Multiplex PCR assay for detection of Actinobacillus pleuropneumoniae, Pasteurella multocida and Haemophilus parasuis in lungs of pigs from a slaughterhouse

A CRISPR/Cas12a-assisted rapid detection platform by biosensing the apxIVA of Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae is an important respiratory pig pathogen that causes substantial losses in the worldwide swine industry. Chronic or subclinical infection with no apparent clinical symptoms poses a challenge for preventing transmission between herds. Rapid diagnostics is important for the control of epidemic diseases. In this study, we formulated an A. pleuropneumoniae species-specific apxIVA-based CRISPR/Cas12a-assisted rapid detection platform (Card) that combines recombinase polymerase amplification (RPA) of target DNA and subsequent Cas12a ssDNase activation. Card has a detection limit of 10 CFUs of A. pleuropneumoniae, and there is no cross-reactivity with other common swine pathogens. The detection process can be completed in 1 h, and there was 100% agreement between the conventional apxIVA-based PCR and Card in detecting A. pleuropneumoniae in lung samples. Microplate fluorescence readout enables high-throughput use in diagnostic laboratories, and naked eye and lateral flow test readouts enable use at the point of care. We conclude that Card is a versatile, rapid, accurate molecular diagnostic platform suitable for use in both laboratory and low-resource settings.

An improved multiplex PCR for Actinobacillus pleuropneumoniae, Glaesserella australis and Pasteurella multocida

Glaesserella australis, a newly described bacterial species, has been isolated from pig lungs that displayed lesions very similar to those caused by Actinobacillus pleuropneumoniae, prompting the need for a validated diagnostic tool. In this work, we have altered a multiplex PCR used for the identification of cultures of G. australis, A. pleuropneumoniae and Pasteurella multocida to be more sensitive and then evaluated the use of the altered diagnostic tool on cultures and directly on tissues. The altered multiplex PCR was validated using 47 related species, both type/reference strains and field isolates. The sensitivity was assessed by serial dilutions and used a mixture of target bacteria in different concentrations. Further, 166 lung samples from 54 farms from four Australian States were used to validate the ability of the multiplex PCR to detect bacteria in lung swabs. The multiplex PCR was specific for the three target species. The assay could detect a minimum of 40 colony forming units (CFU) of G. australis, 786 CFU of A. pleuropneumoniae and 238 CFU of P. multocida. The multiplex PCR yielded more positives than coventional bacteriological examination. From a total of 166 lung samples, 51.9%, 51.9% and 5.6% of farms were PCR positive for P. multocida, A. pleuropneumoniae and G. australis, respectively. The results suggested that the new multiplex PCR was specific, sensitive and out performed traditional culture. The prevalence of G. australis was not very high, but it was the dominant pathogen in infected pigs.

In vitro susceptibility of swine pathogens to feed additives and active ingredients with potential as antibiotic replacements

AIMS

The rise in antibiotic resistance requires the reduction of antibiotic use in all sectors. In animal production, many commercial alternatives to antibiotics have been developed for incorporation into feeds, but a lack of evidence on their antibacterial activity limits confidence in their application. We aim to compare the antibacterial activity of feed additives and active ingredients to better understand their usefulness.

METHODS AND RESULTS

The antibacterial activity of 34 active ingredients and feed additives, including medium- and short-chain organic acids and essential oils, was tested against pure cultures of five bacterial swine pathogens. Antibacterial activity was observed using an agar plug diffusion method and quantified via broth microdilution. A diverse range of antibacterial activities were observed. The highest inhibitory activity against Staphylococcus aureus and Streptococcus suis was exhibited by the C12 monoglyceride (0.49 mg ml^-1 ). The monoglyceride of C12 was more effective than C12:0 against Strep. suis, but neither C12:0 nor its monoglyceride showed efficacy against the gram-negative micro-organisms tested. The most active against Escherichia coli were the C6:0 medium-chain organic acids and potassium diformate (1.95 mg ml^-1 ). For Salmonella Typhimurium, potassium diformate, sodium diformate, and a blend of C8:0/C10:0 (each 1.96 mg ml^-1 ), and for Actinobacillus pleuropneumoniae, eugenol (0.49 mg ml^-1 ) showed the most promising activity.

CONCLUSIONS

We identified broad-spectrum antibacterial activity, such as the C6:0 MCOA, and those with interesting narrow-spectrum activity, notably the killing of Strep. suis by C12 monoglyceride. We have identified additives that show the most promising bioactivity against specific pathogens.

SIGNIFICANCE AND IMPACT OF THE STUDY

We broadly compare a large collection of feed additives and active ingredients for their antibacterial activity against a diverse panel of bacterial swine pathogens. This provides a solid base of evidence which can drive the development of feed supplementation strategies with the aim of reducing dependency on antibiotic use in swine production.

Prevalence of Haemophilus parasuis"Glaesserella parasuis" in pigs in China: A systematic review and meta-analysis

Haemophilus parasuis, a gram-negative bacterium as an early commensal colonizer in the upper respiratory tract of weaning pigs (Sus scrofa), is one of the most important bacterial pathogens affecting pig populations. It is the causative agent of Glässer's disease, causing systemic infection and polyserositis, meningitis, and arthritis. H. parasuis infection can result in high mortality and morbidity with, the significant economic losses for pig producers. To estimate the overall disease prevalence of H. parasuis in pigs from China, we performed a meta-analysis using five bibliographical databases: PubMed, ScienceDirect, CNKI, Wanfang, and VIP Chinese Journal Databases. A total of 41 articles published between 2005 and 2019, fulfilled the final inclusion criteria. The overall prevalence of H. parasuis in pigs in China was 27.8 % with the highest prevalence between 2011 and 2015 (41.0 %). In terms of pig age, the point estimate of H. parasuis prevalence was higher in suckling piglets (29.2 %) compared with that for other pig ages. The prevalence in the serum subgroup (29.8 %) was higher than that in the nasal swab subgroup (12.5 %). The results of the present meta-analysis showed that H. parasuis infection was common in pig populations in China; therefore, effective control measures are necessary to reduce this threat to pig populations.

Prevalence and antimicrobial susceptibilities of bacterial pathogens in Chinese pig farms from 2013 to 2017

Bacterial diseases of swine are a kind of multifactorial and uncontrollable diseases that commonly exist in pig farms all over the world and will lead to huge economic losses every year. In this study, a detailed and overall survey was carried out to better understand the prevalence and antimicrobial susceptibilities of bacterial diseases from 2013 to 2017 in China. A total of 19673 bacterial strains were isolated from 44175 samples collected from 9661 pig farms that distributed in 16 Chinese major pig breeding provinces. The results showed that the average isolation rates of Streptococcus suis (SS), Haemophilus parasuis (HPS), Escherichia coli (E. coli), Pasteurella multocida (Pm), Actinobacillus pleuropneumoniae (APP), Brodetella bronchiseptica (Bb), Salmonella enteria (SE), Erysipelothrix rhusiopathiae (E. rhusiopathiae) were 16.9%, 9.7%, 6.3%, 3.4%, 0.3%, 1.5%, 2.3% and 0.9%, respectively. The isolate rates of E. coli, APP and SE showed an increasing trend from 2013 to 2017. The seasonal prevalence characteristics of SS, HPS and Pm were obviously higher from April to August for first two bacteria and higher at February, March, April, and October for Pm. The dominant serotypes for SS, HPS were serotype 2 and serotype 5 (changed from serotype 4), respectively. The SS, HPS, and Pm showed very high antibiotic resistance rates to almost 8 common antibiotics (β-lactam, aminoglycoside, macrolides, lincomycin, tetracycline, quinolone, polymyxin, and sulfonamide) and an obvious increasing trend of antibiotic resistance rates from 2013 to 2017. In conclusion, the study provides detailed information on the prevalence and antimicrobial susceptibilities of different bacterial pathogens of swine from 2013 to 2017 in China. These data can provide a foundation for monitoring epidemiological patterns of bacterial diseases in the Chinese swine herds, as well as provide insight into potential antibiotic resistance profiles in these pathogens.

EFFECT OF BACTERIAL AGENTS OF PORCINE RESPIRATORY DISEASE COMPLEX ON PRODUCTIVE INDICES AND SLAUGHTER WEIGHT

Abstract Porcine respiratory disease complex comprises the interaction of two or more infectious agents. The major bacterial agents involved were investigated in 115 finishing pigs at a farm in São Paulo State, Brazil: Actinobacillus pleuropneumoniae (serology, bacterial culture, and multiplex PCR), Mycoplasma hyopneumoniae (Mhyo) (nested PCR), Pasteurella multocida (multiplex PCR), Haemophilus parasuis (PCR multiplex), and Streptococcus sp. (bacterial culture). Macroscopic and microscopic lung lesions were evaluated, and zootechnical indices were recorded. Mhyo occurred in 113 animals (98.3%), seventeen of which were co-infected with Streptococcus sp. The finding of emphysematous lung was associated with significantly lower final and carcass weight at slaughter. Although vaccinated against Mhyo with an inactivated immunogen, almost 100% of the animals were infected. Mhyo infection with and without Streptococcus sp. co-infection was related to lung lesions of varying degrees and lower slaughter and carcass weight.

Survey of porcine respiratory disease complex-associated pathogens among commercial pig farms in Korea via oral fluid method

Oral fluid analysis for herd monitoring is of interest to the commercial pig production in Korea. The aim of this study was to investigate pathogen-positive rates and correlations among eight pathogens associated with porcine respiratory disease complex by analyzing oral fluid samples from 214 pig groups from 56 commercial farms. Samples collected by a rope-chewing method underwent reverse-transcriptase polymerase chain reaction (RT-PCR) or standard polymerase chain reaction (PCR) analysis, depending on the microorganism. Pathogens were divided into virus and bacteria groups. The former consisted of porcine reproductive and respiratory syndrome virus and porcine circovirus type 2 (PCV2), and the latter Pasteurella multocida, Haemophilus parasuis, Actinobacillus pleuropneumoniae, Mycoplasma hyopneumoniae (MHP), Mycoplasma hyorhinis, and Streptococcus suis (SS). All pathogens were detected more than once by PCR. Age-based analysis showed the PCR-positive rate increased with increasing age for PCV2 and MHP, whereas SS showed the opposite. Correlations between pathogens were assessed among 36 different pair combinations; only seven pairs showed statistically significant correlations. In conclusion, the oral fluid method could be a feasible way to detect various swine respiratory disease pathogens and, therefore, could complement current monitoring systems for respiratory diseases in the swine industry.

Unusual severe cases of type 1 porcine reproductive and respiratory syndrome virus (PRRSV) infection in conventionally reared pigs in South Korea

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) causes a loss of approximately US$ 70 million every year to the South Korean pork industry. There are two distinct genotypes: European (type 1) and North American (type 2). In South Korea, type 1 and type 2 PRRSV are widely distributed and have evolved continuously since the infection was first described. Here, we present two field cases of type 1 PRRSV infection with unusually severe pathogenicity.

CASE PRESENTATION

The first case farm was a two-site production system comprising farrow-to-grower and grower-to-finish units and was historically free from PRRSV infections. The PRRSV vaccine had not been used in both units. In October 2014, pigs in the grower-to-finish unit experienced severe respiratory distress with the mortality rate reaching to 22%. Despite antibiotic treatment, clinical signs were still noticed in most pigs. The second case farm was also a two-site production system, but had two separate farrow-to-grower units (unit A and unit B). Historically, type 1 PRRSV was continuously present in unit A, but unit B was free from PRRSV. Thus, all grower pigs of unit B were vaccinated before being moved to the grower-to-finish unit. In November 2014, severe respiratory distress was seen in pigs of the grower-to-finish unit. Significant respiratory distress was observed in only the grower herd moved from unit B, and the mortality of those pigs was ~50%. However, no disease was shown in the grower pigs from unit A.

CONCLUSIONS

To our knowledge, the present study is the first observation of the cases of infection by highly pathogenic type 1 PRRSV in South Korea. The Korean type 1 PRRSV strains have undergone unique evolutionary dynamics for the last decade in this country. Although there are known to be three clusters of Korean type 1 PRRSV, their pathogenicity could not be categorized owing to their high level of genetic diversity. Therefore, further studies are needed to demonstrate the novel classification of Korean type 1 PRRSV strains according to their virulence factors.

The challenge of detecting herds sub-clinically infected with Actinobacillus pleuropneumoniae

The introduction into a naïve herd of animals sub-clinically infected with Actinobacillus pleuropneumoniae (App) is frequently the cause of clinical pleuropneumonia and the identification of such infected herds is a priority in the control of disease. Different serological tests for App have been developed and a number of these are routinely used. Some are species-specific whereas others identify more specifically the serotype/serogroup involved which requires updated information about important serotypes recovered from diseased pigs in a given area/country. Serotyping methods based on molecular techniques have been developed lately and are ready to be used by most diagnostic laboratories. When non-conclusive serological results are obtained, direct detection of App from tonsils is sometimes attempted. This review addresses different techniques and approaches used to monitor herds sub-clinically infected by this important pathogen.