A blocking ELISA using a monoclonal antibody for the serological detection of Mycoplasma hyopneumoniae

Detection of Mycoplasma hyopneumoniae by ELISA and nested PCR from blood samples and nasal swabs from pigs in Slovakia

The aim of our study was to map the situation of swine mycoplasmoses on four farms in the region of Eastern Slovakia. The primary agent of Enzootic pneumonia of swine isMycoplasma hyopneumoniae. After reviewing the health status of conventional herds and evaluation of clinical symptoms, paired samples of nasal swabs and venous blood samples were collected from 38 pigs with clinical signs of respiratory disease. Nasal swab samples were tested by nested PCR, while blood samples were used to detect antibodies againstM. hyopneumoniaeby blockingELISA. The presence ofM. hyopneumoniaewas confirmed by nested PCR in four pigs (10.5%) and by blocking ELISA in 16 pigs (42.1%) of all four farms. This work presents for the first time comparison of different methods to diagnoseM. hyopneumoniaeinfection on pig farms in Eastern Slovakia.

Development of a blocking ELISA for detection of serum neutralizing antibodies against newly emerged duck Tembusu virus

Background

Since April 2010, domesticated ducks in China have been suffering from an emerging infectious disease characterized by retarded growth, high fever, loss of appetite, decline in egg production, and death. The causative agent was identified as a duck Tembusu virus (DTMUV), a member of the Ntaya virus (NTAV) group within the genus Flavivirus, family Flaviviridae. DTMUV is highly contagious and spreads rapidly in many species of ducks. More than 10 million shelducks have been infected and approximately 1 million died in 2010. The disease remains a constant threat to the duck industry; however, it is not known whether DTMUV can infect humans or other mammalians, despite the fact that the virus has spread widely in southeast China, one of the most densely populated areas in the world. The lack of reliable methods to detect the serum antibodies against DTMUV has limited our ability to conduct epidemiological investigations in various natural hosts and to evaluate the efficiency of vaccines to DTMUV.

Methodology/Principal Findings

A neutralizing monoclonal antibody (mAb) 1F5 binding specifically to the E protein was developed. Based on the mAb, a blocking enzyme-linked immunosorbent assay (ELISA) was developed for the detection of neutralizing antibodies against DTMUV. The average value of percent inhibition (PI) of 350 duck serum samples obtained from DTMUV-free farms was 1.0% ±5.8% (mean ± SD). The selected cut-off PI values for negative and positive sera were 12.6% (mean +2SD) and 18.4% (mean +3SD), respectively. When compared with a serum neutralizing antibody test (SNT) using chicken embryonated eggs, the rate of coincidence was 70.6% between the blocking ELISA and SNT, based on the titration of 20 duck DTMUV-positive serum samples.

Conclusions/Significance

The blocking ELISA based on a neutralizing mAb allowed rapid, sensitive, and specific detection of neutralization-related antibodies against DTMUV.

Diagnóstico da pneumonia enzoótica suína pela técnica da imunoperoxidase

Avaliou-se a técnica da imunoperoxidase como método auxiliar para a detecção de Mycoplasma hyopneumoniae em suínos naturalmente infectados. Foram colhidos 80 fragmentos de pulmões de 40 animais provenientes de granjas consideradas negativas e 40 de granjas com diagnóstico positivo de pneumonia enzoótica. Com a utilização de soro policlonal específico (IgG de coelho anti- M. hyopneumoniae) observou-se correlação positiva de 77% entre os diagnósticos microscópicos e imunoistoquímicos, enquanto que a correlação entre os diagnósticos macroscópico e imunoistoquímico foi de 49%. Nas granjas consideradas negativas observou-se presença de discreta imunorreação em 22,5% dos casos, o que poderia indicar a existência de reação cruzada com outros microrganismos. Nas granjas com diagnóstico positivo para pneumonia enzoótica a técnica da peroxidase-anti-peroxidase (PAP) revelou diferentes graus de intensidade, variando de fraca imunomarcação até espesso depósito amarronzado no epitélio ou na luz das vias aéreas, ou ainda no interior de macrófagos, com relação direta entre a intensidade das lesões e da imunorreação. A técnica imunoistoquímica possui sensibilidade de 95% e especificidade de 77,5%, podendo ser recomendada como ferramenta auxiliar, rápida e de baixo custo para o diagnóstico de pneumonia enzoótica suína em laboratórios de rotina em histopatologia.

Use of a Mycoplasma hyopneumoniae nested polymerase chain reaction test to determine the optimal sampling sites in swine

A number of polymerase chain reaction (PCR)-based diagnostic tests have been developed for Mycoplasma hyopneumoniae, including one from this research group. This report presents further development, optimization, and standardization of a nested PCR test. Detection sensitivity was 1 fg of M. hyopneumoniae chromosomal DNA (approximately 1 organism). This exceeded the sensitivity of or compared favorably with other published PCR tests. Polymerase chain reaction primers to porcine beta2-microglobulin were included as internal controls for amplifiable chromosomal DNA from porcine samples. To standardize the test, a number of samples from experimentally infected pigs, including nasal, tonsil, tracheobronchial swabs, lung tissue, bronchial alveolar lavage (BAL) fluid, and tracheobronchial brush samples, were examined by PCR. Samples obtained from BAL fluid and tracheobronchial sites were most predictive of infection, whereas nasal swabs and lung tissue were not reliable indicators of experimentally induced infection. In conclusion, the nested PCR developed for this study was found to be a highly sensitive and specific diagnostic tool for M. hyopneumoniae, but the enhanced sensitivity may be unnecessary if the proper sites are sampled.

Seroepidemiology of Mycoplasma hyopneumoniae in pigs from farrow-to-finish farms

A prospective study was carried out on three intensive farrow-to-finish farms. The aims were to estimate the incidence of Mycoplasma hyopneumoniae infection, to determine when pigs become infected and the pattern of transmission of infection and to verify the relationship between seroconversion and clinical signs. One batch of pigs per farm was followed from farrowing-to-slaughter. Blood samples were taken at 10, 27, 70, 94, 125 and 147 days of age, from 44, 48 and 44 pigs per farm. Colostrum and blood samples were also taken from the sows. Animals were checked clinically once a week and coughing rates were recorded. Antibodies against M. hyopneumoniae were detected by a blocking ELISA. At 27, 70 and 94 days of age most pigs on the three farms were seronegative, suggesting that no circulation of M. hyopneumoniae occurred during the growing period. Thereafter, a high proportion of pigs seroconverted, indicating that infection occurred soon after the transfer of the animals to the finishing houses. Differences were detected between farms in the incidence of seroconversion. Seropositive pigs were widely distributed among the finishing pens, suggesting that in addition to direct contact, other methods of transmission, such as indirect or airborne transmission, may have been important. Coughing started at around the same time as seroconversion. The results showed that the critical period for the transmission of M. hyopneumoniae is around the beginning of the finishing period, when pigs have low concentrations of antibodies against the agent.

A nested PCR assay for the detection of Mycoplasma hyopneumoniae in tracheobronchiolar washings from pigs

A nested polymerase chain reaction (PCR) was developed for the detection of Mycoplasma hyopneumoniae, the etiological agent of enzootic pneumonia, in tracheobronchiolar washings from live pigs. Two nested pairs of oligonucleotide primers were designed from the sequence of a specific DNA probe (I 141; accession number U02537). The primer combination was Hp1/Hp3 for the first step PCR while the nested primers (Hp4/Hp6) allowed amplification of a 706 bp fragment. All strains of M. hyopneumoniae tested in this study could be detected by the nested PCR. DNA from other bacterial species isolated from the respiratory tract of pigs or from other mycoplasmal species were not amplified. The detection limit was estimated to be 1 fg, corresponding approximately to one organism, while in the one step PCR previously described 4 x 10(2) organisms were required. The nested PCR was evaluated on 362 tracheobronchiolar lavages collected from pigs at 2, 4 and 6 months of age in eight herds chronically infected with M. hyopneumoniae. The nested PCR was compared to a blocking ELISA performed with sera collected from the same pigs at the same ages, and to an immunofluorescence test at slaughter on 65 lungs from 6-month old pigs. The comparison indicated that the nested PCR was significantly (p<0.05) more sensitive (157 positive results of 362 samples) than ELISA (118 positive results of 362 samples) for detection of M. hyopneumoniae infection. Nested PCR was also significantly more sensitive (54 positive results of 65 samples) than immunofluorescence (29 positive results of 65 samples) for detection of M. hyopneumoniae in pig lungs at slaughter. Moreover, the nested PCR was used to confirm the absence of the mollicute in a pig herd without any history of M. hyopneumoniae infection. Thus, nested PCR appears to be a useful test to assess M. hyopneumoniae infection on pig farms.

Epidemiological investigation of the influence of environmental risk factors on respiratory diseases in swine--a literature review

The influence of environmental and management factors on respiratory diseases in pigs is reviewed from an epidemiological point of view. The suitability of methods for the investigation of risk factors is discussed including aspects of study design, case definition, exposure assessment and data analysis. The results of published studies suggest a causal web of factor interaction, the analysis of which provides considerable challenges for current epidemiological techniques. New approaches to the problem should be further explored in the future in order to provide reliable advice to decision makers.

The prevalence of Mycoplasma hyopneumoniae in pig herds in western Finland based on the demonstration of antibodies in colostrum by ELISA

Swine enzootic pneumonia causes heavy economical losses in fattening herds. The aim of this study was to get an estimate of the prevalence of Mycoplasma hyopneumoniae in the province of Vaasa in Western Finland. There were 112 farrowing herds randomly chosen for a survey. Farmers were asked to milk colostrum samples from every sow. Owners of 22 herds did not send enough samples for a herd diagnosis. Altogether 1773 samples (mean 18.1 samples/herd) were analysed in an indirect ELISA for antibodies to Mycoplasma hyopneumoniae. Thirty-five herds were concluded to be infected with Mycoplasma hyopneumoniae. In these herds the mean prevalence of samples with antibodies was 16.3% (range 2.3%-70.0%, median 8.6%). The infected herds were significantly larger than the rest of the herds (no. of sows 27.0 vs. 18.4 respectively). The true prevalence of Mycoplasma hyopneumoniae infection in the province of Vaasa was estimated to be somewhat lower than the apparent prevalence of 39%. The application of colostrum serology is discussed.

Efficacy of doxycycline in feed for the control of pneumonia caused by Pasteurella multocida and Mycoplasma hyopneumoniae in fattening pigs

A multicentre, controlled, randomised and blinded study was carried out in three French pig herds to assess the efficacy of doxycycline administered in the feed for the control of pneumonia. About 20 per cent of 363 pigs from the three fattening units were diseased at the start of the study. Pneumonic lesions were found on pigs examined postmortem and Pasteurella multocida was isolated from the lungs of pigs in all the herds. Mycoplasma hyopneumoniae infection was confirmed either by detection in pneumonic lungs or by seroconversion in pigs sampled three weeks apart. P multocida, Bordetella bronchiseptica and Actinobacillus pleuropneumoniae were isolated from 64 per cent, 50 per cent and 2 per cent, respectively, of 148 nasal swabs. The following variables were significantly different between the treated and untreated groups (P < or = 0.001): the incidence of diseased pigs during the three weeks from the start of treatment (8.1 per cent in treated group v 35.4 per cent in control group), mean daily weight gain over the same period (934 g/day in the treated group v 834 g/day in the control group) and the cure rate of pigs which were diseased at the start of treatment (73.5 per cent in treated group v 35.3 per cent in control group). These data demonstrate that an average dose of 11 mg doxycycline/kg bodyweight per day in feed for eight days was effective in controlling pneumonia due to P multocida and M hyopneumoniae in these fattening pigs.