Tom Meyns

Control of Mycoplasma hyopneumoniae infections in pigs

Abstract Mycoplasma hyopneumoniae, the primary pathogen of enzootic pneumonia, occurs worldwide and causes major economic losses to the pig industry. The organism adheres to and damages the ciliated epithelium of the respiratory tract. Affected pigs show chronic coughing, are more susceptible to other respiratory infections and have a reduced performance. Control of the disease can be accomplished in a number of ways. First, management practices and housing conditions in the herd should be optimized. These include all-in/all-out production, limiting factors that may destabilize herd immunity, maintaining optimal stocking densities, prevention of other respiratory diseases, and optimal housing and climatic conditions. Strategic medication with antimicrobials active against M. hyopneumoniae and, preferably, also against major secondary bacteria may be useful during periods when the pigs are at risk for respiratory disease. Finally, commercial bacterins are widely used to control M. hyopneumoniae infections. The main effects of vaccination include less clinical symptoms, lung lesions and medication use, and improved performance. However, bacterins provide only partial protection and do not prevent colonization of the organism. Different vaccination strategies (timing of vaccination, vaccination of sows, vaccination combined with antimicrobial medication) can be used, depending on the type of herd, the production system and management practices, the infection pattern and the preferences of the pig producer. Research on new vaccines is actively occurring, including aerosol and feed-based vaccines as well as subunit and DNA vaccines. Eradication of the infection at herd level based on age-segregation and medication is possible, but there is a permanent risk for re-infections.

Gastric Helicobacters in Domestic Animals and Nonhuman Primates and Their Significance for Human Health

SUMMARY Helicobacters other than Helicobacter pylori have been associated with gastritis, gastric ulcers, and gastric mucosa-associated lymphoid tissue lymphoma in humans. These very fastidious microorganisms with a typical large spiral-shaped morphology were provisionally designated “H. heilmannii,” but in fact they comprise at least five different Helicobacter species, all of which are known to colonize the gastric mucosa of animals. H. suis, which has been isolated from the stomachs of pigs, is the most prevalent gastric non-H. pylori Helicobacter species in humans. Other gastric non-H. pylori helicobacters colonizing the human stomach are H. felis, H. salomonis, H. bizzozeronii, and the still-uncultivable “Candidatus Helicobacter heilmannii.” These microorganisms are often detected in the stomachs of dogs and cats. “Candidatus Helicobacter bovis” is highly prevalent in the abomasums of cattle but has only occasionally been detected in the stomachs of humans. There are clear indications that gastric non-H. pylori Helicobacter infections in humans originate from animals, and it is likely that transmission to humans occurs through direct contact. Little is known about the virulence factors of these microorganisms. The recent successes with in vitro isolation of non-H. pylori helicobacters from domestic animals open new perspectives for studying these microorganisms and their interactions with the host.

A cross-sectional study of risk factors associated with pulmonary lesions in pigs at slaughter

A cross-sectional study was conducted to identify herd-level factors that may influence the prevalence and severity of macroscopically visible pulmonary lesions in pigs at slaughter. Data were collected following abattoir inspection of 50 randomly-selected batches of 6335 pigs and by interviewing the producers. Macroscopic lung lesions were identified and scored semi-quantitatively in ≥ 80 pigs/herd and the prevalence of pleuritis and pneumonia was 20.76% and 23.85%, respectively. Following multivariable analysis, the seroprevalence of Actinobacillus pleuropneumoniae (P < 0.001) and Mycoplasma hyopneumoniae (P = 0.018) and the number of pigs/nursery pen (P = 0.023) were positively associated, whereas average weaning age was negatively associated (P = 0.001) with the pleuritis score. Risk factors associated with a higher prevalence of pneumonia were the presence of pleuritis (P = 0.001) and the frequent purchasing of pigs (P = 0.020). The findings of this study indicate that the prevalence of pleuritis and pneumonia remains high in Belgium and management factors are central to disease control.

An experimental Helicobacter suis infection causes gastritis and reduced daily weight gain in pigs

Helicobacter suis is a zoonotically important bacterium, that has been associated with gastritis and ulcerative lesions of the pars oesophagea of the stomach in pigs. Its exact role in these pathologies, however, still remains controversial. Therefore, a total of 29 medicated early weaned piglets were inoculated intragastrically or orally, with a total of 2 × 10(9) viable H. suis bacteria and the effect on gastric pathology and weight gain was determined. Twenty-three medicated early weaned piglets were inoculated with a sterile culture medium and used as sham-inoculated controls. The animals were euthanized between 28 and 42 days after inoculation. Infected animals showed a more severe gastritis compared to the control group. There was also a significant reduction of approximately 60 g per day (10%) in weight gain in H. suis inoculated animals compared to the sham-inoculated control animals. In conclusion, this study demonstrates for the first time that a pure in vitro culture of H. suis not only causes gastritis but also a marked decrease of the daily weight gain in experimentally infected pigs.

The effect of vaccination on the transmission of Mycoplasma hyopneumoniae in pigs under field conditions

This study investigated the effect of vaccination against Mycoplasma hyopneumoniae on its transmission in nursery pigs under field conditions. Seventy-two pigs were randomly allocated at weaning into vaccinated (V) and non-vaccinated (NV) groups. Animals in the V group were vaccinated at 3 weeks of age with a commercial M. hyopneumoniae bacterin vaccine. Broncho-alveolar lavage fluid taken at weaning and at the end of the nursery period was assessed for the presence of M. hyopneumoniae by nested PCR, and the reproduction ratio of infection (R(n)) was calculated. The percentage of positive pigs in the V and NV groups was 14% and 36% at weaning, and 31% and 64% at the end of the nursery period, respectively. The R(n)-values for the V and NV groups were 0.71 and 0.56, respectively (P>0.05). The study indicates that vaccination does not significantly reduce the transmission of this respiratory pathogen.

Infection with a low virulent Mycoplasma hyopneumoniae isolate does not protect piglets against subsequent infection with a highly virulent M. hyopneumoniae isolate.

The study aimed to evaluate the effect of an infection with low virulent isolates of M. hyopneumoniae (LV1 and LV2) on the subsequent infection with a highly virulent isolate (HV). Fifty-five, 3-week-old piglets free of M. hyopneumoniae were randomly allocated to 6 different groups. At 4 weeks of age (D0), groups LV1-HV and LV1 were intratracheally inoculated with LV1, groups LV2-HV and LV2 with LV2, and group HV with sterile culture medium. Four weeks later (D28), the pigs of these different groups were either intratracheally inoculated with the highly virulent isolate (groups LV1-HV, LV2-HV, HV) or with sterile culture medium (groups LV1 and LV2). A negative control group consisted of pigs inoculated with sterile culture medium on D0 and D28. All animals were necropsied at 28 days after the second inoculation (D56). Clinical symptoms were evaluated daily using a respiratory disease score (RDS). After necropsy, macroscopic and histopathological lung lesions were quantified and immunofluorescence (IF) testing on lung tissue and nested PCR on BAL fluid were performed for the detection of M. hyopneumoniae. Disease signs and lung lesions were not observed in pigs of the negative control group. In the other groups, there were no or only very mild clinical symptoms from D0 until D28. A significant increase in the average RDS values was, however, observed during D28-D56, especially in groups LV1-HV (1.48) and LV2-HV (1.49), in group HV (0.79), and to a lesser extent in groups LV1 (0.50) and LV2 (0.65) (P<0.05). The clinical symptoms during D28-D56, the lung lesions and intensity of IF staining were more pronounced in groups LV1-HV, LV2-HV and HV compared to groups LV1 and LV2. All pigs, except those from the negative control group, were positive on IF testing and PCR at D56. The present study demonstrates that pigs inoculated with low virulent isolates of M. hyopneumoniae are not protected against a subsequent infection with a highly virulent isolate 4 weeks later and may even develop more severe disease signs. This indicates that subsequent infections with different M. hyopneumoniae isolates may lead to more severe clinical disease in a pig herd.

Case report: Helicobacter suis infection in a pig veterinarian.

This study describes a non‐Helicobacter (H.) pylori Helicobacter (NHPH) infection in a pig veterinarian. The patient suffered from reflux esophagitis and general dyspeptic symptoms and was referred to the hospital for upper gastrointestinal endoscopy. Histologic examination of corpus and antrum biopsies revealed a chronic gastritis. Large spiral‐shaped non‐H. pylori helicobacters could be visualized and were identified as H. suis by PCR. The patient was treated with a triple therapy, consisting of amoxicillin, clarithromycin, and pantoprazole for 10 days. Successful eradication was confirmed after a follow‐up gastrointestinal endoscopy and PCR 10 weeks after treatment. A mild chronic gastritis was, however, still observed at this point in time. This case report associates porcine H. suis strains with gastric disease in humans, thus emphasizing the zoonotic importance of H. suis bacteria from pigs.

Effect of particle size distribution and dietary crude fibre content on growth performance and gastric mucosa integrity of growing–finishing pigs☆

This study was designed to examine the effect of crude fibre (CF) content and particle size of the diet on growth performance, carcass yield and gastric mucosa integrity. The experimental design was a 2×2 factorial trial with 192 pigs fed from 24 to 110 kg bodyweight. Four diets were compared: (1) low fibre finely ground; (2) low fibre coarsely ground; (3) high fibre finely ground; and (4) high fibre coarsely ground. All ingredients were ground before mixing. The high fibre coarsely ground diet resulted in the fewest lesions in the gastric pars oesophagea (P<0.001). Coarse grinding also resulted in the lowest urease activity in the stomach (P=0.006). The feed conversion ratio was worse on the coarsely ground diet than on the finely ground diet (P=0.038), whereas carcass yield was lower for pigs on the high fibre diet vs. the low fibre diet (P<0.001). Coarse grinding feed ingredients in a growing pig diet that is high in CF may reduce macroscopic lesions of the pars oesophagea but such a diet was accompanied in this study by inferior carcass yield.

Effect of administration of organic acids in drinking water on faecal shedding of E. coli, performance parameters and health in nursery pigs.

This study evaluated the effect of altering the pH of drinking water on the excretion of Escherichia coli (haemolytic and total count) by nursery piglets under field conditions as well as their performance parameters and health. The pH of the normal drinking water (pH 8) was lowered by using a mixture of organic acids (lactic, formic, propionic and acetic acid) to obtain a final pH of 6, 5 or 4. Reducing the pH to 4 resulted in the excretion of less faecal E. coli compared to pigs given water of pH 8 (P<0.05), but the fall in pH also significantly decreased water intake. The highest daily weight gain and lowest mortality rate were observed in the group receiving drinking water of pH 5 (P>0.05). No significant differences in the clinical parameters measured were seen between groups. The results of this study suggest that lowering the pH of the drinking water in newly weaned pigs reduces the E. coli load.

Protective immunization with homologous and heterologous antigens against Helicobacter suis challenge in a mouse model.

Helicobacter (H.) suis colonizes the stomach of more than 60% of slaughter pigs and is also of zoonotic importance. Recently, this bacterium was isolated in vitro, enabling the use of pure cultures for research purposes. In this study, mice were immunized intranasally or subcutaneously with whole bacterial cell lysate of H. suis or the closely related species H. bizzozeronii and H. cynogastricus, and subsequently challenged with H. suis. Control groups consisted of non-immunized and non-challenged mice (negative control group), as well as of sham-immunized mice that were inoculated with H. suis (positive control group). Urease tests on stomach tissue samples at 7 weeks after challenge infection were negative in all negative control mice, all intranasally immunized mice except one, and in all and 3 out of 5 animals of the H. cynogastricus and H. suis subcutaneously immunized groups, respectively. H. suis DNA was detected by PCR in the stomach of all positive control animals and all subcutaneously immunized/challenged animals. All negative control animals and some intranasally immunized/challenged mice were PCR-negative. In conclusion, immunization using antigens derived from the same or closely related bacterial species suppressed gastric colonization with H. suis, but complete protection was only achieved in a minority of animals following intranasal immunization.