Assessment of the efficacy of tilmicosin phosphate to eliminate Actinobacillus pleuropneumoniae from carrier pigs.

The aim of this study was to evaluate the efficacy of in-feed medication with tilmicosin phosphate in order to eliminate or reduce the carriage of Actinobacillus pleuropneumoniae in the tonsils of carrier pigs. Two groups of 6 carrier animals received either a non-medicated feed (control group) or feed medicated with 400 ppm of tilmicosin phosphate (treated group) for 30 d. Three sentinel pigs were then introduced in each group and left for 29 d. The presence of A. pleuropneumoniae in tonsils was monitored using several techniques, including polymerase chain reaction (PCR). At the end of the treatment all of the control animals, but only 1 treated pig, were positive by PCR from tonsillar surface material. However, at necropsy, all control and most treated animals, as well as 1 sentinel animal, in both groups were positive by PCR from whole tonsils. In conclusion, under the experimental conditions, in-feed treatment with 400 ppm of tilmicosin phosphate significantly reduced the presence of A. pleuropneumoniae on the surface of tonsils but was unable to completely eliminate the organism from deeper tonsillar tissues and to prevent bacterial shedding by carrier animals.

A descriptive study of the frequency and characteristics of proliferative enteropathy in swine in Ontario by analyzing routine animal health surveillance data.

Routine surveillance data, collected on pathology submissions at the Animal Health Laboratory in Guelph between 1992 and 1997, were analyzed to determine demographic, clinical, and pathologic characteristics of cases of proliferative enteropathy and the frequency of this condition relative to other infectious enteric diseases in swine in Ontario. The most commonly reported disease was Escherichia coli enteritis (average cases/year = 70.0). Among infectious enteropathies that occur typically in neonatal pigs, coccidiosis (28.4 cases/year) and rotaviral enteritis (5.6 cases/year) were reported. Among infectious enteropathies generally associated with diarrhea in weaner and grower/finisher pigs, the most frequently reported was proliferative enteropathy (27.6 cases/year), followed by swine dysentery (23.3 cases/year), transmissible gastroenteritis (19.6 cases/year), and salmonellosis (8.4 cases/year). Diarrhea and bloody diarrhea were reported in 29% and 31%, respectively, of herds diagnosed with proliferative enteropathy. Important gross intestinal lesions included mucosal hypertrophy (62% of cases), hemorrhage (47%), and mucosal necrosis (34%). Histologic intestinal lesions included epithelial hyperplasia (90% of cases), mucosal necrosis (59%), and inflammation (49%). Our results suggest that proliferative enteropathy is a major infectious enteric disease in grower/finisher pigs in Ontario.

Sites of persistence of feline calicivirus.

Various tissues were collected from eight cats persistently infected with feline calicivirus (FCV) strain 255 to determine the sites of viral persistence. Tissues were tested by virus isolation and an immunohistochemical technique in which infected cells were detected in formalin-fixed, paraffin-embedded tissue sections using rabbit antiserum to FCV 255, a biotinylated second antibody and streptavidin-peroxidase. Virus was detected by one or both techniques in tonsillar tissues of each animal, and not in other samples. Infected cells were detected in samples from six of eight kittens, and in each animal were few in number, and were cells of the superficial tonsillar epithelium or the stratum germinativum of the adjacent fossa mucosa. Transmission electron microscopic examination of tissues from three of the cats revealed calicivirus-like particles in cells similar to those identified immunohistochemically. These results confirm that the tonsillar region is the major site of FCV persistence and indicate that virus replication during persistence is confined to the surface epithelium of the tonsil and adjacent fossa mucosa.

Immunohistochemical detection of feline calicivirus in formalin-fixed, paraffin-embedded specimens.

An immunohistochemical technique was developed for detection of feline calicivirus (FCV) in formalin-fixed, paraffin-embedded cultured cells and tissues. Initial trials with cultured cells indicated that the indirect immunoperoxidase method using rabbit antiserum to FCV strain 255, and horseradish peroxidase-labelled antibodies to rabbit immunoglobulin G lacked sensitivity and showed excessive diffuse background staining despite trypsin digestion of sections before staining. An amplified indirect immunoperoxidase technique using commercially available biotinylated antirabbit antibodies and avidin-biotin-peroxidase or streptavidin-peroxidase (SP) complexes proved highly successful. When optimal conditions, including those for trypsinization, inactivation of endogenous peroxidase and blocking were determined, the SP technique was preferred. Applied to tissue of cats in the acute phase of FCV infection, the technique provided clear identification of cells containing FCV antigens in sections in which histological detail was well preserved.