellosis can progress to a chronic condition, resulting in multisystemic infections with high morbidity and mortality rates. Additionally, the bioterrorism potential of certain Brucella species through aerosol transmission poses risks to laboratory workers and livestock handlers. Therefore, there is an urgent need for rapid and precise diagnosis of brucellosis in both animals and humans. Even with the availability of routine diagnostic techniques that are effective they frequently have some limitations. Biosensors, as innovative techniques, have demonstrated significant potential in detecting various pathogens with high efficiency. These biosensors can identify specific analytes, biomolecules of pathogenic bacteria, secreted antibodies against bacteria, and even the bacterial body in real time. Their high sensitivity, selectivity, and user-friendly configurations make them valuable tools for diagnostics. In this comprehensive review, beside the reviewing routine diagnostic tests for detecting brucellosis and discussing the positive and negative aspects of these methods, we explore different types of biosensors and their applications in diagnosing brucellosis. We hope to show how these advancements can result in quicker and more precise disease detection by offering a thorough evaluation of these technologies performance and contrasting it with more conventional diagnostic techniques. This improves patient outcomes by lowering the complications linked to delayed diagnosis in addition to advancing scientific knowledge of brucellosis.

Seroprevalence of brucellosis in camels and humans in the Al-Qassim region of Saudi Arabia and its implications for public health

Brucellosis is a significant zoonotic disease caused by intracellular, gram-negative bacteria from the genus Brucella. Although camels are classified as secondary hosts for Brucella species, they are among the most susceptible and vulnerable animals to brucellosis, particularly Brucella abortus (B. abortus) and Brucella melitensis (B. melitensis). The present study aimed to investigate the epidemiology of camel brucellosis as a zoonotic disease by determining the seroprevalence of brucellosis in both camels and humans, assessing potential risk factors (e.g., age, size, and location), and conducting molecular characterization of Brucella spp. associated with abortion in camels. The Rose Bengal Test (RBT), Antigen Rapid Brucella Antibody Test (ARBT), indirect enzyme-linked immunosorbent assay (I-ELISA), and complement fixation test (CFT) were used to detect brucellosis in both camels and humans. Additionally, a molecular method using polymerase chain reaction was used as a confirmatory technique. A total of 625 camel serum samples and 100 human serum samples were collected in sterile vacuum tubes from various camel farms and individuals across different localities in the Al Qassim region. Additionally, samples from 10 confirmed Brucella-infected camels (including the uterus and supramammary lymph nodes) were analyzed. The results indicated that the overall prevalence of brucellosis in camel sera was 9.72%, as determined by RBT, and 8.16%, as determined by ARBT. In contrast, the overall prevalence of brucellosis in human sera from febrile patients was found to be 17% via RBT. Notably, 57.98% of camel sera that tested positive for Brucella antibodies via RBT were also positive according to I-ELISA and CFT. Furthermore, 42.1%, 70.58%, and 47.05% of human sera that were positive for Brucella antibodies as determined by RBT were also positive according to I-ELISA and CFT, respectively. The highest seropositivity for camel brucellosis was observed in female camels, particularly in the Unaizah area of the Qassim region and among the Homr breed. The prevalence of human brucellosis was highest among females and individuals who consumed raw milk. At the molecular level, B. melitensis biovar 3 was detected in the examined tissues. In conclusion, intervention measures are vital for reducing brucellosis in humans and camels. Public awareness campaigns should highlight the importance of protective clothing when handling aborted she-camels and the need to boil or pasteurize milk. Additionally, studies should differentiate between vaccinated and nonvaccinated camels, and standardizing serological tests for diagnosing brucellosis should be prioritized.

Molecular and serological investigation of Brucella species in kennel and farm dogs in Iran

INTRODUCTION

Brucellosis is still a significant emerging threat to public health, as it can infect humans, wild, domestic animals, and livestock. Hence, the current study aims to determine the frequency of canine brucellosis (CB), its relationship with clinical findings and reproductive disorders in kennel and farm dogs, and its importance on public health.

MATERIALS AND METHODS

From January 2022 to December 2023, a total of 150 blood samples were taken from 100 adult dogs in breeding kennels and 50 shepherd dogs in breeding farms in Kerman, Iran. Rose Bengal test (RBT) and Wright tests were used for the primary screening of Brucella abortus (B. abortus) and Brucella melitensis (B. melitensis) species, and conventional IS711-based PCR and real-time polymerase chain reaction (RT-PCR) were performed to determine the Brucella genus and species in all samples.

FINDINGS

In kennel dogs, 34 % (34/100) had a history of breeding disorders, and 30 % (30/100) were RBT-positive. Moreover, B. canis and B. abortus species were detected in kennel dogs. Among farm dogs, 16 % (8/50) had a history of breeding disorders, and 28 % (14/50) were RBT positive. Additionally, B. canis, B. abortus, and B. melitensis species were detected in farm dogs. Feeding with unpasteurized milk was significantly related to a positive RBT in kennel dogs (p = 0.009), and there was a significant correlation between breeding disorders and seropositivity in kennel (p = 0.045) and farm dogs (p = 0.03).

CONCLUSION

The current study represents a significant advancement in understanding CB in Iran by the first molecular detection of B. canis, revealing B. melitensis and B. abortus as important pathogens in kennel and farm dogs and highlighting the public health significance of disease in Iran.

Immune response and protective efficacy of an experimentally developed inactivated oil adjuvant Brucella abortus vaccine in BALB/c mice

Objectives

This study evaluated the immunogenicity and protective efficacy of an inactivated oil adjuvant B. abortus vaccine in BALB/c mice.

Materials and Methods

Mice in group A (n = 30) received subcutaneous (s.c.) immunization with 0.1 ml of vaccine (1.5 × 107 inactivated B. abortus biovar 3 per mouse) and were boosted 4 weeks later. Group B (n = 30) received normal saline as unvaccinated controls. BALB/c, vaccinated and unvaccinated mice were challenged with B. abortus biovar 3 (3 × 107 cells per mouse) at 6 weeks post-vaccination (WPV). Serum antibody levels were assessed at 0, 1, 2, 3, 4, 5, and 6 WPV using RBPT and i-ELISA. Cellular-mediated immune (CMI) response was evaluated by measuring the skin thickness of vaccinated mice's left and right hind footpads sensitized with B. abortus soluble antigen and PBS, respectively. Bacterial persistence and spleen histopathological lesions were evaluated at 1, 2, and 3 weeks post-challenge.

Results

The vaccinated mice developed B. abortus-specific serum IgG response from 2 WPV. The highest serum IgG titer was observed in 5-6 WPV (p < 0.001). The skin thickness was significantly higher in the left footpad than the right footpad (p < 0.001). Huge cellular infiltration with mononuclear and polynuclear cells was noticed in the dermis and sub-dermis areas of the left footpad. The spleen weight and bacterial load in the spleen were significantly reduced in vaccinated mice compared to unvaccinated control mice (p < 0.001).

Conclusions

The inactivated oil adjuvant B. abortus vaccine induced both humoral and CMI responses, which conferred protection in BALB/c mice against virulent challenge infections.

Study on the value of second-generation sequencing technology in the clinical diagnosis of osteoarticular brucellosis

To assess the value of next-generation sequencing (NGS) technology in the diagnosis of osteoarticular brucellosis pathogenesis. Fifty eight patients admitted to the Department of Orthopaedics, Hebei Provincial Chest Hospital from January 2021 to January 2023 were retrospectively analyzed, and the patients were classified into 48 cases in the osteoarticular brucellosis group and 10 cases in the nonosteoarticular brucellosis group according to the final clinical diagnosis. All patients underwent serum agglutination test (SAT), CT-guided puncture or surgical sampling of lesions for bacteriological culture and NGS after admission. The diagnostic efficacy of these three methods for osteoarticular brucellosis was compared using the final clinical diagnosis as the reference standard. Among the 58 patients with suspected osteoarticular brucellosis, 40 cases (68.97%) were positive by NGS, 33 cases (56.89%) by SAT and 10 cases (17.24%) by culture, and the differences were statistically significant (p < 0.05). Using the final clinical diagnosis as a criterion, the sensitivity of NGS, SAT, and culture for the detection of osteoarticular brucellosis was 83.33%, 62.50%, and 20.83%, respectively, the specificity was 100.00%, 70.00%, and 100.00%, the diagnostic accuracy was 86.20%, 63.79%, and 34.49%, and the κ values were 0.799, 0.590, and 0.504, respectively. NGS has a high pathogen detection rate and sensitivity in the pathogenetic diagnosis of patients with osteoarticular brucellosis and can provide clinical guidance for the diagnosis and management of patients with osteoarticular brucellosis.

Immunogenicity of Brucella Trivalent Immunogen-Containing Polyethyleneimine Nanostructure Targeted with LPS in a Mouse Model

Brucella is a facultative intracellular gram-negative coccobacillus. It is nonsporulating and reproduced in macrophage phagosomes. The use of nanostructures as drug and vaccine carriers has recently received attention due to their ability to control the release profile and protect the drug molecules. This study presents a suitable nano-polyethyleneimine formulation to be used as an immunoadjuvant and LPS along with trivalent candidate antigens of TF, BP26, and omp31 to selectively stimulate the immune response. After designing and evaluating the immunogenic structure by databases and bioinformatics software, recombinant protein cloning and gene expression were performed in Escherichia coli BL21 bacteria. This protein was extracted from the cultured cells, purified by Ni-NTA column. After placing the antigen inside the polyethyleneimine nanostructure, various properties of the nanoparticles, including their size, zeta potential, and retention rate for injection and inhalation of mice, diffusion efficacy, and antigen binding evaluation were evaluated. Mice were treated with different groups of antigens and nanoparticles on days 0, 10, 24, and 38. Two weeks after the last injection, the level of cytokines were investigated in spleen cells, including IFN-γ, IL-4, and IL-12. The serum concentration of IgG2a and IgG1 antibodies were also assessed. The response was consistent with significant production of IgG1, IgG2a, IFN-γ21, IL-12, and IL-4 compared to the controls (P < 0.05). Compared to the positive and negative control groups, recombinant protein and nanoparticles showed a good response in subsequent injections with live bacterial strains. The present study also revealed the potential of the developed recombinant protein as a candidate in the design and manufacture of subunit vaccines against Brucella species. This protein stimulates cellular and humoral immune responses compared to the positive control groups. These findings can be useful in the prevention and control of brucellosis and pave the way for further research by researchers around the world.

Enhanced diagnostic accuracy of combined serological and bacteriological tests for brucella infection

OBJECTIVE

To analyze the effects and value of combining serological and bacteriological tests in diagnosing Brucella infection.

METHODS

In this retrospective study, patients suspected of having Brucella infection admitted to Lishui Second People's Hospital from January 2019 to December 2022 were assessed using serological, bacteriological, and combined (serological + bacteriological) tests. The diagnostic performance of each test was compared using previous clinical results as the gold standard. We also compared the acceptance rate and satisfaction with clinical diagnostic results for the different testing modalities.

RESULTS

The combined examination (serological + bacteriological test) showed higher diagnostic efficiency for Brucella infection compared to single serological and single bacteriological tests (P < 0.05). Similarly, the satisfaction rate for the clinical diagnostic effects of the combined examination was higher than for the serological and bacteriological tests alone (P < 0.05).

CONCLUSION

The combination of serological and bacteriological tests provides superior diagnostic value for Brucella infection, with high diagnostic accuracy, sensitivity, and specificity. It is recommended as the preferred method for clinical diagnosis.

A novel vaccine strategy against Brucellosis using Brucella abortus multi-epitope OMPs vaccine based on Lactococcus lactis live bacterial vectors

Brucella infections typically occur in mucosal membranes, emphasizing the need for mucosal vaccinations. This study evaluated the effectiveness of orally administering Lactococcus lactis (L. lactis) for producing the Brucella abortus multi-epitope OMPs peptide. A multi-epitope plasmid was generated through a reverse vaccinology method, and mice were administered the genetically modified L. lactis orally as a vaccine. The plasmid underwent digestion, synthesizing a 39 kDa-sized protein known as OMPs by the target group. The sera of mice that were administered the pNZ8124-OMPs-L. lactis vaccine exhibited a notable presence of IgG1 antibodies specific to outer membrane proteins (OMPs), heightened levels of interferon (IFN-λ) and tumor necrosis factor alpha (TNF-α), and enhanced transcription rates of interleukin 4 (IL-4) and interleukin 10 (IL-10). The spleen sections from the pNZ8124-OMPs-L. lactis and IRIBA group had less morphological damage associated with inflammation, infiltration of lymphocytes, and lesions to the spleen. The findings present a novel approach to utilizing the food-grade, non-pathogenic L. lactis as a protein cell factory to synthesize innovative immunological candidate OMPs. This approach offers a distinctive way to evaluate experimental medicinal items' practicality, safety, affordability, and long-term sustainability.

Traditional cheese consumption leading to hemodialysis induced by rifampin treatment: A case report

This case report details the journey of a 51-year-old man residing in a remote Iranian village, involved in livestock rearing, who was hospitalized due to Brucellosis contracted from consuming traditional cheese and dairy products. Initially treated with doxycycline and rifampin, complications arose during antituberculosis therapy, with the patient developing symptoms of nausea, vomiting, and edema alongside renal function deterioration necessitating medication cessation. Subsequent manifestations of proteinuria, toxic hepatitis, and nephrotic syndrome prompted renal biopsy, revealing drug-induced glomerular and tubular damage. Swift cessation of rifampicin, combined with prednisolone therapy, led to symptom amelioration, resulting in the cessation of dialysis and the patient's discharge within three weeks. This case underscores the intricate relationship between traditional cheese consumption, medication-induced renal complications, and the importance of timely intervention and appropriate management in achieving a successful patient outcome.

Brucellosis: Unveiling the complexities of a pervasive zoonotic disease and its global impacts

One zoonotic infectious animal disease is brucellosis. The bacteria that cause brucellosis belong to the genus Brucella. Numerous animal and human species are affected by brucellosis, with an estimated 500,000 human cases recorded annually worldwide. The occurrence of new areas of infection and the resurgence of infection in already infected areas indicate how dynamically brucellosis is distributed throughout different geographic regions. Bacteria originate from the blood and are found in the reticuloendothelial system, the liver, the spleen, and numerous other locations, including the joints, kidneys, heart, and genital tract. Diagnosis of this disease can be done by bacterial isolation, molecular tests, modified acid-fast stain, rose bengal test (RBT), milk ring test, complement fixation test, enzyme-linked immunosorbent assay, and serum agglutination test. The primary sign of a Brucella abortus infection is infertility, which can result in abortion and the birth of a frail fetus that may go on to infect other animals. In humans, the main symptoms are acute febrile illness, with or without localization signs, and chronic infection. Female cattle have a greater risk of contracting Brucella disease. Human populations at high risk of contracting brucellosis include those who care for cattle, veterinarians, slaughterhouse employees, and butchers. Antibiotic treatment of brucellosis is often unsuccessful due to the intracellular survival of Brucella and its adaptability in macrophages. A "one health" strategy is necessary to control illnesses like brucellosis.

Hunting for Answers: Assessing Brucella spp. Seroprevalence and Risks in Red Deer and Wild Boar in Central Portugal

Between 2016 and 2023, a cross-sectional study was conducted in the central region of Portugal in order to better understand the epidemiology and public health risks resulting from the handling and consumption of game animals infected with Brucella spp. The seroprevalence and risk factors for Brucella spp. seropositivity were evaluated. Antibodies against Brucella spp. were determined using a commercial enzyme-linked immunosorbent assay (ELISA) according to the manufacturer's instructions. Results showed that in the 650 serum samples collected from red deer (n = 298) and wild boars (n = 352) in Portugal, 21.7% (n = 141; 95% CI: 18.6-25.1%) tested positive. Wild boar had a significantly higher prevalence (35.5%; 95% CI: 30.5-40.8%) than red deer (5.4%, 95% CI: 3.1-8.6%; p ≤ 0.001). Risk factors for seropositivity were investigated using multivariable logistic regression models. The odds of being seropositive was 8.39 (95% CI: 4.75-14.84; p ≤ 0.001) times higher in wild boar than in red deer. Correlations between sex, age, body condition, and seropositivity could not be observed. The higher seroprevalence in wild boar suggests that this species may primarily contribute to the Brucella spp. ecology in central Portugal.

The Reasons Behind Long-Term Endemicity of Brucellosis in Low and Middle-Income Countries: Challenges and Future Perspectives

Brucellosis is a neglected worldwide zoonotic disease with more than 500,000 new human cases each year. Direct contact with infected animals and consumption of undercooked animal origin foods are the main routes of brucellosis transmission to humans. Although long endeavor has been applied to control and eliminate brucellosis from animal and human populations in developing countries especially in low- and middle-income countries (LMICs), the disease is still endemic in these regions. Many common or unique factors including raw milk consumption, unhygienic slaughter of livestock, extensive husbandry, budgetary limitations, misdiagnosis, and other conditions play a role in long-term endemicity of brucellosis in these locations. It has been shown that One Health is the only practical approach to control brucellosis; however, applying such methods is challenging in low-resource areas. In such conditions, brucellosis is continuously maintained in animals and repeatedly spread to human populations. In this article, factors playing a critical role in brucellosis endemicity, and the real conditions challenging the application of One Health approach in control of brucellosis are highlighted.

Brucellosis: epidemiology, pathogenesis, diagnosis and treatment-a comprehensive review

Background: Brucellosis is a pervasive zoonotic disease caused by various Brucella species. It mainly affects livestock and wildlife and poses significant public health threats, especially in regions with suboptimal hygiene, food safety, and veterinary care standards. Human contractions occur by consuming contaminated animal products or interacting with infected animals. Objective: This study aims to provide an updated understanding of brucellosis, from its epidemiology and pathogenesis to diagnosis and treatment strategies. It emphasizes the importance of ongoing research, knowledge exchange, and interdisciplinary collaboration for effective disease control and prevention, highlighting its global health implications. Methods: Pathogenesis involves intricate interactions between bacteria and the host immune system, resulting in chronic infections characterized by diverse clinical manifestations. The diagnostic process is arduous owing to non-specific symptomatology and sampling challenges, necessitating a fusion of clinical and laboratory evaluations, including blood cultures, serological assays, and molecular methods. Management typically entails multiple antibiotics, although the rise in antibiotic-resistant Brucella strains poses a problem. Animal vaccination is a potential strategy to curb the spread of infection, particularly within livestock populations. Results: The study provides insights into the complex pathogenesis of brucellosis, the challenges in its diagnosis, and the management strategies involving antibiotic therapy and animal vaccination. It also highlights the emerging issue of antibiotic-resistant Brucella strains. Conclusions: In conclusion, brucellosis is a significant zoonotic disease with implications for public health. Efforts should be directed towards improved diagnostic methods, antibiotic stewardship to combat antibiotic resistance, and developing and implementing effective animal vaccination programs. Interdisciplinary collaboration and ongoing research are crucial for addressing the global health implications of brucellosis.

Effects of major OMPs and LPS of Brucella on the control of activation of bone marrow-derived dendritic cells and proliferation of T-lymphocytes in mice

Background

Brucella outer membrane proteins (OMPs) are highly immunogenic, and lipopolysaccharides (LPS) are also considered significant antigens, making them potential candidates for subunit vaccines.

Aims

To investigate the effects of Brucella OMPs and LPSs on mouse bone marrow-derived dendritic cells (BMDC) activation and T-lymphocyte proliferation.

Methods

BMDC were isolated and cultured in vitro, and subsequently co-cultured with Brucella recombinant proteins (rOMP10, rOMP19, rBP26, rOMP25, and rOMP31), as well as smooth LPS (S-LPS) or rough LPS (R-LPS). The expression of maturation markers on the surface of BMDCs was determined using flow cytometry, while the expression of TLR receptors was determined using RT-PCR. The levels of inflammatory cytokines were measured using iELISA, and the impact on the proliferation of mouse T-lymphocytes was assessed using the MTT method.

Results

The impact of LPS on BMDC maturation, TLRs-mediated cytokine secretion, and antigen presentation was found to be limited. In contrast, rOMP10, rOMP19, and rBP26 were observed to promote BMDC maturation, increase the expression of TLR-2 and TLR-4 mRNA, and activate T-lymphocyte proliferation by significantly increasing the expression of pro-inflammatory cytokines (TNF-α, IFN-γ, IL-6, IL-12) and antigen-presenting molecules. However, rOMP25 and rOMP31 did not promote BMDC maturation, inhibited the expression of MHCI and MHCII antigen-presenting molecules, and increased the expression of inflammation-suppressing cytokines (IL-10 and IL-4), resulting in the inhibition of T-lymphocyte proliferation.

Conclusion

Brucella OMP10, OMP19, and BP26 play an important role in activating the host immune response, while OMP25 together with OMP31 may play a role in Brucella immune escape.

Immunoinformatics analysis of Brucella melitensis to approach a suitable vaccine against brucellosis

BACKGROUND

Brucellosis caused by B. melitensis is one of the most important common diseases between humans and livestock. Currently, live attenuated vaccines are used for this disease, which causes many problems, and unfortunately, there is no effective vaccine for human brucellosis. The aim of our research was to design a recombinant vaccine containing potential immunogenic epitopes against B. melitensis.

METHODS

In this study, using immunoinformatics approaches, 3 antigens Omp31, Omp25, and Omp28 were identified and the amino acid sequence of the selected antigens was determined in NCBI. Signal peptides were predicted by SignaIP-5.0 server. To predict B-cell epitopes from ABCpred and Bcepred servers, to predict MHC-I epitopes from RANKPEP and SYFPEITHI servers, to predict MHC-II epitopes from RANKPEP and MHCPred servers, and to predict CTL epitopes were used from the CTLPred server. Potentially immunogenic final epitopes were joined by flexible linkers. Finally, allergenicity (AllerTOP 2.0 server), antigenicity (Vaxijen server), physicochemical properties (ProtParam server), solubility (Protein-sol server), secondary (PSIPRED and GRO4 servers) and tertiary structure (I-TASSER server), refinement (GalaxyWEB server), validation (ProSA-web, Molprobity, and ERRAT servers), and optimization of the codon sequence (JCat server) of the structure of the multi-epitope vaccine were analyzed.

RESULTS

The analysis of immunoinformatics tools showed that the designed vaccine has high quality, acceptable physicochemical properties, and can induce humoral and cellular immune responses against B. melitensis bacteria. In addition, the high expression level of recombinant antigens in the E. coli host was observed through in silico simulation.

CONCLUSION

According to the results in silico, the designed vaccine can be a suitable candidate to fight brucellosis and in vitro and in vivo studies are needed to evaluate the research of this study.