Evaluation of two commercial PRRSV antibody ELISA kits with samples of known status and singleton reactors

Development and application of a blocking ELISA based on a N protein monoclonal antibody for the antibody detection against porcine reproductive and respiratory syndrome virus 2

Porcine reproductive and respiratory syndrome (PRRS) is one of the most widespread illnesses in the world's swine business. To detect the antibodies against PRRSV-2, a blocking enzyme-linked immunosorbent assay (B-ELISA) was developed, utilizing a PRRSV-2 N protein monoclonal antibody as the detection antibody. A checkerboard titration test was used to determine the optimal detection antibody dilution, tested pig serum dilution and purified PRRSV coated antigen concentration. After analyzing 174 negative pig sera and 451 positive pig sera, a cutoff value of 40 % was selected to distinguish between positive and negative sera using receiver operating characteristic curve analysis. The specificity and sensitivity of the assay were evaluated to equal 99.8 % and 96 %, respectively. The method had no cross-reaction with PCV2, PRV, PPV, CSFV, PEDV, TGEV, and PRRSV-1 serum antibodies, and the coefficients of variation of intra-batch and inter-batch repeatability experiments were both <10 %. A total of 215 clinical serum samples were tested, and the relative coincidence rate with commercial ELISA kit was 99.06 %, and the kappa value was 0.989, indicating that these two detection results exhibited high consistency. Overall, the B-ELISA should serve as an ideal method for large-scale serological investigation of PRRSV-2 antibodies in domestic pigs.

Comparison of the pathogenicity of porcine reproductive and respiratory syndrome virus (PRRSV)-1 and PRRSV-2 in pregnant sows

To date, few studies related to the evaluation of the pathogenicity of different PRRSV isolates using a reproductive model have been undertaken, and the main focus has remained on respiratory models using young pigs. This study aimed to evaluate the pathogenicity of two PRRSV-1 isolates (D40 and CBNU0495) and two PRRSV-2 isolates (K07-2273 and K08-1054) in a reproductive model. Pregnant sows were experimentally infected with PRRSV at gestational day 93 or used as an uninfected negative control. Sera were collected at 0, 3, 7, 14, and 19 days post-challenge (dpc) for virological and serological assays. At 19 dpc, all sows were euthanized, and their fetuses were recovered by performing cesarean section and immediately euthanized for sample collection. Here, compared to the other isolates, the CBNU0495 isolate replicated most efficiently in the pregnant sows, and K07-2273 produced the highest rate of reproductive failure even though it did not replicate as efficiently as the other isolates in sows and fetuses, indicating that vertical transmission and reproductive failure due to PRRSV infection do not have any significant correlation with the viral loads in samples from sows and fetuses. Similarly, the viral loads and the histopathological lesions did not show any correlation with each other, as the PRRSV-2-infected groups displayed more prominent and frequent histopathological lesions with lower viral loads than the PRRSV-1-infected groups. However, viral loads in the myometrium/endometrium might be related to the spreading of PRRSV in the fetuses, which affected the birth weight of live fetuses. This study contributes to a better understanding of the pathogenicity of the most prevalent Korean PRRSVs in a reproductive model.

Seroprevalence of the viral pig diseases among backyard pigs in Chiang Mai, Thailand

The Participatory One-Health Disease Detection project (PODD) (www.cmonehealth.org) developed a health-based surveillance system with the local government of Chiang Mai community ownership that has been created a mobile application on smartphone for reporting an abnormal event, especially animal health. Previously, the PODD project has obtained a significant number of pig abnormal events. Therefore, there are likely to be some diseases that are currently circulating among backyard pigs. A cross-sectional serological study was undertaken to determine the risk factors for virus infection and prevalence of antibodies against the classical swine fever virus (CSFV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus type 2 (PCV2) and influenza A virus (IAV) among backyard pigs in Chiang Mai, Thailand. Antibodies against the CSFV, PRRSV and PCV2 in backyard pigs were shown in swine level to be 14 % (95 % CI: 9-20), 14 % (95 % CI: 10-19), and 15 % (95 % CI: 8-23), respectively. For the household level, antibodies against the CSFV, PRRSV and PCV2 were found to be 23 % (95 % CI: 13-37), 22 % (95 % CI: 14-23), and 48 % (95 % CI: 32-63), respectively, while antibodies against IAV were shown to be absent. The use of artificial insemination for breeding purposes has been considered to be a significant risk factor associated with PRRSV (OR = 21.08, 95 % CI: 1.92-232.02) and CSFV (OR = 7.7, 95 % CI: 1.49-39.90) infections. Meanwhile, a risk factor for PCV2 infection was found to significantly involve the feeding of pigs with commercial feed (OR = 9.64, 95 % CI: 1.85-50.26). The findings of this study indicate that infections with CSFV, PRRSV, and PCV2 remain a significant concern and may have an impact on the growth performance of the backyard pigs. The lack of antibodies against the influenza A virus has indicated a low degree of interspecies transmission of influenza A among backyard pigs in Chiang Mai, Thailand. Effective control measures need to be prepared and implemented, and these should include the strict regulation of pig imports as a free source of the viruses along with effective animal quarantine, policies, and appropriate vaccination programs.

Antibody responses to porcine reproductive and respiratory syndrome virus, influenza A virus, and Mycoplasma hyopneumoniae from weaning to the end of the finisher stage in fourteen groups of pigs in Ontario, Canada

Background

Respiratory diseases are among the most important factors affecting swine farm productivity in Canada. The objectives of this study were to investigate antibody responses to porcine reproductive and respiratory syndrome virus (PRRSV), influenza A virus (IAV), and Mycoplasma hyopneumoniae (M. hyopneumoniae) from weaning to the end of the finisher stage on a subset of commercial swine farms in Ontario, Canada, and to examine the association between nursery diet and antibody responses.

Results

Overall, older pigs were more likely to test seropositive for PRRSV and less likely to test seropositive for M. hyopneumoniae (p <  0.001). Pigs were more likely to test seropositive for IAV at weaning and the end of the grower and finisher stages compared to the end of nursery (p <  0.001). Pigs that were seropositive for IAV were more likely to test seropositive for both PRRSV and M. hyopneumoniae (p <  0.001). Two, 9, and 4 groups that had more than 20% of pigs seropositive to PRRSV, IAV, and M. hyopneumoniae, respectively, from the end of nursery to the end of finisher were classified as seropositive. Pigs fed a plant-based (low complexity) diet during nursery were more likely to be seropositive for PRRSV (p <  0.001) but there were no significant differences in seropositivity to IAV or M. hyopneumoniae due to nursery diet complexity.

Conclusions

This study provides information regarding changes in serum antibody in pigs across different stages of production and highlights periods of vulnerability. Additionally, these findings may encourage further research into the effects of nursery diet complexity on disease susceptibility and immune response.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-02756-6.

Comparison of six commercial ELISAs for the detection of antibodies against porcine reproductive and respiratory syndrome virus (PRRSV) in field serum samples

Porcine reproductive and respiratory syndrome (PRRS) is one of the most common infectious diseases of swine globally. Since the course of PRRS virus (PRRSV) infection is subclinical, laboratory diagnosis is necessary to detect the virus or specific antibodies. The aim of this study was to assess the sensitivity and specificity of IDEXX PRRS X3 Ab Test (IDEXX, USA), Civtest Suis E/S (Hipra, Spain), INgezim PRRS 2.0 (Ingenasa, Spain), VetExpert PRRS Ab ELISA 4.0 (BioNote, Korea), Pigtype PRRSV Ab (Qiagen, Germany) and PrioCHECK PRRSV Antibody ELISA (ThermoFisher, USA), using serum samples obtained from 5 conventional PRRSV-positive and 5 PRRSV-negative Polish pig farms. Specificity of ELISAs ranged from 94.2% (ThermoFisher) to 100% (IDEXX and Hipra). ThermoFisher ELISA had the highest detection rate and detected 67.2% samples from PRRSV-positive farms as positive but considering its low specificity some of the positive results may be incorrect. IDEXX ELISA considered as a reference detected 64.8% positive sera in PRRSV-positive farms. On the other hand Hipra Elisa identified only 51.8% of samples as positive. The diagnostic sensitivity of five ELISAs relative to IDEXX ranged from 80.3% (Hipra) to 96.3% (ThermoFisher). Our study showed significant differences in specificity and diagnostic sensitivity between the compared kits. The differences in the performance appeared to be practically negligible on farms where early infection with PRRSV occurred. However, on PRRSV-negative farms, or farms with PRRSV stable sow herds, some ELISAs can give results not reflecting the infection status in specific age groups.

OptisampleTM: Open web-based application to optimize sampling strategies for active surveillance activities at the herd level illustrated using Porcine Respiratory Reproductive Syndrome (PRRS)

Porcine reproductive and respiratory syndrome virus (PRRSv) infection causes a devastating economic impact to the swine industry. Active surveillance is routinely conducted in many swine herds to demonstrate freedom from PRRSv infection. The design of efficient active surveillance sampling schemes is challenging because optimum surveillance strategies may differ depending on infection status, herd structure, management, or resources for conducting sampling. Here, we present an open web-based application, named 'OptisampleTM', designed to optimize herd sampling strategies to substantiate freedom of infection considering also costs of testing. In addition to herd size, expected prevalence, test sensitivity, and desired level of confidence, the model takes into account the presumed risk of pathogen introduction between samples, the structure of the herd, and the process to select the samples over time. We illustrate the functionality and capacity of 'OptisampleTM' through its application to active surveillance of PRRSv in hypothetical swine herds under disparate epidemiological situations. Diverse sampling schemes were simulated and compared for each herd to identify effective strategies at low costs. The model results show that to demonstrate freedom from disease, it is important to consider both the epidemiological situation of the herd and the sample selected. The approach illustrated here for PRRSv may be easily extended to other animal disease surveillance systems using the web-based application available at http://stemma.ahc.umn.edu/optisample.

Ability of ELISAs to detect antibodies against porcine respiratory and reproductive syndrome virus in serum of pigs after inactivated vaccination and subsequent challenge

BACKGROUND

In this study, six enzyme-linked immunosorbent assays (ELISA), intended for routine porcine reproductive and respiratory syndrome virus (PRRSV) herd monitoring, are tested for their ability to detect PRRSV specific antibodies in the serum of pigs after vaccination with an inactivated PRRSV type 1 vaccine and subsequent infection with a highly pathogenic (HP) PRRSV field strain. For this reason, ten piglets (group V) from a PRRSV negative herd were vaccinated twice at the age of 2 and 4 weeks with an inactivated PRRSV vaccine. Ten additional piglets (group N) from the same herd remained unvaccinated. Three weeks after second vaccination, each of the piglets received an intradermal application of an HP PRRSV field strain. Serum samples were taken before first vaccination as well as before and 3, 7, 10 and 14 days after HP PRRSV application. All serum samples were tested for PRRSV RNA by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) as well as for PRRSV antibodies with all six study ELISAs.

RESULTS

At the beginning of the study (before vaccination), all of the piglets were PRRSV antibody negative with all study ELISAs. They also tested negative for PRRSV RNA measured by RT-qPCR. From day 3 after HP PRRSV application until the end of the study, a viremia was detected by RT-qPCR in all of the piglets. On day 0 (day of HP PRRSV application), nine out of ten piglets of the pre-vaccinated group tested PRRSV antibody positive with one of the tested ELISAs, although with lower S/P values than after infection. On day 10 after HP PRRSV application, all study ELISAs except one had significantly higher S/P or OD values, respectively more positive samples, in group V than in group N.

CONCLUSIONS

Only one of the tested ELISAs was able to detect reliably PRRSV antibodies in pigs vaccinated with an inactivated PRRSV vaccine. With most of the tested ELISAs, higher S/P values respectively more positive samples after PRRSV infection were seen in the pre-vaccinated group than in the non-vaccinated.