Evaluation of a single dilution ELISA system for detection of seroconversion to bovine viral diarrhea virus, bovine respiratory syncytial virus, parainfluenza-3 virus, and infectious bovine rhinotracheitis virus: comparison with testing by virus neutralization and hemagglutination inhibition

Bovine Parainfluenza-3 Virus Detection Methods and Prevalence in Cattle: A Systematic Review and Meta-Analysis

Bovine parainfluenza-3 virus (BPI3V) is an important respiratory pathogen in cattle, contributing to syndromes in the bovine respiratory disease complex (BRDC). Despite its significance, the understanding of its prevalence remains fragmented, especially within the larger framework of BRDC. This systematic review and meta-analysis aimed to determine the global prevalence of BPI3V in cattle using varied detection methods and to highlight associated risk factors. Of 2187 initially retrieved articles, 71 were selected for analysis, covering 32 countries. Depending on the detection method employed, the meta-analysis revealed significant variations in BPI3V prevalence. In the general cattle population, the highest prevalence was observed using the antibody detection method, with a proportion of 0.64. In contrast, in cattle with BRDC, a prevalence of 0.75 was observed. For the antigen detection method, a prevalence of 0.15 was observed, exclusively in cattle with BRDC. In nucleic acid detection, a prevalence of 0.05 or 0.10 was observed in the general and BRDC cattle populations, respectively. In virus isolation methods, a prevalence of 0.05 or 0.04 was observed in the general and BRDC cattle populations, respectively. These findings highlight the differences in the detection ability of different methods in identifying BPI3V. Other factors, such as country, study year, coinfections, farm size, the presence of respiratory signs, sex, and body weight, may also affect the prevalence. Most studies were anchored within broader BRDC investigations or aimed at detecting other diseases, indicating a potential under-representation of focused BPI3V research. BPI3V plays an important role in BRDC, with its prevalence varying significantly based on the detection methodology. To further understand its unique role within BRDC and pave the way for targeted interventions, there is an evident need for independent, dedicated research on BPI3V.

Technical Note: Using enzyme-linked immunosorbent assays to evaluate humoral responses to vaccination against respiratory viruses in beef cattle

This experiment evaluated humoral responses in beef calves vaccinated against parainfluenza-3 virus (PI3), bovine respiratory syncytial virus (BRSV), and bovine herpesvirus-1 (BHV-1) using serum neutralization (SN) tests or enzyme-linked immunosorbent assays (ELISA). Blood samples were collected from 50 overtly healthy Angus-influenced steers (183 ± 3 kg of body weight, 212 ± 2 d of age) on days 0, 21, 35, and 49 of the experiment. Steers were vaccinated against respiratory viruses on days 0 and 21. Blood was processed for serum collection and frozen in duplicates. One of the duplicates was analyzed for antibodies against BRSV, PI3, and BHV-1 using commercially available ELISA (IDEXX Switzerland AG, Liebefeld-Bern, Switzerland), and results reported as sample:positive control (S/P, %) ratio. The other duplicate was analyzed for antibodies against the same vaccine antigens via SN. This method reports results as titers, the greatest dilution that provides complete protection of the cells, which were transformed with base 2 log for statistical analyses. Samples were classified as positive for the presence of antibodies by SN if log-transformed titer ≥ 2 for all viruses, and by ELISA if S/P ratio ≥ 50% for BHV-1 or ≥ 20% for PI3 and BRSV. Day effects were detected (P < 0.01) for SN and ELISA across all vaccine antigens, as antibody levels increased after vaccine administration. Linear fits were detected (P < 0.01) across all vaccine antigens when regressing the SN and ELISA results; as SN titer increased, the ELISA S/P ratio linearly increased (P < 0.01). Kendall (τ) and Spearman's rank (ρ) correlations were also detected (P < 0.01) between SN and ELISA results across all vaccine antigens. The SN and ELISA were very strongly correlated (ρ ≥ 0.83) for BHV-1 and PI3 and strongly correlated (ρ = 0.66) for BRSV. Cohen's kappa coefficient for diagnosis agreement between methods was strong for BHV-1 and PI3 (κ ≥ 0.88), but weak (κ = 0.47) for BRSV. The sensitivity of the ELISA in yielding true positive results approached 100% across all antigens. The specificity of the ELISA in yielding negative results was satisfactory for BHV-1 and PI3 assays (84.0% and 88.5%, respectively) but not for BRSV (34.4%). Despite limitations in detecting true BRSV negatives, results from this experiment indicate that the commercial ELISAs tested herein can be used as surrogate for SN tests in quantifying humoral responses to vaccination against BHV-1, PI3, and BRSV in beef cattle.

Sero-prevalence and risk factors of infectious bovine rhinotracheitis virus (type 1) in Meru County, Kenya

The aim of the study was to determine the antibody sero-prevalence of Bovine Herpesvirus-1 which cause Infectious Bovine Rhinotracheitis (IBR) and to identify risk factors associated with BHV-1 antibody seropositivity among smallholder dairy farms in Meru County, Kenya. A cross-sectional study was conducted in the Naari area of Meru County, Kenya between September-October 2016 and March-April 2017. The 149 farmers were randomly selected from members of the Naari Dairy Farmers Cooperative Society who were actively delivering milk to the society at the time of the study. Serum samples were obtained from 403 female dairy cattle. Farm level management and animal factors were collected through direct interviews with the owner or someone who was knowledgeable about the animals. All serum samples were processed with an indirect enzyme-linked immunosorbent assay (gB ELISA) to determine the presence of antibodies to BHV-1. The overall farm-level and animal-level sero-prevalences of BHV-1 antibodies were 30.9 % (95 % CI: 23.6%-39.0%) and 17.4 % (95 % CI: 13.8%-21.4%), respectively. In the final multivariable analysis, the factors significantly associated with BHV-1 antibodies included; age of the dairy cattle (OR = 1.200, p = 0.001), age of the principal female farmers (OR = 0.182, p = 0.001) and rearing goats in the farm (OR = 26.77, p = 0.000). There was a significant interaction between rearing goats on the farm and age of the dairy cattle (p < 0.010); younger cattle seemed to have been exposed to BHV or a cross-reacting caprine herpesvirus when goats were on the farm. The results showed that BHV-1 was circulating among the cattle population in the Naari area of Meru County. Given that there is not BHV-1 vaccination use in this study population, training on the importance of biosecurity and vaccination for BHV-1 are recommended to reduce the transmission and impacts of BHV-1.

Seroprevalence of respiratory viral pathogens of indigenous calves in Western Kenya

Most studies of infectious diseases in East African cattle have concentrated on gastro-intestinal parasites and vector-borne diseases. As a result, relatively little is known about viral diseases, except for those that are clinically symptomatic or which affect international trade such as foot and mouth disease, bluetongue and epizootic haemorrhagic disease. Here, we investigate the seroprevalence, distribution and relationship between the viruses involved in respiratory disease, infectious bovine rhinotracheitis virus (IBR), bovine parainfluenza virus Type 3 (PIV3) and bovine viral diarrhoea virus (BVDV) in East African Shorthorn Zebu calves. These viruses contribute to the bovine respiratory disease complex (BRD) which is responsible for major economic losses in cattle from intensive farming systems as a result of pneumonia. We found that calves experience similar risks of infection for IBR, PIV3, and BVDV with a seroprevalence of 20.9%, 20.1% and 19.8% respectively. We confirm that positive associations exist between IBR, PIV3 and BVDV; being seropositive for any one of these three viruses means that an individual is more likely to be seropositive for the other two viruses than expected by chance.

Aspects of bovine herpesvirus 1 and bovine viral diarrhoea virus herd-level seroprevalence and vaccination in dairy and beef herds in Northern Ireland

Background

Infections with bovine herpesvirus 1 (BoHV-1) and bovine viral diarrhoea (BVD) virus cause diseases of cattle with a worldwide distribution. The primary objective of the present study was to describe aspects of herd-level BoHV-1 and BVDV seroprevalence (based on testing of pooled sera) and control on farms in Northern Ireland, including vaccine usage.

An indirect antibody ELISA test (SVANOVA, Biotech AB, Uppsala, Sweden) was applied to serum pools which were constructed from serum samples taken for a cross-sectional study of a convenience sample of 500 Northern Irish dairy and beef cow herds in 2010, for which vaccination status was determined by telephone survey. The herd-level seroprevalence of BoHV-1 and BVDV in Northern Ireland was estimated in non-vaccinating herds and associations between possible risk factors (herd type and herd size (quartiles)) and herd-level prevalence were determined using chi-squared analysis.

Results

The herd-level seroprevalence (of BoHV-1 and BVDV) in non-vaccinating herds was 77.3% (95% CI: 73.6–80.9%) and 98.4% (95% CI: 97.3–99.5%) respectively in the cross-sectional study. A significant difference existed in BoHV-1 herd-level seroprevalence between dairy and beef herds (74.7% vs 86.5% respectively; p < 0.02) though not for BVDV seroprevalence (98.5% vs 98.3% respectively; p > 0.91). A significant association was found between herd size (quartiles) and herd-level classification for BoHV-1 herd-level seroprevalence based on cut-off percentage positivity (COPP) (p < 0.01) while no such association was found for BVDV (p = 0.22).

15.5% and 23.8% of farmers used BoHV-1 and BVDV vaccines, respectively. BoHV-1 vaccine was used in 30% of dairy herds and in 11% of beef herds, while BVDV vaccine was used in 46% and 16% of dairy and beef herds, respectively.

Conclusions

The results from this study indicate that the true herd-level seroprevalences to bovine herpesvirus 1 and bovine virus diarrhoea virus in non-vaccinating herds in Northern Northern Ireland are 77.3% (95% CI: 73.6–80.9%) and 98.4% (95% CI: 97.3–99.5%), respectively. The present study will assist in guiding regional policy development and establish a baseline against which the progress of current and future control and eradication programmes can be measured.

Quantitative single serum-dilution liquid phase competitive blocking ELISA for the assessment of herd immunity and expected protection against foot-and-mouth disease virus in vaccinated cattle

A single serum-dilution liquid phase ELISA (slpELISA) was standardized to be used for serological evaluation of herd immunity against foot-and-mouth disease. The absorbance value at a dilution 1:64 of each serum sample was interpolated in a standard curve by plotting the antibody titers of six control sera determined by end point dilution liquid phase ELISA (lpELISA), against the absorbance values for the same control sera at 1:64 dilutions. A straight line was obtained by linear regression analysis (r>0.90) in the titer range of 1.40-2.40. The reliability of the antibody titers was confirmed by the simultaneous titration of 60 cattle sera by slpELISA and lpELISA, which showed an acceptable correlation (R(2)>0.87) for viral strains A24/Cruzeiro, A/Argentina/01, O1/Campos and C3/Indaial. Titers obtained by both methods were not significantly different (p>0.05), thus confirming that slpELISA could be used successfully to replace the conventional serial dilution ELISA for the assessment of protection status of cattle in epidemiological studies. In addition, this quantitative slpELISA provides an adequate method for monitoring the effectiveness of vaccination campaigns and is also suitable for the assessment of seroconversion of naive animals during early stages of infection.

Efficacy of an intranasal modified live bovine respiratory syncytial virus and temperature-sensitive parainfluenza type 3 virus vaccine in 3-week-old calves experimentally challenged with PI3V

Two experimental parainfluenza type 3 virus (PI3V) challenge studies were undertaken to evaluate the efficacy of a single intranasal dose of an attenuated live vaccine containing modified live bovine respiratory syncytial virus (BRSV) and temperature-sensitive PI3V in 3-week-old calves. In the first study, vaccine efficacy was evaluated in colostrum deprived calves. Nasal shedding of PI3V was highly significantly reduced in vaccinated calves challenged 10 days or 21 days after vaccination. In the second study, vaccine efficacy was assessed in calves with maternal antibodies against PI3V by challenge 66 days post-vaccination. Vaccination also significantly reduced PI3V excretion after challenge in this study. In both studies, clinical signs after challenge were very mild and were not different between vaccinated and control calves.

Detection of antibodies and risk factors for infection with bovine respiratory syncytial virus and parainfluenza virus-3 in beef cattle of Yucatan, Mexico

We collected blood samples from 756 > or =2-year-old cattle in 54 herds in Yucatan, Mexico, and used all of those to determine the antibody seroprevalences (in an indirect enzyme-linked inmunosorbance assay) to bovine respiratory syncytial virus (BRSV) and risk factors for animal-level seropositivity. We used 728 of the same samples (from 52 of the same herds) to do the same for parainfluenza virus-3 (PIV3). Cattle were selected by two-stage cluster sampling. Herd-level and animal-level risk factors were obtained through a personal interview. We analyzed the data by using a random-effects multivariable logistic regression model for clustered observations. All herds had at least 3 (BRSV) or 5 (PIV3) seropositive animals. The animal-level true seroprevalences were: 90.8% (86.5, 95.2%) and 85.6% (80.9, 90.4%) for BRSV and PIV3, respectively. Animals in large herds and old animals had the highest odds of being seropositives to BRSV, and those risk factors plus animals born on the farm for PIV3 infection.

Effects of intravenous triacylglycerol emulsions on lymphocyte responses to mitogens in fasted dairy cows undergoing intense lipomobilization

The objective of the study was to assess the effects of intravenous infusion of triacylglycerol (TAG) emulsions derived from different lipid sources on responses to mitogens of peripheral blood mononuclear cells (PBMC) isolated from fasted dairy cows. Six multiparous, non-pregnant, non-lactating Holstein cows were used in a replicated 3×3 Latin Square design. For 4 d, cows were fasted and infused intravenously with a 20% TAG emulsions derived from tallow (TA), linseed oil (LO) or fish oil (FO). Fasting was employed to induce energy deficit and lipid mobilization. Emulsions were administered for 20 to 30 min every 4 h throughout the 4 d fast at a rate of 0·54 g TAG/kg BW/d. Blood samples were taken before the first infusion, and then every 24 h during the fast. Blood was utilized to assess DNA synthesis, IgM and interferon-gamma (IFN-γ) secretion by PBMC stimulated with mitogens. In TA infused cows there was a decline of PBMC ability to respond to mitogens, which was significant 48 h after initiation of the infusion period for DNA synthesis and IFN-γ secretion. In LO or FO infused cows, PBMC responses to mitogens were not altered during the infusion period, and in some cases PBMC responses to mitogen was improved at 72 and 96 h after initiation of treatments. Effects of TAG infusion on PBMC responses to mitogens depended on the lipid source suggesting that LO or FO can attenuate the negative effects of fasting on immune functions.

Lymphocyte functions in dairy cows in hot environment

This study was carried out to ascertain the effects of intense high environmental temperatures (HET) on lymphocyte functions in periparturient dairy cows. The study was undertaken from the beginning of March through the end of July 2003 in a commercial dairy unit located approximately 40 km north of Rome. Thirty-four Holstein cows were utilised in the study. Twenty-two of these cows gave birth in spring (SP cows), from 28 March to 30 April. The remaining 12 cows gave birth in summer (SU cows), between 15 June and 2 July. The two groups of cows were balanced for parity and were fed the same rations. Blood samples were taken 4, 3, 2 and 1 week before calving, and 1, 2 and 4 weeks after calving, in order to evaluate peripheral blood mononuclear cell (PBMC) function in vitro, and to determine plasma cortisol concentrations. After isolation, the PBMC were stimulated with mitogens and their response in terms of DNA synthesis and IgM secretion was measured. During spring, either the day (9-20 h) or the night (21-8 h) temperature humidity index (THI) was below the upper critical THI (72) established for dairy cows. During summer, the mean daily THI values were 79.5+/-2.9 during the day and 70.1+/-4.7 during the night. Furthermore, during summer, three heat waves (a period of at least 3 consecutive days during which there were less than 10 recovery hours) occurred. Recovery hours were intended hours with a THI below 72. The first heat wave lasted 5 days, the second 6 days, and the third 15 days. Compared to the SP cows, over the entire periparturient period the extent of DNA synthesis and IgM secretion levels were lower (P ranging from <0.01 to 0.0001) and higher (P<0.01) respectively, in the SU cows. Before calving, the SU cows also presented higher (P<0.01) concentrations of plasma cortisol compared to the SP cows. This study indicates that the effects of HET on the immune response depend on the specific immune function under consideration, and that neuroendocrinal changes due to HET may play a role in the perturbation of immune functions.

Prevalence and epidemiological features of bovine viral diarrhoea virus infection in Lithuania

The objectives of the present work were to estimate the level of bovine viral diarrhoea virus (BVDV) infection in cattle herds at the different Lithuanian districts and to determine factors influencing the course of BVDV infection. The studies were explored in 147 intensive dairy cattle breeding herds from 27 different Lithuanian regions in 1997-2001. BVDV infection was diagnosed in all investigated regions. The existing variations in the structure of cattle population determined different distribution patterns of BVDV infection. The number of seropositive animals ranged from 11.9 to 100%. It must be pointed out that 29.9% of the herds were not infected with BVDV and in 32.7% of the herds from 70 to 100% of cattle were seropositive to BVDV. A positive correlation between the number of seropositive cattle, and the size of herds and age of animals was determined. Sex of animal had no influence on the prevalence of BVDV. It was estimated that the annual incidence risk of infection with BVDV decreases with the animal age.

Immunogenicity of bovine parainfluenza type 3 virus proteins encapsulated in nanoparticle vaccines, following intranasal administration to mice

Stimulation of long lasting, protective immunity to respiratory viruses is often difficult to achieve with conventional respiratory vaccines. Polymeric nanoparticles, incorporating viral proteins have been shown to offer sustained release of antigen, with consequent prolongued stimulation of the respiratory immune system. In this paper the efficacy of two nanoparticle vaccines (poly-lactide-co-glycolide, PLGA; polymethylmethacrylate, PMMA), incorporating proteins of bovine parainfluenza type 3 virus (BPI-3) was investigated. As a preliminary to experiments in calves, it was considered essential to demonstrate immunogenicity of the experimental vaccine in mice. Mice immunised with PLGA nanoparticles, containing BPI-3 proteins, developed higher levels of virus-specific antibody than mice immunised with the PMMA vaccine or with soluble viral proteins alone. Immunoblotting using serum from the vaccinated mice, demonstrated strong reactions against the major BPI-3 proteins.

Retrospective analysis of serum and nasal mucus from cattle in Northern Ireland for evidence of infection with influenza A virus

Eighty-four pairs of acute and convalescent serum samples collected in 1998 and 1999 from 17 outbreaks of respiratory disease, milk drop syndrome or diarrhoea in cattle were tested by haemagglutination inhibition against human influenza viruses A/Eng/333/80 (HIN1) and A/Eng/427/88 (H3N2). Antibodies to these viruses were present in the convalescent sera of 56.5 per cent and 58.8 per cent cattle tested, respectively, with 56 per cent of the animals seroconverting to one or both viruses. Titres were typically higher to A/Eng/427/88 (H3N2). Further testing of a subset of 21 of these serum pairs against the predominant H1N1 and H3N2 human and porcine strains circulating when the samples were collected revealed that the highest reactivity, in terms of both the magnitude of the recorded titres and the number of positive sera, was to human H3N2 strains. The titres to human H1N1 strains and to both porcine subtypes were low or absent. Attempts to isolate influenza A virus from nasal mucus or swab samples from 142 cattle from 46 cases of respiratory disease and/or milk drop syndrome by passage in embryonated specific pathogen-free eggs were unsuccessful.

ELISA de bloqueio monoclonal para o diagnóstico sorológico de infecções pelo herpesvírus bovino tipo 1 (BHV-1)

Um ensaio imunoenzimático do tipo ELISA de bloqueio com anticorpo monoclonal (ELISA-M) foi desenvolvido e padronizado para a detecção de anticorpos contra o vírus da Rinotraqueíte Infecciosa Bovina (Herpesvírus Bovino tipo 1; BHV-1). Foram utilizadas nesta avaliação 266 amostras de soros bovinos, sendo 148 negativos e 118 positivos em testes de soroneutralização (SN). Em comparação com este último, o ELISA-M demonstrou uma sensibilidade de 92,37%, especificidade de 92,56%, valor preditivo positivo de 90,83%, valor preditivo negativo de 93,83% e precisão de 92,48%. O índice de concordância (k) entre os testes foi de 0,85. O ELISA-M apresentou como vantagens a rapidez e a praticidade de execução. Com base nestes resultados, o ELISA-M foi considerado uma alternativa apropriada para o diagnóstico sorológico de infecções pelo BHV-1. Entretanto, o teste não foi capaz de diferenciar anticorpos induzidos por BHV-1 ou BHV-5.

Detection of IgM responses to bovine respiratory syncytial virus by indirect ELISA following experimental infection and reinfection of calves: abolition of false positive and false negative results by pre-treatment of sera with protein-G agarose

The IgM responses in three panels of sera generated by infection and reinfection of calves with bovine respiratory syncytial virus (BRSV) were measured by indirect ELISA (I-ELISA). The effect of depleting serum IgG by pre-treatment with protein G agarose (PGA) was evaluated. Following primary infection a weak IgM response was detected in the untreated sera of 3 out of 4 calves with maternally derived antibody (MDA). Both the magnitude and duration of the specific IgM responses in these calves were increased by pre-treatment with PGA. In addition, the fourth infected calf tested gave a single positive IgM result following PGA treatment. Transient or persistent IgM responses which were abolished by pre-treatment of sera with PGA were detected in 4/8 calves following reinfection. These were considered to be false positive results, consistent with the influence of IgM rheumatoid factor (IgM-RF). One of these calves and two additional calves showed transient increases in IgM which were resistant to PGA treatment. These were considered to represent specific IgM responses to reinfection. The results indicate the ability of PGA treatment to eliminate both false positive and false negative results and emphasise the necessity for controlling the influence of IgM-RF in IgM-specific indirect ELISAs.

Studies on the efficacy of intranasal vaccination for the prevention of experimentally induced parainfluenza type 3 virus pneumonia in calves

The efficacy of intranasal vaccination in preventing or limiting disease of the lower respiratory tract induced by parainfluenza 3 (PI3) virus was evaluated under experimental conditions, using a commercially available live vaccine containing a temperature-sensitive strain of PI3 virus. In a preliminary study four colostrum-deprived calves were vaccinated intranasally at one week and again at two months of age, and two similar calves were given an intranasal placebo. After the second vaccination serum antibodies to PI3 virus were detected in all four vaccinated calves, but not in the control animals. Seventeen days after the second vaccination all six calves were challenged with virulent PI3 virus, and they were killed six days later. The clinical scores and the extent of pulmonary consolidation were reduced in the vaccinated animals; PI3 virus was detected in the upper and lower respiratory tract of the control calves but in none of the vaccinated calves. In a larger scale study with 14 colostrum-fed calves, seven were vaccinated at one week and again at five weeks of age, and seven were given an intranasal placebo. Two weeks after the second vaccination all 14 calves were challenged with virulent PI3 virus. The clinical scores and lung consolidation were significantly reduced in the vaccinated calves in comparison with the controls. Six days after infection, 10 of the 14 calves were killed; PI3 virus was detectable in the nasal secretions of all seven control calves but in only one of the vaccinated animals, and PI3 viral antigen was detected in the lungs of the control calves but not in those of the vaccinated animals. One of the vaccinated calves had developed a severe clinical response after the challenge, but it had only minor lung consolidation when killed.

Evaluation of an immunofluorescent antibody test to detect bovine herpesvirus 1-specific IgM

An indirect immunofluorescent antibody test (IIFAT) was developed to detect bovine herpesvirus 1 (BHV-1)-specific IgM. All sera were treated with protein-G agarose prior to testing to eliminate the possibility of false-positive results due to IgM-isotype rheumatoid factor (IgM-RF). Specific IgM was first detected 8 days after experimental infection of 3 calves free of maternally derived antibody, with peak responses occurring 2-7 days later. Seroconversion was detected in all 3 calves using a single-dilution enzyme-linked immunosorbent assay. Following reinfection at 30 days postinfection, a low-level IgM response was detected in only 1 calf. Seroconversion was detected in 2 calves. There was no evidence of activation of IgM-RF by infection or reinfection with BHV-1. When 87 acute and convalescent serum pairs collected from 21 outbreaks of respiratory disease were tested, specific IgM was detected in 58 animals (66.6%) from 19 (90.5%) outbreaks. Seroconversion was detected in 44 of these animals (50.6%) from 17 outbreaks (81.0%). The correlations between these 2 assays on a calf and outbreak basis were 79.3% and 90.5%, respectively. Specific IgM was detected in 17/20 sera (85.0%) collected from an additional outbreak. No virus was detected by virus isolation or immunofluorescent staining in nasal mucus samples collected at the same time. Detection of specific IgM by IIFAT is a useful technique for the serodiagnosis of BHV-1 infection.

Isotype- and subclass-specific responses to infection and reinfection with parainfluenza-3 virus: comparison of the diagnostic potential of ELISAs detecting seroconversion and specific IgM and IgA

Isotype- and subclass-specific indirect enzyme-linked immunosorbent assays were developed to detect parainfluenza-3 virus-specific IgG1, IgG2, IgM, and IgA responses. Sera were treated with protein G-agarose prior to testing for specific IgM and IgA to eliminate the possibility of false-positive results due to IgM-rheumatoid factor and to remove interisotypic competition due to specific IgG. IgM and IgA absorbance values were expressed as a percentage of the absorbance values of positive reference sera included on each plate (S/P%), and respective positive/negative threshold values of 15.0% and 28.0% were determined. The mean interval between experimental infection of 3 calves and initial detection of specific IgG1 and IgG2 responses was 8.0 and 9.3 days respectively, rising rapidly to an initial plateau 13.7 and 11.0 days postinfection (dpi). Reinfection of these calves at 30 dpi resulted in further rapid increases, with higher plateau values reached 13.0 (IgG1) and 13.7 (IgG2) days later. The mean interval between infection and the first positive IgM and IgA responses was 6.7 and 12.3 days, respectively. IgM S/P% values peaked at 13.0 dpi, with all 3 calves showing a secondary anamnestic response to reinfection, peaking 4.7 days later. The IgA response to initial infection was weak, with only 2 calves showing an obvious peak response at 15.0 dpi. A strong anamnestic IgA response to reinfection occurred in 2 calves, with a peak response 9.5 days later. Apparent biphasic and triphasic IgM and IgA responses were evident in some calves. Acute and convalescent serum samples from 80 calves involved in 17 outbreaks of respiratory disease were tested for specific IgM and IgA. Positive IgM results were detected in 15 outbreaks, with 71 sera from 44 calves testing positive. Although IgA-positive results were detected in the same 15 outbreaks, only 42 sera from 31 calves were positive. In a previous study, seroconversion was detected in 21 of these calves from 10 outbreaks. Thus the diagnostic potential of the assays was in the order IgM > IgA > seroconversion. The correlations between IgM and IgA, IgM and seroconversion, and IgA and seroconversion results for each calf were 73.8%, 58.8% and 62.5%, respectively.

Evaluation of an IgM-specific indirect enzyme-linked immunosorbent assay for serodiagnosis of bovine respiratory syncytial virus infection: influence of IgM rheumatoid factor on test results with field sera

A commercially available indirect enzyme-linked immunosorbent assay for measuring bovine respiratory syncytial virus (BRSV)-specific IgG was adapted to measure virus-specific IgM. Using this assay, the development of rapid IgM responses in experimentally infected calves was observed 7-9 days postinfection, with peak absorbance values ranging from 1.698 to 2.873. When absorbance values were expressed as a percentage of a positive reference serum, a positive/negative threshold of 22% was determined by testing serum samples from 59 healthy 3-5-month-old calves. Acute and convalescent serum samples collected from 151 calves during 38 outbreaks of respiratory disease were tested, and 130 sera were positive. To determine the number of false-positive results due to the presence of IgM rheumatoid factor, a method for depleting serum IgG by pretreatment of sera with a suspension of protein-G-agarose was developed. All sera that initially tested IgM positive were retested following depletion of serum IgG. False-positive IgM reactions were detected in 23 sera (17.7%). Specific IgM responses were confirmed in 107 sera from 84 calves. Evidence of BRSV infection was detected in 34 of 38 outbreaks. In contrast, seroconversion was detected in 69 calves from 24 outbreaks, confirming the diagnostic potential of the IgM assay. Overall correlation between IgM and seroconversion results was 74.2%. Intra- and interassay reproducibility were 12.50% and 17.48%, respectively (mean coefficients of variation).