Serological and bacteriological observations on experimental infection with Salmonella hadar in chickens

Over the past 3 years the frequency of Salmonella hadar infections has increased in Belgium in both poultry and humans. Therefore, the course of infection with S. hadar in poultry was investigated. One day-old and 4 week-old specific pathogen-free chickens were orally infected with one of two S. hadar strains, SH1 or SH2. Mortality was 6% (SH1) and 17% (SH2) in birds infected at 1 day-old. Chickens infected at 1 day-old with SH2 showed a mild diarrhoea. The S. hadar faecal excretion in birds infected at 1 day-old remained high throughout the experiment until 12 weeks post-inoculation (pi). Faecal excretion was lower in older birds. Antibodies to S. hadar were observed from 2 weeks pi (SH2, infected at 1 day-old) or 4 weeks pi (SH1, both groups; SH2, chickens infected at 4 weeks of age). The percentage of chickens with antibodies was higher after infection at 1 day-old than after infection at 4 weeks of age. In a second experiment 1 day-old chicks were infected with SH1 and autopsied at regular intervals until 42 days pi. SH1 was isolated from the caeca from 3 h pi onwards and from the liver and spleen from 18 h until 14 days pi. Serous typhlitis and omphalitis were the main lesions. The number of macrophages in the lamina propria of the caecal tonsils was slightly increased from 18 h until 2 weeks pi. In the liver, inflammation was observed in the portal triads and in the sinusoids. This study indicates that infections with S. hadar lead to intense colonisation of the gut and extensive faecal shedding. It may also cause invasive infections in 1 day-old chickens.     

A novel strategy to select Bifidobacterium strains and prebiotics as natural growth promoters in newly weaned pigs

The study addresses the first two weeks of piglet weaning and is aimed at i) identifying new probiotic strains of Bifidobacterium spp. and non-digestible oligosaccharides (NDO) able to increase the level of autochthonous bifidobacteria in the gut, and ii) finding the best probiotic doses, and probiotic-NDO combinations for piglet growth and gut health.Initially, on a total of 60 pigs we administered 12 strains of 4 bifidobacteria species taken from our collection of strains of different ecological origin. We found the most promising probiotic candidates to be two strains of B. animalis subsp. lactis (M 354 and Ra 18) and one strain of B. choerinum (Su 891), as these led to an increase in the number of viable bifidobacteria in the caecum. In a second trial, a different set of 64 piglets were fed a diet containing a galacto-oligosaccharide (1%) from milk whey, and two fructo-oligosaccharides (4%) from chicory inulin and sugar beet (SbFOS). There was virtually no effect on the hindgut microbiota, except for SbFOS at 4% which tended to increase the endogenous bifidobacteria. Then, in a third trial employing 128 weaning pigs, the probiotic strains Ra 18 and Su 891 were tested individually, at different doses (0; 10⁷; 10⁹; 10¹¹ per pig per day) and combined with 0% or 2% SbFOS supplementation. It was found that Ra 18 improved the live weight growth linearly, while the Su 891 did not. The FOS supplementation showed no interaction with the Ra 18 or Su 891 probiotics for growth performance and no effect on this response criterion.Our selection procedure has highlighted that B. animalis subsp. lactis Ra 18, at 10¹¹ CFU per pig per day, appears to be the best probiotic choice for improved growth performance in weaning piglets.     

Experimental Eimeria debliecki infections in nursing and weaned pigs

Three litters of six, 3-day-old nursing pigs were inoculated via a stomach tube with 8.0 X 10(5), 1.6 X 10(6) or 5.0 X 10(6) sporulated oocysts of Eimeria debliecki and four groups of six, 4-week-old weaned pigs were inoculated with 8.0 X 10(5), 1.6 X 10(6), 5.0 X 10(6) or 1.0 X 10(7) sporulated oocysts of E. debliecki to determine its pathogenicity. Clinical coccidiosis or deaths did not result from infections. Infections were confined to the jejunum and occasionally the duodenum. Microscopic lesions of mild to moderate villous atrophy were observed in one nursing pig given 5.0 X 10(6) oocysts and three weaned pigs given 1.6 X 10(6), 5.0 X 10(6) and 1.0 X 10(7) oocysts and examined 5 days post-inoculation. Pathogenic bacteria or viruses were not demonstrated in any pigs. Results of this study indicate that E. debliecki is not a cause of neonatal or weaning diarrhea in pigs.     

Deletion of sodCI and spvBC in Salmonella enterica serovar Enteritidis reduced its virulence to the natural virulence of serovars Agona, Hadar and Infantis for mice but not for chickens early after infection

Salmonella enterica serovars Typhimurium, Enteritidis, Dublin, Choleraesuis or Gallinarum can colonise liver and spleen in particular hosts while infections with serovars Infantis, Agona, Hadar, etc. are usually limited to gastrointestinal tract. Reasons for this behavior are unknown, although it has been shown that sodCI and spv genes exhibit a strict distribution between more and less virulent serovars and they influence Salmonella virulence. However to what extent the presence or absence of these genes is associated with the increased virulence of serovars which possess them has never been addressed experimentally. In this study we therefore first confirmed the exclusive association of spvB and sodCI genes with the former group of serovars. In the next step we removed these two genes from S. Enteritidis genome and compared the virulence of such a mutant with the virulence of S. Infantis, S. Agona and S. Hadar for chickens and highly sensitive Balb/C mice. Single strain infection showed that the deletion of these two genes from S. Enteritidis resulted in the reduction of its virulence for mice but not for chickens. Mixed infection further confirmed these observations and indicated that in mice but not in chickens the virulence of sodCI and spv mutant was reduced to the natural virulence of serovars Infantis, Agona and Hadar. Although sodCI and spv genes do not influence S. Enteritidis virulence for chickens directly, they may be of an indirect effect through the increased persistence of S. Enteritidis in mice and increased probability of the reintroduction of S. Enteritidis into poultry flocks.     

Herd-level risk factors for faecal shedding of Salmonella enterica in Spanish fattening pigs

Herd-level risk factors for faecal shedding of Salmonella enterica were investigated in a cross-sectional study on Spanish finishing units. For this purpose, 10 faecal samples were collected from 10 different pens containing pigs close to market weight in a total of 232 fattening units. The total sample size was proportionally distributed according to the fattener census in each of the regions and provinces of the country in order to ensure a sample representative of the entire swine population. All samples were individually examined by culture of 25 g of faecal material. Data regarding characteristics and management of each fattening unit were collected by means of a questionnaire. Logistic regression was used to detect relationships between the detection of faecal shedding of S. enterica and potential herd-level risk factors. The feeding of pelleted feed was associated with an increased risk of culture-positive faecal samples (OR = 2.28; 95% CI: 1.22, 4.26). The odds of a farm being Salmonella positive were associated with its size. Fattening units that slaughtered more than 3500 pigs per year had a higher risk for Salmonella faecal shedding (OR = 1.78; 95% CI: 0.96, 3.31). Interventions at these two points should be considered when designing or managing growing pig facilities to reduce Salmonella faecal shedding by fatteners.     

Maladaptive behavioural patterns of early weaned, indoor raised pigs

The objective of the present study was to investigate the growth rate and maladaptive behaviour of early (day 14 of lactation) or late (day 28 of lactation) weaned pigs of either sex kept under different light intensities. Maladaptive behaviour was diagnosed when piglets were kept under a high light intensity but not when kept under a low light intensity. The time, spent engaged in maladaptive behaviour was not higher for barrows than for gilts. Lesions on 'recipient' animals were more severe in larger pigs with a greater rate of weight gain than in smaller ones. 'Perpetrator' pigs grew more slowly during the 46 days after weaning (P = 0.0013) than the non-preparator-pigs. 'Recipient' animals were significantly heavier and had higher rates of weight gain (P = 0.0003) than the 'perpetrator' pigs.     

Herd prevalence of Salmonella enterica infections in Danish slaughter pigs determined by microbiological testing

As a part of a nationwide programme to survey and control salmonella in pig herds, a microbiological survey of 1363 pig herds was performed in Denmark. A total of 13 468 slaughter pigs were examined at slaughter by culture of 5 g of caecal contents. Overall, 30 different serotypes of Salmonella enterica were isolated from 832 pigs (6.2%). The predominant serotype was S. Typhimurium, comprising 536 (64.4%) of the isolates. Four hundred and forty-eight isolates of S. Typhimurium were examined by phage typing, resulting in detection of 17 different phage types (definitive types, DT) with DT12 being the most frequent (49.1%).

Salmonella enterica was found in 302 herds (22.2%), S. Typhimurium was found in 61.1% of these. 279 (23.1%) large herds (producing more than 2600 slaughter pigs per year) were found to be salmonella positive compared with 23 (14.7 %) small herds (annual production of 500 to 550 slaughter pigs). Practical constraints in the study design did not allow for a firm conclusion on the interplay among herd size, geographical location and occurrence of salmonella.

In 284 of 302 infected herds (94.0%) only one serotype was detected. Infections with two different serovars were seen in 18 herds (6.0%).     

Salmonella enterica level in French pig farms effluents: Experimental and field data

The study aimed to (1) validate the mini-MSRV-MPN method to quantify Salmonella enterica in pig slurry, (2) estimate the effect and interaction on temperature, time and initial Salmonella load on the survival of the 2 strains of Salmonella typhimurium (PF 1690 and DT104 100/706/037) during slurry storage and (3) identify Salmonella contaminated finishing pig batches and assess the level of contamination of their slurry. The mini-MSRV-MPN method was compared to direct isolations on brilliant green agar supplemented with rifampicin to quantify Salmonella in pig slurry. Doelhert uniform shell design was used to study the effect of different parameters on the survival of the 2 strains of Salmonella in pig slurry. Environmental samples of faecal material and a sample of the slurry of 50 batches of finishing pigs were analysed by bacteriological classical method to identify Salmonella. Quantification was performed on pools of faeces and in slurry using the mini-MSRV-MPN technique. This method proved to be suited to quantify Salmonella in pig slurry. Temperature, time of slurry storage and their interaction influenced Salmonella decrease. 12 batches of pigs tested Salmonella positive. Quantification was possible in 5 batches of faecal samples (2.4–350 MPN g^− 1 of Salmonella). Quantification was achieved in 2 out of 6 positive samples of slurry (1.6 and 110 MPN mL^− 1 of Salmonella).     

Dietary nucleotide supplementation reduces occurrence of diarrhoea in early weaned pigs

In the weaning period, transition from sow's milk to the post-weaning diet causes the withdrawal of important nutrients as milk nucleotides, which are known to be determinant for the development of the gastrointestinal tract and immune function. The objective of these investigations was to study the effect of including these nucleotides in solid diets for piglets. Nucleotide composition of sow's milk was analyzed using 5 sows at 21 days of lactation. The average free nucleotide concentration was 102.8 ± 9.16 μmol/100 mL. Two experiments were performed to assess the effect of a product based on this composition (Nucleoforce Piglets®) on digestive adaptation and incidence of diarrhoea of nursery piglets. In Exp. 1, three groups of 6 piglets were weaned at 21 days of age and fed with a diet supplemented with 0 (control), 1000 or 2000 ppm of nucleotides, and a fourth group of 6 piglets was maintained in lactation. Seven days after weaning, piglets were euthanized and samples of jejunal mucosa were processed for histological measurements. Villus height decreased from 448 μm in un-weaned pigs to 275 μm in the control group 7 days after weaning. Although there were no differences in feed intake among groups, the reduction in villous height was less pronounced (P < 0.001) in nucleotide supplemented groups showing a villous height of 351 and 378 μm with the doses of 1000 or 2000 ppm respectively. In Exp. 2, 384 early weaned pigs were fed during 14 days with a diet supplemented with 0 (control), 750 and 1000 ppm of nucleotides. ADG and ADFI were not modified by the treatment, but nucleotide supplementation reduced the number of pigs treated with antibiotic as a result of diarrhoea (15.63% vs 3.13% and 1.56%; for control, 750 and 1000 ppm; P < 0.001). These results suggest that dietary supplementation with nucleotides from yeast might help to prevent post-weaning diarrhoea in piglets.     

Experimental model of enterotoxigenic Escherichia coli infection in pigs: potential for an early recognition of colibacillosis by monitoring of behavior

The hypothesis that altered behavior is a sign for an early recognition of disease was tested. The experiment was conducted to evaluate the behavioral patterns of pigs in a model of postweaning colibacillosis. Twenty-five weaned pigs (from a herd that was previously found to be highly susceptible to F4⁺ Escherichia coli strains) were randomly assigned into 5 groups, kept in isolated pens under the controlled ambiental conditions. One day after weaning, the pigs from three groups were intragastrically inoculated (via orogastric tube) with either F4ac⁺ (1466 or 2407) or F4⁻ (1467) nonenterotoxigenic E. coli (non-ETEC) strains, respectively. The pigs from the fourth group were inoculated with F4ac⁺ ETEC strain M1823 and the remaining 5 pigs that received broth containing 1.2% sodium bicarbonate were kept as noninoculated controls. The pigs were examined daily and the frequency and duration of their behavioral patterns, such as eating, drinking, lying, standing, urinating, defecating, rooting and playing were monitored for 300 h during a period of 10 days. In this model, three conditions were also observed in F4-susceptible pigs: (1) acute fatal diarrheal disease; (2) moderate diarrhea and weight loss and (3) no diarrhea and weight loss. The incidence (both frequency and duration) of defecating was significantly higher (P<0.05) in pigs inoculated with F4ac⁺ ETEC strain M1823 as compared to that of noninoculated (control) pigs. Pigs inoculated with F4ac⁺ non-ETEC strain 1466 had a significantly lower frequency of eating (P<0.05) and frequency/duration of drinking (P<0.05) than did the controls. The 1466-inoculated pigs, had an increased diarrhea score, but frequency/duration of defecating was not significantly different. Pigs inoculated with F4ac⁺ non-ETEC strain 2407 spent more time in lying (P<0.05) than did noninoculated pigs. Conversely, the pigs that received F4⁻ non-ETEC strain 1467 laid shorter (P<0.05) and ate/drank less frequently (P<0.05) than the controls. It was concluded that the changed occurrence of defecating and eating in pigs that were inoculated with either F4ac⁺ ETEC (M1823) or non-ETEC (1466) strain, respectively, was consistent with the pending clinical disease, i.e. postweaning colibacillosis.     

Experimental infection of neonatal pigs with CNF toxin-producing strains of Escherichia coli

To examine and compare the pathogenicity of cytotoxic necrotising factor (CNF)-producing Escherichia coli, two litters of piglets were infected orally with 10¹⁰E coli O88 or 10¹⁰E coli O32 strains. Of the six piglets infected with E coli O88, two died within 24 hours and three developed blood-stained diarrhoea. The other piglets were killed one, five, six and eight days after infection, when bacterial cultures indicated an overwhelming bacteraemic infection with E coli O88 in the early stages followed by clearance through the large intestine. The pathological changes consisted of an early enteritis, progressing to enterocolitis and a bacteraemic spread to the lungs. The histopathological changes were characteristic of toxaemic effects in brain, heart, liver and kidney, and characterised by congestion, oedema and exudation. Infection with E coli O32 produced a milder but similar enterocolitis, also with bacterial colonisation in the lungs. The histopathological findings again reflected a toxaemia. The enteritis was more persistent after E coli O32 infection and the strain persisted in large numbers in the intestine. No evidence of bacterial adherence to the intestinal mucosa was found with either strain. Enteroinvasion was only evident in one E coli O884-nfected piglet, but the consistent occurrence of interstitial pneumonia showed the predilection of these organisms for the lung. The results confirm the toxigenic properties of CNF⁺E coli and suggest an important role for this organism in enteric infection of young pigs.     

Experimental infection in pigs with encephalomyocarditis virus

Non-suppurative myocarditis in pigs that were experimentally infected with encephalomyocarditis (EMC) virus is reported. Two of the four pigs that were infected with the virus died suddenly from myocardial failure, and all four had gross and microscopic changes consistent with EMC infection. This confirms the pathogenic potential of some strains of EMC virus for young pigs.     

Age at primary infection with Salmonella enterica serovar Typhimurium in the chicken influences persistence of infection and subsequent immunity to re-challenge

Salmonella enterica remains one of the most important food-borne pathogens of humans and is often acquired through consumption of infected poultry meat or eggs. Control of Salmonella infections in chicken is therefore an important public health issue. Infection with S. enterica serovar Typhimurium results in a persistent enteric infection without clinical disease in chickens of more than 3 days of age, and represents a source for contamination of carcass at slaughter and entry into the human food chain. Data presented indicate a profound effect of age at initial exposure on the persistence of infection and a lesser effect on the development of effective immunity to re-challenge. The percentage of birds positive for Salmonella was high until 8–9 weeks of age, regardless of the age at which the birds were infected (1, 3 or 6 weeks). The birds infected at 3 and 6 weeks of age produced a more rapid and higher antibody response (IgY and IgA) than those infected at 1 week of age, but in all cases infection persisted for a considerable period despite the presence of high antibody levels. Following a re-challenge infection with S. Typhimurium, all three previously-infected groups had fewer bacteria in the gut, spleen and liver compared with age-matched birds receiving a parallel primary infection. However, the birds primary infected at 3 and 6 weeks of age cleared infection more rapidly than those infected at a younger age. Interestingly older-primed birds had higher specific T lymphocyte proliferative responses and specific circulating levels of IgY antibody at time of re-challenge. Although birds initially infected at 1 week of age and those that were previously uninfected produced a stronger antibody response following re-challenge, they were slower to clear Salmonella from the gut than the older-primed groups which expressed a stronger T lymphocyte response. The data presented indicate that clearance of Salmonella from the gut is age-dependent and we propose that this relates to the increased competence of the enteric T cell response. The findings that Salmonella persists beyond 8–9 weeks, irrespective of age at exposure, has implications for the broiler sector and indicates the need to remain Salmonella free throughout the rearing period. Moreover, the re-challenge data demonstrates that infection at a young age is less effective in producing protective immunity than in older chickens. This feature of the development of protective immunity needs to be considered when developing vaccines for the broiler sector of the poultry industry.     

Genomic lineage of Salmonella enterica serovar Dublin

Thirty five strains of the host adapted Salmonella serotype Dublin (S. Dublin) have been characterized by IS200 patterns, ribotyping, pulsed-field gel electrophoresis (PFGE), restriction fragment polymorphism after hybridization with five randomly cloned DNA-framents of S. enteridis (RFLP), and plasmid profiling in order to divide the strains into ‘genomic lines’. For comparison, 20 other strains of 9 different group-D serotypes were included. The IS200 patterns were identical in all strains of S. Dublin examined. These patterns were different from those observed in other group-D Salmonella with the exception of one strain S. Enteritidis phage type 11 and a strain of S. Rostock. The insertion element IS200 was not detected in strains of S. Dar-es-Salam, S. (II) 9,12:z -, and S. Panama. RFLP, based on probing with five random cloned chromosomal fragments gave the same pattern in all strains except for one isolate from the UK. This strain was also found to have an unique PFGE pattern and ribotype. Among the remaining strains, three different PFGE patterns and 7 different ribotypes were observed. Based on all four typing methods, 8 different ‘genomic lines’ of S. Dublin were identified. The same grouping could be obtained from the use of ribotyping alone, but PFGE and RFLP were found to provide valuable information on possible relationships between ribotypes. Seven different plasmid profiles and a group of strains without plasmids were observed. In several cases, the same plasmid profile was shown to be present in more than one ‘genomic line’.     

Effects of spray-dried animal plasma and immunoglobulins on performance of early weaned pigs

Five experiments were conducted to evaluate the effects of dietary spray-dried porcine plasma (SDPP) and spray-dried bovine plasma (SDBP) and their various molecular weight fractions on performance of pigs weaned at approximately 14 or 21 d of age. In addition, the efficacy of various levels of the immunoglobulin G (IgG)-rich fraction of SDPP and SDBP were evaluated. Experiment 1 evaluated the dietary addition of SDPP and three of its fractions (IgG-rich, albumin-rich, and low molecular weight fractions). Pigs fed SDPP grew faster and consumed more feed than the controls during the first week (P < 0.05). The IgG-rich fraction resulted in improvements in ADG and ADFI that were similar to those of pigs fed SDPP. The albumin-rich fraction had no effect on growth rate, but the low molecular weight fraction decreased feed intake as well as growth rate. Experiments 2 and 3 evaluated SDPP and graded levels of its IgG-rich fraction in pigs weaned at 21 or 14 d, respectively. In Exp. 2, pigs fed SDPP grew faster and consumed more feed than the controls during the first week (P < 0.05). Pig performance was enhanced with the addition of the IgG-rich fraction that provided 80% of the amount of IgG in the SDPP diet. In Exp. 3, there was no response to SDPP during the first week, but a positive growth response to SDPP (P < 0.01) occurred by the end of wk 2 (0 to 14 d). Feeding the IgG-rich fraction increased growth rate compared with controls (P < 0.05). Over the entire experiment, the greatest ADG occurred with the IgG-rich fraction that provided 128% of the amount of IgG provided by SDPP (quadratic; P < 0.05). Two additional experiments assessed feeding SDBP and bovine IgG-rich fractions to early weaned pigs. In Exp. 4, SDPP was superior to SDBP in stimulating growth and feed intake, but this difference did not occur in Exp. 5. In both experiments, the IgG fraction of bovine plasma seemed to be as effective at improving growth as SDPP and more effective than SDBP. The results indicate that both porcine and bovine plasma are beneficial to young pig performance during the first week after weaning and that the IgG fraction of plasma is the component that is responsible for the enhancement in growth rate and feed intake.     

Recurrence of Chlamydia suis infection in pigs after short-term antimicrobial treatment

The effect of short-term antimicrobial treatment on natural excretion of Chlamydia suis in rectal swabs and C. suis and Chlamydophila psittaci in nasal swabs was investigated in 47 clinically normal piglets by quantitative real-time PCR. Pigs were treated IM with 4 mg/kg enrofloxacin for 5 days (n = 22) or 2.5 mg/kg enrofloxacin for 3 days followed by 100 mg/mL tiamulin (n = 25). Antimicrobial treatment reduced the number of pigs positive for chlamydiae and the quantity of chlamydial DNA in positive swabs for a few days, but chlamydial excretion recurred in both groups. Short-term antimicrobial treatment at dosages recommended for treatment of other bacterial infections in pig herds was not effective in eliminating naturally occurring subclinical chlamydial infection in pigs.