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Biomedical subjects

D L Harris

Publications and source records attributed to D L Harris.

At least 127 records · Page 7Linked to original sources
PubMed1979

Immunity to Swine dysentery in recovered pigs.

The immune status of 29 pigs recovered from swine dysentery (SD) was evaluated after reexposure to Treponema hyodysenteriae. Pigs which had recovered from SD and remained asymptomatic for 4 to 6, 9 to 13, and 16 to 17 weeks after initial inoculation were reexposed to 1.5 X 10(9) viable cells of T hyodysenteriae per pig. Pigs which had recovered from SD were not shedding T hyodysenteriae, as determined by selective cultural examination of feces, before they were reexposed. Of 29 pigs reexposed to T hyodysenteriae, 27 were resistant to SD. In contrast, 23 of 28 control pigs developed signs of SD when exposed to T hyodysenteriae for the first time. Significant differences in immunity were not observed between pigs from the three convalescent periods. Serum agglutinins to T hyodysenteriae were present in recovered pigs for approximately 8 weeks after inoculation.

Animals↗
PubMed1978

Isolation of Treponema hyodysenteriae from sources other than swine.

Fecal samples were collected from animals and environments on 3 swine farms and cultured for Treponema hyodysenteriae. Each farm was a farrow-to-finish operation and, at the time of sampling, swine dysentery was enzootic among 8- to 22-week-old pigs. Pathogenic T hyodysenteriae was isolated from pigs on all 3 farms. On farm A, nonpathogenic T hyodysenteriae was isolated from a sample of lagoon water. On farm B, pathogenic T hyodysenteriae was isolated from a waste-holding pit. On farm C, a dog was observed to be eating feces of pigs that had swine dysentery. The dog was diarrheic and a fecal sample yielded a pathogenic isolant of T hyodysenteriae. Further isolation attempts were unsuccessful after the dog was removed from the infected premises. Isolation of pathogenic and nonpathogenic organisms from waste-holding systems emphasizes the need for cultural techniques in detecting pathogenic T hyodysenteriae.

Animals↗
PubMed1978

Swine dysentery: studies of gnotobiotic pigs inoculated with Treponema hyodysenteriae, Bacteroides vulgatus, and Fusobacterium necrophorum.

Transmission experiments were carried out in gnotobiotic pigs to determine whether lesions typical of swine dysentery could be produced by oral inoculation of Treponema hyodysenteriae in combination with Bacteroides vulgatus or Fusobacterium necrophorum, or both. Each of the organisms had been isolated from swine with early lesions of the disease. Lesions were not found in 6 pigs inoculated with T hyodysenteriae alone, in 4 pigs given F necrophorum and T hyodysenteriae, or in 4 pigs given B vulgatus and F necrophorum. Lesions typical of swine dysentery developed in 8 pigs given B vulgatus, F necrophorum, and T hyodysenteriae as well as in 3 of 4 pigs given B vulgatus and T hyodysenteriae. In both of these groups, the inoculated bacteria were recovered from the colon, and T hyodysenteriae was demonstrated in the colonic crypts, epithelium, and lamina propria. The pathogenicity of the T hyodysenteriae was shown by the development of characteristic signs and lesions of swine dysentery in 12 of 14 naturally farrowed pigs inoculated with T hyodysenteriae alone.

Animals↗
PubMed1978

Experimental infection with Treponema hyodysenteriae in guinea pigs.

Outbred and inbred (Hartley strain) guinea pigs (GP) were inoculated intragastrically with pathogenic and nonpathogenic Treponema hyodysenteriae. GP 3 to 16 weeks old received T. hyodysenteriae after a fasting period of 36 to 72 h. Infected GP with pathogenic T. hyodysenteriae developed a diarrheal and/or depressive condition, with mucus but not blood in the feces. Of 88 GP, 40 had gross lesions resembling those of swine dysentery. Lesions were limited mainly to the large intestine. TP used as controls or inoculated with nonpathogenic T. hyodysenteriae did not develop these lesions in the large intestine. These studies suggest that the GP may be used as an animal model for swine dysentery.

Animals↗
PubMed1978

Genetics of Treponema: characterization of Treponema hyodysenteriae and its relationship to Treponema pallidum.

Saturation reassociation assays with 125I-labeled treponemal DNAs show that Treponema hyodysenteriae is genetically unrelated to T. pallidum (Nichols), T. phagedenis biotype Reiter, and T. refringens biotype Noguchi. Pathogenic and nonpathogenic isolates of T. hyodysenteriae exhibited 28% sequence homology and had an extremely low guanine-plus-cytosine content (25.8%).

Base Sequence↗
PubMed1978

Microtitration agglutination for detection of Treponema hyodysenteriae antibody.

A microtitration agglutination test for the detection of Treponema hyodysenteriae antibody in swine and rabbit sera is described. The following methods provided the best test results: antigen produced from the spirochete after a culturing period of 36 to 44 h at 38 degrees C, washed antigen inactivated with 0.01% Merthiolate at 4 degrees C for 24 to 36 h, sera heated at 56 degrees C for 30 min, a diluent of phosphate-buffered saline (0.01 M, pH 7.2), and test results read macroscopically after 18 to 24 h of incubation at 38 degrees C. The test enabled detection of antibody against pathogenic T. hyodysenteriae with a high level of consistency and sensitivity. Sera against nonpathogenic T. hyodysenteriae produced low agglutinating titers (less than or equal to 1:8) when reacted against antigen from pathogenic isolates. Inactivated antigen remained stable for 7 to 10 days. Specificity of the reaction in the agglutination test was shown by absorption studies.

Agglutination Tests↗
PubMed1978

Parenteral immunization of pigs against infection with Treponema hyodysenteriae.

Six intravenous injections of formalin-inactivated Treponema hyodysenteriae were given to 8 specific-pathogen-free pigs at 6-day intervals. The 8 vaccinated and 8 control pigs were challenged intragastrically with pure cultures of T hyodysenteriae 7 and 8 days after the last intravenous injection. Clinical signs of swine dysentery were observed in all 8 control pigs, but was observed in only 1 of the immunized pigs. Three control pigs died. These findings suggest that parenteral immunization with T hyodysenteriae provided a marked degree of protection against subsequent intragastric challenge exposure with the homologous isolate of T hyodysenteriae.

Animals↗
PubMed1978

Transmission of swine dysentery by carrier pigs.

Swine dysentery (SD) was transmitted to healthy pigs by contact with experimentally-induced carrier pigs. Carrier pigs were produced by exposure of specific pathogen-free (SPF) swine to swine acutely affected with SD. When carrier pigs became acutely affected with SD, they were allowed to recover naturally or were treated with dimetridazole or ronidazole. Recovery was based on disappearance of clinical signs of SD. At a given time after recovery, normal SPF swine were housed with the carriers in a disinfected isolation unit to determine the ability of carriers to transmit SD. In each of 3 experiments, carriers that had recovered and remained asymptomatic for 11 to 25 days transmitted SD to contacts in 14 to 51 days. In 2 experiments, pathogenic Treponema hyodysenteriae was isolated from carriers 12 days before clinical SD was observed in contacts. Carriers which had recovered and remained asymptomatic for 70 and 90 days transmitted SD to contacts in 1 of 3 experiments. Treponema hyodysenteriae was isolated only from contacts with clinical signs of SD. In 4 experiments, carriers that had been treated with nitroimidazole compounds and subsequently recovered for 19 to 44 days failed to transmit SD. Culture of fecal samples on trypticase soy agar with 5% bovine blood and 400 microgram of spectinomycin/ml was helpful in predicting the carrier state, but phase contact contact microscopy of wet fecal smears was not.

Animals↗
PubMed1978

Enteropathogenicity testing of Treponema hyodysenteriae in ligated colonic loops of swine.

Multiple, ligated loops of swine colon were used as an in vivo model in which to test enteropathogenicity of isolates of Treponema hyodysenteriae. Gross and microscopic lesions observed in 21 of 22 colonic loops in pigs killed 48 to 72 hours after inoculation with isolates known to be enteropathogenic were characteristic of swine dysentery. These lesions were not observed in 12 loops exposed to uninoculated media or in 12 loops inoculated with nonpathogenic isolates of T hyodysenteriae. The swine-loop technique provides a relatively rapid, economical, reliable model in which to test enteropathogenicity of T hyodysenteriae isolates.

Animals↗
PubMed1977

Enteropathogenicity of various isolates of Treponema hyodysenteriae.

Isolates of Treponema hyodysenteriae from 25 geographically separated outbreaks of swine dysentery were tested for their ability to produce the disease. Clinical signs and lesions typical of acute swine dysentery were produced in 52 of 68 (75%) susceptible specific pathogen-free pigs that had been orally inoculated with pure cultures of 23 of 25 beta-hemolytic isolates. In addition, 13 weakly beta-hemolytic isolates of nondysentery origin with morphology similar to T. hyodysenteriae did not produce disease when orally inoculated into susceptible specific pathogen-free pigs. Two of these latter isolates, Puppy and B296, and one pathogenic, beta-hemolytic isolate failed to produce disease when orally inoculated into puppies.

Animals↗
PubMed1977

An evaluation of primary care preceptorships.

Participants and nonparticipants in a primary care preceptorship experience were compared on self-reported competencies in basic skills and performance of clinical procedures. A pre--post analysis of participating students was done, documenting the effect of the preceptorship experience on the students' career choices, practice site selections, and competencies in basic skills and in performance of clinical procedures. The experience tended to give precepting students more than nonprecepting students a feeling of confidence in skill areas and in performance of clinical procedures.

Career Choice↗
PubMed1976

Selective medium for isolation of Treponema hyodysenteriae.

Pure cultures of six pathogenic isolates of Treponema hyodysenteriae, the colonic mucosal scrapings of seven pigs with acute swine dysentery, and feces from seven unaffected pigs were diluted in phosphate-buffered saline and plated on Trypticase soy agar with 5% citrated bovine blood (TSA) and TSA with various levels of spectinomycin (TSA-S). The plates were incubated at 42 degrees C in a vented GasPak jar with a cold palladium catalyst and either 80:20 H2-CO2 by evacuation and refilling or a H2-CO2 generator envelope. Viable cell counts of the six pathogenic isolates were not altered by plating on TSA-S with 400 mug of spectinomycin per ml (TSA-S400) as compared with TSA alone. Dilutions of colonic mucosal scrapings from seven pigs with acute swine dysentery showed numbers of T. hyodysenteriae to be unchanged when plated on TSA-S400. Flora other than T. hyodysenteriae present in acute swine dysentery was inhibited, on the average, by 99.99%. Plating of dilutions of feces of unaffected pigs on TSA-S400 showed inhibition of flora that averaged more than 99.9%. Pathogenicity of T. hyodysenteriae was not altered by isolation or serial passage on TSA-S400.

Animals↗