Mesenteric lymphangitis and sepsis due to RTX toxin-producing Actinobacillus spp in 2 foals with hypothyroidism-dysmaturity syndrome.

Actinobacillus suis-like organisms (ASLOs) have been isolated from the genital, respiratory, and digestive tracts of healthy adult horses, horses with respiratory disease, and septic foals. Two foals with congenital hypothyroidism-dysmaturity syndrome from separate farms developed ASLO infection. At necropsy, both had contracted carpal flexor tendons, thyroid hyperplasia, and thrombotic and necrotizing mesenteric lymphangitis and lymphadenitis; one foal also had mandibular prognathism. Numerous ASLOs were isolated from tissues from both foals, including intestine. Biochemical testing and mass spectrometric analysis of the two Actinobacillus isolates did not allow unequivocal identification. Comparative genetic analysis was done on these and similar isolates, including phylogeny based on 16S rRNA, rpoB and recN genes, as well as RTX (repeat in toxin) toxin typing of apxIA-apxIVA and aqxA genes. One isolate was identified as Actinobacillus suis sensu stricto, based on the presence of apxIA and apxIIA but not aqxA, whereas the other isolate had aqxA but neither apxIA nor apxIIA, consistent with A equuli ssp haemolyticus. Based on genotypic analysis of the isolates included for comparison, 3 of 3 equine ASLOs and 2 of 5 A equuli isolates were reclassified as A equuli subsp haemolyticus, emphasizing the importance of toxin genotyping in accurate classification of actinobacilli.

Studies on the virulence of two field isolates of the classical Swine Fever virus genotype 2.3 rostock in wild boars of different age groups.

The virulence of two isolates of the classical swine fever virus (CSFV) was studied in experimentally infected wild boars of different ages. The isolates, originating from wild boars shot in Mecklenburg-Western Pomerania (isolate '1829-NVP') and in Rhineland-Palatinate (isolate '11722-WIL'), belong to the genetic subgroup 2.3 Rostock. Clinical picture, transient viraemia, virus excretion and gross lesions at necropsy as well as a failure of virus detection at the end of the experiment revealed that this virus subtype was only moderately virulent. Whereas one subadult wild boar and both 7-week-old wild boar piglets infected intranasally became sick and died, only one of three 8-week-old animals which survived after contact infection remained CSFV positive until the end of the experiment [34 days post infection (dpi)], although neutralizing antibodies were present. This underlines the role of young boars in CSF epidemics. The isolate '11722-WIL' was shed by an infected adult wild boar and was transmitted to susceptible piglets. Interestingly, all animals which became sick and died also were found to be infected with a secondary pathogen. Therefore, we assume that after infection with moderately virulent CSFV simultaneous infections with other pathogens may be important for the clinical course and the outcome of the disease as well as for a spread of the virus in field.

Neospora caninum and Waddlia chondrophila strain 2032/99 in a septic stillborn calf.

Characteristics of an intracellularly growing micro-organism isolated from an aborted bovine foetus are described. The organism replicated within cytoplasmic vacuoles, was resistant to penicillin and exhibited structural characteristics compatible with Waddlia chondrophila. An ELISA specific for Chlamydia spp., immunofluorescence tests using antibodies directed against Chlamydia spp. or Simkania negevensis, and PCR using Chlamydia-specific primers showed that the agent was distinct from Chlamydiae or S. negevensis. Determination of 16S and partial 23S ribosomal RNA gene sequences in combination with the PCR results and the morphological, antigenic and developmental characteristics provided evidence that the isolate 2032/99 can be classified as W. chondrophila or a closely related organism.

Detection of European porcine reproductive and respiratory syndrome virus in porcine alveolar macrophages by two-colour immunofluorescence and in-situ hybridization-immunohistochemistry double labelling.

Two groups of five pigs aged 6 weeks were each infected oronasally with one of two different European isolates of porcine reproductive and respiratory syndrome virus (PRRSV). The animals were killed sequentially at 4, 7, 14 or 21 days post-inoculation for examination. The methods used consisted of histopathology, and mono- and double-labelling techniques based on in-situ hybridization, immunofluorescence and immunohistochemistry. Porcine alveolar macrophages (PAMs) contained large amounts of PRRSV antigen and PRRSV RNA, as shown by double labelling with (1) either PRRSV immunofluorescence or PRRSV-specific in-situ hybridization with digoxigenin-labelled riboprobes, and (2) immunolabelling with Mac 387 antibody for calprotectin. Expression of PRRSV-RNA was not detectable in cytokeratin-positive hypertrophic and proliferating pneumocytes or in cells of alveolar ducts or bronchiolar epithelium. The use of two-colour immunofluorescence with confocal laser scanning microscopy and double labelling with in-situ hybridization-immunohistochemistry showed that PAMs were the only pulmonary target cells. This contradicts earlier reports that epithelial pulmonary cells may also be infected by PRRSV.

Porcine reproductive and respiratory syndrome virus (PRRSV): kinetics of infection in lymphatic organs and lung.

Pigs were infected by the oronasal route with European isolates of the porcine reproductive and respiratory syndrome virus (PRRSV; I10 and Cobbelsdorf). The kinetics of infection in lymphatic organs and the lung were analysed by immunofluorescence detection of virus antigen, re-isolation of the virus and reverse transcription--polymerase chain reaction (RT-PCR) for PRRSV-specific RNA. The kinetics of PRRSV infection proceeded in three phases, irrespective of the varying infestation of lymphatic organs within the first days post-infection (p.i.). First, an early acute infection of lymphatic organs developed within the first week and was characterized by a high number of antigen-positive macrophages. Second, a delayed acute infection of the lung was observed, which was most pronounced during the second and third week p.i. when a high number of infected alveolar macrophages was observed. The acute infection of lymphatic organs had resolved at this time. Infected cells in the lung were predominantly located in pneumonic lesions. Third, a persistent infection was demonstrated by RT-PCR and immunohistology when the experiments were terminated at day 49 p.i. The virus persisted in lymphatic organs, especially in the tonsils, and in the lung. At this stage, indications for a re-occurrence of acute infection were observed in restricted areas of the lung.

Arterivirus PRRSV. Experimental studies on the pathogenesis of respiratory disease.

Pigs were infected with the porcine respiratory and reproductive syndrome virus (PRRSV) by the oronasal route. We studied the development of histological lesions, sites of virus infection and of inflammatory infiltrates by quantitative evaluation of reactive cells. The animals developed a multifocal interstitial pneumonia. Clinical signs of pneumonia were observed from day 7 to 21. In the first stage, an acute alveolitis was found, which was characterised by a hyperplasia of type II pneumocytes within the septa and an accumulation of macrophages in the alveolar spaces. Within 2-4 days p.i., virus infected cells were prominent in lymphatic organs, but their number declined rapidly during the following days. In the following period, the number of virus antigen positive cells increased in the lung. An interesting discrepancy existed between the relatively small number of virus specific cells and the degree of intensive pneumonia. As a first step to analyse mechanisms leading to the induction of pneumonia, we studied transcriptional expression of cytokines and other immunomodulatory molecules by semiquantitative RT-PCR.

[The reasons for the occurrence of non-specific reactions in the immunodiffusion test for enzootic bovine leukosis]. / Zu Ursachen für das Auftreten unspezifischer Reaktionen im Immundiffusionstest bei enzootischer Rinderleukose.

A batch of enzootic bovine leucosis antigen earmarked for immunodiffusion testing exhibited unspecific responses to cattle sera, which prompted an investigation of the underlying causes. Evidence was produced, for the first time ever, that such reactions were attributable to an antigen-antibody reaction caused by Mycoplasma arginini.

[Antibiotic resistance of mycoplasmas from cell cultures]. / Antibiotikaresistenz von Mykoplasmen aus Zellkulturen.

Investigations were conducted on 36 mycoplasma isolates to elucidate their resistance behaviours to kanamycin, gentamycin, neomycin, tylosin, oxytetracycline, chloramphenicol, and tiamulin. Only the latter proved to be highly effective, whereas all 36 strains were absolutely resistant to kanamycin, gentamycin, and neomycin, while 16 strains were resistant to all of the above antibiotics but tiamulin. Comparison of resistograms was found to provide some limited way of comparing strains and possibilities for detection of sources of contamination. Tiamulin may be used for improvement of cell cultures on account of its good cellular compatibility and high effectiveness on mycoplasmas.