Experimental reproduction of postweaning multisystemic wasting syndrome (PMWS) in pigs in Sweden and Denmark with a Swedish isolate of porcine circovirus type 2.

An experimental model using 3-day-old snatch-farrowed colostrum-deprived piglets co-infected with porcine circovirus type 2 (PCV2) and porcine parvovirus (PPV) is at present one of the best methods to study factors affecting development of postweaning multisystemic wasting syndrome (PMWS). A Swedish isolate of PCV2 (S-PCV2) retrieved in 1993 from a healthy pig has been used in this model to reproduce PMWS in pigs from Northern Ireland. This virus has been present in the Swedish pig population for at least a decade without causing any known PMWS disease problems, despite its potential pathogenicity. The reasons for this are unknown, but could be related to genetics, absence of triggers for PCV2 upregulation (infectious agent and/or management forms) within Swedish pig husbandry. In order to confirm the pathogenicity of S-PCV2, Swedish and Danish pigs were experimentally infected with this isolate according to the established model. Swedish pigs were also infected with a reference isolate of PCV2 (PCV2-1010) to compare the severity of disease caused by the two isolates in Swedish pigs. Both Danish and Swedish pigs developed PMWS after the experimental infection with S-PCV2. Antibodies to PCV2 developed later and reached lower levels in serum from pigs infected with S-PCV2 than in pigs inoculated with PCV2-1010. In general, pigs infected with S-PCV2 showed more severe clinical signs of disease than pigs infected with PCV2-1010, but pigs from all PCV2-inoculated groups displayed gross and histological lesions consistent with PMWS. All pigs inoculated with PPV, alone or in combination with PCV2, displayed interleukin-10 responses in serum while only pigs infected with PPV in combination with PCV2 showed interferon-alpha in serum on repeated occasions. Thus, the pathogenicity of S-PCV2 was confirmed and a role for cytokines in the etiology of PMWS was indicated.

Experimental infections with Actinobacillus pleuropneumoniae in pigs--I. Comparison of five different parenteral antibiotic treatments.

SPF pigs aged 10 weeks were infected intranasally with Actinobacillus pleuropneumoniae serotype 2. After the onset of clinical symptoms of respiratory disease, which occurred 20 h post-infection, parenteral treatment with ceftiofur, danofloxacin, enrofloxacin, penicillin or tiamulin was initiated (n = 8 per group). Untreated groups, of which one was infected, served as controls. The uninfected control group did not show any signs of disease, while the infected control group was severely affected by the infection and also expressed a decreased weight gain following the challenge. Based on clinical signs, the magnitude of pathological lesions in the respiratory tract found at necropsy performed 17 days post-infection and the number of reisolates of A. pleuropneumoniae made at necropsy, treatments with the quinolones (danofloxacin and enrofloxacin) and the cephalosporine (ceftiofur) were superior to those with penicillin and tiamulin. The latter groups also developed antibodies to A. pleuropneumoniae to a larger extent. Some of the pigs treated with ceftiofur and danofloxacin developed antibodies to A. pleuropneumoniae, and the microbe was reisolated from approximately 50% of these animals. In contrast, pigs treated with enrofloxacin did not develop antibodies to A. pleuropneumoniae, and the challenge strain was not found at necropsy. The performance with respect to daily weight gain and feed conversion corresponded well with the clinical signs developed and the findings made at necropsy. The decreased growth recorded during the acute phase of the disease was, to a large extent, caused by a reduced feed intake.

Experimental infections with Actinobacillus pleuropneumoniae in pigs--II. Comparison of antibiotics for oral strategic treatment.

The present study was aimed at scrutinizing the efficacy of oral antimicrobial treatments at experimental challenge using a strain of Actinobacillus pleuropneumoniae serotype 2 known to cause severe disease. SPF pigs aged 10 weeks were infected intranasally and the antimicrobial treatments were initiated 5 h prior to that exposure. Several antimicrobial drugs, as well as the length of the treatment period, were elucidated. The outcome of the challenge was monitored by registration of clinical symptoms, weight gains and the development of serum antibodies to A. pleuropneumoniae. At necropsy, the magnitude of pathological lesions in the respiratory tract and the rate of reisolation of the infective strain were recorded. Animals that became diseased displayed a decreased growth rate caused, to a large extent, by a reduced feed intake. The performance with respect to daily weight gain and feed conversion corresponded well with the clinical signs developed and serologic reactions, as well as with the findings made at necropsy. The results obtained among pigs treated with enrofloxacin, but also with florfenicol or chlortetracycline, were superior to those of pigs treated with penicillin, tiamulin or tilmicosin. A positive effect was obtained using a strategic in-feed medication against infection with A. pleuropneumoniae. Provided that the drug used is effective against the target microbe, initiating treatment prior to infection appeared to be more important than the length of the treatment. It should, however, be remembered that A. pleuropneumoniae was reisolated from all but one medicated group following an experimental challenge given after initiating the medication. Consequently medical treatment as described did not eradicate the microbe.

Mucosal immune responses in calves orally vaccinated with a live auxotrophic aroA Salmonella dublin strain.

The mucosal immune responses were studied in two calves orally vaccinated with the live aroA mutant strain, Salmonella dublin SL5631, and in two non-vaccinated control calves. Intestinal secretions were collected through a permanent fistula in place during a 5-week period. Vaccinated calves responded with high IgM and IgA titres against the S. dublin lipopolysaccharide. Both IgA and the IgM titres appeared already after 3 days and IgM somewhat earlier than the IgA titres. Both antibody titres remained high for 2 weeks after the third and final vaccine dose. The calves also showed marked T-cell responses in lymphocytes collected from mesenterial lymph nodes and the spleen.

Antibody response and protection against challenge in mice vaccinated intraperitoneally with a live aroA O4-O9 hybrid Salmonella dublin strain.

An auxotrophic Salmonella dublin (O9,12) strain, SL5631, with a deletion affecting gene aroA, was made into a partial diploid expressing the rfb (O-antigen-repeat-unit-specifying) gene cluster of Salmonella typhimurium (O4,12). By use of O4- and O9-specific antisera in indirect immunofluorescence assays, the resulting hybrid SL7103 was shown to express both the O4- and O9-antigen epitopes in the same bacterium. Qualitative and quantitative sugar analyses by gas-liquid chromatography on peralditol acetates of phenol-water-extracted lipopolysaccharides showed that the S. dublin and S. typhimurium repeating units (estimated on the basis of their tyvelose and abequose contents, respectively) were present in approximately equimolar amounts. The SL7103 hybrid auxotroph was avirulent when given intraperitoneally to NMRI mice in a dose of 10(8) CFU and elicited a protective immunity against intraperitoneal challenge with either virulent S. dublin (50% lethal dose of ca. 1.5 x 10(4) CFU versus < 1 x 10(1) CFU in nonimmunized mice) or virulent S. typhimurium (50% lethal dose of ca. 1 x 10(5) versus < 1 x 10(1) CFU in nonimmunized mice). Compared with the protection elicited in homologous systems (S. dublin SL5631 against S. dublin and S. typhimurium SL1479 against S. typhimurium), the protective efficacy of the hybrid was reduced approximately 70-fold against S. dublin challenge and 100-fold against S. typhimurium challenge. Vaccination with S. typhimurium SL1479 conferred no protection against S. dublin challenge, and vaccination with S. dublin SL5631 conferred no protection against S. typhimurium challenge. The protection elicited by the hybrid strain SL7103 is supposed to be mainly a consequence of serum antibodies directed against the immunodominant O4 and O9 epitopes.

Oral vaccination of calves with an aromatic-dependent Salmonella dublin (O9,12) hybrid expressing O4,12 protects against S. dublin (O9,12) but not against Salmonella typhimurium (O4,5,12).

Three groups of six calves each, 5 to 7 weeks old, were orally vaccinated with the live aromatic-dependent delta aroA Salmonella dublin (O9,12) hybrid strain SL7103 with the O4,12-specifying rfb gene cluster from Salmonella typhimurium. SL7103 was given in three weekly doses, increasing from 2 x 10(9) to 1 x 10(11) bacteria per ml, was well tolerated, and caused mild, short-term temperature increases which diminished with each immunization. The strain was shed for up to 1 week. Strain SL7103 elicited significant (P < 0.001) and equal anti-S. dublin and -S. typhimurium lipopolysaccharide serum antibody responses and skin delayed-type hypersensitivity immune responses. Six vaccinated calves orally challenged with 10(10) CFU (equivalent to 1,000 50% lethal doses) of the virulent parent strain S. dublin SVA47 were protected and experienced only transient fever and mild mucoid diarrhea. However, six vaccinated calves orally challenged with 3 x 10(9) CFU and another six challenged with 3 x 10(8) CFU (equivalent to 1,000 50% lethal doses) of the virulent S. typhimurium SVA44 became bacteremic with a profuse hemorrhagic diarrhea and had to be sacrificed within 2 to 7 days. The results suggest that the S. typhimurium antilipopolysaccharide immunity was insufficient to provide a solid protective efficacy against oral S. typhimurium infection. The immunohistopathological examination revealed that S. typhimurium SVA44 could be found in all layers of the intestinal mucosa and the lymphatic tissues of the Peyer's patches. In contrast, S. dublin SVA47 was found predominantly in the columnar enterocytes of the jejunum and ileum and the follicle-associated epithelium over the Peyer's patches. In addition, SVA47 was found in the glandular tissues of the duodenal and tonsillar areas and in the lungs. This suggests that the S. typhimurium and S. dublin strains have different virulence traits determining their tissue localization and dissemination.

Experimental oral Salmonella dublin infection in calves. A bacteriological and pathological study.

Groups of calves (6-7, 12-14 and 24-28 weeks old) were orally infected with different numbers of the virulent Salmonella dublin strain SVA47. For the 6-7 weeks old calves the LD50-dose was estimated to be 1 x 10(7) bacteria. A dose of 10(9) bacteria was lethal within 24 hrs with the calves dying from septicemia and an acute necrotizing panenteritis. Calves 12-14 weeks old given 2 x 10(10) SVA47 bacteria succumbed to a progressive enteritis within one week. The 24-28 weeks old calves were resistant to an infective dose of 1 x 10(10) SVA47 bacteria. In the 6-7 and 12-14 weeks old calves SVA47 could be recovered from the entire intestinal tract, the liver and the spleen. In the oldest calves S. dublin SVA47 was recovered only from fecal specimens. However, the immunohistopathological examinations, using an S. dublin O-antigen-specific mouse monoclonal antibody and PAP-staining, showed the presence of S. dublin SVA47 in all tissues of the intestinal canal from calves of all ages and with a special affinity for the columnar enterocytes of the terminal jejunum and ileum, the follicle-associated epithelium over the Peyer's patches, and glandular tissues in the duodenum, tonsillar area and the lungs. Surviving calves responded with serum antibody titers against the O-antigenic lipopolysaccharide which appeared in the order IgM followed by IgA, IgG1 and IgG2.

Salmonella dublin experimental infection in calves: protection after oral immunization with an auxotrophic aroA live vaccine.

Salmonella dublin strain SL5631, which is auxotrophic for p-amino-benzoic acid and 2,3-dihydroxybenzoate because of a deleted aroA gene, was given orally in a dose of 10(10) live bacteria to 6 calves 5-7 weeks old. The calves tolerated the strain well, had a transient mucoid diarrhea and sacrificed animals showed a moderate acute inflammation in the ileum on day 2. The salmonella strain was seen lining the mucosal epithelium using immunohistopathology. Already in calves sacrificed on day 6 the damage was less pronounced and signs of regeneration were obvious. The healing process was more accentuated in calves sacrificed on day 14. The results demonstrated the attenuating effect of the deleted aroA gene. Groups of 5-7 weeks old calves (n = 25) orally immunized with 10(8), 10(9) and 10(10) S. dublin SL5631 at weekly intervals were challenged 2, 6 or 15 weeks after the immunization. All calves were protected against oral challenge with 10(10) bacteria of the virulent S. dublin strain, which equals 1,000 LD50 doses. At autopsy, calves were sacrificed 3 weeks after challenge, all calves had normal intestinal findings with only slightly enlarged mesenteric lymph nodes. The protective effect is surmised to involve cell-mediated as well as humoral defense mechanisms.

Histiocytic ulcerative colitis in a boxer. A case report.

A case of canine histiocytic ulcerative colitis, a disease of boxers, is here described. It appears that this disease has not been previously reported in Scandinavia. The diagnosis was established at necropsy of a 5-month-old boxer, which had shown bloody diarrhoea since the age of four weeks. Treatment with antibiotics had only given a temporary remission of the condition. Macroscopical findings included thickening of the wall of the descending colon and rectum, multiple ulcers in the rectocolonic mucosa and marked enlargement of the colonic lymph nodes. Microscopically the lesions were characterized by large accumulations of PAS-positive histiocytes, mixed with cells of the plasma cell type, in the mucosa and submucosa of the rectum and descending colon and in the colonic lymph nodes. The importance of using proctocolonoscopy and colon biopsy for the clinical diagnosis of this condition is stressed.