Immunoproteomic and Immunoinformatic Approaches Identify Sensitive Antigens for Diagnosing Anisakis pegreffii Infection

Anisakis are foodborne parasites that opportunistically parasitize humans, leading to acute abdominal symptoms and allergies. Besides gastroscopy, no other diagnostic technique is available. Consequently, it is necessary to identify specific biomarkers and then develop molecular techniques for diagnosing Anisakis infection. In the present study, we used immunoproteomic and immunoinformatic approaches to identify sensitive antigens for diagnosing Anisakis pegreffii infection. A total of three proteins, including Ani609 (VDK51609), Ani941 (VDK75941), and AniS13, were identified based on immunoinformatic results. Then, the indirect ELISA method was developed based on the recombinant proteins, showing a similar diagnostic capability to that of parasitic soluble proteins. Next, a Gaussia luciferase immunoprecipitation assay (LIPS) was further developed upon the fusion of the proteins and Gaussia luciferase. The LIPS method indicated that A. pegreffii infection could be detected in rats as early as 1 week post infection, especially for Ani941. Overall, we identified the novel antigens using immunoproteomic and immunoinformatic approaches and then developed a sensitive method for diagnosing A. pegreffii infection, particularly for the early stage.

A σC-protein-based indirect enzyme-linked immunosorbent assay for clinical detection of antiavian reovirus antibodies

Avian reovirus (ARV) is the causative agent of avian viral arthritis and causes significant economic losses to the global poultry industry. For clinical diagnosis, detecting ARV-specific antibodies is crucial. We successfully expressed the ARV-σC protein in insect cells using the baculovirus expression vector system, achieving an expression level of approximately 200 mg/L. We developed an indirect enzyme-linked immunosorbent assay (iELISA) using the ARV-σC protein as a coating antigen to detect antibodies against it. The inter-batch and intrabatch coefficients of iELISA variation were less than 10%. Its sensitivity (1:12,800 diluted in serum) was 4 times higher than that of the indirect immunofluorescence assay (IFA; 1:3200 diluted in serum), and it showed no cross-reactivity with antibodies against other common avian viruses (such as Infectious bursal disease virus, Newcastle disease virus). The practicality of the iELISA was further evaluated using clinical samples. 300 clinical sera from chickens vaccinated with the ARV attenuated vaccine and 20 SPF sera were tested using both the iELISA and the IFA, demonstrating a 100% conformity rate. In conclusion, these results suggest that the iELISA developed in this study is a rapid, sensitive, and specific method that could serve as an effective diagnostic tool for monitoring and controlling avian viral arthritis.

Anti-SARS-CoV-2 IgM Antibody Levels Measured by an In-House ELISA in a Convalescent Latin Population Persist over Time and Exhibit Neutralizing Capacity to Several Variants of Concern

BACKGROUND

The coronavirus, SARS-CoV-2, is the causative agent for COVID-19, first registered in Wuhan, China and responsible for more than 6 million deaths worldwide. Currently, RT-PCR is the gold-standard method for diagnosing COVID-19. However, serological tests are needed for screening acute disease diagnosis and screening large populations during the COVID-19 outbreak.

OBJECTIVES

Herein, we described the development and validation of an in-house enzyme-linked immunosorbent assay (ELISA) for detecting the levels of anti-spike-1-RBD IgM antibody (CovIgM-ELISA) in well-defined serum/plasma panel for screening and identifying subjects infected with SARS-CoV-2 in a Latin population.

METHOD

In-house CovIgM-ELISA has the format of an indirect ELISA. It was optimized by checkerboard titration using recombinant SARS-CoV-2 spike-S1-RBD protein as an antigen.

RESULTS

We found that, compared to the RT-PCR as the standard method, the in-house CovIgM-ELISA displayed sensitivities of 96.15% and 93.22% for samples collected up to 30 or 60 days after infection, respectively, as well as 95.59% specificity with 97.3% accuracy. The agreement kappa value (κ) of our CovIgM-ELISA was substantial when compared to RT-PCR (κ = 0.873) and the anti-SARS-CoV-2 IgM ELISA (InBios Int) (κ = 0.684). The IgM levels detected in the population positively correlated with the neutralizing activity against the wild-type, Alpha and Delta variants of concern, but failed to neutralize Omicron.

CONCLUSIONS

These data indicate that our in-house CovIgM-ELISA is a compatible performing assay for the detection of SARS-CoV-2 infection.

Development of an Indirect ELISA to Distinguish between Porcine Sapelovirus-Infected and -Vaccinated Animals Using the Viral Nonstructural Protein 3AB

Porcine sapelovirus (PSV) is a new pathogen that negatively impacts the pig industry in China. Affected pigs experience severe diarrhea and even death. Vaccination is used to control disease outbreaks, and sensitive diagnostic methods that can distinguish infected animals from vaccinated animals (DIVA) are essential for monitoring the effectiveness of disease control programs. Tests based on the detection of the nonstructural protein (NSP) 3AB are reliable indicators of viral replication in infected and vaccinated animals. In this study, the recombinant PSV 3AB protein was expressed by a prokaryotic expression system, and an indirect ELISA method was established. Serum samples from healthy animals, immunized animals, and infected animals were evaluated. The ELISA method identified 3AB with high sensitivity (99.78%) and specificity (100.0%), and no cross-reaction was observed with serum antibodies against porcine reproductive and respiratory syndrome virus (PRRSV), infection with classical swine fever virus (CSFV), pseudorabies virus (PRV), bovine viral diarrhea virus (BVDV), porcine epidemic diarrhea virus (PEDV), or foot-and-mouth disease virus (FMDV). The ELISA method described here can effectively distinguish infected and vaccinated animals and is an important inexpensive tool for monitoring serum and controlling PSV.

Detection of Antibodies against Feline Morbillivirus by Recombinant Matrix Enzyme-Linked Immunosorbent Assay

Feline morbillivirus (FeMV) has been associated with feline health, although its exact role in pathogenesis is still debated. In this study, an indirect enzyme-linked immunosorbent assay (i-ELISA) targeting a recombinant matrix protein of FeMV (rFeMV-M) was developed and assessed in comparison to a Western blotting (WB) assay. The i-ELISA was evaluated using blood samples from 136 cats that were additionally tested with real-time reverse-transcription PCR (RT-qPCR). The i-ELISA exhibited a sensitivity of 90.1%, specificity of 75.6%, positive predictive value of 88.2%, and negative predictive value of 79.1%. The agreement between i-ELISA and WB analyses was substantial (a κ coefficient of 0.664 with a 95% confidence interval of 0.529 to 0.799). Within the study group, 68.4% (93/136) of the cats were serologically positive in the i-ELISA and 66.9% (91/136) in the WB assay, with 11.8% (11/93) of false positivity with the i-ELISA. However, only 8.1% (11/136) of the cats tested positive for FeMV using RT-qPCR (p < 0.001). The developed i-ELISA proved effective in identifying FeMV-infected cats and indicated the prevalence of FeMV exposure. Combining FeMV antibody detection through i-ELISA with FeMV RT-qPCR could offer a comprehensive method to determine and monitor FeMV infection status. Nevertheless, this assay still requires refinement due to a significant number of false positive results, which can lead to the misdiagnosis of cats without antibodies as having antibodies. This study also provided the first evidence of seroprevalence against FeMV among cat populations in Thailand, contributing valuable insights into the geographic distribution and prevalence of this virus.

Schistosoma japonicum extracellular vesicle proteins serve as effective biomarkers for diagnosing parasite infection

Schistosoma species are the causative agent of schistosomiasis and shows worldwide distribution. There is a great need to develop a sensitive diagnostic approach for controlling the disease. Previously, we identified large numbers of Extracellular Vesicle (EV) proteins from Schistosoma japonicum (S. japonicum), but rarely these proteins have been evaluated for their diagnostic potential. In the present study, we performed bioinformatic analyses of S. japonicum identified EV-associated proteins from the previous study and then identified Schistosoma-specific proteins with potentially secreted capability. Among them, we selected SJCHGC02838 protein, SJCHGC05593 protein, SJCHGC05668 protein and a hypothetical protein (SJHYP) to evaluate their diagnostic potential for detecting S. japonicum infection. First, we determined the expression of these four proteins at the transcript levels using qRT-PCR and revealed that all these genes showed higher expression in adult stage. Then, we cloned the full-length cDNA for each protein into a prokaryotic expression vector and successfully generated the recombinant proteins. Upon the purification of recombinant proteins, we developed an indirect ELISA method to evaluate the diagnostic potential of these purified recombinant proteins. The results showed high sensitivity for detecting Schistosoma infection. Additionally, these proteins also displayed a good potential for detecting Schistosoma infection, especially SJCHGC05668 protein at an early stage. The diagnostic potentials of these recombinant proteins were further evaluated by Western blot and comparatively analyzed by our previously developed cfDNA methods.

Establishment of an ELISA Based on a Recombinant Antigenic Protein Containing Multiple Prominent Epitopes for Detection of African Swine Fever Virus Antibodies

African swine fever virus (ASFV) poses a significant threat to the global pig industry, necessitating accurate and efficient diagnostic methods for its infection. Previous studies have often focused on a limited number of epitopes from a few proteins for detecting antibodies against ASFV. Therefore, the current study aimed to use multiple B-cell epitopes in developing an indirect Enzyme-Linked Immunosorbent Assay (ELISA) for enhanced detection of ASFV antibodies. For the expression of recombinant protein, k3 derived from 27 multiple peptides of 11 ASFV proteins, such as p72, pA104R, pB602L, p12, p14.5, p49, pE248R, p30, p54, pp62, and pp220, was used. To confirm the expression of the recombinant protein, we used the Western blotting analysis. The purified recombinant K3 protein served as the antigen in our study, and we employed the indirect ELISA technique to detect anti-ASFV antibodies. The present finding showed that there was no cross-reactivity with antibodies targeting Foot-and-mouth disease virus (FMDV), Porcine circovirus type 2 (PCV2), Pseudorabies virus (PRV), Porcine reproductive and respiratory syndrome virus (PRRSV), and Classical swine fever virus (CSFV). Moreover, the current finding was sensitive enough to find anti-ASFV in serum samples that had been diluted up to 32 times. The test (k3-iELISA) showed diagnostic specificity and sensitivity of 98.41% and 97.40%, respectively. Moreover, during the present investigation, we compared the Ingenasa kit and the k3-iELISA to test clinical pig serum, and the results revealed that there was 99.00% agreement between the two tests, showing good detection capability of the k3-iELISA method. Hence, the current finding showed that the ELISA kit we developed can be used for the rapid detection of ASFV antibodies and used as an alternative during serological investigation of ASF in endemic areas.

Seroprevalence of Anti-SARS-CoV-2 Antibodies in Cats during Five Waves of COVID-19 Epidemic in Thailand and Correlation with Human Outbreaks

Human-to-animal SARS-CoV-2 transmission was observed, including a veterinarian contracting COVID-19 through close contact with an infected cat, suggesting an atypical zoonotic transmission. This study investigated the prevalence of SARS-CoV-2 antibodies in cats during human outbreaks and elucidated the correlation between cat infections and human epidemics. A total of 1107 cat serum samples were collected and screened for SARS-CoV-2 antibodies using a modified indirect ELISA human SARS-CoV-2 antibody detection kit. The samples were confirmed using a cPass™ neutralization test. The SARS-CoV-2 seropositivity rate was 22.67% (199/878), mirroring the trend observed in concomitant human case numbers. The waves of the epidemic and the provinces did not significantly impact ELISA-positive cats. Notably, Chon Buri exhibited a strong positive correlation (r = 0.99, p = 0.009) between positive cat sera and reported human case numbers. Additionally, the cPass™ neutralization test revealed a 3.99% (35/878) seropositivity rate. There were significant differences in numbers and proportions of positive cat sera between epidemic waves. In Samut Sakhon, a positive correlation (r = 1, p = 0.042) was noted between the proportion of positive cat sera and human prevalence. The findings emphasize the need for ongoing surveillance to comprehend SARS-CoV-2 dynamics in both human and feline populations.

Development of an indirect ELISA system for diagnosis of porcine edema disease using recombinant modified Stx2e antigen

AIM

This study aimed to develop a sensitive and specific recombinant antigen protein indirect enzyme-linked immunosorbent assay (ELISA) kit to detect the Shiga toxin (Stx)-producing Escherichia coli (STEC) antibodies against porcine edema disease (ED).

METHODS AND RESULTS

The recombinant antigen was co-expressed with the STEC-derived Stx2e A2-fragment and Stx2e B protein in E. coli BL21(DE3) pLysS cells and purified using maltose-binding protein open columns. We used a Shiga-like toxin 2 antibody to test the specificity of the recombinant antigen in an indirect ELISA, which was detected in antigen-coated wells but not in uncoated wells. We tested the indirect ELISA system using samples from the STEC-immunized pig group, the commercial swine farm group, and healthy aborted fetal pleural effusion group; five and twenty samples, respectively, were positive for STEC in the former, whereas all three samples were negative for STEC in the latter.

CONCLUSIONS

This newly developed indirect ELISA may be a specific method for diagnosing STEC infections in pigs.

Establishment of an Indirect ELISA Method for the Detection of the Bovine Rotavirus VP6 Protein

The objective of this study was to develop an indirect ELISA utilizing a polyclonal antibody against bovine rotavirus (BRV) VP6 protein. To achieve this, pcDNA3.1-VP6, a recombinant eukaryotic expression plasmid, was constructed based on the sequence of the conserved BRV gene VP6 and was transfected into CHO-K1 cells using the transient transfection method. The VP6 protein was purified as the coating antigen using nickel ion affinity chromatography, and an indirect ELISA was subsequently established. The study found that the optimal concentration of coating for the VP6 protein was 1 μg/mL. The optimal blocking solution was 3% skim milk, and the blocking time was 120 min. The secondary antibody was diluted to 1:4000, and the incubation time for the secondary antibody was 30 min. A positive result was indicated when the serum OD450 was greater than or equal to 0.357. The coefficients of variation were less than 10% both within and between batches, indicating the good reproducibility of the method. The study found that the test result was positive when the serum dilution was 217, indicating the high sensitivity of the method. A total of 24 positive sera and 40 negative sera were tested using the well-established ELISA. The study also established an indirect ELISA assay with good specificity and sensitivity for the detection of antibodies to bovine rotavirus. Overall, the results suggest that the indirect ELISA method developed in this study is an effective test for detecting such antibodies.

Serosurvey and associated risk factors for bovine viral diarrhea virus infection in cattle in Egypt

Bovine viral diarrhea virus (BVDV), is widely spread, poses a considerable risk of infection in the majority of dairy farms, causing respiratory, gastrointestinal, and reproductive problems. The aim of this study was to determine the seroprevalence and the risk variables associated with the seroprevalence of BVDV infection in cattle in four Egyptian governorates. A total of 680 blood samples were collected from cattle and examined for the presence of antibodies against BVDV using indirect ELISA (iELISA). Reproductive and management factors were considered, and epidemiological surveys were conducted. The total seroprevalence of BVDV in cattle was 18.24% (124/680) and it was significantly higher in females 19.66% (116/590), cattle older than 8 years 22.14% (62/280), dairy animals 22.65% (94/514), introduction of new animals to herd 21.39% (89/416), breeding with artificial insemination 28.46% (74/260), animals with history of abortion 28.76% (49/357), or during lactation stage 23% (89/387). The present findings suggest that BVD is prevalent in Egyptian dairy cattle and has an impact on farm productivity and production. Therefore, older, lactating, and aborted animals should also be identified for the disease, pose a risk of infection, and be handled appropriately.

Expression and self-assembly of virus-like particles from porcine parvovirus and its application in antibody detection

Porcine parvovirus (PPV) is a major causative agent in reproductive pig disease. The swine industry faces a significant economic and epizootic threat; thus, finding a reliable, quick, and practical way to detect it is essential. In this investigation, recombinant PPV VP2 protein was expressed in the Escherichia coli ( E. coli) expression systems. As shown by electron microscopy (TEM), Western blot, and hemagglutination (HA) assays, the recombinant VP2 protein was successfully assembled into virus-like particles (VLPs) after being expressed and purified. These VLPs had a structure that was similar to that of real PPV viruses and also exhibited HA activity. These VLPs induced high levels of PPV-specific antibody titers in mice after immunization, indicating that the VLPs may be beneficial as potential candidate antigens. VLPs were used as the coating antigens for the VLP ELISA, and the PPV VLPs-based ELISA displayed a high sensitivity (99%), specificity (93.0%) and agreement rate (98.3%) compared to HI assay, and the agreement rate of this ELISA was 97.5% compared to a commercial ELISA kit. Within a plate, the coefficient of variation (CV) was 10%, and between ELISA plates, the CV was 15%. According to a cross-reactivity assay, the technique was PPV-specific in contrast to other viral illness sera. The PPV VLP indirect-ELISA test for PPV detection in pigs with an inactivated vaccine showed that the PPV-positive rate varied among different sample sources from 88.2 to 89.6%. Our results indicate that this ELISA technique was quick, accurate, and repeatable and may be used for extensive serological research on PPV antibodies in pigs.

Higher antibody titres against Pseudogymnoascus destructans are associated with less white-nose syndrome skin lesions in Palearctic bats

Introduction

Serological tests can be used to test whether an animal has been exposed to an infectious agent, and whether its immune system has recognized and produced antibodies against it. Paired samples taken several weeks apart then document an ongoing infection and/or seroconversion.

Methods

In the absence of a commercial kit, we developed an indirect enzyme-linked immunosorbent assay (ELISA) to detect the fungus-specific antibodies for Pseudogymnoascus destructans, the agent of white-nose syndrome in bats.

Results and Discussion

Samples collected from European Myotis myotis (n=35) and Asian Myotis dasycneme (n=11) in their hibernacula at the end of the hibernation period displayed 100% seroprevalence of antibodies against P. destructans, demonstrating a high rate of exposure. Our results showed that the higher the titre of antibodies against P. destructans, the lower the infection intensity, suggesting that a degree of protection is provided by this arm of adaptive immunity in Palearctic bats. Moreover, P. destructans infection appears to be a seasonally self-limiting disease of Palearctic bats showing seroconversion as the WNS skin lesions heal in the early post-hibernation period.

In Vivo Validation of Novel Synthetic tbp1 Peptide-Based Vaccine Candidates against Haemophilus influenzae Strains in BALB/c Mice

Haemophilus influenzae is a Gram-negative bacterium characterized as a small, nonmotile, facultative anaerobic coccobacillus. It is a common cause of a variety of invasive and non-invasive infections. Among six serotypes (a-f), H. influenzae type b (Hib) is the most familiar and predominant mostly in children and immunocompromised individuals. Following Hib vaccination, infections due to other serotypes have increased in number, and currently, there is no suitable effective vaccine to induce cross-strain protective antibody responses. The current study was aimed to validate the capability of two 20-mer highly conserved synthetic tbp1 (transferrin-binding protein 1) peptide-based vaccine candidates (tbp1-E1 and tbp1-E2) predicted using in silico approaches to induce immune responses against H. influenzae strains. Cytokine induction ability, immune simulations, and molecular dynamics (MD) simulations were performed to confirm the candidacy of epitopic docked complexes. Synthetic peptide vaccine formulations in combination with two different adjuvants, BGs (Bacterial Ghosts) and CFA/IFA (complete/incomplete Freund's adjuvant), were used in BALB/c mouse groups in three booster shots at two-week intervals. An indirect ELISA was performed to determine endpoint antibody titers using the Student's t-distribution method. The results revealed that the synergistic use of both peptides in combination with BG adjuvants produced better results. Significant differences in absorbance values were observed in comparison to the rest of the peptide-adjuvant combinations. The findings of this study indicate that these tbp1 peptide-based vaccine candidates may present a preliminary set of peptides for the development of an effective cross-strain vaccine against H. influenzae in the future due to their highly conserved nature.

Developing an Indirect ELISA for the Detection of African Swine Fever Virus Antibodies Using a Tag-Free p15 Protein Antigen

African swine fever (ASF) is one of the most severe diseases caused by the ASF virus (ASFV), causing massive economic losses to the global pig industry. Serological tests are important in ASF epidemiological surveillance, and more antigen targets are needed to meet market demand for ASFV antibody detection. In the present study, ASFV p15 protein was fusion-expressed in Escherichia coli (E. coli) with elastin-like polypeptide (ELP), and the ELP-p15 protein was purified using a simple inverse transition cycling (ITC) process. The ELP tag was cleaved off using tobacco etch virus protease (TEVp), resulting in a tag-free p15 protein. Western blot analysis demonstrated that the p15 protein reacted strongly with ASFV-positive serum. The p15 protein was used as a coating antigen in an indirect ELISA (iELISA) for detecting ASFV antibodies. The p15-iELISA method demonstrated high specificity to ASFV-positive sera, with a maximum detection dilution of 1:1600. Moreover, the method exhibited good reproducibility, with less intra-assay and inter-assay CV values than 10%. Therefore, p15-iELISA offers a novel approach for accurately detecting ASFV antibodies with significant clinical application potential.

Validation of an indirect ELISA assay for assessment of autoantibodies against full-length TRIM21 and its individual domains

Anti-SSA-autoantibodies are common in patients with rheumatologic disease, especially Sjögren's syndrome, systemic lupus erythematosus and rheumatoid arthritis. They consist of both autoantibodies towards Ro60 and Ro52, the latter also known as TRIM21. TRIM21 is an intracellular protein consisting of four domains; PRY/SPRY, Coiled-Coil, B-box and RING. The aim of this study was to establish an indirect ELISA detecting autoantibodies towards both the full-length TRIM21 protein and its four domains. We expressed the five constructs, created, and validated indirect ELISA protocols for each target using plasma from anti-SSA positive patients and healthy controls. Our findings were validated to the clinically used standards. We measured significantly higher levels of autoantibodies towards our full-length TRIM21, and the PRY/SPRY, Coiled-Coil and RING domains in patients compared to healthy controls. No significant difference in the level of autoantibodies were detected against the B-box domain. Our setups had a signal to noise ratio in the range of 30 to 184, and an OD between 2 and 3. Readings did not decline using NaCl of 500 mM as wash, affirming the high binding affinity of the autoantibodies measured. Our protocols allow us to further study the different autoantibodies of anti-SSA positive patients. This creates the possibility to stratify our patients into subgroups regarding autoantibody profile and specific pheno- or endotype.

Comparative Analysis of Different ELISA Methods for the Serodiagnosis of Przhevalskiana silenus Infestation in Goats

Przhevalskiana silenus (warble fly) grubs cause myiasis in goats, in mountainous and semi-mountainous areas and different regions in Pakistan, and cause substantial losses to livestock. The palpation method for detecting warble flies generally neglects the infestation intensity; therefore, the development of a reliable and efficient diagnostic technique is extremely necessary. This study compared three indirect enzyme-linked immunosorbent assay (ELISA) methods for detecting anti-P. silenus antibodies using the hypodermin C (HyC) purified from Hypoderma spp. Larvae collected in cattle (local isolate, Microbiology Laboratory, PMAS-Arid Agriculture University, Rawalpindi), the crude antigen from the first instar stage of P. silenus, and a commercial Bovine Hypodermosis Antibody ELISA kit (IDEXX Laboratory), for accurately estimating the seroprevalence of goat warble fly infestation (GWFI) in the Pothwar plateau, Punjab, Pakistan. The ELISA with the crude antigen of P. silenus proved very sensitive and specific, 91% and 93%, respectively. The optical density exhibited a monthly variation, and the antibody titer began increasing from June, continually increased from July to December, and gradually decreased thereafter until March. The study confirmed the endemic status of GWFI in the Pothwar region and identified that ELISA based on the crude antigen of P. silenus was a more sensitive and specific immunodiagnostic method for determining seroprevalence, and could be employed for initiating nationwide eradication campaigns.

I329L protein-based indirect ELISA for detecting antibodies specific to African swine fever virus

African swine fever (ASF) is a disease that causes severe economic losses to the global porcine industry. As no vaccine or drug has been discovered for the prevention and control of ASF virus (ASFV), accurate diagnosis and timely eradication of infected animals are the primary measures, which necessitate accurate and effective detection methods. In this study, the truncated ASFV I329L (amino acids 70-237), was induced using IPTG and expressed in Escherichia coli cells. The highly antigenic viral protein I329L was used to develop an indirect enzyme-linked immunosorbent assay (iELISA), named I329L-ELISA, which cut-off value was 0.384. I329L-ELISA was used to detect 186 clinical pig serum samples, and the coincidence rate between the indirect ELISA developed here and the commercial kit was 96.77%. No cross-reactivity was observed with CSFV, PRRSV, PCV2, or PRV antibody-positive pig sera, indicating good specificity. Both intra- assay and inter-assay coefficients were below 10%, and the detection sensitivity of the iELISA reached 1:3200. In this study, an iELISA for ASFV antibody detection was developed based on the truncated ASFV I329L protein. Overall, the I329L-ELISA is a user-friendly detection tool that is suitable for ASFV antibody detection and epidemiological surveillance.

Seroprevalence and Risk Factors for Toxoplasma gondii Infection in Horses

BACKGROUND

Toxoplasma gondii is classified as intracellular protozoa and is one of the major zoonotic parasites. Most warm-blooded intermediate hosts, including humans, are commonly infected by this parasite. The epidemiology of T. gondii infection in Egyptian horses is currently poorly understood.

METHODS

420 blood samples were randomly collected from horses raised in four governorates in Northern Egypt (110 each from Giza and Kafr El Sheikh, and 100 each from Qalyubia and Gharbia) to investigate the existence of antibodies against T. gondii using a commercial ELISA kit, and to ascertain the risk factors for the infection.

RESULTS

the antibodies for T. gondii were found in 16.2% (68/420) of the examined horses, with no significant differences among the four studied governorates. The highest prevalence rate was observed in Giza. The results revealed that sex, breed, age, and contact with domestic ruminants or cats were recognized as potential risk factors. The high prevalence rate was found in mixed breed horses (OR = 2.63, 95% CI: 0.95-7.26), mares (OR = 2.35, 95% CI: 1.31-4.19), and horses aged over 10 years (OR = 2.78, 95% CI: 1.30-3.44). Moreover, the likelihood of seropositivity for T. gondii infection was higher in horses raised in environments with cats (OR = 1.97, 95% CI: 1.13-3.44, p = 0.017) or domestic ruminants (OR = 2.16, 1.21-3.86, p = 0.010). This report confirms that horses in Northern Egypt are exposed to T. gondii and thus raises the possibility that people and other animals could contract the disease.

CONCLUSIONS

routine examination and management of T. gondii infection in horses in these governorates is advised.

Establishment and Application of an Indirect ELISA for the Detection of Antibodies to Porcine Streptococcus suis Based on a Recombinant GMD Protein

S. suis is an important zoonotic pathogen from sick and recessive carrier pigs that poses a serious threat to animal husbandry production and public health. It usually causes horizontal transmission among pigs. The morbidity and mortality of this disease are very high. Human infection is caused through direct or indirect contact with sick pigs. The two large-scale outbreaks in China were due to the outbreak of S. suis on pig farms, which spread to human infection; thus, detecting S. suis in pig herds is crucial. At present, the commercial S. suis ELISA type 2 kits on the market can only detect single serotypes, high probabilities of interaction reactions, and biosafety risks when using inactivated S. suis as an antigen. Phosphate-3-glyceraldehyde dehydrogenase (GAPDH), muramidase-released protein (MRP), and dihydrolipoamide dehydrogenase (DLDH) are important S. suis type 2, S. suis type 7, and S. suis type 9 protective antigens. This study purified the GMD protein (B-cell-dominant epitopes of GAPDH, MRP, and DLDH antigens) and used a diverse combination of dominant epitopes of the multiple different antigens as coated antigens, improving the sensitivity and safety of the indirect ELISA experiments. An indirect ELISA method (GMD-ELISA) was developed for detecting S. suis antibodies. The antigen-antibody response was optimized using checkerboard titration. The results of testing using ELISA for Salmonella enterica (S. enterica), Escherichia coli (E. coli), Staphylococcus aureus (SA), and Streptococcus pyogenes (S. pyogenes) were all negative, indicating that this method had strong specificity. The results were still positive when the dilution ratio of S. suis-positive serum reached 1:6, 400, thus indicating that the method had high sensitivity. The results of the reproducibility assay for indirect ELISA showed that the intra-assay coefficient of variation and the inter-assay coefficient of variation were less than 10%, indicating that the method had good repeatability. We investigated the seroprevalence of S. suis in 167 serum samples collected in East China, and 33.5% of the samples were positive for antibodies against S. suis, indicating that the prevalence of S. suis is high in pig farms in Eastern China. The novel GMD-ELISA is a convenient, sensitive, and specific diagnostic method that provides technical support for rapid diagnosis and epidemiological investigation.

Novel p22 and p30 dual-proteins combination based indirect ELISA for detecting antibodies against African swine fever virus

Introduction

African swine fever virus (ASFV) infection is one of the most complex and fatal hemorrhagic viral diseases, causing a devastating loss to the swine industry. Since no effective vaccine is available, prevention and control of ASFV heavily depends on early diagnostic detection.

Methods

In this study, a novel indirect ELISA was established for detecting antibodies against ASFV using dual-proteins, p22 and p30. Recombinants p22 and p30 were expressed and purified from E.coli vector system by recombined plasmids pET-KP177R and pET-CP204L. p22 and p30 were mixed as antigens for developing the indirect ELISA.

Results

Through optimizing coating concentrations of p30 and p22, coating ratio (p30: p22 = 1:3), and serum dilution (as 1:600), the established ELISA performed higher specificity, sensitivity, and repeatability against ASFV-positive serum. Furthermore, 184 clinical serum samples from suspected diseased pigs were verified the established ELISA in clinical diagnosis. The results showed that compared with two commercial ELISA kits, the established ELISA possessed higher sensitivity and almost uniform coincidence rate.

Conclusion

The novel indirect ELISA based on dual-proteins p30 and p22 performed a valuable role in diagnostic detection of ASFV, providing a broad insight into serological diagnostic methods of ASFV.

Development and evaluation of an indirect enzyme-linked immunosorbent assay based on a recombinant SifA protein to detect Salmonella infection in poultry

Salmonella is an important zoonotic pathogen that not only endangers food safety and human health, but also causes considerable economic losses to the poultry industry. Therefore, it is essential to establish a rapid, sensitive, and specific diagnostic method for the early detection of Salmonella infection in poultry. In this study, we developed a novel enzyme-linked immunosorbent assay (ELISA) for the detection of anti-Salmonella antibodies using a recombinant SifA protein. Amino acid sequence comparison revealed that SifA is a relatively conserved secretory protein across Salmonella serotypes. Therefore, we hypothesized that SifA can serve as a detection antigen for diagnostic testing. The SifA protein was expressed in Escherichia coli and used as a coating antigen to establish an SifA-ELISA. Control sera from specific-pathogen-free (SPF) chickens infected with Salmonella or several other non-Salmonella pathogens were then tested using the SifA-ELISA. Specificity testing demonstrated that the SifA-ELISA could detect antibodies against 3 different serotypes of Salmonella, whereas antibodies against other non-Salmonella pathogens could not be detected. Compared to the SifA-ELISA, the Salmonella plate agglutination test (PAT) failed to detect antibodies in serum samples from chickens infected with Salmonella Typhimurium. This result suggests that our SifA-ELISA may be better than PAT at detecting Salmonella infection. Comparing clinical sera, we observed a similar rate of Salmonella positivity between SifA-ELISA and PAT (92.6%). In addition, anti-SifA antibodies were continuously detected during Salmonella infection of SPF chickens, demonstrating that SifA-ELISA could consistently detect high levels of antibodies for at least 8 wk. Furthermore, the intra-assay and interassay coefficients of variation (CV) of the SifA-ELISA were below 10%, which is considered acceptable. In summary, the SifA-ELISA established here is a promising and reliable method for detection of anti-Salmonella antibodies in poultry and may contribute to the early diagnosis of Salmonella infection.

A highly efficient indirect ELISA and monoclonal antibody established against African swine fever virus pK205R

African swine fever (ASF) is a contagious infectious disease with high lethality which continuously threatens the global pig industry causing huge economic losses. Currently, there are no commercially available vaccines or antiviral drugs that can effectively control ASF. The pathogen of ASF, ASF virus (ASFV) is a double-stranded DNA virus with a genome ranging from 170 to 193 kb and 151 to 167 open reading frames in various strains, which encodes 150-200 proteins. An effective method of monitoring ASFV antibodies, and specific antibodies against ASFV to promote the development of prevention techniques are urgently needed. In the present study, pK205R of ASFV was successfully expressed in mammalian cells using a suspension culture system. An indirect enzyme-linked immunosorbent assay (ELISA) based on the purified pK205R was established and optimized. The monoclonal antibody (mAb) against pK205R recognized a conservative linear epitope (²VEPREQFFQDLLSAV¹⁶) and exhibited specific reactivity, which was conducive to the identification of the recombinant porcine reproductive and respiratory syndrome virus (PRRSV) expressing pK205R. The ELISA method efficiently detected clinical ASFV infection and revealed good application prospects in monitoring the antibody level in vivo for recombinant PRRSV live vector virus expressing the ASFV antigen protein. The determination of the conserved linear epitope of pK205R would contribute to further research on the structural biology and function of pK205R. The indirect ELISA method and mAb against ASFV pK205R revealed efficient detection and promising application prospects, making them ideal for epidemiological surveillance and vaccine research on ASF.

The Indirect ELISA and Monoclonal Antibody against African Swine Fever Virus p17 Revealed Efficient Detection and Application Prospects

Since 2018, the outbreak and prevalence of the African swine fever virus (ASFV) in China have caused huge economic losses. Less virulent ASFVs emerged in 2020, which led to difficulties and challenges for early diagnosis and control of African swine fever (ASF) in China. An effective method of monitoring ASFV antibodies and specific antibodies against ASFV to promote the development of prevention techniques are urgently needed. In the present study, ASFV p17 was successfully expressed in CHO cells using a suspension culture system. An indirect enzyme-linked immunosorbent assay (ELISA) based on purified p17 was established and optimized. The monoclonal antibody (mAb) against p17 recognized a conservative linear epitope (3TETSPLLSH11) and exhibited specific reactivity, which was conducive to the identification of recombinant porcine reproductive and respiratory syndrome virus (PRRSV) expressing p17. The ELISA method efficiently detected clinical ASFV infection and effectively monitored the antibody levels in vivo after recombinant PRRSV live vector virus expressing p17 vaccination. Overall, the determination of the conserved linear epitope of p17 would contribute to the in-depth exploration of the biological function of the ASFV antigen protein. The indirect ELISA method and mAb against ASFV p17 revealed efficient detection and promising application prospects, making them ideal for epidemiological surveillance and vaccine research on ASF.

Research Note: A novel peptide-based ELISA for efficient detection of antibody against chicken infectious anemia virus

Chicken infectious anemia virus (CIAV) is the pathogen of chicken infectious anemia. Currently, due to the lack of effective diagnostics technology and prevention approach, CIAV has spread globally and caused huge economic losses to poultry industry. In this study, a novel peptide-based ELISA (pELISA) for efficient detection of antibody against CIAV was developed. The peptide (25CRLRRRYKFRHRRRQRYRRRAF45) used in pELISA was highly conserved in VP1 protein of different CIAV isolates. The specificity and reproducibility showed that the pELISA only reacted with sera against CIAV, not with sera against other pathogens tested, and the CV of the intra-/inter-assay of the pELISA was 6.8 to 9.22%. Moreover, the comparison assay using 56 clinical samples showed that the positive rate of the pELISA and the commercial ELISA kit (IDEXX) was 85.7 and 80.4%, respectively. The pELISA generated here provides a rapid and efficient serological detection method for diagnosis of CIAV infection and evaluation of the efficacy of CIAV vaccination.