Reactions to Gudair® vaccination identified in sheep used for biomedical research.

CASE REPORT: We report Gudair® vaccination (against ovine Johne's disease, Mycobacterium avium subsp. paratuberculosis) site reactions in sheep used as a surgical model in biomedical research and discuss the actual and potential impact these lesions may have on surgical procedures, particularly in otology. Nine female Merino-cross sheep (Ovis aries) were enrolled in a project designed to investigate the healing capabilities of the malleus bone in the middle ear. The sheep were 12-18 months of age. Eight sheep had lesions near the base of the right ear that were discovered when surgery was performed. The size of the lesions varied and all lesions had a thick capsule containing various amount of caseous material. Two lesions had a draining tract where purulent material was apparent at the lowest point. The prescapular lymph nodes were not palpable in any of the sheep. Aerobic growth of various organisms was reported from four sheep lesions when the purulent material was transferred to a broth media. Histopathological examination revealed intralesional Mycobacteria and focal caseous necrosis or granulomatous dermatitis and cellulitis in seven of the eight lesions. Mild necrotising to granulomatous dermatitis and cellulitis was described in the lesion where organisms were not found. CONCLUSIONS: The lesions were confirmed at the end of the study to be associated with the vaccination and did not cause any known adverse effects on the research. However, it is important to acknowledge the risk of contamination these lesions could have on a sterile surgical site.

Displacement pattern of the normal pars flaccida in the gerbil.

OBJECTIVE: The aim of the current study was to assess the mechanical stiffness properties of the normal pars flaccida and to compare the results with those obtained in earlier studies on the pars tensa. BACKGROUND: Postinflammatory changes such as retraction pockets and cholesteatoma develop in the pars flaccida as well as in the pars tensa of the tympanic membrane. In these authors' previous experimental studies, stiffness changes are shown to develop early in the pars tensa in response to purulent otitis media and otitis media with effusion. These changes are suggested to be precursors to a later development of retraction pockets and cholesteatoma. In the clinical situation, retraction pockets are often found in the pars flaccida only. This study will establish the stiffness properties of the normal pars flaccida and form a base for forthcoming studies of the pars flaccida in response to otitis media with effusion and purulent otitis media, as well as retraction pocket formation and cholesteatoma. METHODS: A measure for the mechanical stiffness properties of the normal pars flaccida in the gerbil was assessed as its displacement for a given transtympanic pressure. The method used was moiré interferometry, which is a noncontacting optical technique to measure the shape of the surface of an object. RESULTS: The displacement of the pars flaccida was a nonlinear and asymmetric function of pressure. The displacement per pressure unit rose steeply at low middle ear pressures to level out and reach a steady state at higher pressures. The displacement versus pressure characteristics for the pars flaccida strongly differed from those of the pars tensa. The pars tensa seemed more elastic. CONCLUSION: Reference values for displacement versus pressure characteristics of the normal gerbil pars flaccida were obtained using a moiré interferometry method. The mechanical stiffness properties of the normal pars flaccida were strongly different from those of the pars tensa.

Tympanic membrane changes in experimental cholesteatoma in the gerbil.

HYPOTHESIS: The current study aimed to analyze changes of the acoustic stiffness properties and coincident morphologic changes of the tympanic membrane (TM) in early stages of cholesteatoma. The results were compared with those obtained in previous studies of otitis media with effusion and purulent otitis media. BACKGROUND: The pathophysiology of the cholesteatoma development process remains unclear. Changes of the physical properties of the TM seem to play an important role. In chronic middle ear disease, atrophic regions and retraction pockets of the TM are often present. Such changes of the TM may facilitate the development of cholesteatoma. METHODS: Early stages of external ear canal cholesteatoma were produced in the Mongolian gerbil by closing the external meatus with a suture. Acoustic admittance measurements were performed after 1, 2, or 3 months after surgery. After completed measurements, the TMs were analyzed morphologically. RESULTS: The acoustic stiffness of the TM was significantly increased in all cholesteatoma ears compared to normal control ears. A pronounced thickening and proliferative activity of the entire TM was observed in the early stage of cholesteatoma. The outer keratinizing epithelium showed an increased number of cell layers and an increased keratin production. The fibrous layer was thickened because of an increased amount of collagen fibers combined with minor edema. CONCLUSIONS: The thickness of the fibrous layer was almost doubled, mostly because of an increased amount of collagen fibers. The acoustic stiffness was significantly increased in all cholesteatoma ears. The results of the acoustic admittance measurements are comparable with those obtained in previous studies on purulent otitis media and otitis media with effusion.

Tympanic membrane displacement patterns in experimental cholesteatoma.

Tympanic membrane (TM) stiffness changes in the pars tensa in response to experimentally induced ear canal cholesteatoma by obstruction of the ear canal were studied. To this aim TM displacement versus pressure was measured with a high resolution, differential moiré interferometer. The measurements were performed on fresh, isolated gerbil temporal bones after removal of the cholesteatoma bulk. Besides an overall stiffness reduction we found that local stiffness variations were present in nine out of 18 studied ears. The stiffness changes as a function of time after ear canal obstruction had a pattern similar to those previously shown to develop in response to various forms of otitis media, showing that the TM stiffness properties decrease in a similar way in response to different inflammatory middle ear diseases. The stiffness changes correlated with an increased overall TM thickness and increased thickness of the lamina propria in particular as measured in histology sections. The stiffness changes may play an important role in the pathophysiology of cholesteatoma.

Shape and displacement patterns of the gerbil tympanic membrane in experimental otitis media with effusion.

This study assesses the visco-elastic properties of the tympanic membrane (TM) in isolated gerbilline temporal bones as a function of time after inducing experimental otitis media with effusion (OME). To do this we measured the TM displacements produced by application of sequences of static pressures across the TM, with a high resolution, real-time, differential moiré interferometer, and the results were compared with measurements on healthy ears. Two methods of producing OME were used: in one group tubal plugging was performed to produce mild OME (the 'TP group'); in the other group electro-cauterization of the nasopharyngeal orifice of the Eustachian tube was used to cause a severe form of OME (the 'EC group'). The measurements were performed from one day up to ten weeks after surgery. In the TP group the displacement fringe patterns were normal, i.e. qualitatively they resembled the patterns of the control group. Quantitatively there was a significant decrease of displacement for a given pressure on the first day after surgery, followed by a trend of increase with time; after seven to ten days the displacement was larger than in the control group. In the EC group the displacement was significantly reduced after half a week, followed by a trend of increase with time, similar to what was found in the TP group; at one week the displacement was larger than in the control group, and at ten weeks the largest displacement was recorded. In the EC group the displacement patterns were often irregular; in some cases with changes suggesting the presence of weak spots in the TM where retraction pockets most likely could develop. OME seems to affect the stiffness of the TM promptly so that it is a potential parameter for early diagnosis. The stiffness changes may, if measurable in the clinical situation, become prognostic parameters in the treatment of OME.