Comparison of three in-house ELISAs for the detection of hepatitis E virus infection in pigs under field conditions

Antigenic Characterization of ORF2 and ORF3 Proteins of Hepatitis E Virus (HEV)

To evaluate the antigenic properties of Hepatitis E Virus (HEV) Open Reading Frame 2 and 3 (ORF2 and ORF3) codified proteins, we expressed different portions of ORF2 and the entire ORF3 in E. coli, a truncated ORF2, was also expressed in baculovirus. A panel of 37 monoclonal antibodies (MAbs) was raised against ORF2 (1-660 amino acids) and MAbs were mapped and characterized using the ORF2 expressed portions. Selected HEV positive and negative swine sera were used to evaluate ORF2 and ORF3 antigens' immunogenicity. The MAbs were clustered in six groups identifying six antigenic regions along the ORF2. Only MAbs binding to the sixth ORF2 antigenic region (394-608 aa) were found to compete with HEV positive sera and efficiently catch the recombinant antigen expressed in baculovirus. The ORF2 portion from 394-608 aa demonstrated to include most immunogenic epitopes with 85% of HEV positive swine sera reacting against the region from 461-544 aa. Only 5% of the selected HEV sera reacted against the ORF3 antigen.

Development of an indirect ELISA based on recombinant capsid protein to detect antibodies to bovine leukemia virus

Serological testing and culling infected animals are key management practices aiming eradication of bovine leukemia virus infection. Here, we report the development of an indirect ELISA based on BLV recombinant capsid protein (BLVp24r) to detect anti-BLV antibodies in cattle serum. The BLVp24r was expressed in Escherichia coli and purified by affinity chromatography, and then used to set up the ELISA parameters. The Polysorp® plate coated with 50ng of antigen/well and bovine serum diluted 1:100 gave the best results during standardization. Using sera from infected and non-infected cattle we set up the cutoff point at 0.320 (OD450nm) with a sensitivity of 98.5% and specificity of 100.0%. Then, we tested 1.187 serum samples from dairy (736 samples) and beef cattle (451 samples) with unknown status to BLV. We found that 31.1% (229/736) and 9.5% (43/451) of samples amongst dairy and beef cattle, respectively, had IgGs to BLV. The rate of agreement with a commercial competitive ELISA was 84.3% with a κ value of 0.68. Thus, our BLVp24r iELISA is suitable to detect BLV infected animals and should be a useful tool to control BLV infection in cattle.

Public health risks associated with hepatitis E virus (HEV) as a food-borne pathogen

Hepatitis E virus (HEV) is an important infection in humans in EU/EEA countries, and over the last 10 years more than 21,000 acute clinical cases with 28 fatalities have been notified with an overall 10-fold increase in reported HEV cases; the majority (80%) of cases were reported from France, Germany and the UK. However, as infection in humans is not notifiable in all Member States, and surveillance differs between countries, the number of reported cases is not comparable and the true number of cases would probably be higher. Food-borne transmission of HEV appears to be a major route in Europe; pigs and wild boars are the main source of HEV. Outbreaks and sporadic cases have been identified in immune-competent persons as well as in recognised risk groups such as those with pre-existing liver damage, immunosuppressive illness or receiving immunosuppressive treatments. The opinion reviews current methods for the detection, identification, characterisation and tracing of HEV in food-producing animals and foods, reviews literature on HEV reservoirs and food-borne pathways, examines information on the epidemiology of HEV and its occurrence and persistence in foods, and investigates possible control measures along the food chain. Presently, the only efficient control option for HEV infection from consumption of meat, liver and products derived from animal reservoirs is sufficient heat treatment. The development of validated quantitative and qualitative detection methods, including infectivity assays and consensus molecular typing protocols, is required for the development of quantitative microbial risk assessments and efficient control measures. More research on the epidemiology and control of HEV in pig herds is required in order to minimise the proportion of pigs that remain viraemic or carry high levels of virus in intestinal contents at the time of slaughter. Consumption of raw pig, wild boar and deer meat products should be avoided.

In house ELISA based on recombinant ORF2 protein underline high prevalence of IgG anti-hepatitis E virus amongst blood donors in south Brazil

Hepatitis E Virus (HEV) is a zoonotic pathogen responsible for causing acute hepatitis in human, especially in developing countries. Diagnosis of HEV usually relies on the detection of antibodies mostly by enzyme-linked immunosorbent assay (ELISA). In the present study, we designed a new indirect ELISA (iELISA) based on a short recombinant peptide derived from the capsid protein (ORF2p) and demonstrated its potential for detecting human IgG against HEV genotype 3. The best polystyrene plate (Maxisorp^®), optimal ORF2p coating antigen concentration (0,67μg/well) and primary antibody dilution (1:100) were determined. This iELISA showed a sensitivity of 91.4% and specificity of 95.9%. The comparison of our in house iELISA with a commercial assay (RecomWell, Mikrogen^®) showed 94.25% of agreement and a kappa index of 0.88. The ORF2 recombinant ELISA was used to screen 780 blood donors for anti-HEV IgG and we found that 314 (40,25%) of these donors were IgG positive. This high prevalence of antibodies suggests, for the first time, that the Southern Brazil region might be endemic to Hepatitis E Virus genotype 3.

Hepatitis E Virus: A Cross-Sectional Serological and Virological Study in Pigs and Humans at Zoonotic Risk within a High-Density Pig Farming Area

An increase in autochthonous hepatitis E virus (HEV) infections has been recorded in Italy suspected to be zoonotically transmitted from pigs; this study was carried out to determinate the seroprevalence and risk factors associated with hepatitis HEV exposition, both in swine and humans working in pig farms, located within a high-density pig farming area in Piedmont region, north-western Italy. The presence of viral RNA in human and swine samples was also evaluated, and phylogenetic analysis was performed on HEV-positive samples. Forty-two swine farms were sampled; 142 workers were enrolled in the study and classified into two groups: (i) 69 workers with occupational contact with swine (including veterinarians and farmers) recruited in the 42 sampled farms; (ii) 73 without occupational contact with swine. Forty-one of 42 (97%) swine farms resulted positive to enzyme-linked immunosorbent assay test for HEV antibodies (Abs). Overall seroprevalence in swine was 50% (441/879), with seropositivity rate higher in sows (333/469, 71%). HEV RNA in stool samples was detected in animals from 13 of 42 tested farms (31%), and a higher positivity resulted in weaners (40/246, 16.3%). Phylogenetic analysis classified all HEV isolates within genotype 3 (subtypes 3f, 3e, 3c). All humans were negative for HEV viral genome in blood. Five of 142 sera were positive for IgG anti-HEV with an overall prevalence of 3.52% with no statistically significant differences in prevalence rates between workers at zoonotic risk and the control group (5.7% versus 1.3%). In contrast, a significant difference (OR 10.1) was observed within the subgroup including subjects exposed for short periods (veterinarians) compared with those who worked for long periods (farmers) suggesting a correlation between the time of exposure and the likelihood of HEV infection. Reporting HEV infection is not mandatory in Italy, but a constant epidemiological surveillance should be ensured to clarify the epidemiology of this disease.

A Novel Blocking ELISA for Detection of Antibodies against Hepatitis E Virus in Domestic Pigs

Hepatitis E virus (HEV) infects both humans and animals, with an overall human mortality rate generally less than 1%, but as high as 20% among pregnant women. HEV strains fall into 4 major genotypes. Zoonotic genotypes 3 and 4 associate with sporadic human and animal HEV cases in many industrialized countries. To date, collective evidence implicates pigs as the main HEV reservoir, justifying the importance of monitoring HEV infection rates in pig herds to prevent human illness. Due to the lack of a robust in vitro cell culture system for viral propagation, no “gold standard” assay has yet been developed to detect HEV infection in domestic pigs. 1E4, a monoclonal antibody (mAb) specific for the C-terminal 268 amino acids of HEV genotype 4 ORF2 capsid protein (sORF2-C), was generated and conjugated to horseradish peroxidase (HRP) for use in a blocking ELISA (bELISA). Optimal sORF2-C coating antigen concentration (8 μg/ml), HRP-1E4 dilution (1:1000), and test pig serum dilution (1:20) were determined using a checkerboard titration test. A cut-off value of 16.9% was chosen to differentiate between positive vs. negative sera after mean percent inhibition (PI) testing of 230 negative pig sera. Compared with the indirect ELISA (iELISA), western blot, and a commercial ELISA kit for detecting anti-HEV antibodies in human sera, the bELISA showed no statistical differences and statistically high coincidence of 93.23%, 92%, and 95% with the other tests, respectively. A blocking ELISA (bELISA) for detecting anti-HEV antibodies in pig serum samples was developed with high sensitivity and high specificity comparable to that of the indirect ELISA. The bELISA results exhibited high agreement with iELISA, western blot, and a commercial ELISA kit designed to detect human anti-HEV antibodies. Therefore, bELISA should serve as an ideal method for large-scale serological investigation of anti-HEV antibodies in domestic pigs.