Development and evaluation of a MAb based competitive-ELISA using helicase domain of NS3 protein for sero-diagnosis of bovine viral diarrhea in cattle and buffaloes

Development and evaluation of a monoclonal antibody-based blocking ELISA to detect antibodies against the E2 protein of bovine viral diarrhea virus-1

With the rapid development of cattle industry, bovine viral diarrhea virus (BVDV) is becoming widespread in China, which causes serious economic losses to the industry. Effective vaccination and viral surveillance are critical for the prevent and control of BVDV infection. In the present study, the immunogenic domain of E2 protein of BVDV-1 was expressed by prokaryotic pET-28a vector. Monoclonal antibodies (mAbs) against E2 protein were prepared and systemically examined by western blot, immunofluorescence assay, blocking ELISA (bELISA) and virus neutralization test (VNT). The mAb 1E2B3, which showed good reactivity and neutralizing activity to BVDV-1 strains, was selected for ELISA establishment. After a series of screening and optimization, a novel bELISA for highly sensitive and specific detection of BVDV-1 antibodies was established, using HRP-labeled 1E2B3 and recombinant E2 protein. ROC analysis of 91 positive and 84 negative reference bovine serum samples yielded the area under the curve (AUC) of 0.9903. A diagnostic specificity of 96.43 % and a sensitivity of 95.6 % were achieved when the cutoff value was set at 24.31 %. There was no cross reaction to the positive sera of classical swine fever virus (CSFV), BVDV-2, border disease virus (BDV), bovine parainfluenza virus type 3 (BPIV3), infectious bovine rhinotracheitis virus (IBRV), foot-and-mouth disease virus (FMDV), Mycoplasma bovis (M.bovis) and Brucella. The total agreement rate of bELISA with VNT was 93.96 % (249/265). In addition, the result of bELISA was positively correlated with neutralizing antibody titer, and the bELISA could well distinguish the serum samples before and after BVDV vaccination. These results indicate that the established bELISA in this study is specific, sensitive, simple and convenient, which provides technical support for the vaccine efficacy evaluation, prevention and control of BVD in the future.

Evidence of BVDV in Pigs from North Eastern Part of India- Genetic Profiling and Characterisation

Introduction:

The work has been attempted to detect and genetically characterise the nature of Bovine Viral Diarrhea Virus (BVDV) isolates from the porcine population of the north east.

Methods and Material:

The samples have been collected over a two year period and are from areas where there is a mixed and integrated rearing of livestock in close proximity. The isolates were identified, cloned and sequenced using BVD specific genomic primers for two important domains viz., E-2 and 5’ UTR.

Results:

Porcine BVD Sequences were analysed phylogenetically. Divergence in 3 sequences is noted in the 5’ UTR region that are forming a clear outlier group while E-2 sequences are coming close to BVDV group but forming a separate cluster.

First report on serological evidence of bovine viral diarrhea virus (BVDV) infection in farmed and free ranging mithuns (Bos frontalis)

Despite reports of BVDV infection in several domestic and wild ruminants, no information exists for mithun (Bos frontalis) species. Hence, this study was undertaken to determine prevalence of BVDV infection in mithuns, which contribute significantly to local economy in the North Eastern region of India. Blood and serum samples were collected between 2013 and 2016 from mithuns (n = 466) belonging to the states of Nagaland, Mizoram, and Arunachal Pradesh. Serum samples were tested for BVDV antibodies by a commercial ELISA and leukocytes were tested for BVDV by real-time RT-PCR. The overall true seroprevalence rate was 13.1% (95% confidence interval, CI: 6.9-17.8%) with higher prevalence in mithuns reared under semi-intensive system (27.5%) than in free-ranging mithuns (7.6%). Among the three states, seroprevalence (16.2%) was highest in Nagaland, while prevalence rates varied markedly among geographical locations. Age-wise data showed highest seroprevalence rate in >6-year-old animals (20.6%) than 2-6 years old (16.9%), 6 months-2 years old (8.5%), and <6-month-old animals (11.3%). The seroprevalence was higher in males (20.9%) than in females (12.1%). Among the four mithun strains, higher prevalence was evident in Manipur (30.3%) than Arunachal (21.3%), Nagaland (11.7%), and Mizoram strain (10.2%). However, no BVDV genomic RNA could be detected. The results provide first serological evidence of BVDV infection in mithun species and extend the knowledge on BVDV host range. The baseline data will help further investigations on epidemiology of BVD in mithun and its impact on mithun production.

Simple Indirect Enzyme-Linked Immunosorbent Assay to Detect Antibodies Against Bovine Viral Diarrhea Virus, Based on Prokaryotically Expressed Recombinant MBP-NS3 Protein

BACKGROUND

Bovine viral diarrhea (BVD) is an economically important disease of cattle distributed worldwide. Diagnosis of BVD relies on laboratory-based detection of its viral causing agent or virus specific antibodies and the most common laboratory method for this purpose is Enzyme-Linked Immunosorbent Assay (ELISA).

OBJECTIVES

The current study was aimed to develop a simple indirect ELISA to detect antibodies against Bovine Viral Diarrhea Virus (BVDV) in the sera of infected cattle.

MATERIALS AND METHODS

A new simple indirect ELISA method was developed to detect BVDV infection by prokaryotically (Escherichia coli, BL21 strain) expressed recombinant whole nonstructural protein 3 (NS3) of BVDV (NADL strain). Four hundred bovine serum samples were evaluated by the newly developed NS3-ELISA and virus neutralization test (VNT) as the gold standard method to diagnose BVD. Among these samples, 289 sera had been previously tested by a commercial ELISA kit.

RESULTS

Statistical analyses showed a very high correlation between the results of the developed NS3-ELISA and VNT (kappa coefficient = 0.935, P < 0.001), with the relative sensitivity and specificity of 94% and 98.8%, respectively. There was also a high correlation between the results of NS3-ELISA and the commercial ELISA kit (kappa coefficient = 0.802, P < 0.001) with the relative sensitivity and specificity of 90.72% and 91.15%, respectively.

CONCLUSIONS

The newly developed simple indirect ELISA showed high sensitivity and specificity with respect to VNT. Developing such a simple, sensitive, and specific ELISA which is much less expensive than the available commercial ELISA kits can improve the detection of BVDV infections, help to eliminate the disease from herds, and decrease economic losses caused by this disease.

Epidemiology of bovine viral diarrhoea among tropical small holder dairy units in Kerala, India

Prevalence of bovine viral diarrhoea among 385 dairy cattle reared under a small holder system in Trichur District of Kerala State in India was determined through an ELISA targeting antibodies against p80-p125 non-structural protein of the virus. Prevalence was 24.7% among the total population, but was higher (52%) when 85 animals having infertility problems alone were considered. Significant serum biochemistry differences between animals could be noticed only in total protein, globulin and phosphorous, all of which were low in seropositive animals. All animals which were seronegative for antibodies were screened by another ELISA targeting the E(rns) protein of the viral nucleocapsid to detect persistently infected (PI) animals. The single, positive animal had only a transient period of antigens in the blood, indicating absence of PI animals in the study population. High prevalence of the disease in isolated small holder units even in the absence of PI animals is discussed in view of identifying the common source of infection and initiating control measures.

Epitope mapping of bovine viral diarrhea virus nonstructural protein 3

Six consecutive overlapped coding regions (F1-F6) of whole NS3 molecule of bovine viral diarrhea virus (BVDV) were cloned into pMAL-c2X plasmid vector and expressed in Escherichia coli cells (BL21 strain). The recombinant proteins were then purified by amylose resin to determine the most immunogenic domain(s) of the NS3 molecule. Evaluation of the recombinant proteins was carried out by indirect ELISAs using several bovine sera (previously characterized by virus neutralization test, a commercial ELISA kit, and a newly developed NS3-ELISA) and 6 monoclonal antibodies. The experiments showed that the most immunogenic domain of the NS3 protein was the fourth designed fragment (F4), a 122 amino-acid (AA) region of about 13.5 kDa (nucleotide 1003-1368; residue 335-456). Purified recombinant F4 was also evaluated as single ELISA antigen (F4-ELISA) for the detection of anti-BVDV antibodies in sera of infected cattle. Although this small recombinant fragment of NS3 protein was almost completely soluble and expressed more efficient respect to whole NS3 molecule, it did not show enough sensitivity and specificity to be a proper substitute for NS3 as ELISA antigen to detect specific antibodies against BVDV. However, statistical analyses showed a medium correlation between the results of the developed F4-ELISA and virus neutralization test (kappa coefficient=0.63, P<0.001), with the relative sensitivity and specificity of 78.05% and 84.91%, respectively, suggesting the potential use of this fragment as an ELISA antigen along with other antigens or monoclonal antibody(s) in a competitive ELISA.

Development and evaluation of a truncated recombinant NS3 antigen-based indirect ELISA for detection of pestivirus antibodies in sheep and goats

The aim of this study was to develop an indirect ELISA using the helicase domain of bovine viral diarrhoea virus (BVDV) NS3 protein instead of full-length NS3 protein for detection of BVDV and BDV antibodies in sheep and goats and its validation by comparing its sensitivity and specificity with virus neutralization test (VNT) as the reference test. The purified 50 kDa recombinant NS3 protein was used as the coating antigen in the ELISA. The optimal concentration of antigen was 320 ng/well at a serum dilution of 1:20 and the optimal positive cut-off optical density value was 0.40 based on test results of 418 VNT negative sheep and goat sera samples. When 569 serum samples from sheep (463) and goats (106) were tested, the ELISA showed a sensitivity of 91.71% and specificity of 94.59% with BVDV VNT. A good correlation (93.67%) was observed between the two tests. It showed a sensitivity of 85% and specificity of 86.6% with VNT in detecting BDV antibody positive or negative samples. This study demonstrates the efficacy of truncated recombinant NS3 antigen based ELISA for seroepidemiological study of pestivirus infection in sheep and goats.

Evaluation of neuraminidase antigen based competitive enzyme-linked immunosorbent assay in chickens vaccinated with avian influenza inactivated vaccine

A competitive enzyme-linked immunosorbent assay (c-ELISA) was developed as a serologic diagnostic tool to detect antibodies against NA subtype 3 of avian influenza virus (AIV). The NA antigen used in this c-ELISA was obtained by pronase treatment of allantoic fluid of specific-pathogen-free (SPF) eggs infected with AIV. The NA specific monoclonal antibodies were produced from purified NA. The N3 c-ELISA was carried out on serum samples collected from both SPF chickens and commercial layers to confirm whether the N3 c-ELISA was capable of detecting specific N3 antibodies. The positive cutoff percentage inhibition value was 6.13%. The sensitivity and specificity of the N3 c-ELISA were 83.7% and 95.6%, respectively, which indicated that N3 c-ELISA can detect the antibodies from SPF chickens or commercial chickens vaccinated with H9N3 subtype of AIV.

Evidence of a humoral immune response against the prokaryotic expressed N-terminal autoprotease (N(pro)) protein of bovine viral diarrhoea virus

Bovine viral diarrhoea virus (BVDV) is an economically important pathogen of cattle and sheep belonging to the genus Pestivirus of the family Flaviviridae. Although the BVDV non-structural N-terminal protease (N(pro)) acts as an interferon antagonist and subverts the host innate immunity, little is known about its immunogenicity. Hence, we expressed a recombinant BVDV N(pro)-His fusion protein (28 kDa) in E. coli and determined the humoral immune response generated by it in rabbits. The antigenicity of the N(pro) protein was confirmed by western blot using anti-BVDV hyperimmune cattle, sheep and goat serum, and anti-N(pro) rabbit serum. When rabbits were immunized with the N(pro) protein, a humoral immune response was evident by 4 weeks and persisted till 10 weeks post immunization as detected by ELISA and western blot. Despite N(pro)-specific antibodies remaining undetectable in 80 serum samples from BVDV-infected sheep and goats, BVDV hyperimmune sera along with some of the field cattle, sheep and goat sera with high BVDV neutralizing antibody titres were found positive for N(pro) antibodies. Our results provide evidence that despite the low immunogenicity of the BVDV N(pro) protein, a humoral immune response is induced in cattle, sheep and goats only with repeated BVDV exposure.